924Board.org

[Itsarhythmcar]

I recently purchased a 924 base which was stored in someone’s backyard for a very long time with the hopes of restoring it. It’s been difficult but fun and now I understand why a car should never be undriven. The current hangup is the brakes. Most components have been replaced or rebuilt but the car still hardly stops. The pedal goes to the floor with limited stopping power. I’m currently attempting to locate the vacuum lines related to the brake booster. However, the part number on the brake booster doesn’t match the number in my parts catalog or any of the Porsche auto parts stores. The correct part number for my 4 lug, non sport option, 924 appears to be 477 612 107G. My brake booster has the blue VW/Audi sticker on it with part number 477 611 907D. Could this be a European brake booster? Is it the same part? Or could it be related to my braking problem?
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1980 924 base
1995 Miata
1999 Isuzu Trooper
2008 Mazdaspeed 3

[Ozzie]

I'd suspect the master cylinder. if the booster was duff the pedal would be hard with no stopping power
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Itsarhythmcar]

Thank you Ozzie.

I agree that the symptom is consistent with air in the system. Since the master cylinder is a new ATE part and I’m able to bleed the brakes on all four corners (after clearing the gunk from the RF caliper bleed port!), I began searching for another solution.

So far it also has new brake hoses, wheel cylinders, brake shoes-plus adjustment, and rebuilt calipers. Also worthy of note: the booster was full of fluid.

Due to your suggestion, I’ll redouble my efforts to find an air leak. I wonder if there’s any possibility the new master cylinder is faulty.

Rain is expected all week. The project will be delayed a bit.
_________________
1980 924 base
1995 Miata
1999 Isuzu Trooper
2008 Mazdaspeed 3

[Harm]

[Itsarhythmcar]

Harm,

I have to learn to be more clear. I’m sorry for confusing everyone.

The old master cylinder was replaced after I found fluid in the booster. The fluid was drained out and the MC replaced. Now there is no fluid leak.

After that procedure, I was not able to bleed the brakes from the RF corner. Therefore, I began replacing other brake components which seemed wise. My insanity increased after a caliper rebuild did not solve the brake bleed issue. Joy ensued when my wife’s sewing needle dug through the gunk in the bleed port and a stream of fluid poured out upon the bleed procedure.

My joy was short lived when the pedal went to the floor and the car barely slowed (similar to having air in system).

I began to assume it had to be something else but an air leak is the most likely.

If I haven’t confused the whole 924 community with my rambling, I welcome any further thoughts. This car will be fun if it will stop. It’ll be a keeper.
_________________
1980 924 base
1995 Miata
1999 Isuzu Trooper
2008 Mazdaspeed 3

[Harm]

No problemo

Do/did you read the Haynes Workshop Manual for these cars?

With or without air vacuum, the car should still be able to come to a stop, be it you'll have to bring more muscle power to the breaking pedal.
Is your car able to come to a full stop with the setup you now have?
My guess is your answer is no.

Will your 924 come to a full stop using the Handbrake?

Does your pedal feel way better when the hand break is up (and standing stil)?

Have you adjusted the rear drum brakes by hand? You'll have to set the adjusters manually. They do not auto adjust.

Kind regards,
Harm.
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Porsche 924 NA 1982 LY7A/A3A3 _ Greater driving pleasure never harmed anyone.

[KDJones2000]

If you put the calipers on backwards (left on right, right on left), you will not get full bleeding of air and you will get what you describe.

Where are your bleeder, at the front or back of the calipers?
_________________
1987 924S SPEC car
Team Toofah Racing
1988 944 Turbo S

[Itsarhythmcar]

Although I haven’t been been able to work on the 924, I feel like I’m being pointed in the right direction thanks to the help I’m finding here.

I do have a Haynes manual which is mostly helpful.

You’re correct, the car will not come to a full stop, however it will stop using the handbrake. And, the pedal may feel better with the handbrake engaged.

The rear brakes were adjusted by hand and then checked a second time. This is my first time adjusting rear brakes so it’s possible I’m doing it wrong. This is now a conspicuous area so I’ll be sure to get it right.

I believe the calipers are on the correct sides. They’re on the back of the rotors with the bleed screw on top.

It may be a full week before I get back outside. I’m feeling encouraged that this issue will be solved. Thank you!
_________________
1980 924 base
1995 Miata
1999 Isuzu Trooper
2008 Mazdaspeed 3

[Ozzie]

I had to bleed several times to get a good pedal.
I try to use a different color fluid when I do a bleed to visually see the new stuff come out.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Rasta Monsta]

You might find it helpful to raise the rear and put the car on jackstands to adjust. You can then pull the wheels, and then the drums, so you can visualize what is happening when you make your adjustments to ensure you are doing it right.

Symptoms point toward show adjustment.
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[MikeJinCO]

Second to Ozzie, I think mine had to be bled 5 or 6 times to get them to work as moderately well as they do after rebuilding the MC. It can get very frustrating. Hopefully you have already replaced the hoses.

I did not completely follow the story, but if fluid got into the booster I have heard -not verified- that it can ruin the diaphragm in the booster. Someone else would have to confirm that. Google brake booster testing, it is a pretty simple process.
_________________
Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[!tom]

Sounds like the M/C still needs bleeding. It's easy to get an air bubble trapped in there somewhere. Might need to remove it from the car and do a bench bleed.
_________________
78 924 NA
5-lug

[jacobroufa]

If you've got a leakdown tester it can readily be turned into a brake bleeding system with the right cap fitting on the fluid reservoir. Since starting to use this way a couple years ago I have not had any issues with air in my brake lines... Just a thought.

[Ozzie]

There is an adjustment at the top of the brake pedal area, the rod going to the brake booster must have some play allowing the MC rod to fully extend before attaching to pedal.
Otherwise when pedal is released the MC doesnt come all the way back to refill from the fluid tank. (remains slightly depressed)
The new MC may be a little different and this need adjusting.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Itsarhythmcar]

Finally had time today to go back to work on the brakes.

After properly adjusting the rear brakes, the car stops...mostly.

First, thank you for the help. Second, the current condition is: The car stops fine at slow speeds. However, in high speed, hard stops there is an initial bite from the brakes then a somewhat dead spot in the middle of the pedal travel followed by better braking as the pedal is pushed nearly to the floor.

I believe I’ll check for a vacuum leak at the booster. Does that seem reasonable?

Thanks again for the help.
_________________
1980 924 base
1995 Miata
1999 Isuzu Trooper
2008 Mazdaspeed 3