E30 M3 5-lug -- Long Pedal

[Digitalwave]

I recently transferred an E30 M3 5-lug conversion from an 87 325iS over to a 91 318iS chassis. Pretty self explanatory, but I have not been able to get rid of the long and soft brake pedal since making the swap.

Previously I was running the stock 17/22mm MC, and the 318iS has the same. I am running the same pads, rotors, etc. that were on there before.

The car sat with no brakes or lines attached for about 2 months indoors. I put rubber caps over the hard lines and they were not dripping. There was still fluid in the reservoir the whole time. I'm not ruling out that air might have entered the ABS pump or MC.

However, the car has been both pressure and manually bled for about 2 bottles of fluid at this point. The car still stops, the pedal is just long and soft. It had great feel in the car it came out of. The ABS was also activating when it shouldn't be -- it was being overly sensitive.

My goal is to get the pedal feel back, and then figure out what's wrong the ABS. They may be related, but I think the pump is a pass through device when the system is powered down, so theoretically disconnecting it would effectively "disconnect" ABS to help me isolate the problem, right?

The only thing I can think of trying next is a different set of pads. Perhaps my track pads (which have a ton of life yet) have worn unevenly, leaving a gap and a soft pedal.

Any other troubleshooting ideas would be helpful!

[FredK]

I had a similar problem of the ABS activating when it shouldn't have, and it ended up being the sensors being swapped from left to right. It would activate in the first inch of travel when there was barely any braking force.

As for having a long pedal, there aren't many ways that this happens unless there's a leak in the system somewhere, or you have air in the system. If you pump the pedal, does the brake feel get better? If so, your MC might be on its way out.

[Digitalwave]

It doesn't seem to build when I pump the brakes.

I didn't realize the L and R were different sensors. I easily could have swapped the two. Good call on that Fled.

[Digitalwave]

Got to mess with the car a bit today. I did indeed install the wheel speed sensors backwards, so that should hopefully fix the ABS triggering problem.

I bled the brakes again. I only got a tiny amount of more air out. I don't think it will have fixed the soft pedal, but I haven't been able to drive it again yet.

The brakes worked great on the chassis they came out of. So from chassis to chassis the only things different now are the ABS pump, master cylinder, brake booster, and hard lines. All the brakes are bleeding well so the lines aren't clogged (not that that would make a soft pedal).

Fred, which MC are you running with your 5 lug? My other chassis had the same 17/22mm stock MC and it had a great pedal feel.

My inclination is that the problem would be in the MC or ABS pump, as I don't think the brake booster could cause a long/soft pedal, right?

The other thing I was going to try was a different set of brake pads.

[FredK]

I have run the 17/22 stock MC with a booster and without, and am now running a dual master system with a balance bar.

I haven't really had any problems with long pedal travel. If you haven't touched the MC and booster, it'd be weird for them to go bad just from sitting. I think it's still an issue of having air in the system, but you could try swapping out one component at a time to get to the bottom of this, even though it would suck to do so. Sorry I don't have any other words here!

[Digitalwave]

My new theory is I put the rotors on the wrong side of the car (I had them off for a while and mixed them up), mismatching the worn track pads and rotors. One of the front pads has a noticeable gap from the uneven wear on the pad. I also had put the retaining clips on the front calipers for the first time (they didn't fit with the wheels I had been running). Maybe that shifted the pads a little.

I have new rotors and pads to try this weekend. I am hopeful it will fix the problem.

[FredK]

Might as well start off with the easy stuff, especially since you knew everything else was already functional before the swap. Good luck, and let us know how things work out!

[AndrewBird]

The calipers should adjust the first time you step on the brakes, unless the guide bushing are seized up and the caliper isn't sliding like it should.

I'm double check the part number on the MC. Maybe the previous owner put in a different one. Or maybe the 318 pedal box/pedal is different?

[FredK]

The pedals are identical, and the pedal boxes, while they changed between airbag and non-airbag cars, did not change functionality.

I have tried the 17/22mm and a 23.8mm straight bore MC with this setup and there wasn't any mush because of the difference in MC size.

[Digitalwave]

I've got brass guide bushings but even then, the forums seem to indicate that pads wear wedge-shaped. The piston has adjusted, but a portion of the pad isn't worn evenly and probably has to travel further. I'm guessing this was exacerbated by either swapping the rotors side to side and/or putting the retaining clips back on.

The car still stops great when you get on the pedal, it's just much farther than it was.

I didn't find part numbers but both MC's were embossed 17/22mm (front and rear).

I also forgot to report that the wheel speed sensors WERE on backwards, and swapping them back fixed the ABS problem from the OP!

Thanks for the feedback guys. I will report back this weekend with the new rotors/pads/clips installed.

[Digitalwave]

Glad to report that new rotors, pads, and retention clips 100% cured the problem. The brakes are tight, strong, and better than ever. The pedal feels great.

I should note that I never ran the retention clips on my front calipers. The pads and rotors had about 7 track days on them. I think that was detrimental to the wear on my pads, which should have had a ton of life left. Hopefully the new set will wear better now that I am running the clips.