924Board.org

MikeDanger · Joined: 21 Nov 2002 Posts: 774 Location: Denver

Im trying to figure out what the problem most likely is.

I know the clutch and brake share the reservoir. So i noticed that after a few shifts, the gears start to grind to the point where i have to jam it into gear. I bled the clutch but no dice. But a few minutes later the brake starts to fade also, to the point i found out why they call it an emergency brake!
So what should i check/replace?
Thanks
Mike

Paul · Posted: Fri May 13, 2005 12:45 pm Post subject:

Let's start with the easy stuff, how much fluid is in the reservoir?
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Owned and repaired 924s since 1977
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gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Sounds to me like you are due for new clutch master and slave cylinders.

Replace both when one is required, the other is going to die soon anyway.

Can't find a leak on the ground you say? Check the carpet, the missing fluid is probably soaking the carpet under your dashboard right now....

leadfoot · Posted: Fri May 13, 2005 5:55 pm Post subject:

Sounds like that air has got into the lines.
If you pump the brakes does it hold pressure after that, if it does then bleed the lines, otherwise you have a leak in the system.
Leadfoot

MikeDanger · Joined: 21 Nov 2002 Posts: 774 Location: Denver

Ok but why does it affect both my clutch and brake?
See i noticed it first in the clutch, when even though i was pushing the pedal to the floor the gears were grinding, then a few minutes later i noticed a loss of braking power. I bled the clutch saw no air. and dont seem to be loosing any fluid.
But see it seemed like it happened after a few uses of the pedals, becuase when the car is cold its ok.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Have you followed the advise and checked your fluid level?

Could be that the system fluid was too low due to losses from a leaking clutch master cylinder, then air entered the brake system because fluid was gone from the reservoir.

Could also be that the brake fluid is contaminated, and moisture in the fluid is boiling after you start using the brakes leading to bubbles in the brake fluid and loss of braking power.

leadfoot · Posted: Sat May 14, 2005 10:39 am Post subject:

In the hydraulic setup the clutch and brake lines are both run from the master cylinder. Either low fluid levels, air in the lines (you may be introducing in new air due to a leak after you bleed the system, it can also take a couple of goes to get all the air out) or old fluid, the hydroscopic quality of the fluid is below miniumum count. This is how compressable the fluid is, the older it gets the more it will compress.
As suggested what are your levels at?? did you find pumping the brakes help efficiency??
Leadfoot

Paul · Posted: Sat May 14, 2005 10:45 am Post subject:

If the brake fluid is clean and full, what kind of brake fluid are you using?

MikeDanger · Joined: 21 Nov 2002 Posts: 774 Location: Denver

Hmmm well the level doesnt seem to change. Remeber the first few uses of the pedals, seems fine.
I have no idea when the fluid was changed in either the brakes or clutch.
But when i bled the clutch i just used some prestone dot3/4 stuff. the fluid was running clean.
the resi never went empty, i had help when i bled it.
What are the chances its the clutch hose?
I already got a used brake MC from a 944 (should be ok for an 80 931S right?)
But im thinking it might be something other than that.
pumping didnt seem to do much. and again id didnt seem to be leaking.

Paul · Posted: Sat May 14, 2005 3:10 pm Post subject:

There's almost no chance that this is being caused by the pressure hose that runs between the master and slave. When this hose fails, the clutch pedal goes to the floor and stays there.

Sometimes the supply hose from the reservoir to the clutch master can leak air. This would not cause your issue with the brakes, however.

I suggest you bleed both systems (with a pressure bleeder if you can) until you get new fluid at all the bleeder screws.

MikeDanger · Joined: 21 Nov 2002 Posts: 774 Location: Denver

well i was going to get speed bleeders for sure dont knowabout the pressure bleeder unless its cheap enough. However i am looking at upgrading to 951 or boxster brakes if i find a deal.
But am i right the 944brake MC is the same as the 931? because i remeber some cars have a different MC

Paul · Posted: Sun May 15, 2005 6:49 am Post subject:

Performance Products has the pressure bleeder for about $50.

Once you've used one, you'll never try it the old way again.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

No, the 944 master brake cylinder is not the same as any 924 master cylinder.

To use the 944 part, you would have to convert your brake system to "front and rear", instead of the "diagonal" system that the car was built with.

On top of that, the 944 master cylinder has a larger bore, and was designed to be used with a larger vacuum booster, so the pedal effort would be higher if you use it with the smaller 924 vacuum booster.

The other difference would be the fact that the 944 like the 81 and later 924 and 931 have the stop light switch on the pedal assembly, while the 80 and early 924 and 831 have the stop light switch on the master cylinder. Converting to stop light on the pedal assembly only requires the stop light switch to be mounted, and pulling the switch wiring taht into the passenger compartment.

MikeDanger · Joined: 21 Nov 2002 Posts: 774 Location: Denver

well i also have an 81, but this 80 is an "S" with the 944 suspension/brakes so i though maybe there was a chance they were the same

Joes924Racer · Posted: Fri May 20, 2005 2:07 pm Post subject:

I use a vacuum pump off the bleeders then put speed
bleeders on to finish up. A vacuum pump only works with
the regular bleeders. With one youll get old fluid and bubbles out
like now whitch is what you want right.
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