RenesisEvo's Mazda Diary
Discussion
I always enjoy the reader's cars threads, and so it's about time I did one of my own. I've started a few but they've vanished into the ether. I bought this car almost 2 years ago, and a lot has happened since then...
Despite my username, this isn't about an RX-8 - sadly yet to scratch that itch (mostly because the one time I tried I didn't fit in the car). Following 2 years of E39 M5 ownership, for various reasons I wanted something cheap and simple, and fun - stress-free motoring. I also wanted something eligible for showroom-class club-level motorsport (hillclimbs, sprints etc.) and trackdays without breaking the bank. Enter the MX-5. I drove a late example (NC3.75) at Silverstone on a Mazda event and loved it. I couldn't stretch to a facelifted NC, an NB (Mk2) promised too much rust, and whilst I tempted by an NA (Mk1), finding a good one was difficult and again - rust.
Coming up to Christmas 2015, whilst still trying to sell my M5, I noticed an advert for an early NC (Mk3). It ticked a lot of boxes - firstly, 2.0 Sport, so 6-speed gearbox, LSD and about 160bhp - near enough the top spec in other words. Folding soft-top, so the best power:weight available. Full service history, various fluids replaced, waxoiled underneath, BBR exhaust, lowered and geometry by the renowned Wheels in Motion (WIM) and as a bonus a factory hardtop. It also had proper tyres all round (Michelin Pilot Sports), a good sign. The downsides were minor - the colour being silver, as I had wanted a copper red car, but I could compromise. It wasn't galaxy grey, which I really can't abide by. The mileage was high (north of 100k), but I've ran loads of cars above that figure so wasn't worried.
Frustratingly, with the M5 still not sold all I could do was try not to look at the advert while I tried to move it on. Before long the ad vanished, and I thought nothing more of it. I eventually sold the M5, and life went on. Then, idly browsing eBay in those empty days between Christmas and New Year, I saw the very same car advertised again. I immediately arranged to view the car. Turns it out it was in Malvern, Worcestershire - the very same place the chap who bought my M5 came from. Small world! The viewing and test drive was good, a deal was struck, insurance/tax arranged and I collected a week later, meaning I was only down to 1 car for all of three weeks. Here are some pics from day 1:
Pleasingly, my other car's registration is also 'OV', and it being back in Oxfordshire it was a nice match - the car was on a private plate. I wasn't sure about the aftermarket Voodoo gearknob (the car was supplied with all the original parts - including orange indicators, gearknob, long aerial, a trombone brush for the drain holes) but I've grown to like it and have left it on the car. Does feel cold in the winter though!
A quick survey revealed a few minor things to do:
The battery box lid was split. There's also a lug snapped off the battery box itself.
The battery clamp was looking very sorry for itself. There was a lot of copper sulphate deposit around the positive terminal as well.
Damaged boot seal
Steering wheel has seen better days, but not surprising given the mileage.
Needs a thorough clean!
The drivers' seatbelt was also slow to retract/return when released, a common problem on Mk3 MX-5s. Mazda issued a service bulletin, 08-001/11, detailing the issue and ways to resolve it. The wheels look ok from 20ft, but up close they are in desparate need of a refurb. The wheel nuts have seen better days, so too the wheel centres. A few minor cosmetic issues in and out, plus a collapsed driver's seat bolster on the outside, not that you can really tell, the leather is holding up well. It also lacks the BOSE stereo, not a deal-breaker (it does have an aux lead already fitted).
So I formed a list of things to do:
Thorough clean inside & out
Check fluids and tyre pressures
Replace battery box cover
Replace battery clamp and fittings
Replace boot seal
Wheel refurb
Sort out the seatbelt
Drive it!
Despite my username, this isn't about an RX-8 - sadly yet to scratch that itch (mostly because the one time I tried I didn't fit in the car). Following 2 years of E39 M5 ownership, for various reasons I wanted something cheap and simple, and fun - stress-free motoring. I also wanted something eligible for showroom-class club-level motorsport (hillclimbs, sprints etc.) and trackdays without breaking the bank. Enter the MX-5. I drove a late example (NC3.75) at Silverstone on a Mazda event and loved it. I couldn't stretch to a facelifted NC, an NB (Mk2) promised too much rust, and whilst I tempted by an NA (Mk1), finding a good one was difficult and again - rust.
