Strat_928

Hey guys,,, I posted this some time ago I think, over a year,,, but here is the background as we have not been able to sort it out yet.

1983s, early VIN 1108
Symptoms -
1 - For over a year or more, my brakes have been releasing slowly. Approx 2-3 seconds before fully released.
2 - I have also driven in the 95+ degee heat for a little while and found the problem sometimes worsens, to the point that after a full stop and trying to hit the gas,,, the car would not move,,, brakes fully engaged without my foot on the pedal, had to wait 6-7 second it seems before I could move,,,, then took a few hundred feet to fully disengage ,,, could tell there was drag while driving for a little while. - This condition has only happened once however, to this extreme
3 - The car does NOT pull or brake unevenly.... ever. When the brakes release, it seems like all are releasing the same.
4 - My mechanic has 1 928 and 3 944s and does brakes and suspension for a living and this one has him stumped right now, he has not seen it before.
5 - The harder you brake, especially to a full stop,,, the longer it takes to release. Light pedal = quicker release, but always a little lag. This started a little over a year ago and has acted the same way ever since, no better, no worse. I have driven around VIR 2.5 laps with the Porsche parade last August and ran for 2 straight hours on a fun run at SITM this year in the mountains, with it doing the same thing the whole time. Again no better, no worse. Braking is not the issue, only releasing.

Equipment -
1 - Current Brake Master Cylinder was new in 2011, still seems to be in good shape, but I do have a new one to use if needed, if I do install it and it does not fix it however, I am out a couple hundred bucks - so I am trying to understand before replacing more parts. I understand that this could end up being the culprit if there is seal damage etc. So I am not writing off changing it out.
2 - The 2 brake pressure regulators, under the Master, used to control front to back pressure, were swapped out for a re-conditioned/used pair. That one we did just throw money at.. But no change afterwards. It was relatively inexpensive.
3 - New SS braided brake lines were installed a year ago
4 - DOT 4 Super Blue ATE fluid is being used. Flushing and filling have been done and went fine,, fluid moves in and out with no issues. Right now we do not suspect clogs or line issues.

Testing -
1 - The issue only appears when the engine is running, brake system charged.
2 - We did try this test, which to me, seems to indicate it is not stuck cailpers, pad issues or something mechanical like that.
- Car in the air on lift, wheels spinning free - engine OFF - hit brake, then release and another person turns the wheel. Seems to work normally and release
as soon as the brake pedal is released! Every wheel releases normally with the engine off. There is no problem with the engine off it seems.
- Car in the air as above, but with engine running - same sequence for every wheel,,, every wheel releases slowly, 2-3 seconds.
3 - My Mechanic attests that the wheel, brake hardware all appear to be normal and in good shape, rotor wear, pads are new etc, bleeding went fine etc.

So after looking at a few other posts elsewhere, it is starting to sound like something is not turning off the booster quickly or the master cylinder is not opening all the way etc. (Wally I saw one of your posts referring to pedal settings and how the master is working, that helped get me to this point)

So there you go guys - have at it! HELP!

GlenL

Well... the slow release sounds familiar. Mine did that, too. Since it doesn't pull it must be system-wide and likely the master cylinder. Another option could be the action of the brake pedal itself. I'm doubtful but wouldn't hurt to get under the dash and did a little R&R on the moving parts there.

Mine has behaved itself since I did some major drivetrain work. Really odd since it didn't involve the brakes at all. No flushing or bleeding or anything. The brakes would stay ON for a second or so and then release like normal. Now it's good and I didn't do anything to address or actually affect it. I noticed that it was "fixed" right away when trying out my new clutch, tranny and CV joints. It was jacked up for almost two months during the job. The brake calipers remained on the hoses the whole time. Weird.

Good luck.

Strat_928

Yeah I am hoping it is not intermittent ... it is at least consistent over the past year plus, so I am thinking it is going to stay that way until I figure it out. Right now I am leaning toward vacuum/boost release vs mechanical issue since it works without the engine on.

Thanks for ideas

Mrmerlin

well you could try to pull the vacuum line from the booster and plug the line so it will run,
then go for a test drive if its still the same then replace the brake master cylinder.

NOTE it sounds like different brake fluids have been mixed,
thus the seals have swollen ,
this may also carry over to the calipers and they may require a rebuild.
also put a piece of wire into the booster port and see if its filled with brake fluid if so replace the booster.
In fact it may be wise to replace both parts, booster and MC. further testing is needed

Strat_928

Those all sound like good ideas, I have not returned the new master cylinder yet. I was also wondering if there is a place to unplug the vacuum line and see if we can detect where the slow pressure release is.

