Brake temps

[dunc_sx]

My rear brakes have been getting hotter than I think they should, certainly always a fair bit hotter than the fronts. Would this be considered normal? I have new disks, calipers and pads on the back and the cockpit bias is set almost fully to the front to try and help it. The brakes have been going off after about 10-15mins hard use with too much travel in the pedal and not enough braking, each time the fluid has been dot 5.1 and was replaced before the last race where it happened again. Brakes are fine up to about 10/15mins. I suspect one of the following to be the main suspect:-

1) Cockpit brake bias is not working, I'm not overly familiar with it's operation but an experienced (with radicals) mechanic had a look at it for me and seemed reasonably happy
2) Bias needs adjusted at the actual BMC's to get a better operating window for the cockpit adjuster
3) Rear brakes just run hotter because they are a smaller setup?

Any comments on this, the brakes are not binding but I've only started to monitor the brake temps so I don't have any previous data to go by.

Any advise appreciated,

Dunc.

Edit: Any good ways to test the brake bias while not driving? Would spinning the wheels and seeing which start to resist the most under low pressure force be reasonable?

[Martin B]

What pads are you using?

I use race brake fluid, I used to find 5.1 went off a bit but not as quickly as you are getting though.

Do you have 4 pot or 2 pot rear calipers?

[dunc_sx]

Performance friction, have always used these without problems. 2 pot rear calipers, rear brake temps are approx 50 to 100°C hotter (I don't have the data to hand). It feels like I'm going to loose the brakes which is not good.

I'm just about to add ducting to the front but not too sure what to do about the back. The two circuits in question are Donington GP and Castle Combe, would they be considered to be particularly tough on brakes?

Dunc.

Edited by dunc_sx on Thursday 18th August 11:52

[Martin B]

Do you have the Radical front brake ducts on the upright?

I take it you have vented 4 pots front, solid discs with 2 pots on rear?
(Mine are vented 4 pots front, solid disc 4 pots rear, same size caliper pistons and master cylinders front and back)

I run PF 01s, rears used to get very hot and wear out much quicker than the fronts and had enough bias adjustment to sort that now.

Do you bleed/flush the brakes before every event?

Could it be hat your front calipers need a rebuild and are simply not working as well as the brand new rear ones?

It made quite a difference when I fitted new master cylinders this year and when I rebuilt the calipers last year.

Edited by Martin B on Thursday 18th August 12:07

Edited by Martin B on Thursday 18th August 12:11

[splitpin]

I wouldn't worry about which tracks, as clearly you have a significant brake problem, 'particular track irrespective'.

As with any car, the bias adjuster if not properly maintained is notorius for going AWOL.

You can get a reasonable idea of whether or not it's functioning properly by tilting the car on it's side so one side's front and rear wheels are clear, applying a bit of brake using such as a wedge and feeling by hand the turning resistance and whether it can be adjusted via the bias; remember you should only use the bias adjuster with 'brakes off'.

Pot levels/any leaks anywhere? It sounds like air to me and I'd take a guess that probably the problems are at the front end which is making the rears do serious overtime; Temperature wise, I'd expect the rear calipers to be much the same temp as the fronts, if anything slightly cooler.

Another thought is that perhaps the front caliper pistons / seals are on the way out?

[dunc_sx]

Martin B said:

Do you have the Radical front brake ducts on the upright?

I take it you have vented 4 pots front, solid discs with 2 pots on rear?
(Mine are vented 4 pots front, solid disc 4 pots rear, same size caliper pistons and master cylinders front and back)

I run PF 01s, rears used to get very hot and wear out much quicker than the fronts and had enough bias adjustment to sort that now.

Do you bleed/flush the brakes before every event?

Could it be hat your front calipers need a rebuild and are simply not working as well as the brand new rear ones?

It made quite a difference when I fitted new master cylinders this year and when I rebuilt the calipers last year.

Martin,

I have the front duct pieces and ducting tubing to fit, I'm going to point it close to the disk.

Yes fluid is flushed and rebled before each race weekend.

I hadn't considered the fronts being to blame, adjusting the bias enough would balance the work each caliper was doing though?

Trev,

It could well be air butI'd expect that to be bad constantly, not consistently mid race or mid session. What do you think?

Anyone know how ducting to the rear brakes works?

Cheers,

Dunc.

[splitpin]

dunc_sx said:

Trev,

It could well be air butI'd expect that to be bad constantly, not consistently mid race or mid session. What do you think?

Anyone know how ducting to the rear brakes works?

Cheers,

Dunc.

So would I Dunc, but I know from experience that any air in the system can manifest itself in totally weird and wonderful ways.