Coming up to Christmas 2015, whilst still trying to sell my M5, I noticed an advert for an early NC (Mk3). It ticked a lot of boxes - firstly, 2.0 Sport, so 6-speed gearbox, LSD and about 160bhp - near enough the top spec in other words. Folding soft-top, so the best power:weight available. Full service history, various fluids replaced, waxoiled underneath, BBR exhaust, lowered and geometry by the renowned Wheels in Motion (WIM) and as a bonus a factory hardtop. It also had proper tyres all round (Michelin Pilot Sports), a good sign. The downsides were minor - the colour being silver, as I had wanted a copper red car, but I could compromise. It wasn't galaxy grey, which I really can't abide by. The mileage was high (north of 100k), but I've ran loads of cars above that figure so wasn't worried.
Frustratingly, with the M5 still not sold all I could do was try not to look at the advert while I tried to move it on. Before long the ad vanished, and I thought nothing more of it. I eventually sold the M5, and life went on. Then, idly browsing eBay in those empty days between Christmas and New Year, I saw the very same car advertised again. I immediately arranged to view the car. Turns it out it was in Malvern, Worcestershire - the very same place the chap who bought my M5 came from. Small world! The viewing and test drive was good, a deal was struck, insurance/tax arranged and I collected a week later, meaning I was only down to 1 car for all of three weeks. Here are some pics from day 1:
Pleasingly, my other car's registration is also 'OV', and it being back in Oxfordshire it was a nice match - the car was on a private plate. I wasn't sure about the aftermarket Voodoo gearknob (the car was supplied with all the original parts - including orange indicators, gearknob, long aerial, a trombone brush for the drain holes) but I've grown to like it and have left it on the car. Does feel cold in the winter though!
A quick survey revealed a few minor things to do:
The battery box lid was split. There's also a lug snapped off the battery box itself.
The battery clamp was looking very sorry for itself. There was a lot of copper sulphate deposit around the positive terminal as well.
Damaged boot seal
Steering wheel has seen better days, but not surprising given the mileage.
Needs a thorough clean!
The drivers' seatbelt was also slow to retract/return when released, a common problem on Mk3 MX-5s. Mazda issued a service bulletin, 08-001/11, detailing the issue and ways to resolve it. The wheels look ok from 20ft, but up close they are in desparate need of a refurb. The wheel nuts have seen better days, so too the wheel centres. A few minor cosmetic issues in and out, plus a collapsed driver's seat bolster on the outside, not that you can really tell, the leather is holding up well. It also lacks the BOSE stereo, not a deal-breaker (it does have an aux lead already fitted).
So I formed a list of things to do:
Thorough clean inside & out
Check fluids and tyre pressures
Replace battery box cover
Replace battery clamp and fittings
Replace boot seal
Wheel refurb
Sort out the seatbelt
Drive it!
Edited by RenesisEvo on Thursday 14th December 22:20
Such a fun car to drive, the miles added quickly - couldn't resist taking this picture, I happened to park at the right moment:
Here it is, roof off, on a driving day around Bridgnorth, one of its first proper trips out. I had a fantastic time. The car is really suited to B-roads, with more than sufficient power to make progress and overtake where required, but without murdering tyres and gulping fuel. Driving back it was barely registering single digits on the thermometer (well, the car doesn't have one but you get the idea), but I was happy with a hat, gloves and the furnace pointed at the footwell. I only popped the roof back up for the final motorway stretch in the dark.
One thing I noticed - a clonk every time I opened and closed the driver's door. Tightening up the bolt holding the check strap fixed that.
I ordered a load of bits from MX5parts.co.uk - it would be easy to spend a LOT of money with them! - and set about addressing a few things.
First up, replacing the seatbelt guides. As the image from the service bulletin shows, there was a design change to the guides on the seatback. The driver's side was on back order, so I changed the passenger side first, even though it had no issue!
Above is the early design - notice how wrinkled the seatbelt is.
And the later design in place. Now the seatbelt can sit flat.
New boot seal!
Much cleaner now too.
The headlights definitely need a proper polish. For the time being, I gave them a quick once-over by hand
using Autoglym SRP, not particularly aggressive cutting compound but it made a difference. Sealed with (now unavailable) Werkstatt Jet.
Headlight after.
