Jimjacqmx5

That should have read. "The Saga continues" ........ Ok.

Problem is, after all previous suggestions and efforts, my pedal now has no feel or 'pedal' until 1cm off the firewall and then the brakes go on and nearly put you through the window.

Quick catch up.
I have just installed brand new master cylinder in my 1991 C2.
Initially there was no pedal and we thought it was air in the system.
The system has no been bled MANY times with a power bleeder and by foot pumping as well.
Master cylinder was full of fluid prior to install,
ABS pump has been bled,
Mechanics also did the suggested hammer, pst cycle when bleeding to sort ABS.
Pedal issue is the same whether ABS relays are in or not or if ecu is connected or not, ABS is still working as it kicks in when the brakes do finally 'grab' in the last cm of throw.

There must be an issue other than air in the system, this feels REALLY weird.
It's like you are pressing against nothing and then it grabs but even at the point it grabs, there is no 'pedal' as such.

Even when there is some air in the system there is still some semblance of pedal 'feel' albeit mushy, but this is NO pedal or feel at all, It's like you are pushing against nothing.

What is going on? Could it be some wierd going on in the vacuum booster?
I know a dead booster usually causes a 'hard' pedal, but could it 'over' boost somehow?
As it is, I am sadly missing a very important competition round tomorrow which will cost me the series and no one can figure out what is going on.
The guys working on it are experienced Porsche mechanics and have never felt a pedal like it ever.
Very pissed off.

Jimjacqmx5

25 views and no suggestions, this really is a pickle!

Metal Guru

If it were my car and given all the efforts to clear the system of air, I'd assume that the new master cylinder is defective.

LouZ

Note: I never had to adjust or change my MC, so this is all speculative on my part, but I would also think that the problem lies with the MC.

You state that the pedal goes nearly to the floor - then grabs like hell. I would believe that with air in the line, you would not see this kind of reaction.

This seems to indicate to me that the "throw" of the MC rod is not properly adjusted, and you have to push in too far prior to engaging the MC.

Indycam

Can you pump up the pedal ?
If you can pump up the pedal you have air in the system .
If you can not pump up the pedal you do not have air in the system .

When you start to push down on the pedal does the piston in the master start to move ?
Or do you have to push down the pedal far before the piston in the master starts to move ?

If you block the out put from the master does the pedal go hard ?

Jimjacqmx5

Thank you for the input. The shop is closed today, but Ill check these suggestions tomorrow.

race911

Ever put a brake pressure gauge on the line(s)? This is getting pretty esoteric, save the common comment that the new master is bad.

tbennett017

+1 on LouZ... I know a M/C mis-adjustment can act like this.

LouZ

Did it get fixed? Any feedback?

Jimjacqmx5

My power bleeder arrived yesterday so we are going to have another crack at that.
All of the other suggestions have been followed up. Master is definately ok, it goes rock hard if blocked off at the abs unit. At one stage the pedal came good but then went away, so I'm hoping that even after much bleeding, there is still some air in there. Although I reckon they have pumped about 2 gallons of fluid through it.

We did the hammer, pst cycle as suggested, we also changed out the relays on the ABS and even disconnected abs and pedal was still going basically to the floor. They even switched out the rear calipers for my original '90 single pots to see if the calipers were an issue.

Half of the mechanics from the various Porsche places here have put in their 2c worth and still no good. None of them have come across this before. I just want my bloody car back. Ive been without it for 8 weeks and I desperately need to go for a good hard drive!

It's just weird, it's like it has nothing at all, but then grabs like it is MASSIVELY over servoed just off the floor. Even if the throw was wrong, it shouldn't grab like that when the brakes finally work.

Indycam

I don't think air in the system would make the brakes grab like it is massively over servoed . Air makes the brakes do the opposite of grab . What happens if you undo the electrical connector to the abs brain ? If you run the fluid lines around the abs pump what happens ?

Jimjacqmx5

I know they pulled the relays out of the ABS unit and that made no diffrence. They also pulled the plug on the abs ecu and that made no difference.

Steve Weiner-Rennsport Systems

This IS an odd one,......

Assuming for the moment that that flex brake lines are not obstructed from normal age & deterioration, this looks like either an MC, booster or ABS controller problem.

I've had bad MC's right out of the box (rarely) so I don't discount such occurrances.

Since the PST-2 & Hammer apparently didn't show any codes and cycling the ABS pump didn't change anything, if I were working on this car, I would check intake vacuum at the booster and make certain its doesn't leak. Assuming again that this didn't cure the problem, I'd install a known good used (or new) MC to see if that changed anything. Finally, I'd swap a known good ABS controller to see if that did the trick.

PorscheZen

I ruined an MC once with the foot-pump method...

According to Adrian Streather's book, one should not use a foot to bleed a 964. But then again, I have a C2. I'm assuming the brake system is the same for C4.

Indycam

Then I guess that the ABS unit is the problem .
Was it the problem before the master was changed ,
was it the problem after the master was changed .

If you plumb the brake fluid around the abs unit ,
do the brakes work "normal" sans abs ?