E36 M3 brake all around, 25mm BMC, PEDAL STILL SPONGEY!!

[E30stan]

Greetings,
So i finally got the 25 mm brake master cylinder installed and bled the brakes profusely. Mind you i have e36 m3 brakes on all 4 corners, stock booster, and of course the 25 mm BMC from a e32 750i(i believe). Besides the fact that there was a small penny sized disk between the BMC and the grommet that i had contemplated not installing, i choose to keep it there in case it helped to keep the pinholes from being blocked up with just the grommet installed.

With that little hiccup out of the way, the pedal stiffened up really nice as i was bleeding the brakes. The problem is that once i went for a drive, the pedal feels incredibly spongy at first? The car stops well but it requires maybe 5 inches of travel to actually really bite down. If i pump the pedal once and then pump it progressively firmer as im approaching a stop it seems to act much more consistently. In other words, its almost as if i need to pump the pedal once to build pressure, then as i normally apply the pedal in a progressive manner as usual it acts fine. Its when i don't pump the pedal once that i find that im making the pedal travel much to far?!?

My expectations were that the pedal should engage much like a newer 135 for example, right at the top and only requiring about an inch of travel to make impressive stops?

Im thinking that it could be the brake booster not being able to keep up with the other upgraded brake components? Or it could be the BMC that i purchased in used condition?

Sorry for the long post, any thoughts?

And heres a little inspiration:)

[DER E30]

Sorry I don't have any advise, but WOW that's an awesome looking car and swap!

[E30-323ti]

Ah, I see the problem....





... car is far too mint / hawt looking.

Seriously though.
If they bleed up firm they should be staying firm.
Have a look to see if your fluid level is dropping at all, I had an old mazda GTX that had a leeky BMC, and was pumping back into the booster, so wasn't at all visible.
Also, have a look if the calipers need an overhaul, could be something funky with the guide-pins/bushes that with the rotor torque it's twisting the calipers on the guides or getting piston knock-back???

[berlow94]

Interested to see how this plays out. I have similar set up, E36 M3 MC, IX booster but I have massive's race kit all around (wilwood 6 piston up front, 4 piston in back). Car stops like crazy, but the pedal throw is way more then I want and never really gets firm. Doesn't make it too easily to modulate the brakes either.


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[E30stan]

Sorry I don't have any advise, but WOW that's an awesome looking car and swap!

Thumbs up!

Ah, I see the problem....





... car is far too mint / hawt looking.

Seriously though.
If they bleed up firm they should be staying firm.
Have a look to see if your fluid level is dropping at all, I had an old mazda GTX that had a leeky BMC, and was pumping back into the booster, so wasn't at all visible.
Also, have a look if the calipers need an overhaul, could be something funky with the guide-pins/bushes that with the rotor torque it's twisting the calipers on the guides or getting piston knock-back???

Interesting point about the internal leakage, ill have to check on the fluid level asap. While i highly doubt the calipers are the culprit, since i rebooted, cleaned, and lubricated, its worth a look. Thanks for the input!

Interested to see how this plays out. I have similar set up, E36 M3 MC, IX booster but I have massive's race kit all around (wilwood 6 piston up front, 4 piston in back). Car stops like crazy, but the pedal throw is way more then I want and never really gets firm. Doesn't make it too easily to modulate the brakes either.


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Sounds like a fierce setup you have!

I even tried disconnecting the brake booster vacuum line for a short while to remove any assist, that just made the pedal require an elephant foot:) Same amount of pedal travel:(

I should probably just pony up the $175 or so for a new BMC?

Funny thing is, when i pulse the pedal, like mentioned above, the car stop incredibly sharp and well balanced. Albeit this could be the symptoms of a failing BMC.

Any experience out there with the 25mm BMC upgrade and how the pedal should perform?

[E30stan]

Interested to see how this plays out. I have similar set up, E36 M3 MC, IX booster but I have massive's race kit all around (wilwood 6 piston up front, 4 piston in back). Car stops like crazy, but the pedal throw is way more then I want and never really gets firm. Doesn't make it too easily to modulate the brakes either.


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After some discussion, it seems I should bench bleed the brake master cylinder. Or in my case, disconnect the two hard lines, then plug in some pigtails I h ave lying around from some old brake lines, then route two vacuum hoses into the reservoir, and finally pump the brakes until the master cylinder gets properly purged from air. Hope this helps someone else in my same shoes.

For what it's worth, this is the first time I've ever had an issue with a brake master cylinder having air. Usually they are recently removed and therefore still filled with fluid in critical crevices around the piston chamber. It's likely that if a brake master cylinder has been sitting on a shelf for a long while, the fluid seeps out entirely, don't quote me on that though:)

[BenM]

What is your rear setup? Full MZ3 Trailing Arms or Ti rear trailing arms? If the latter, then check to make sure your calipers are mounted with the bleeder screws pointed up. If not then you will never get them fully bled (ask me how I know lol).

If you still have ABS, try to cycle the ABS unit remove any possibly trapped air in there. I can't remember the procedure off the top of my head, but it should be easily found if searching.