I took the car to the PistonHeads Sunday Service at Santa Pod, and did a handful of runs up the strip, recording a best of 16.0 elapsed, not bad given I was being as kind as I reasonably could be to the clutch. Mostly comprehensively beaten by much more powerful cars - but managed two 'victories' over a VW Eos.
Photo by Chris Teagles
And a nice touch - a carbon PH smiley thanks to fellow PHer Alex L (thank you!)
Here it is, roof off, on a driving day around Bridgnorth, one of its first proper trips out. I had a fantastic time. The car is really suited to B-roads, with more than sufficient power to make progress and overtake where required, but without murdering tyres and gulping fuel. Driving back it was barely registering single digits on the thermometer (well, the car doesn't have one but you get the idea), but I was happy with a hat, gloves and the furnace pointed at the footwell. I only popped the roof back up for the final motorway stretch in the dark.
One thing I noticed - a clonk every time I opened and closed the driver's door. Tightening up the bolt holding the check strap fixed that.
I ordered a load of bits from MX5parts.co.uk - it would be easy to spend a LOT of money with them! - and set about addressing a few things.
First up, replacing the seatbelt guides. As the image from the service bulletin shows, there was a design change to the guides on the seatback. The driver's side was on back order, so I changed the passenger side first, even though it had no issue!
Above is the early design - notice how wrinkled the seatbelt is.
And the later design in place. Now the seatbelt can sit flat.
New boot seal!
Much cleaner now too.
The headlights definitely need a proper polish. For the time being, I gave them a quick once-over by hand
using Autoglym SRP, not particularly aggressive cutting compound but it made a difference. Sealed with (now unavailable) Werkstatt Jet.
Headlight after.
I took the car to the PistonHeads Sunday Service at Santa Pod, and did a handful of runs up the strip, recording a best of 16.0 elapsed, not bad given I was being as kind as I reasonably could be to the clutch. Mostly comprehensively beaten by much more powerful cars - but managed two 'victories' over a VW Eos.
Photo by Chris Teagles
And a nice touch - a carbon PH smiley thanks to fellow PHer Alex L (thank you!)
Edited by RenesisEvo on Thursday 14th December 21:11
MX5parts have some good bits, but the price of the intermittent wiper upgrade was a bit steep - getting on for £90. So I sourced a used RX-8 stalk from eBay for a much more reasonable sum of £35. It's plug and play - just remove the old one, and fit the new one. I did some research which showed that the same part is also fitted to the first-gen (BK) Mazda 3 saloon - the hatchback has an additional rear wiper control which would be weird/useless on an MX-5. However, there are naff all 3 saloons in the UK, nevermind parts for them! A nice easy upgrade that makes a big difference when it's raining.
Before
Comparison between the stalks
After
Before
Comparison between the stalks
After
After what felt like a lifetime of waiting, the driver's side seatbelt guide turned up.
Before
After
As per the service bulletin I also pulled out and washed the seatbelts, and let them dry out with the roof off. The driver's side was better, but still pretty slow and reluctant to return. To investigate further I'll need to take the seat out and remove a lot of the trim panels to access the seatbelt reel. Replacing the reel is an option, but not a cheap one - nearly £300! So worth a bit of time checking for any other issues first.
Before
After
As per the service bulletin I also pulled out and washed the seatbelts, and let them dry out with the roof off. The driver's side was better, but still pretty slow and reluctant to return. To investigate further I'll need to take the seat out and remove a lot of the trim panels to access the seatbelt reel. Replacing the reel is an option, but not a cheap one - nearly £300! So worth a bit of time checking for any other issues first.
Oh no!
The cause!
I pumped a load of air in and crawled to an ATS Euromaster just a mile away, as they've repaired tyres for me before. Sadly this couldn't be repaired, and I wasn't prepared to pay the ridiculous price they quoted for a new tyre. Even the price on their website was far less!
I wanted to stay with the Pilot Sports as they had been impressive in the wet and dry, with bags of grip and feel. Shopping around, I found Kwik Fit were doing a good deal on the Pilot Sport 4, which had just been released. I took a punt on their mobile fitting service (I'd never take a car into a Kwik Fit centre!) and replaced both rear tyres, at a cost of £209 all in, which seemed very reasonable to me.
The service was great, I even held a brolly for the guy as the rain came down hard just as he was finishing up. Luckily I remembered to check the tyre pressures soon after, because even though the technician had asked me what I wanted (29 psi), they were miles above.