Are you losing any fluid anywhere even if you don't really know where? I.e. are the pot levels keeping stable?

Obviously, it's logical that if fluid can get out, air can get in.

We had some trouble with the nipples on our front Wilwoods; brakes kept going spongey after a period of intensive use, very small fluid loss, but only when really hard on them; very difficult to find/discern static.

No ducting whatsoever on our ventilated rears on the Pro - they're just fine.

Proper ducting and shrouds on our four pot fronts - they're just fine too - want me to post a pic?

By fine, I mean as good as it gets with those Wilwoods - compared to such as Hi-Specs, they are totally 'wooden' until there's a decent amount of heat in discs & pads and thus calipers. No probs when they're up to temp.

I still think your first test is/move should be to find out whether that bias adjuster is actually doing anything/it's stuff i.e. that it's not stuck leaving the backs doing way too much work; normally you'd immediately notice that, but if you've always had it, it's surprising how much one subconciously adapts how one drives to get round it. Are you going through rear pads like beggary compared to the fronts? That would be a sure sign: I'd expect to get say twice the life out of a rear pad compared to a front one.

Edited by splitpin on Thursday 18th August 19:07

[BertBert]

Could be a bias problem. Which locks up first, fronts or rears?

Are the front and rear M/Cs supposed to be the same diameter piston with the 4/2 pot setup?

Bert

[dunc_sx]

Cheers for the input guys, I agree that investigating the bias should be the first step. 97% sure the system is leakless, the rear calipers were replaced because the thread on the LHS one had become damaged and was leaking from there. Since then it's been new rear disks, pads and calipers and strict inspecting of the brakes and BMC levels.

Martin the BMCs haven't been changed neither have the brake specs (just like for like replacement parts where required).

Cheers,

Dunc.

[BertBert]

Did it happen before the change or rear calipers? Are the new ones the same as the old?
Bert

[dunc_sx]

Hi Bert, only noticed this after the caliper change - the calipers were direct replacements but had a slightly newer look to them (black with radical written on them), apart from that pretty sure they were the same. Same connections, size and fitted the short pitch upright lugs - they came from Radical.

Dunc.

[Martin B]

If the only real difference is brand new rear calipers then I think they are just operating bettwer because they are new, maybe the fronts need stripping, cleaning and new seals. When I did mine the brakes improved but I did all four calipers at the same time so the improvement was at both ends ofthe car not just at one end.

Are the pads all the same age front and rear? If you fitted new pads on the rear but left the old ones on the front that will make a difference. I have found pads go off with time.

[dunc_sx]

Pads all round fitted at the same time, thanks for the advice I'll get cracking on the investigations

[splitpin]

dunc_sx said:

Hi Bert, only noticed this after the caliper change - the calipers were direct replacements but had a slightly newer look to them (black with radical written on them), apart from that pretty sure they were the same. Same connections, size and fitted the short pitch upright lugs - they came from Radical.

Dunc.

R on them suggests they might be Hi-Specs rather than Wilwoods?

So said, clearly The Big R wouldn't have supplied calipers which were incompatible with the existing fronts, so still don't think that's the fundamental issue. Nor do I think age of pads would have made that dramatic a problem, but that's by the by now anyway.

As said earlier, bias functionality should be first port of call - simply watching what happens to the bias bar in terms of which BMC gets the most shove when the pedal gets pushed may well indicate to you what's what. Then get it up on it's side with aa bit of brake wedged on, which may prove via your hands what your eyes may have already suggested to you.

[dunc_sx]

There it is, single split pin through the pad (same pad shape as my old wilwoods) and an annoying 1/4" bleed nipple. Wilwood don't make them anymore but Radical recon they had a couple hanging around.

Dunc.

[SportsLibre]

That radical calliper is the re-badged Willwood. I have one of each on my car as the original owner apparently replaced it at some point.

The problem as previously stated is likely that the rears are now working properly, whereas the bias/fronts...?

[panas]

This is almost certainly bias ajuster and this is a simple mechanical device and very easy to see if it is working. If you follow the cable you will see that it is connected to a balace bar that inturn is connected to both the front and rear master cylenders and the brake peddle, the bar is just a threaded bar really with a ball like nut that is located to the peddle as you rotate the ajuster you should see the threaded bar turn and you can easaly se the piviot point moving down the bar. The usall problem is the grub screw that connects the cable inner to the the balence bar starts slipping and this is an easy fix with a very small allen key the other common problem is people bleading the brackes with out pushing the cluch in as the cable fouls on the cluch peddal and that really mullers it and normally needs a new cable but you might be lucky and get away with it. sorry about the english and grammer but you should be able to get the point

[dunc_sx]

OK thanks guys, I'll check all this stuff out

Dunc.