Discussion
Did my second track day at Goodwood on Saturday - car performed faultlessly except for one thing: We were on a cool-down lap and I didn't touch the brakes once until I came up to the chicane when the pedal sank almost to the floor! Quick bit of panicking and pumping on the pedal restored some braking ability and I made it around - luckily I was only going slowly at the time!
However, I decided to call it a day at that point - it was about 3:30 anyway, so no problem. The brakes have recovered fine, and I checked the fluid when I got home and it was right up to the top.
Am I correct in my assumption that it was the fluid boiling? Seems a bit odd because i'd not used the brakes at all for about a minute??
However, I decided to call it a day at that point - it was about 3:30 anyway, so no problem. The brakes have recovered fine, and I checked the fluid when I got home and it was right up to the top.
Am I correct in my assumption that it was the fluid boiling? Seems a bit odd because i'd not used the brakes at all for about a minute??
Sounds like it to me, similar to the problems we've had on the racing taz.. go into one corner brakes are fine,
go into the next and the pedal goes to the floor.
In your case i assume the theory goes that you had been braking very hard so the fluid pressure was high,and everything is very hot. on the cooldown your off the brakes so line pressure is lower ( and maybe you have a dragging pad still putting heat in to the caliper?) the fluid now boils up as the presure is lower.
With brake fade you'd just get a very hard pedal an no brakes..
My advice would be to
a) change the fluid
b) strip down and carefully inspect the brakes ( i.e. pads out clean everything up and check the pistons and pads move freely.
c) probably also worth removing and checking the bleed nipples and maybe replacing them a few quid...
we traced the problem on the taz to a damaged seat on the nipple and caliper, very occasionaly letting the pressure off with a slight leak.
G
p.s the above could be total rubbish but seemed to make sense to us.
go into the next and the pedal goes to the floor.
In your case i assume the theory goes that you had been braking very hard so the fluid pressure was high,and everything is very hot. on the cooldown your off the brakes so line pressure is lower ( and maybe you have a dragging pad still putting heat in to the caliper?) the fluid now boils up as the presure is lower.
With brake fade you'd just get a very hard pedal an no brakes..
My advice would be to
a) change the fluid
b) strip down and carefully inspect the brakes ( i.e. pads out clean everything up and check the pistons and pads move freely.
c) probably also worth removing and checking the bleed nipples and maybe replacing them a few quid...
we traced the problem on the taz to a damaged seat on the nipple and caliper, very occasionaly letting the pressure off with a slight leak.
G
p.s the above could be total rubbish but seemed to make sense to us.
Thanks for that, Graham. I suspected it was the fluid, obviously, but just wanted to check before replacing it. Might have a gander at all the brake bits too, but I have a very limited mechanical knowledge, so not sure about fiddling with them too much!
Thanks for the advice, though - much appreciated.
Thanks for the advice, though - much appreciated.
sounds to me like the brake fluid ,if you are using standard brke fluid it will boil as you said so a change to dot 4 should solve or speak to your local specalist . also change of pads to green stuff or mintex they dont fad when they get hot plus grooved disc,s if you are going to do trackdays regular.hope that is of help.
gary judd
gary judd
I must admit that ChopperEllis's 996 turbo which was there as well seemed to stop almost on a sixpence compared to mine! But his brakes are about the size of a planet.
The thing I thought was odd was that we both got vibrations through the steering wheel when the brakes got hot - mine certainly more so than his, but is this normal, or should we be expecting a vibration-free experience?
The thing I thought was odd was that we both got vibrations through the steering wheel when the brakes got hot - mine certainly more so than his, but is this normal, or should we be expecting a vibration-free experience?
you will get some vibration but if it is excesive then your disc,s are warped if they do this with normall driving then they are might be worth getting them checked. I had the same when i done my first trackdays but got grooved disc,s ,greenstuff pads and dot 4 fluid now it stops on a sixpence much better than the standard set up even for road driving
gary judd
gary judd
To minimise this effect, NEVER use your handbrake at a trackday as it transmits any heat through the system (sorry if I'm teaching you to suck eggs). Even after a cooling down lap, they'll still be damned hot, so just leave it standing on the level, or in gear. And, yes, use high performance fluids as well, but these can compromise performance on the road, so use caution and common sense...