About the same time, I'd noticed a rattle when starting and turning the car off, and occasionally when driving. One look underneath showed the culprit:
The bandclamp holding the exhaust tailpipe on had corroded right through, and it was rattling around the pipe. Such was the state of the clamp I couldn't tell what to replace it with. So I called BBR - who very kindly offered to give me a clamp free of charge, all I had to do was collect. How's that for customer service? Lucky for me BBR are in Brackley, Northants, which wasn't far away, so I made a detour one day and collected a shiny new clamp.
There I learned that BBR had never seen my car - and more to the point, the exhaust was actually for a turbo-charged engine. They have another version for naturally-aspirated. Clearly the backbox had been sourced from another car. It also explained some of the low-rpm 'boom', with the turbo usually filtering out those frequencies. If I had the equipment and welding skills, I could open the backbox and fit a Helmholtz resonator or quarter-wave tube, tuned to cancel the right frequency, but it would be easier and a lot cheaper to get a new backbox. I love the sound high up the range - really hard-edged and purposeful, without being thrashy or strained (perhaps the last few hundred rpm are), so I've stuck with it.
A quick browse on eBay and another £5 saw me in possession of a second band clamp, and I replaced both at the same time.
Curiously it was just evident that the old clamps also had the 'W2' marking indicating stainless steel, so I was a bit curious how it had rusted so badly. Something to monitor.
With the tyres sorted I could take part in a navigational scatter rally, organised by a friend, with another mate wielding the map and plotter. The sun was shining and a great day was had, even if we were a bit confused, lost once or twice, and definitely got a whiff of the clutch in the afternoon.
With fellow nav rally competitors, including the battle-bus Volvo with very sharp crew. The green NA MX-5 just creeping into shot was driven by the winning crew. Notice the MK3, car, Mk2, car, Mk1 line-up - purely by accident!
I happend to park next to a 2008 PHRT (power retracting hard top), almost a twin of mine:
The drop in ride height of my car was very obvious, it makes a big difference visually.
I then took part in a hillclimb school day at Shelsley Walsh hillclimb, which was just brilliant fun. I did 9 runs in total, being conservative on the last few as I wanted to drive home, and there's no room for error! I realised that I really should learn the car's limits somewhere a little more forgiving - a trackday was needed. As ever, I left the hardtop on, as at the time I was stuck for places to put it, other than on the car. Plus unsure of the rules for open cars, it was simpler to keep it on, despite the small weight penalty. In hindsight I could have asked another participant to help me take it off and store it in the paddock.
The only problem I had all day was that the car decided to celebrate reaching 120,000 miles on the drive there by developing a horrendous rattle. It seemed to independent of gear and engine speed, so I feared clutch. It was most apparent on idle. Weirdly, the car drove fine. A few people helped me check the car over, and I elected to carry on with the day. I completed all the runs and got the car home without any issues.
Jacking the car up with some borrowed tools and borrowed driveway (I seriously lack space to store things!), I found the cause of the horrible noise.
A metal plate stuck inbetween the propshaft and torque tube, it was able to move but couldn't fall out. I looked high and low but couldn't find anywhere it could have dropped out from, the manifolds and heatshields all looked intact. A mystery. Perhaps I ran over it and it got stuck? I may never know.
One thing I did notice was the state of the gaitors around the dampers, completely shot:
Sorting this would turn out to be the opening of a very large (read: expensive) can of worms. I'll do that update next time, as it's a long story!
With fellow nav rally competitors, including the battle-bus Volvo with very sharp crew. The green NA MX-5 just creeping into shot was driven by the winning crew. Notice the MK3, car, Mk2, car, Mk1 line-up - purely by accident!
I happend to park next to a 2008 PHRT (power retracting hard top), almost a twin of mine:
The drop in ride height of my car was very obvious, it makes a big difference visually.
I then took part in a hillclimb school day at Shelsley Walsh hillclimb, which was just brilliant fun. I did 9 runs in total, being conservative on the last few as I wanted to drive home, and there's no room for error! I realised that I really should learn the car's limits somewhere a little more forgiving - a trackday was needed. As ever, I left the hardtop on, as at the time I was stuck for places to put it, other than on the car. Plus unsure of the rules for open cars, it was simpler to keep it on, despite the small weight penalty. In hindsight I could have asked another participant to help me take it off and store it in the paddock.
