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xpernet · Posted: Mon May 31, 2004 5:30 pm Post subject: Sinking Pedals !

Hey Guys,

Since we bought the 77' 924, all pedals, except the accelerator, need to be depressed very deeply to fully utilize them! Especially the Clutch! Eventhough my father pushes is it all the way to the metal, the gears sometimes grind while shifting. We tried to adjust the cable, but no use. Should I need a shorter cable? And which car uses the same cable so i can obtain one from it?

Also, the brake pedals are stiff when the car is off, but when I crank it up, with my foot on the brake pedal, it sinks! I also hear a sound, as if something is being deflated! Much more of a hissing sound. Is that normal in most 924? I installed a Brand New VW golf, Brake Fluid pump which is identical to the one I had. Braking got better, but the pedal kept sinking...

Thanks in Advance Guys!

xpernet
_________________
1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body

"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche

924RACR · Posted: Mon May 31, 2004 11:05 pm Post subject:

The sinking when you start the car shows that the brake booster is working, that's good.

Either you'll need to replace the clutch cable (shouldn't be too bad from a dealer), or take a stack of large washers, remove the cable from the pedal, insert these shims on the cable at the firewall, and reinstall the cable. They'll take up the slack and you'll be able to tension it properly. Do it NOW, before you trash your transmission!!! Be sure to lubricate the pivot points for the pedal while you're in there.

Back to the brakes. I'm not sure which part you replaced, the booster or the master cylinder? Can you clarify? As for pedal sinking, if you're sitting at a standstill and you hold pressure on the brake pedal, does it continue to sink until it hits the floor? If so, that's because fluid is (most likely) leaking past the seals in the master cylinder. It is also possible that it's leaking out at the wheels, but that should be pretty obvious due to a) loss of fluid, b) puddles of that brake fluid on the ground c) no freakin' brakes!

I highly recommend you fix both of these problems completely before driving any further due to high risk of damaging the car and yourself.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

dgz924s · Joined: 03 Nov 2002 Posts: 592 Location: Kansas

Speaking of pedals.....can the brake pedal be adjusted for level with the gas pedal? On a 87 924 of course....If so how is it adjusted? TIA Dal

924RACR · Posted: Tue Jun 01, 2004 12:30 am Post subject:

Yes, but you shouldn't do that, because if you did, it'd bottom out when things are not working - brake fade or a circuit failure - and you wouldn't be able to stop the car. I assume you're talking about adjusting it for heel-toeing, correct? In this case, it should be set up (and mine is) so that when your brake pedal is about where you are putting it when threshold braking, it's next to your gas pedal. Naturally, this means it's a bit higher than the gas pedal without applying the brakes. Then, when you're screaming into a corner full on the binders, the gas pedal will be right there when you need it - not closer to you.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

dgz924s · Joined: 03 Nov 2002 Posts: 592 Location: Kansas

Correct assumption. Of all the work I have done this one area is the most difficult. The pedal arrangement and my lack of consistancy when applying heel/toe. Several issues...one the brake pedal is too small so when I try to roll my foot that won't work. Try to use my heel and I hit too low on the gas pedal to get a decent blip. In order to blip, my foot needs to be as high up on the pedal as possible, can't use heel unless you are a contorsionist or really pidgeon toed. Wings sit too close to the brake pedal. There is real fine line I have as I don't want to accidentaly hit the gas wing when needing the brake.
I am considering welding a piece of 3/8 round steel bar to the upper portion of the accelerator near where the pedal mounts. Then make the bar with a small piece of flat steel as a small pedal and weld it to stick out just enough for my toes can tap it. It would be up and out of the way this way. Place the ball of my foot on the brake and roll my toe to hit the gas.
I was curious to see if I could adjust another way. Thanks! Dal

xpernet · Posted: Tue Jun 01, 2004 1:39 am Post subject:

Thanks 924RACR

As for the part, its the master cylinder. When i pressure tha brake at still and crank up the car, the pedal sinks till it raches a point. It won't go all they way. And the braking is good. But i think its the rotors who are giving that sinking effect! Ill work on the clutch soon. Its not THAT bad. Slight grinding when my dad doesn't depress it correcltly!
_________________
1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body

"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche

dgz924s · Joined: 03 Nov 2002 Posts: 592 Location: Kansas

I did not see any mention on bleeding the brakes. Have you done this? Both pedals with the same problem to me suggests air in the lines. If not try bleeding the brakes and slave cylinder. The grinding could be the clutch is not getting fully engaged due to the air in the system. Dal

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

You need to adjust the rear brake shoes.

