Braking Issue when Hot

[Motorhole]

Okay, so I hit Oulton Park on Tuesday and the car would've been great, save for one thing - progressively worsening brake judder, but only when hot!

Basically, every session, the first lap would be fine, until you brake for the last corner and you'd feel a bit of vibration. Same again after passing the start-finish straight, then braking downhill into turn 2 for the 2nd lap it would start to get really bad and I'd have to back off completely after the hairpin.

Basically, pedal starts to go quite hard and the whole car shakes - but only under brakes and as above, only once they've got a good bit of heat in them - and it gets progressively worse with each subsequent braking zone, until the shaking is horrific and I have no confidence in the brakes. Don't notice it on the straights. Doesn't happen at all at lower speeds - even when hot, slowing down to come into the pit lane the issue wasn't apparent. So ONLY when hot, ONLY when braking v. hard from speed. Needless to say it's never an issue on the road.

Setup is E36 M3 gubbins up front (it's definitely the front that's the prob!) with OEM Mintex discs and Pagid pads. Pedal box with twin m/s, bias bar and (obviously) servo delete.

I'm going to take the discs off and get the runout checked at the weekend - but they look good and there's no obvious buildup of pad material. Also - the offside front caliper is an upside-down nearside one. This is the only thing I know is amiss - but it does appear to be properly bled - which means it should be working properly? Nevertheless I am going to replace this for a correct one. Also I wonder if the exhaust might be cooking the offside control arm bush, making it soft and causing wheel shimmy when braking hard? The OEM heat shield that normally sits there has been removed.

Any other suggestions/ideas would be most welcome Needless to say it's a difficult issue to troubleshoot on the road!

[DanThe]

Check your PAS reservoir to pump hose, I had a similar judder and it turned out to be slightly kinked

[Motorhole]

Cheers Dan, I'll add that to my list of things to check out!

[initial_g]

I had a simular issue Id upgraded the bakes to ds2500 pads and 280mm discs... but left stock fluid in, I run high temp blue race fluid now and its sorted it

[Motorhole]

Thanks for the suggestion. I have AP Racing Dot 5.1 fluid in it which should be okay for track applications right? I do have new fluid to go in because the current stuff has been in there for over a year - albeit only a couple of short events and a thousand road miles or so.

Wouldn't have thought I could be boiling that just after a lap right? Also if anything, pedal seems to go harder with the vibration rather than softer.

[Willeh]

What does the pad wear look like? Have you checked the caliper bushes? The high heat and load could be making them pliable, letting the caliper do all sorts of spastic stuff.

[Motorhole]

Potentially yeah. Calipers were freshly refurbished ones but its a possibility. Seems there is some measurable wear in the guide pins themselves (2nd hand carriers) so will replace these. I dont think 2mm play is excessive movement for a floating caliper though? Have had to borrow a dial indicator so havnt measured runout yet - but it's deffo not a kink/obstruction in the PAS plumbing, nor is it a softening lollipop bush.

[Mikey_Boy]

Hope you are keeping well fella

I'd change the fluid out for starters - DOT 5 fluid is wickedly hydrophilic as you know so it could be off spec and causing you issues..

Another avenue to explore is hub bearings - if the hub is out of round that can cause the judder and gets worse as speed and heat increases - basically throws the disc out a tadge and gives you the judder.

Good luck

[Motorhole]

Not bad Mikey! I was going to give you a shout actually, see if you fancied tagging along but still having little faith in the car wasn't sure it would be worth your while turning up and signing on

Will flush the fluid as a matter of course, cheers. As for the hubs - the wheel bearings were new FAG ones about 1000 miles ago. I did have that exact issue before I swapped them out - and score marks from the caliper on the inside of the wheel to show it. Clearance is tight...

[Motorhole]

Well that might be a good call Mikey...

Disc run out is 0.02 mm offside, 0.07 mm nearside. Bit high nearside but I doubt anywhere close to enough to cause my symptoms. Runout on the hubs is negligible and there is no play or noise when turned. However the offside bearing doesn't feel right. It has a 'sticky point' when you turn it and its like you can feel some friction from within. Feels worse when you put a lateral load on the bearing with your hand and turn it back and forth through the sticking point...

[Mikey_Boy]

That's quite high run out to be fair - factor in expansion with heat and that *could* be the cause.. Worth a try???

[Motorhole]

Perhaps...I can't find a spec figure but 0.05 mm seems to be batted about various forums a lot.

I think I'm going to replace the bearing - maybe I d*cked something up on the installation, though don't know how. Have done a few E30 wheel bearings in the past without a problem. I've also got a correct offside recon caliper to fit and new guide pins for good measure.

I think I'll purchase some new discs too but will just take 'em along to my next trackday and swap them out if the problem rears its head again. Probably more cost effective than getting the old ones resurfaced and it may or may not be needed.

[Demlotcrew]

Are the brakes binding at all?

[Motorhole]

Shouldn't be...two freshly refurbed calipers. Definitely not sticking on the sliders anyway. I'll double check the pistons next time I'm down the lockup, only getting a short while there at a time at the moment

[Motorhole]

Well, thus far I've changed the wrong-handed caliper, replaced the offside wheel bearing, replaced a brake pipe I wasn't 100% with from the build (it entered the union for the offside flexi at a slight angle) and I've replaced the guide pins and bushes.

I've also purchased some new rear discs. The old ones that were on there were the same 318ti solid discs I got with the rear arms - just cleaned them up and fitted them back on as there wasn't a lot of wear. However the chance came up to get a brand spanking pair of grooved DBA discs for £65. So these have to go on, but more a nice to have really. And I've used this issue as an excuse - and that I've been working crazy overtime - to purchase a pair of the OEM spec M3 Evo floating discs to replace the 1-piece Mintex discs that were on the front beforehand.

Fingers crossed.

[Demlotcrew]

Going to a floating disk is going to make a massive difference, its an upgrade well worth having.

Do you still run the inline pressure reducer to the rear brakes?

[Motorhole]

Do you still run the inline pressure reducer to the rear brakes?

Nope, I'm using a pedal box with twin master cylinders and bias bar, so no valves or any other gubbins - save for the hydraulic brake light switch on the front circuit. What're your thoughts?

[Demlotcrew]

I think that its possible that the fronts are working too much and are out of balance and thus are overworked causing excessive heating.

[Motorhole]

It's a possibility. That would definitely be exacerbated by 1-piece discs and I have seen plenty reports of M3 owners complaining of hot brake judder on 1-piece discs - but then the E36 is much heavier than a stripped E30.

Next day out is Blyton Park. It's open enough there for me to play around with the brake bias a bit without fear of a big rear lockup ruining my day

[Demlotcrew]

Thought about a modern ABS?

With the MK60's two pressure sensors you can fine tune the balance very accurately #shameless plug

[Motorhole]

Thought about a modern ABS?

With the MK60's two pressure sensors you can fine tune the balance very accurately #shameless plug

Ha! Nice bit of kit! Bit overkill for my bag of bolts though. Perhaps when I eventually move onto Version 2.0

[Demlotcrew]

Version 2.0?

[Motorhole]

Haha yes. "Version 2.0". For when most of the niggles have been ironed out of this one and I've had some fun driving it, time to take it apart again. Bearing in mind when I started this, my mechanical knowledge was limited to changing wheels and oil, a lot has been learnt and there's a lot I would do differently. Plus it gives me the chance to reduce (more) weight and add power