The only problem I had all day was that the car decided to celebrate reaching 120,000 miles on the drive there by developing a horrendous rattle. It seemed to independent of gear and engine speed, so I feared clutch. It was most apparent on idle. Weirdly, the car drove fine. A few people helped me check the car over, and I elected to carry on with the day. I completed all the runs and got the car home without any issues.
Jacking the car up with some borrowed tools and borrowed driveway (I seriously lack space to store things!), I found the cause of the horrible noise.
A metal plate stuck inbetween the propshaft and torque tube, it was able to move but couldn't fall out. I looked high and low but couldn't find anywhere it could have dropped out from, the manifolds and heatshields all looked intact. A mystery. Perhaps I ran over it and it got stuck? I may never know.
One thing I did notice was the state of the gaitors around the dampers, completely shot:
Sorting this would turn out to be the opening of a very large (read: expensive) can of worms. I'll do that update next time, as it's a long story!
Edited by RenesisEvo on Thursday 14th December 22:14
RenesisEvo said:
After what felt like a lifetime of waiting, the driver's side seatbelt guide turned up.
Before
After
As per the service bulletin I also pulled out and washed the seatbelts, and let them dry out with the roof off. The driver's side was better, but still pretty slow and reluctant to return. To investigate further I'll need to take the seat out and remove a lot of the trim panels to access the seatbelt reel. Replacing the reel is an option, but not a cheap one - nearly £300! So worth a bit of time checking for any other issues first.
I looked into replacing the reel and found aftermarket ones really cheap, what I don't know is if the OE type have accident pre-tensioners fitted so haven't gone much further with it because as you point out, it requires a lot of digging.Before
After
As per the service bulletin I also pulled out and washed the seatbelts, and let them dry out with the roof off. The driver's side was better, but still pretty slow and reluctant to return. To investigate further I'll need to take the seat out and remove a lot of the trim panels to access the seatbelt reel. Replacing the reel is an option, but not a cheap one - nearly £300! So worth a bit of time checking for any other issues first.
If you're on FB you might have seen or find this useful: https://www.facebook.com/groups/6240650278/permali...
Google 'tyre repair string' and put some in your boot too, you could have repaired that tyre yourself in less than 3 minutes start to finish.
Edited by Evoluzione on Saturday 16th December 10:45
Evoluzione said:
I looked into replacing the reel and found aftermarket ones really cheap, what I don't know is if the OE type have accident pre-tensioners fitted so haven't gone much further with it because as you point out, it requires a lot of digging.
If you're on FB you might have seen or find this useful: https://www.facebook.com/groups/6240650278/permali...
Google 'tyre repair string' and put some in your boot too, you could have repaired that tyre yourself in less than 3 minutes start to finish.
Thanks very much, will look into that! Great thing about PH, lots of people with lots of useful information! The rear tyres were half worn so I'm not fussed about replacing them but certainly will look at that for any future problems.If you're on FB you might have seen or find this useful: https://www.facebook.com/groups/6240650278/permali...
Google 'tyre repair string' and put some in your boot too, you could have repaired that tyre yourself in less than 3 minutes start to finish.
Before I get to the suspension, I managed to conduct a bit of an experiment (if you don't like science much, feel free to skip!)
On the very rare occasion I had to drive the car with the soft-top up, I noticed there was an unpleasant amount of noise in the cabin, mostly in the form of a coarse roar (hard to put into words). Now, whilst the MX-5 is of course, not a refined car in any stretch, I do want to get to the point where I'm happy to drive the car for a good few hours, in order to get to some really good roads or places (like, Wales or Scotland). The noise currently makes it a bit unbearable, plus it means the stereo (CD, aux or radio) has to be turned up excessively loud to hear with any clarity. To fix the problem, first I need to understand it a bit better.
Fortunately, I was able to borrow some equipment to measure the noise in the car. I drove the car up and down the same bit of road, at two different speeds (as best as I could manage without cruise), with all the different roof configurations - no roof, soft top up, and hard top on. I must have made for an odd sight driving with the roof off with a pair of headphones on! The headphones carry microphones that measure exactly what you hear. A bit of data processing later, and we have some graphs:
Here we can see a frequency spectrum of the noise (the vertical axis is power spectrum density, in dB(A) - not to be confused with sound pressure level, also available in dB), from 0 to 5kHz. The first thing that stands out is that with no roof, there is a lot more noise above 2.5kHz. This is all generated from the air passing over the car. Of course without any roof there is significantly more turbulent airflow, and so more noise. There isn't a night and day difference between the hard-top and soft-top, however - showing that graphs can't always convey the true nature of a sound.
