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Re: brake pedal travel

PostPosted: Mon Jul 04, 2016 3:21 pm
by RotoFlexible
I had the same issue when I installed +2 calipers on my S2 (no servo involved). The problem resulted from pad retraction. There is a thread on it in here somewhere, but in summary:

- Look for visible clearance between the pad and rotor. If you can wiggle the pad, there's too much clearance.
- If you find clearance, watch the pad while an assistant steps on the pedal. If the clearance closes up and then re-appears, that piston has a retraction problem.
- To fix the problem, remove the pistons, clean everything, and lubricate the seals and bores with caliper grease. You can use the Girling Crimson grease, but I have used Permatex Ultra Disc Brake Caliper Lube successfully.

It took a couple of tries to get this right, but now my pedal is as good as it was with the original calipers.

Good luck!

Re: brake pedal travel

PostPosted: Mon Jul 04, 2016 3:45 pm
by SF69Elan
Andrew, thanks for this information. This sounds similar to one of the scenarios that Rohan had also highlighted. I'll definitely check the pad/rotor clearance this week and if that looks like the culprit I'll proceed with a cleaning/rebuild of the calipers. I think the last rebuild w/ new seals, etc. was done by the previous owner back in 1998 (that's the date on the receipt for the parts, at least).


Re: brake pedal travel

PostPosted: Mon Jul 04, 2016 10:48 pm
by PBK
Rich, firstly the existing pedal was drilled, a spacer plate was made to accept the standard pedal pad and the two were bolted together. To suit my preference in how I use the brake and accelerator together the pad was bolted about half an inch higher up the pedal so that as the pedal swings and engages, the face of the pedal relative to the accelerator is just as I like it. In my car we determined the height by depressing the pedal once until strong resistance was achieved. A "guestimate" of how much high I wanted the pedal was made with the assistance of the tech.

I forgot to put in my previous post that I initially tried this set up without booster and didn't like it. With the booster it is very, very good. Initial retardation can't possibly have changed by this change. However, you just don't get preoccupied with the fact the pedal is so low.

The slightest ease of pressure and reload of the pedal can induce the ABS in a following M3!

I had committed much time and expense doing most if not all of the things suggested earlier in the thread by Brake "experts" who were baffled.
Confidence for me is the key. In 38 years of Racing, Sprinting, Hillclimbing and Tarmac Rallies a solid pedal, first time, everytime was my number one requirement.

This works for me and may suit you - easy enough to try!

I would be interested in your view if you do. I wonder how many people represent perceived excessive pedal travel as sponginess.

Cheers Peter

Re: brake pedal travel

PostPosted: Tue Jul 05, 2016 12:17 am
by SF69Elan
Hi Peter - thanks very much for providing the details of how you modified the pedal. That definitely helps me understand more clearly the modifications that you've made. It sounds like that together with the booster ended up giving you feel and confidence you were looking for.

The more I think about this, since the seals on the master cylinder and calipers were likely most recently replaced somewhere between 16 and 18 years ago, I think my first steps should likely be a rebuild of those with new seals and pistons.


Re: brake pedal travel

PostPosted: Tue Jul 05, 2016 4:06 am
by PBK
Rich, and so you should refresh. This "issue" would really be a simple resolution if the cars had an adjustable master cylinder rod connected directly to the pedal.