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Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

I changed my rear shoes on saturday and the car was fine all weekend.
i adjusted the handbrake cable...so that it came on nice and tight with just 2 clicks up.

mondays drive, the brake pedal travelled a small amount further before stopping the car and i put it down to the rear shoes bedding in....and thought i would adjust the star adjusters when i got home.

yesterday as soon as i start the car, the brake pedal travels right down freely and i feel resistance just before the pedal is on the floor!! = [
...and that is where my brakes work.

pumping the pedal brings the stopping point of the pedal only a small amout higher.

as they are not auto adjusting, i double checked the rear shoes' star adjusters and made sure they were set correctly. the handbrake is still operating as it should.

have i missed something silly?
tiny
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*****1981 - 924 - Auto - London, UK******

Lizard · Posted: Wed Oct 25, 2006 3:43 am Post subject:

you either have an airlock in the system, or your MC is leaking.
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3 928s,

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

thank you lizard, i agree..

after readin a beauty of a thread with the same issues:
http://www.924board.org/viewtopic.php?t=13284

it seems that the Master Cylinder wants an overhaul. i suspect an internal leak as no fluid is showing externally.

friday is the day i will:

1.replace the rear slave cylinders as the bleed nipples are rusted solid/broken
2.replace the flexi hoses
3.replace the master cylinder (ouch goes the wallet)
4.bleed the whole system.

hopefully that'll sort it
Tiny
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*****1981 - 924 - Auto - London, UK******

Paul · Posted: Wed Oct 25, 2006 10:01 am Post subject:

Also check the booster to see if it has brake fluid in it, especially if there is a streak of rust on the booster underneath the MC.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
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Owned and repaired 924s since 1977
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Nobbi · Joined: 24 Aug 2006 Posts: 1398 Location: Germany

The rear brakes should have a little "Metall-Piece"(dont know the english word) that prevent that the Star-adjusters move in any direction after adjustment! That Piece is welded on right in place where the Cylinder and the adjusters sit.On nearly all cars ive seen so far its missing!
without that thing its sometimes enough to brake ones and the adjustment is history, especially when you overhauled everything to make it freely moving !!
That "Bracket" or istallation plate were all the shoes and stuff is mounted on is the same as for the Volkswagen beetle 1303.

Nobbi

Lizard · Posted: Thu Oct 26, 2006 12:52 am Post subject:

thats interesting Nobbi, as I have never seen one that is broken off.
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3 928s,

Joes924Racer · Posted: Thu Oct 26, 2006 2:33 am Post subject:

How are you bleeding the brakes, the 2 person
loosen the bleeder valve n pump the pedal to the floor
then tighten valve n return pedal if so youmight want
to get a vaccum pump.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

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

Master cylinders don't really go bad that often on 924s.

I suspect that most Assumed Master Brake Cylinder Failures are actually misadjusted rear brake shoes.

When you replaced the brake shoes, did you take the time to clean, inspect, and lubricate the sliding surfaces on the splash/backing plate that the brake shoes slide on?

Did you check the brake shoes to make sure that the sliding surfaces were smooth, and that the friction material was properly mounted on the metal backing so only the sliding surfaces of the brake shoes make contact with the backing plates?

If you do not check these things when you assemble the brakes it is possible that the shoes will not center properly within the brake drums. If they do not center properly when you reassemble the brake shoes, at some point while you are driving the car and step on the brakes, the additional force of applied by stepping on the brake padel could cause the shoes to re-center themselves when the force applied overcomes the friction on the sliding surfaces. This would result is excessive brake shoe to drum clearance, and the brake pedal will sink. Does this sound familar?

Two clicks to parking brake full stopping power is too tight. According to the Porsche Service Manual, it should be move to contact at two clicks, and full parking brake at five clicks. With the parking brake set for full power at two clicks you are going to have brake shoe to drum contact with the braking brake full in the "OFF" position, and rapid brake shoe wear leading to excessive brake shoe clearance. The drum brake shoes are designed to fully retract to a no contact position, when they are not being applied. On a 924, the rear drum brakes are not self-adjusting, meaning you have to manually adjust the rear brake shoes to compensate for wear to keep the brake shoe to drum clearance at a minimum to optimize brake performance. Yes, for those of you with Euro Model 924s, I know that some of the late model cars came with self0adjusting rear brake shoes. BUT, no U.S. model cars came with them. This is the opposite of disc brakes, which are designed to ride on the brake rotors at all times. Again, this will appear to many as a Failed Master Cylinder, when it is actually the result of improper parking brake adjustment.

How is it that you just noticed that the bleed valves were both frozen? Bleeding the complete brake system is a part of all brake shoe of pad replacement procedures. You should have replaced all of the brake fluid from the master cylinder to the brake slave cylinders, and the calipers when you replaced the brake pads.

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

wOw gohim you rock!
what a fantastic person to have on the board, thanks man.

yea, you're totally right. when i changed the pads i realised i should have changed the cylinders too, as the nipples were rusted on and PO rounded them off too.

i fitted new rear cylinders yesterday, and took the time to manually adjust the brakes as you mentioned - properly.

after flushing new brake fluid through with a mighty vac, the brakes are spot on.

i did have a new master cylinder waiting for me at GSF (on hold) but it wasn't required. wallet says yay!

air must have got in when i changed the shoes.

i will readjust the handbrake as the haynes states.

thanks all for your excellent help = ]

tiny
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*****1981 - 924 - Auto - London, UK******