Bad Master Cyl? Next steps?

[lateracer]

Problem: I've lost nearly all pressure in my brake pedal. I did some searching here and it sounds like I've got a bad master cylinder. I'm ready to replace it, but I could use a little advice.

How it started: Went to flush/bleed brakes in my 86 325e. New-to-me car hasn't seen a brake flush in a decade probably. While pumping pedal with a rear bleeder valve opened, what I'm assuming to be trash in the lines clogged up the bleeder. Pumping the pedal fixed the first few little clogs, but eventually a big one showed up. I pumped the pedal a few times really hard and it felt like something popped. Suddenly it was really easy to pump the pedal, but there was no pressure.

Now, when I push the pedal with a bleeder open nothing comes out and I don't lose any fluid. I can apply a vacuum to a bleeder and it will pull fluid from the reservoir, but still no pressure.

My questions:

1. How should I proceed? I feel like I should blow out the lines with air, replace the rubber lines and rebuild the calipers. First car with ABS where I've messed with brakes though. Concerned about getting air in the ABS unit and not being able to get it out, damaging it and/or just screwing things up worse in general.
2. ABS delete? Thoughts/opinions? Worth the effort? Seems simple enough. It's a dedicated Auto-X/track car, so I'm OK without it. Don't care about the weight savings by removing it, more interested in making the system simple and easy to work on.

[jlevie]

What I'd do would be to replace all of the soft brake lines and the master cylinder (since it sounds like it has failed) and check to see if brake fluid is in the brake booster. If there's fluid in the booster it also needs to be replaced. Using a pressure bleeder with the lines from the master cylinder cracked open purge the air from the master. Then proceed to flush and bleed the brakes.

A full flush can be done by pushing a measured 250cc through each rear caliper and 150cc through each front caliper. Just in case air has gotten into the ABS unit, take the car out on a rainy day to an empty praking lot and get on the brakes hard enough to engage the ABS. Then re-bleed.

ABS is a good thing to have. I'd never consider deleting it. On the track, I make it a habit of just having the ABS engage in every braking zone. That is all that the tires can take.

[Massive Lee]

Lateracer.

Before you spend money on new brake lines and MC, I strongly suggest getting the help from a expert wrencher who knows how to bleed. Just as with making love, most people pretend they are experts, but very few really qualify. Bleeding is not as easy as many think. Also, vacuum bleeding is not that great. Get a pressure bleeder and at least a quart of cheap fluid. f nothing comes out of the rear, maybe the rear lines have swollen inside. But I doubt.

[Goya20]

master cyl

i changed the master cyl in late october got it bled and still had a spongy pedal. yesterday i got the system flush and the same thing. some one told me did the mechanic bench bled it and i told him no. can i still bench bleed the recent master cylinder to fix the problem or i have to get a new one?

[Massive Lee]

If the MC is new, then your problems are caused by a bad bleeding.

Please get a pressure bleeder. It is cheap. Then while the pressure pushes fluid thru the system and escapes by the caliper bleeder, have a friend pump the brake pedal repetitively and slowly. This will bench bleed the MC...

[lateracer]

Thanks for all the good info.

Think I'm going to replace the MC and lines along with a full round of caliper rebuilds. I'm going to give bleeding the system another shot. I've done it successfully on other cars in the past and since it's going to be on the track, I need to figure this out at some point. Got a local shop that I like. I'll have them check my work. Will update when the job is complete.

[Goya20]

they bled the system 4 times and flush the entire systme and bled my slave clyinder too. what they didnt do was the 2 man process can that b the problem

[Massive Lee]

Hi Goya20. "They" flushed the system 4 times. But did "they" do it properly at least once?

I know quite a few shop mechanics who have no clue how to properly bleed brakes. No kidding.

[Goya20]

they swore that they did it right and it was my brand new master cylinder was the problem

[Massive Lee]

they swore that they did it right and it was my brand new master cylinder was the problem

If they know it is the brand new master cylinder being the culprit, shouldn't they have replaced the defective one right away? It is not serious to let a car without brakes go out.

[Goya20]

true

[Massive Lee]

Hi Goya

Maybe if there was another e30 friend in your neighborhood with experience, he could help you bleed the brakes. I totally understand your frustration of being at the mercy of a repair shop.

[Goya20]

yea exactly imma start going to jersey to these new guys shop on here. rather give local r3v guys the business

[lateracer]

Update: Looks like it's fixed.

So I took the whole system apart and blew some compressed air through the lines. Lots of crap blew out. Seriously think this car hasn't seen a fluid flush in at least 5 or more years.

Replaced all of the rubber lines with SS lines and rebuilt all the calipers. More crap in the calipers too. I was able to remove all the varnish and clean up the pistons with some steel wool. Getting all the crud out of the cylinder took a while and there was some minor pitting in the chamber, but nothing that looked like it would compromise the integrity of the caliper.

Did my best to bench bleed the new MC. Installed everything and filled up with some cheap DOT 3/4. Following some of the techniques I picked up here (12+ pedal pushes, not pushing the pedal all the way to the floor, closing the valve before the end of the last push) I got the system bled. I do have to say that effective bleeding techniques for this car are different than others I've done.

In addition to almost never raining, it's the holidays, so there are pretty much no empty, wet parking lots here in San Diego. To engage the ABS, I eventually found a gravel road that seemed to work well enough. Re-bled the system and brought it in to a local shop. They gave it a thumbs up.

(fingers crossed) I think I'm good for now.

Thx again everyone.