By narrowing down the range, the difference becomes more evident:
The left arrow, just above 200Hz, is the noise from the tyres - more specifically, the noise from the resonance of the air volume inside the tyres. This is common to all cars, and can be removed by fitting foam inside the tyre. This wasn't the source of the irritating noise, however. Using a neat bit of software, I was able to place bandstops to remove bits of the spectrum, then play back the sound, to narrow down what the source of the noise I was hearing was. It turned out to be the region between 1050 and 1200Hz, shown by the right arrow. With the soft-top, you can see a large peak just above 1100Hz, which isn't there with the hardtop in place. This region of noise is typically radiated from the tyres - the tread hitting the road. No amount of Dynamat or equivalent will solve this - foam will be needed to attenuate it. Assuming there aren't any ways to reduce the amount of noise getting into the cabin. I suspect a fair amount comes up from the drain holes, that start just behind the headrests, so the noise source is very close to your ear. The plan then, when time allows, is to take out the seats and trim around the roof, seal anything that can be sealed, and perhaps introduce some foam (a scrapped luxury car would be a good source) where possible. Not loads - but adding a kg or two is going to be less noticeable than making the cabin a lot more bearable.
Out of interest, here's what happens when you increase the speed:
As expected, there's more noise across the board - but there's a big increase in the peak in the 1000-1200Hz region. So now I know what the noise is, I just need to find the time to take the car apart and try and improve it. I do like it when a simple exercise (with the right equipment, mind) gives a very clear answer on what needs to be done.
On the very rare occasion I had to drive the car with the soft-top up, I noticed there was an unpleasant amount of noise in the cabin, mostly in the form of a coarse roar (hard to put into words). Now, whilst the MX-5 is of course, not a refined car in any stretch, I do want to get to the point where I'm happy to drive the car for a good few hours, in order to get to some really good roads or places (like, Wales or Scotland). The noise currently makes it a bit unbearable, plus it means the stereo (CD, aux or radio) has to be turned up excessively loud to hear with any clarity. To fix the problem, first I need to understand it a bit better.
Fortunately, I was able to borrow some equipment to measure the noise in the car. I drove the car up and down the same bit of road, at two different speeds (as best as I could manage without cruise), with all the different roof configurations - no roof, soft top up, and hard top on. I must have made for an odd sight driving with the roof off with a pair of headphones on! The headphones carry microphones that measure exactly what you hear. A bit of data processing later, and we have some graphs:
Here we can see a frequency spectrum of the noise (the vertical axis is power spectrum density, in dB(A) - not to be confused with sound pressure level, also available in dB), from 0 to 5kHz. The first thing that stands out is that with no roof, there is a lot more noise above 2.5kHz. This is all generated from the air passing over the car. Of course without any roof there is significantly more turbulent airflow, and so more noise. There isn't a night and day difference between the hard-top and soft-top, however - showing that graphs can't always convey the true nature of a sound.
By narrowing down the range, the difference becomes more evident:
The left arrow, just above 200Hz, is the noise from the tyres - more specifically, the noise from the resonance of the air volume inside the tyres. This is common to all cars, and can be removed by fitting foam inside the tyre. This wasn't the source of the irritating noise, however. Using a neat bit of software, I was able to place bandstops to remove bits of the spectrum, then play back the sound, to narrow down what the source of the noise I was hearing was. It turned out to be the region between 1050 and 1200Hz, shown by the right arrow. With the soft-top, you can see a large peak just above 1100Hz, which isn't there with the hardtop in place. This region of noise is typically radiated from the tyres - the tread hitting the road. No amount of Dynamat or equivalent will solve this - foam will be needed to attenuate it. Assuming there aren't any ways to reduce the amount of noise getting into the cabin. I suspect a fair amount comes up from the drain holes, that start just behind the headrests, so the noise source is very close to your ear. The plan then, when time allows, is to take out the seats and trim around the roof, seal anything that can be sealed, and perhaps introduce some foam (a scrapped luxury car would be a good source) where possible. Not loads - but adding a kg or two is going to be less noticeable than making the cabin a lot more bearable.