Try Castrol SRF fluid - you can find it in Demon Tweeks....
www.castrol.com.au/products/pdf/B768%20SRF%20Racing%20Brake%20Fluid.pdf
www.castrol.com.au/products/pdf/B768%20SRF%20Racing%20Brake%20Fluid.pdf
gary judd said:
sounds to me like the brake fluid ,if you are using standard brke fluid it will boil as you said so a change to dot 4 should solve or speak to your local specalist . also change of pads to green stuff or mintex they dont fad when they get hot plus grooved disc,s if you are going to do trackdays regular.hope that is of help.
gary judd
Errr Forget Dot 4. Use Dot 5.1. Close to racing fluid but not as expensive or needs replacing everytime it is used.
It is a Cerbera so should be running fast road pads anyway. I don't think anything other than performance pads are available for those callipers.
Braking technique can also play a big big factor. Try squeezing them rather than last minute standing on them. Gives time for the weight transfer to happen which means that you have more grip and the ability to apply more braking without locking up. Braking a bit earlier will also pay a lot of dividends.
Wheel vibration can be warped discs or disc deposits or flat spotted tyres or tyres that have marbles(rubber debris) embedded in them and thus causing the vibration.
Apart from the fluid, the brakes have been fine; took it round Brands GP a few weeks ago and no problems at all.
But I have been taking it easy on the brakes and braking early as you say, Steve. I knew they were a weak point and didn't want to push them.
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What's this DOT x and DOT x.y stuff, then? Do I go into my local motor factors and ask for DOT x brake fluid? Or local TVR dealer. Or specialist? (who is a damn long way away - you know who you are!). And I assume that replacing the fluid is one of those jobs that people say is 'easy' but in reality is quite fiddly and requires a couple of specialist tools which I probably don't have?
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The wheel vibration is interesting - I thought it might be warped disks, but I can't see how it would be marbles - that would imply that I wasn't on the racing line the whole way round!!
Surely not 
But I have been taking it easy on the brakes and braking early as you say, Steve. I knew they were a weak point and didn't want to push them.
[thick mode]
What's this DOT x and DOT x.y stuff, then? Do I go into my local motor factors and ask for DOT x brake fluid? Or local TVR dealer. Or specialist? (who is a damn long way away - you know who you are!). And I assume that replacing the fluid is one of those jobs that people say is 'easy' but in reality is quite fiddly and requires a couple of specialist tools which I probably don't have?
[/thick mode]
The wheel vibration is interesting - I thought it might be warped disks, but I can't see how it would be marbles - that would imply that I wasn't on the racing line the whole way round!!
Surely not The DOT numbers refer to different formulations of brake fluid. DOT 3 and Dot 4 are used in ordinary cars but Dot 5.1 is a higher spec with a higher boiling point. Get it from Halfords (expensive) or a decent Motor Factors. I use the Comma brand and had no trouble. Mixes with Dot 3/Dot 4 so no problems there. I would fluch the fluid out of the system and replace it with Dot 5.1 and see how you go. If the vibration is warped discs then the brakes have overheated. They can take a significant time to cool down. Goodwood is hard on brakes because of the speeds involved. It is hard on tyres because of the cornering speeds.
Marbles don't have to be on the racing line. Tread can slough off the tyre and create its own marbles. If that is the case then it does indicate quite hard use or low tyre pressures.
Marbles don't have to be on the racing line. Tread can slough off the tyre and create its own marbles. If that is the case then it does indicate quite hard use or low tyre pressures.
Futie, did you get any leakage at the master cylinder end? - it often happens if you boil the brake fluid and then that neatly strips the paint off your engine bay, so worth checking. I boiled the fluid in my Cerbera at Snetterton earlier this year. Don't worry about it, it just proves you were driving properly. Oh and it always seems to happen when you have been off the brakes for a while (eg the cool down lap). I have never bothered to figure out why... it just does.
However, in line with everyone else's comments, definitely replace the fluid (once its boiled, its efficiency is compromised). Most modern high performance cars are already specced at Dot 4 and that should be sufficient but don't forget that non synthetic fluid is seriously hydrophilic, so it should be replaced regularly to maintain efficiency.
For what its worth I use AP600 in the caterham and have never even had a soft pedal.
cheers
However, in line with everyone else's comments, definitely replace the fluid (once its boiled, its efficiency is compromised). Most modern high performance cars are already specced at Dot 4 and that should be sufficient but don't forget that non synthetic fluid is seriously hydrophilic, so it should be replaced regularly to maintain efficiency.
For what its worth I use AP600 in the caterham and have never even had a soft pedal.
cheers
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