Brake Bleed Issues

[vintage914racer]

Hi all. I'm new to e30s and have found this site incredibly helpful. I'm hoping someone can help with a brake issue I'm encountering. I've searched to forums to no avail.

Replaced the MC and ABS pump today, as well as bothof the hardlines that go from the MC to the abs pump because they were broken. After attempting to bleed the system I am not getting any fluid at any of the calipers. I tried vacuum bleeding and the two person method. It appears that fluid is going somewhere when pumping the pedal, but I can't tell where. It is not leaking out anywhere and I've gone through quite a bit of fluid. I've bled plenty of brakes before so I know how it should be done, yet I am not having any success.

Any thoughts, suggestions, etc?

[vintage914racer]

I didn't have my pressure bleeder with me so I was tried the old fashioned two person pedal method and the vacuum method (mityvac).

[u3b3rg33k]

How much fluid did you use so far?

[vintage914racer]

maybe 24 ounces or so

[jlevie]

The only place that 24oz of fluid could go and lot be visible would be into the brake booster. Which would mean that the master cylinder is bad. Brake fluid is really bad for the rubber parts in a booster and will cause quick failure of the booster. Remove the master cylinder, dismount the brake booster and flush it out with alcohol.

[vintage914racer]

That's what I was afraid of...

Thanks for your help.

[vintage914racer]

One more question. Is there any difference between a girling MC and an ATE MC. Are they interchangeable?

[87-325ic]

YES THEY ARE!!!!

well it was for me, for now. i took off the ATE and put on the Girling, so long as the # of holes are the same (ABS/ non ABS).

only difference, girling has a slightly wider push rod thing. but it doesnt make any functional difference.

good luck.

also, since you replaced the abs pump, i would imagine some of it is going there, but you said you replaced the MC, how could it now be bad to let the fluid reach the booster?

[vintage914racer]

When I bought the car it didn't have a MC so I replaced it. The PO also broke one of the hard lines so I replaced it and unfortunately I found the stripped out the threads on the ABS pump where that line connected. So, I installed another ABS pump with good threads along with the new MC.

When I bench bled the MC I was getting fluid from both outlets. Given this information, would it still make sense that it is going into the booster?

[jlevie]

Since brake fluid will kill a booster in short order, and since 24oz of fluid has "gone missing", I'd want to be sure that the fluid wasn't going into the booster. You can find that out by removing the master cylinder and using a bit of rag on a wire to probe into the booster to its bottom edge. If the rag come out wet, you'll have to pull and clean the booster.

When you say a new master cylinder do you mean a new or rebuilt part? I've had such poor luck with generic rebuilt parts that I won't use them any more. The rebuilys are much cheaper, but it is aggravating to sometimes have to go through more than one to get one that works.

[vintage914racer]

I'll pull the MC tonight to see if fluid is making it into the booster. The MC I put on came off a pals car. It was working prior to installation.

Is removing the booster a difficult job?

[jlevie]

Removing the booster is something of a pain because of the location of the nuts. The job is easier if you remove the driver's seat.

[vintage914racer]

Good news. Fluid isn't leaking into the booster.

I hooked up my pressure bleeder tonight, but I am only getting fluid at the driver's front caliper. I can't imagine that 3 out of 4 flex lines have collapsed, therefore I think I should focus my efforts elsewhere. I really don't think it's MC related either because when I bench bled it again today I was getting fluid out of both outlets.

Any suggestions on what I should investigate further?

[vintage914racer]

Update:

After confirming that the mc is working properly and indeed not leaking into the booster I looked in other directions. I disconnected the respective hardlines and co firmed that there are no obstructions in the lines from front to back. The flex lines are also obstruction free. From here the only thing I can think of is an issue with the abs pump.

It appears that fluid is getting to the inlets of the abs pump, but not to the outlets. Does an abs pump internal failure seem reasonable? I searched the archives but couldn't find any instances of this kind of issue.

[jlevie]

A failure inside of the ABS unit that blocks fluid flow isn't unknown.