The 924 has the brake connected in a "cross", right front to left rear, and left front to right rear. The rear brake shoes are not self-adjusting, and when the shoes wear, and the clearances rise when you step on the brake pedal, the fluid is used to move the rear brake shoes to the contact point, instead of being used to increase brake pad and shoe friction on the discs (in the front) and the shoes (in the rear).

If you take the time to adjust the rear brake shoes, the brake pedal fell will improve (firm up), and the car will brake much better.

I bet that the parking brake is not working well right now either. After you get the rear brake shoes adjusted properly, go back and adjust the parking brake. How well the parking brake works will give you an indication of how well adjusted the rear brake shoes are (and whether it is time to adjust them again), if you adjust the parking brake properly, immediately following the initial correct adjustment of the brake shoes.

You do not need to adjust the parking brakes each time you adjust the rear brake shoes.

Rob O · Joined: 26 Nov 2002 Posts: 86 Location: Oak Ridge, NJ

I have noticed recently that my brake pedal sinks slowly when I stop at a light. I have already bled the brakes with a pressure bleeder and replaced the flexible lines to the calipers. I also converted the car to 4 wheel disk brakes this past winter. At this point, I am assuming the MC needs to be replaced. What bothers me is that the pedal only sinks sometimes. While sitting at other stops, the pedal does not move at all. Is this consistent with a MC problem?

Thanks,

Rob
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'81 Weissach Ed. (gettin' better)

Smoothie · Posted: Sun Sep 04, 2005 1:40 am Post subject:

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

A problem with the brake vacuum booster, or the vaccum hoses running to the brake booster, or the valve in the brake booster vacuum line could cause a similar symptom.

A sticking brake caliper or worn-out caliper might also create a similar symptom.

Have you been watching the brake fluid reservoir? Are you losing fluid? Did you install seal kits in the calipers before you isntalled them, and did you clean the caliper cylinder bores? Did you hone the cylinder bores if you cleaned them?

Joes924Racer · Posted: Sun Sep 04, 2005 10:11 am Post subject:

make sure the pedal supports havent broke loose thatll cause unwanted brake pedal assembly movement.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

Rob O · Joined: 26 Nov 2002 Posts: 86 Location: Oak Ridge, NJ

Thank you for the replies.

I will check the pedal supports.

I am not loosing brake fluid. I did not replace the seals on the calipers before I installed them. I know... The person I bought them from said they had been rebuilt recently. I looked at the seals before I installed and they were (reasonably) clean and not torn so I took his word for it.

I will check the vacuum lines to the booster and let you know what I find. Not sure how to check the valve in the line though.

Thanks,

Rob
_________________
'81 Weissach Ed. (gettin' better)

Rob O · Joined: 26 Nov 2002 Posts: 86 Location: Oak Ridge, NJ

I am reporting back in case anyone else has an intermittent problem with a brake pedal that sinks at stop lights/stop signs.

As per the above advice, I tried to rule out possible causes before I shelled out $140 for a new master cylinder. I checked for sticking calipers, the vacuum lines to the brake booster and the firewall where the pedal cluster mounts. They looked good. About a month ago I replaced the master cylinder with a new unit and the car feels great. Now when I drive my '92 Accord, I feel like there is something wrong with the car because the brakes do not feel as solid as my 924.

Thanks for all of the replies.

Rob
_________________
'81 Weissach Ed. (gettin' better)