[E30stan]

What is your rear setup? Full MZ3 Trailing Arms or Ti rear trailing arms? If the latter, then check to make sure your calipers are mounted with the bleeder screws pointed up. If not then you will never get them fully bled (ask me how I know lol).

If you still have ABS, try to cycle the ABS unit remove any possibly trapped air in there. I can't remember the procedure off the top of my head, but it should be easily found if searching.

The rear brakes are indeed pointing down, its the ti arms with e36 m3 brakes made to fit. The calipers seem to be bled fine?

I just finished bench bleeding the bmc and reinstalling and bleeding all corners again, what a messy job! Anyway, still doesnt feel right. Maybe i set my expectations high? Like i said before, the car stops very quickly its just the pedal travel is boring! Any thoughts?

[Mossman]

I have e36 m3 front brakes and ti rear stuff and my pedal is anything but spongy. I also have an IX booster, and e36 m3 brake master. Never had a hard time bleeding it though. Only difference I can think of is that I ditched ABS. Can't tell in your pics if you still have it, but is there some procedure for "tickling" the ABS if there's a chance air is trapped in there?

[BenM]

The rear brakes are indeed pointing down, its the ti arms with e36 m3 brakes made to fit. The calipers seem to be bled fine?

I just finished bench bleeding the bmc and reinstalling and bleeding all corners again, what a messy job! Anyway, still doesnt feel right. Maybe i set my expectations high? Like i said before, the car stops very quickly its just the pedal travel is boring! Any thoughts?

If the bleeder screws are pointed down, then you will never bleed all the air out of the system. One way is to take a block of wood with a similar thickness to your caliper and after you've unbolted your caliper, stick it between the block of wood with the bleeder screw pointed down. It's a pita to do, but it works. Are you running stock rear Ti Rotors too? If so, then do you have something to take up the difference (I believe it's 10mm since M3 rotors are 20mm thick and Ti rotors are 10mm thick)?

Just to get even more in depth with this, but if you bolt the M3 rear calipers to the Ti Trailing arms and the factory e30/ti lines match up perfectly, then actually have the calipers on backwards. If you swap them so that the softline exits out towards the bottom of the car and the bleeder screws are pointed up, this is the correct orientation of how they are supposed to be.

[berlow94]

Don't jump too quickly to buying new stuff! My IX booster and MC are brand new!
Been checking my fluid, has't leaked at all.
Curious that it felt that way even with the vacuum line unplugged from the booster. I was almost positive that the issue was just the booster. (im coming from an E21 booster)

[wazzu70]

Are your brakes actually spongey, or is the pedal travel longer than you prefer? If the brakes are not spongey, but you want less pedal travel you can change the pedal ratio.

[berlow94]

Wouldn't exactly call them spongy. I wish the pedal was physically harder to push and had less throw.
Forgot to mention I do have a brake bias valve installed. Will that really effect pedal throw?

[E30stan]

If the bleeder screws are pointed down, then you will never bleed all the air out of the system. One way is to take a block of wood with a similar thickness to your caliper and after you've unbolted your caliper, stick it between the block of wood with the bleeder screw pointed down. It's a pita to do, but it works. Are you running stock rear Ti Rotors too? If so, then do you have something to take up the difference (I believe it's 10mm since M3 rotors are 20mm thick and Ti rotors are 10mm thick)?

Just to get even more in depth with this, but if you bolt the M3 rear calipers to the Ti Trailing arms and the factory e30/ti lines match up perfectly, then actually have the calipers on backwards. If you swap them so that the softline exits out towards the bottom of the car and the bleeder screws are pointed up, this is the correct orientation of how they are supposed to be.

Ben, here is the guide i followed to get the e36 rear brakes installed,

http://www.318ti.org/forum/showthread.php?t=35983&page=3

I see what you mean about unbolting the calipers, I think you mean to position them with the bleeder pointed UP in conjunction with the piece of wood. Although i doubt the issue being the rear calipers not fully bled out, Ill have to try that when i get a break.

Are your brakes actually spongey, or is the pedal travel longer than you prefer? If the brakes are not spongey, but you want less pedal travel you can change the pedal ratio.

How would one go about changing said pedal ratio?

[BenM]

Ben, here is the guide i followed to get the e36 rear brakes installed,

http://www.318ti.org/forum/showthread.php?t=35983&page=3

I see what you mean about unbolting the calipers, I think you mean to position them with the bleeder pointed UP in conjunction with the piece of wood. Although i doubt the issue being the rear calipers not fully bled out, Ill have to try that when i get a break.

Yes, sorry that is what I meant. The bleeder screw should be pointing up. That's a pretty good link, take a look at post #38 and look how is bleeder screws are oriented.

The point I was making earlier, was that you can bolt the M3 calipers right up and all the stock Ti softlines fit perfectly, but the calipers are in fact on backwards. The stock E36 M3 rear softlines are routed differently so that the bleeder screw is pointing up. I'll try and get some pics highlighting the differences.