Braking problems

[dede911]

Hi,

During my trackday last sunday, I had serious vibrations in my steering wheel during braking.

The braking was not so responsive as usual.

The pads are Ferodo DS3000 on carrera discs (car is a SC)

Please have a look at the pics.

What do you think?

Also the discs have a strange wear pattern: "hollow" near the center of the disc...

[DRACO A5OG]

Vibration = Rotors may have warped due to extreme heat and pressure.

Do you have air divertors to keep the rotor cool?

[Joe Bob]

Either that or the pads were flaking due to heat and leavings clumps on the rotors.

Once they cool off the material leaves the pads with gentle braking.

['78 SC]

You mentioned track use. I had a similar problem here.

[Porboynz]

I used to race a 2.4 with small M calipers all around. I had cooling ducts which helped but I also bled the brakes after every race meet and between races would often scuff up the discs by hand with a strip of emery cloth to break up the glaze. You probably need to get those front discs skimmed straight again if there is enough metal left and absolutely buy some new pads. Looks like you had some serious braking going on from the way the pad is breaking up, must have been a fun day out.

[dede911]

Yeah, It was a fun day...

This all happened from new pads to this in 4 hours...

It is a rather short track (4 km) with 6 breaking zones, coming down from around 200 km/h to **** second gear or third gear, and all this in around 2 minutes...a tough life for brakes.

It is possible that my bedding in procedure was not OK...

Yes, I do have air diverters, but maybe real duct or more effective. I will check out.

Strange to me is the disc wear: more at the center of the disc, this lead to a "hollow" pattern, where you can see/feel a rounded shape at center of disc.

My caliper is to small to measure this...

Brand of discs is Zimmermann.

Any suggestions?

Thx,

André

[ivangene]

heat, plain and simple.....

you have to have a compound that can handle the heat - either too hot or too cold and you will get this.....

gotta know your operating temps and the pad ratings

[aston@ultrasw.c]

Carrera brakes do have a limited heat capacity but with a few mods they can work very well, even on the track.

I run my 86 on a wide variety of tracks with zero brake fade or boiling fluid, here's the run down:

stock rotors
PFC-97 pads
motul 600 fluid
brake ducts in front valance
rotor block off plates
car lightened to 2,400
caliper piston seal replaced every time rotors are changed
no caliper dust seal
master cylinder catch tank
braided brake lines
bleed brakes before every event
hose off brake/rotor dust after every event

[aston@ultrasw.c]

Wrt your wear pattern, I can't say I've noticed a "hollow" on the rotor but I do see the pads wear more in the middle. This is because the single piston caliper distorts the pad when you stomp on the pedal. It could be the same mechanism on your rotor.

[Gunter]

I'd check this:

If your caliper pistons have the steps, ensure correct 20 degree position!

The step allows a more even clamping-action when brakes are applied but only if set correctly!

Also, if your calipers haven't been rebuild for a while, some pistons may be frozen and this would prevent correct retraction meaning: excessive heat build-up due to unwanted contact between pads and rotors. The inner square seal, when distorted, is designed to retract the pistons but only if the pistons move freely.
Clean the rotor surface from any possible residue.
Try different pads.

[dede911]

I agree that probably the main root cause is heat.

First things I will do is cleaning the discs as Gunther suggest, and then give it a test with stock road pads I still have (track season in Belgium is over)

I have rebuild the caliper with SS pistons, should be trouble free for a time.

If the problem (vibrations in steering wheel) is curred, I will work out some solutions:

-better cooling
-heat sensitive paint to find out real live disc temps to optimize pad tenp?

If I would replace the discs, what brand would you buy?

Sebo has very attractive prices...

Maybe bells with removable discs would a cost effective solution...

aston@ultrasw.c, what is the lifetime of your discs and what brand?

What is the reason for not using dust seals?

[911pcars]

"What is the reason for not using dust seals?"

When subjected to the high temperatures of racing, dust seals melt.

Sherwood

[Bob Kontak]

Originally Posted by DRACO A5OG

Vibration = Rotors may have warped due to extreme heat and pressure.

FWIW - When my Boxster brake "upgrade" squealed at slow stops I read quite a bit and found (well, read) that brake rotors seldom, if ever, warp. Friction creates reactions in the pad material composition and deposits are left on the rotors creating the perception of warping.

Joe Bob mentioned it but it can happen on your daily driver as well if you get them hot and just park it.

[Eagledriver]

You probably just need better pads. The vibration is from pad deposits on the rotor. I use Hawk Blue 9012 pads and Carrera brakes. These pads are very abrasive and will clean off the rotors (and wear them out in about 12 weekends). Yes the rotors wear more in the middle and make a dished shape.

-Andy

[Gunter]

Heat will do a lot of things to braking components and wear and there is a huge difference between just street driving and racing, of course.

After cleaning the rotor surface, I suggest using a dial indicator to see if some uneven wear developed.

People find out what works by trial and error i.e., cross-drilled rotors developed a problem with stress-cracks and part of the solution was to chamfer the holes.

Sometimes I've used anti-squeal shims and other times not. Friction from the pads against the rotors when brakes are not applied is one of the main reasons why unwanted heat develops, IMHO. Not using any dust seals means brake dust and dirt will creep in and possibly prevent the pistons from retracting. In other words, the inner square seal cannot do what it was designed to do. I use special goo to ensure that, when the pistons retract, they pull the pads back as well for just a few thou. Less heat and less wear. I also make sure that the pads can move freely in the calipers which sometimes requires a little filing down the steel portion.

Racing means $$$.

[dede911]

Hi guys,

I cleaned the rotors thoroughly and installed stock pads in front.

It seems that the vibrations are gone but due to the fact that I still have the racing pads (friction coef 0.62) in he rear, and the stock pads front ( less than 0.4), the brake balance is screwed up. This means that during hard braking the rear brake block sooner than than the front...

Next I have to do is to buy me a brake disc thickness gauge to measure the discs.

To do during winter: how to improve cooling.

I can get the "connections" to connect cooling hoses here locally, but nobody has the block-off plates.

Does somebody has an exact drawing so that I can have it lasercut here?

Ordering is US is a lot of "trouble" just for 2 plates...

Anyway thanks a lot for all advice and sharing your experience

André

[lupin..the..3rd]

Originally Posted by ivangene

heat, plain and simple.....

Yes this is it. When they chunk and break apart like that, like brittle burnt toast, you've overheated them. I tried some of the $26 Mintex street pads sold here by our host. In under 5 laps at the track, my front pads were on fire. No, really, they were literally ON FIRE. the pad friction material had caught fire from the heat. I pulled into the pits because the brakes sucked and I smelled something funny. Upon stopping, I saw the smoke coming from the front wheel wells. I have pics somewhere. Upon swapping them out, the pads looked an awful lot like yours.....

[tdatk]

Originally Posted by lupin..the..3rd

Yes this is it. When they chunk and break apart like that, like brittle burnt toast, you've overheated them. I tried some of the $26 Mintex street pads sold here by our host. In under 5 laps at the track, my front pads were on fire. No, really, they were literally ON FIRE. the pad friction material had caught fire from the heat. I pulled into the pits because the brakes sucked and I smelled something funny. Upon stopping, I saw the smoke coming from the front wheel wells. I have pics somewhere. Upon swapping them out, the pads looked an awful lot like yours.....

True story, I was there.

Another point to ponder, I had a hard steering wheel vibration issue when braking hard at the track, my bushing in the upper steering column had givin up, easy to check, just grab the steering wheel and try to push it up or down/ side to side, should be very little to no movement.