Out of interest, here's what happens when you increase the speed:
As expected, there's more noise across the board - but there's a big increase in the peak in the 1000-1200Hz region. So now I know what the noise is, I just need to find the time to take the car apart and try and improve it. I do like it when a simple exercise (with the right equipment, mind) gives a very clear answer on what needs to be done.
Edited by RenesisEvo on Sunday 31st December 18:48
Accelebrate said:
I would have expected a bigger difference between the hard-top and soft-top, must be psychological!
Me too! My suspicion is that the key elements of the noise are coming up from the floor, so whichever roof is on the car won't make a difference to that bit. The spectrum isn't very good for showing small differences in 'volume'. The graph I've shown is the microphone closest to the door. (effectively, your right ear, for a right-hand drive car). If you look at the data for the other one (left ear), there's a bigger difference, with the hardtop clearly better across the board - it's just that, especially above 2kHz, roof-off is so much worse that the difference between the two roofs looks tiny. I've tried a few calculations but the poor repeat-ability between runs (passing traffic, no cruise, slightly different road surface, etc) means the results are all over the place. I need a controlled environment to get a true comparison. The RMS averages are generally within 1-2dB(A) for the 50mph test. At the higher test speed the differences are much more defined - between 1 and 3dB louder with the soft-top as opposed to the hardtop. Bear in mind the logarithmic scale, +3dB(A) is twice the energy level. There's a lot more analysis that I haven't done or shown as it would get very dull very quickly (if it hasn't already).
Another change I made, before the suspension work kicked off, was the battery - fixing the broken cover, and a bit more beside.
Under the cover (flipped round):
Fortunately my landlady also had a MX-5, a Mk3.75 PHRT. Hearing it started up everyday (as they tended to leave at absurdly small hours of the morning), I realised that mine was quite slow to turn over - although it normally always started. However after one occasion where I'd left the car for around 10 days, there wasn't enough left in the battery to start the engine. Having had several years of flat battery woes with my E39 (I blame the tracker), I had little patience for it, despite having a trickle charger, jump leads and another car so I was never stranded.
The Varta battery isn't original - that's a Panasonic, which is curiously short of markings (I have an image somewhere of the one from said Mk3.75, but I can't find it). Anyway, it says 300A - that is 300CCA, I presume. Anyway, the OEM battery is rated at 330. So 10% down (ok 9.1%) on cranking power when fresh. The large copper sulphate deposit on the positive terminal suggested it had seen better days. After some research I went for the biggest battery I could find that would fit in the battery box - a Yuasa HSB053, 430CCA. Plenty of capacity. £60 to Halfords and all was good.
I'd also ordered a fresh clamp and other bits from MX5parts - although the clamp bolts were out of stock (they had 1, I needed two) and I had to wait a few weeks for them to arrive. I then set about replacing all the bits with shiny new ones (always a pleasure)
Notice that the negative (earth) cable has a yellow stripe, but it's on the underside, where it can't typically be seen when installed.
So following the guidance of the MSA Blue Book (Section 2, J, 5.14.5 at the time of writing) I wrapped the cable in yellow insulating tape:
Here you can see the horribly rusty battery box screws. They need drilling out, not something I'm currently equipped to do (and later would be a bit of a pain), so I left them for the time being. The two missing ones still have the threads left behind - clearly someone has tried to take the tray out before.
All in place - yes, I realise the battery band is redundant given the battery has its own handle. But I like the originality and don't care for the extra grams. Also the rusty bolts had to be used until the new ones turned up.
New battery cover on (notice the added 'refer to manual' symbol):
Eventually the clamp bolts arrived. Weirdly, they're 15mm longer than the originals, despite there being no apparent need for it:
This meant I could no longer use a socket to wind on the retaining nuts, so much tedious spanner twirling ensued. In an ideal world I'd cut them down and re-tap the threads, but again I lack the necessary tools, and it seemed a little pointless. Thanks to a friend I applied some fresh penny washers and locknuts, and copper greased the terminals.
The car turned over with much more vigour, and over time has proved to start after very long periods of rest without hesitation. Another small but satisfying improvement.
Under the cover (flipped round):
Fortunately my landlady also had a MX-5, a Mk3.75 PHRT. Hearing it started up everyday (as they tended to leave at absurdly small hours of the morning), I realised that mine was quite slow to turn over - although it normally always started. However after one occasion where I'd left the car for around 10 days, there wasn't enough left in the battery to start the engine. Having had several years of flat battery woes with my E39 (I blame the tracker), I had little patience for it, despite having a trickle charger, jump leads and another car so I was never stranded.
