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After a long hiatus, I have finally had a full season of tracking my E36 M3 with stock brakes. It appears that my car suffers from the soft brake pedal problem discussed quite a bit on these forums. I have read the many threads on this and it appears that cars that have this issue without any obvious problems with the booster, master cylinder, lines, and calipers are only often fixed by moving to a BBK? Is this still the conventional wisdom as many of those posts are from quite a few years ago.
I have checked the brake booster and it works normally. I have a PSI gauge on my brake lines so I can monitor PSI and it does not drop after 10+ minutes with steady pressure from a rod. The pedal travel is long and it reduces confidence when braking on the track.
Separately I've also come to the conclusion that many of the cooling duct systems do not really work well and/or cause more problems than they are worth with pad temperatures.
My car is a fully caged car and I am sorting it out for endurance racing next season. Any thoughts would be appreciated as a BBK is expensive and I like the running costs of the stock system and in general do not have a problem slowing my car down.
📷: @nholmes74
Does your MK20 ABS pump have a bleeder nipple? I connected a line to that nipple and cracked it open to find there was air trapped in my system. That solved the problem for me.
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Yea, if you have a 96+ your ABS should have that bleeder access. 95's don't.
But, I had good success by turning on the pump (shorting 2 pins on the ABS pump relay) and bleeding while the pump is running.
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Do you keep the pump running the entire time you bleed all 4 positions?Originally Posted by aeronaut
OP,
Same problems but I had this issue with a BBK so I dont believe its a solution. I have also had stock brakes that were rock solid.
Having read for a long time about this, my belief is that the ABS pump and trapped air plays the largest contributing factor. Agree with the posters above but I am trying to eliminate it on my car so I will see if I agree with them for long..........
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I don't believe that's needed. A few pedal pumps for each corner (or a few seconds if using a pressure bleeder) is enough to get the air out of the ABS pump. Then pump off, and full bleed.
Unfortunately, I don't think this is full proof, because running the pump doesn't cycle the solenoids. And I'm not sure all the passages are open. But it's an easy process and much cheaper than a BBS...which yea, doens't guarantee a fix.
📷: @nholmes74
Also, I ran the stock brakes for years without issue other than a spongy pedal. I had refreshed calipers, new seals, stainless brake lines, new pads/rotors, brass guide pins, etc etc and they worked great. I'll never say they were amazing or anything, though. I did a test with the car on the lift and the wheels off. I had a friend place a ruler over the top of the caliper and look down at it. I then stepped on the brakes as hard as I could. The caliper flexed visually, I could see it looking outside of the driver side window to the front left caliper. We measured about 6-8mm of caliper flex.
When I was doing this, I had concerns for potentially burning out the pump. My rationale was that in a real world situation the ABS pump normally wouldn't run for more than a few seconds (until the car came to a stop) so having it running for prolonged periods probably wasn't part of the original design.
That being said, I'm no engineer.
Last edited by golgo13; 11-10-2022 at 01:53 PM.
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Golgo,
I tend to disagree with caliper flex causing soft pedal issues as I have driven plenty of OEM (e36/e46) braked cars on track with a completely stiff pedal, and I have also installed a BBK and had a spongy pedal. Ergo, I tend to believe it is trapped air but who knows.
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Can you bleed the pump with just a pressure bleeder? Or do you need to short?
📷: @nholmes74
Oh, I was just sharing my observations. The flex made the system less than confidence inspiring for me based on pedal feel. I agree that the soft pedal wasn't related to the caliper flex.
I was able to bleed the system without actuating the ABS pump.
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I expect if your pump has the bleeder nipple, you don't need to short. Not sure, worst case it may take both? I'd have to cut a pump in half to know for sure.
If you're doing the short-the-relay method, 2 people could do it easily and only need to run the pump ~5sec at a time for each wheel.
Member
Wow. Thank you for all the great responses. The pump is from a 97 M3 and has been used for a good number of track events over the past 3-4 years since I moved it to the donor chassis (94). I will take a look and see if it has the valve. If it has a bleeder valve, what is the process? Have some depress the brakes as you normally would and then crack it open? I assume that is the same with shorting the pump to run it while someone is depressing it.
My car has all of the normal upgrades: brass guide pins, relatively new seals (going to rebuild anyway this off season), stainless lines, race pads (PFC). Fluid needs a bleed except it is only a flew months. I plan on flushing it completely after the rebuild/refresh for the new season.
I would love to focus my efforts to improve brake feel by not buying an expensive BBK and working on different pad compounds and possibly removing the cooling ducts.
📷: @nholmes74
Just bleed it like a normal brake caliper. Pressurize the system, crack the bleeder open until you see fluid/bubbles and leave it open 1-2s. Wash, rinse and repeat until bubbles are gone and the pedal feels better.
Last time I did it, I bled the nipple and then took the car for a drive and triggered the ABS a couple times then brought the car back into the garage and bled the ABS nipple a second time to confirm no air was still trapped in the pump.
YMMV
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