But these are all good. My mech is on a short vacation so I may not return with results for a week or two.

thanks to all!

Mrmerlin

uhh open the hood ,
Remove the intake tube on the driver side,
spray a lil bit of WD 40 onto the junction of the hose fitting thats going into the brake booster,
then carefully pull it out of the booster ,
plug the line with a cap and tape.
go for a test drive.
Not really a need for a mechanic to do this IMHO

Strat_928

Ha,, that is indeed true....😆

I am out of town myself too though, I might be able to get to it before I leave, but if not, still might be a little while thanks for sequence!

I will report back.

Strat_928

Hey, got some time after prepping for the trip last nite.
I pulled vacuum line and taped it and the booster side, luckily I could do it without taking off the air cleaner.

The problem still occurs with no booster. That seems to indicate the seals issue I believe. I will replace the MC later after we get back and hope that is the only place that is bad. I am hopeful for the calipers since we did the test on the lift and each wheel would release, but maybe that did not matter. We will see. Step by Step.

Thanks for your help. I will also try to get a wire into the booster to ensure that is not full of fluid too.

Strat_928

You know,,, now that I read the post again,,, that was probably not sufficient, I did not remove the hose to the booster, just the vacuum line. So I will do the test again when I get back, and do it the right way! it will also be easier to see if there is fluid in the booster that way.

GlenL

The booster only has the vacuum line. It boosts by helping to push on the master cylinder piston like the brake pedal is.

So you checked this on a lift and all four wheels have the same hold-and-release behavior when the pedal is released?

Have you looked at the action of the pedal? Does it seem to be sticking down or does it pop fully up when the foot is lifted off the pedal?

Strat_928

Actually Glen, it does NOT do it when in the air with the engine off but does do it (in the air or not) with the engine on. With the engine off,, press the pedal, release and try to turn the wheel by hand,,, you can turn any wheel normally with no lag. Tested all four.

I pulled the small vacuum line off, not the larger black tube going into the booster.

Finally got my pic ready to upload. When driven with the small vacuum line off, the slow release continues to happen. I also noticed (just now when looking at the picture) the arrow on the black line is pointing out from the booster, not pointing toward the booster.

No the pedal does not pop up or stick,,, always just a slow release as the brakes release. The pedal action tends to follow the release of the brakes.

That why we were leaning towards swollen seals because we changed to Ate Blue Dot 4 brake fluid and have heard that can make them swell.

Strat_928

So Went ahead with the Master Cylinder to see if that was the only thing with swollen seals. Used original fluid this time and now it appears the front calipers are the main culprit.

So I have 4 $15.00 rebuild kits coming and will rebuild all 4 calipers. They could use it anyway as they are 32 years old,,

Will be another couple of weeks to sort that all out and then I will report the progress

Strat_928

UPDATE

Ok - latest situation - problem still occuring
- MC replaced - to remove possible bad MC and seal issue there
- Calipers rebuilt - was about time anyway and remove seal issue
- Repeated an earlier test - as suggest by MrMerlin, pulled vacuum line off and plugged it,,, went for a drive, no drag whatsoever! Release is normal.

This puts me back to to the idea that it is keeping boost up too high when you let off.
So does someone know more about that small valve going into the booster from the vacuum system? Could that be bad and causing the booster to not come down normally?
How about the booster itself? Could that do this as well? Seems like we have to be at the crux of the issue now as we have pretty much addressed the other major players.

Best suggestion now - are there some more tests to try and determine if it is from the booster or the vacuum side?

Thanks in advance - Frenzy is in 4 days!!!! I would hate to go with a crippled car

GlenL

The valve keeps vacuum in the booster. You want vacuum there.

What have you done to fix/check the pedal itself?

Mrmerlin

I am going to guess you also need to swap in a new booster ,its about time.
ATE makes a nice new part,
be very careful about not damaging the sealing surface where the MC seals to the face of the booster.
NOTE when you rebuild the calipers also swap in new stainless steel lines.

NOTE the procedure to RnR the booster,
the pedal is pushed down,
then a cover is placed onto the front 0f the booster to protect the surface,
then a set of vice grip is used to grab the shaft.

NOTE I also put a piece of fuel line on the shaft then clamp the tool on so is wont damage the shaft.

Once the shaft is secured then disconnect the clevis pin and remove the booster.
NOTE the MC must be removed first