924Board.org

[Gatornapper]

STRANGE.

Have new clutch master and slave cylinders, and all new brake fluid flushed early this year.

Suddenly last week pedal isn't returning to the up position always. Sometimes barely comes off the floor.

If I pull it up with my toe, it will sometimes stay up for a while. It is intermittent.

What's really weird is that even when it's barely off the floor, if I press it to the floor it still fully disengages the clutch, and shifts are fine.

Yes, brake fluid reservoir is full.

Anyone have a clue what's going on? Need to bleed slave again?

Seems so weird that it is intermittent. Sometimes pedal comes all the way up and works normally. Sometimes only 1/2 way. Sometimes barely off floor.

TIA,

GN
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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......

[Fasteddie313]

Yeah bleeding..

Some bleed it from the bottom up with a pressure bleeder..
I just left my bleed screw open for quite some time letting it drain through and never had a problem..
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80 Turbo - Slightly Modified

[chuck21401]

I had good luck with a motive power bleeder.

It’s those air bubbles. I finally pushed enough fluid through the system to get them out…then worked like new.


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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[Beartooth]

Yup, definitely bleed it again. One trick I've found for a poor man's power brake bleeder is to use a air blower chuck with a rubber tip to apply pressure to the reservoir through the air bleed hole. Obviously turn the regulator down real low: you want just enough pressure to get the fluid to move (I'd guess around 5 PSI). Hopefully it's just an air bubble in just the wrong spot. Mine has a sort of functional master and slave cylinder, and I've noticed that it'll do something similar unless you step on the pedal with some force. If you slowly push it in, it'll suck itself halfway down every time; stomp on it, and it works and releases normally every time. Not too surprising since they had some pitting when I tore into them; I tried a DIY hone on the master and slave cylinder, but apparently that wasn't enough (the rubber pieces looked fine). Will be replacing those shortly once I finally get the title back and can legally drive it.

Anyway, I mostly bring it up as a possible way of diagnosing a bad master cylinder. One last thing: sometimes the DIY bleeders work great, but clutch hydros especially seem tricky until I get someone to do it the old fashioned way. I don't have a proper power bleeder, of course, but I've tried the check valve bleeder fittings and the sealed catcher setups that are supposed to keep air from getting back in. They all promise easy, one-man bleeding, but they're about 50-50 in practice. Worth a try, assuming you have a willing assistant, before you start tearing into it.
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1980 931 diamond in the rough

[Gatornapper]

Thanks guys - but air in line does not explain:

1. Clutch has worked fine for 6 months, change happened suddenly. We did original bleeding on new slave and master cylinders the old fashioned way: pumper on pedal, me underneath.

2. Problem is intermittent. Comes and goes. This would not happen with air in line. How could pedal come back up to normal with air in line?

3. I have the vacuum bleeding unit from Harbor Freight and it works great. Sucks air out & new fluid in. I'll try that first.

4. Even when pedal is almost on floor, with about 2" of travel - clutch dis-engages fully and gears shift normally. I find this amazing.

I can then lift pedal back to normal position with my toe, and then it will work normally for a while. I cannot explain that - does not make sense.

GN
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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......

[Dutch924-racer]

Does the clutch slip when you drive and rev it to the red line?
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

[jacobroufa]

[Gatornapper]

No clutch slip.

Problem seems to have disappeared on its own. Strange. Pedal now comes all the way up all the time, about 3/4" play in pedal before clutch hits, 3" of travel or so and clutch is fully disengaged as it should be.

Can't see how it could have been air if it is no longer there and I did not do anything.

Weird.

GN

[Gatornapper]

Great idea - thank you.

The problem with the vacuum bleeder is that as there is no seal around the threads of the bleeder screw, and the vacuum draws a lot of air in from around the threads.

This air, however, does not mix in the line itself, as it is past the end of the line. It just produces a lot of bubbles in the fluid that is coming out.....a vacuum is still pulling on the brake line itself, and the line itself is purged completely of air.

I've followed my vacuum bleeds sometimes with old-fashioned 2-person bleeds and found no air in the lines.

A solution I may try is to put a small O-ring around the bleeder screw - but not sure how I'd maintain that seal as the screw is rotated to loosen it.

But I do far prefer the pressure on top approach.

GN

[Gatornapper]

Jacob -

Just ordered the cap w/hose. Will use sprayer can/pump for pressure. Problem finally came back and stayed after being intermittent.

Original bleed was manual - old fashioned way - one person on pedal, another below on bleed screw. Both cylinders are new, reservoir full - no idea where air in line could come from.

Clutch still works - but all in the last 2" to the floor.

Thanks to all.

GN

[Gatornapper]

Received mine yesterday - cap & hose only - using my own pressure spray tank with pressure gauge I put inline.

As my 914 w/o engine is on my lift, I'll need to jack the 931 up to get under it to do the bleeding.

THANKS!

GN