The Varta battery isn't original - that's a Panasonic, which is curiously short of markings (I have an image somewhere of the one from said Mk3.75, but I can't find it). Anyway, it says 300A - that is 300CCA, I presume. Anyway, the OEM battery is rated at 330. So 10% down (ok 9.1%) on cranking power when fresh. The large copper sulphate deposit on the positive terminal suggested it had seen better days. After some research I went for the biggest battery I could find that would fit in the battery box - a Yuasa HSB053, 430CCA. Plenty of capacity. £60 to Halfords and all was good.
I'd also ordered a fresh clamp and other bits from MX5parts - although the clamp bolts were out of stock (they had 1, I needed two) and I had to wait a few weeks for them to arrive. I then set about replacing all the bits with shiny new ones (always a pleasure)
Notice that the negative (earth) cable has a yellow stripe, but it's on the underside, where it can't typically be seen when installed.
So following the guidance of the MSA Blue Book (Section 2, J, 5.14.5 at the time of writing) I wrapped the cable in yellow insulating tape:
Here you can see the horribly rusty battery box screws. They need drilling out, not something I'm currently equipped to do (and later would be a bit of a pain), so I left them for the time being. The two missing ones still have the threads left behind - clearly someone has tried to take the tray out before.
All in place - yes, I realise the battery band is redundant given the battery has its own handle. But I like the originality and don't care for the extra grams. Also the rusty bolts had to be used until the new ones turned up.
New battery cover on (notice the added 'refer to manual' symbol):
Eventually the clamp bolts arrived. Weirdly, they're 15mm longer than the originals, despite there being no apparent need for it:
This meant I could no longer use a socket to wind on the retaining nuts, so much tedious spanner twirling ensued. In an ideal world I'd cut them down and re-tap the threads, but again I lack the necessary tools, and it seemed a little pointless. Thanks to a friend I applied some fresh penny washers and locknuts, and copper greased the terminals.
The car turned over with much more vigour, and over time has proved to start after very long periods of rest without hesitation. Another small but satisfying improvement.
RenesisEvo said:
By narrowing down the range, the difference becomes more evident:
The left arrow, just above 200Hz, is the noise from the tyres - more specifically, the noise from the resonance of the air volume inside the tyres. This is common to all cars, and can be removed by fitting foam inside the tyre. This wasn't the source of the irritating noise, however. Using a neat bit of software, I was able to place bandstops to remove bits of the spectrum, then play back the sound, to narrow down what the source of the noise I was hearing was. It turned out to be the region between 1050 and 1200Hz, shown by the right arrow. With the soft-top, you can see a large peak just above 1100Hz, which isn't there with the hardtop in place. This region of noise is typically radiated from the tyres - the tread hitting the road. No amount of Dynamat or equivalent will solve this - foam will be needed to attenuate it. Assuming there aren't any ways to reduce the amount of noise getting into the cabin. I suspect a fair amount comes up from the drain holes, that start just behind the headrests, so the noise source is very close to your ear.
If this is treadblock noise why is it not showing on the top down measurement? Also, as you increase speed by 25% the frequency does not increase by 25%, which I would expect with tread block noise. The left arrow, just above 200Hz, is the noise from the tyres - more specifically, the noise from the resonance of the air volume inside the tyres. This is common to all cars, and can be removed by fitting foam inside the tyre. This wasn't the source of the irritating noise, however. Using a neat bit of software, I was able to place bandstops to remove bits of the spectrum, then play back the sound, to narrow down what the source of the noise I was hearing was. It turned out to be the region between 1050 and 1200Hz, shown by the right arrow. With the soft-top, you can see a large peak just above 1100Hz, which isn't there with the hardtop in place. This region of noise is typically radiated from the tyres - the tread hitting the road. No amount of Dynamat or equivalent will solve this - foam will be needed to attenuate it. Assuming there aren't any ways to reduce the amount of noise getting into the cabin. I suspect a fair amount comes up from the drain holes, that start just behind the headrests, so the noise source is very close to your ear.
It seems more likely to me that the noise is related to the soft top itself, either a fabric panel vibrating against the frame or possibly a seal chamber or hood frame tube cavity resonating as a quarter wave. Without being in the car though it can be tough to tell!
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