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isuras2 · Joined: 17 Jun 2005 Posts: 458 Location: Phoenix, AZ

I am thinking my braking issues are due to a leaking master cylinder (m/c) so I probably need to rebuild the m/c. Would it be better to rebuild the m/c, buy a used working m/c, buy a rebuilt m/c, or buy a new m/c? Since I am on a tight budget I am leaning towards rebuilding the m/c.

Has anyone permanently connected a vacuum gauge to their car? Would this be a good thing to do or just a waste of time/money and another place for leaks?
Thanks,
_________________
Rob
'80 931 (sold)
'80 924 NA (sold)
Former Omaha Crew

Smoothie · Posted: Thu Aug 18, 2005 12:15 pm Post subject:

Sure a few of us have vacuum gauges in the dash. Mine's shown here - http://www.924board.org/viewtopic.php?t=11407 ..that's a combo boost/vacuum version, but the hook-up is the same for a vacuum-only gauge - to any direct manifold vacuum source.

On the MC - I'm in the habit of rebuilding all of my hydraulic cylinders as needed. It's entirely up to you though. To rebuild, you should have a brake cylinder hone (and a drill) and snap ring pliers.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

isuras2 · Joined: 17 Jun 2005 Posts: 458 Location: Phoenix, AZ

Where is the best place to find a m/c rebuild kit? Porsche dealer is $80US. Is there anywhere cheaper? I have had no luck yet.

I might put a vacuum gauge in, but we'll see.
_________________
Rob
'80 931 (sold)
'80 924 NA (sold)
Former Omaha Crew

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

I think $80 is a good price. Last time I checked over here, a (dual-circuit)m/c kit was over £50 (closer to $100).

Are you sure your braking problems aren't due to a leaking servo (booster)? The master cylinder would have to get pretty bad before you notice an effect on the braking, but even a small leak in the booster can be noticeable.
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

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isuras2 · Joined: 17 Jun 2005 Posts: 458 Location: Phoenix, AZ

I am pretty sure that it isn't the booster as the vacuum doesn't drop when the gauge is connected between the booster and intake, then just connected to the intake. It is about 13-14 inches vacuum. I have sprayed carburetor cleaner around the seams of the booster and no increase in RPMs. It is as if the booster isn't helping during braking and these braking issues happened after replacing some vacuum lines.
_________________
Rob
'80 931 (sold)
'80 924 NA (sold)
Former Omaha Crew

Ozzie · Posted: Thu Aug 18, 2005 10:47 pm Post subject:

An indication of a bad MC is when the pedal sinks slowly to the floor if you hold the foot on the brake.
A hard pedal with little braking effect usually points to the booster/vacuum.

Have you connected your hoses correctly?
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

isuras2 · Joined: 17 Jun 2005 Posts: 458 Location: Phoenix, AZ

Smoothie · Posted: Fri Aug 19, 2005 4:04 am Post subject:

When the MC goes bad, that generally means the seals are worn and fluid slips by them. This leaves you with no braking while making it too easy to press the pedal.
You've opened several topics related to this problem so I don't know where you're at, but did you test the check valve? Adjust the rear brakes? Were incompatible brake fluids ever mixed in your brake system? Tried bleeding the brakes (to see what comes out)? Done anything else?
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

isuras2 · Joined: 17 Jun 2005 Posts: 458 Location: Phoenix, AZ

The check valve should work because I got a new one. The booster is good as the vacuum pressure is the same with that connected and not connected.

The rear brakes haven't been adjusted as the adjusting nut won't turn either way on both drum brakes. I have tried penetrating oil, then pounding a screw driver with a hammer, but no luck. There was only 2 inspection hole rubber plugs so I think water got in there and rusted the adjusting screw/nut assembly. I plan on getting those new and getting in there to replace/repair what needs it.

If the incompatible brake fluids were mixed, they aren't now as the system has been bled. There was no air, or very little, in the system.

That is all I can think of for now. The next thing is to rebuild the master cylinder so I know that would not be the problem. I jsut don't know why my brake problem started after the new vacuum lines were installed.
_________________
Rob
'80 931 (sold)
'80 924 NA (sold)
Former Omaha Crew

Gram · Posted: Fri Aug 19, 2005 7:11 am Post subject:

I bet if the adjusters in your rear drums are frozen, that the rear brakes are well out of adjustment. And is 13 or 14" of vacuum adequate, or do you have a serious vacuum leak? There is a big difference in pedal feel between a leaky master cylinder and poor booster assistance.
_________________
'82 924 NA Euro (hers)
'98 Audi A4 TDI (ours)

Ozzie · Posted: Fri Aug 19, 2005 7:22 am Post subject:

Which way did you fit the Y piece going to the brake booster?
For some reason it made a difference when I had it back to front.
The pedal was harder and I had less braking power.

The pedal test should be with the engine running.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

isuras2 · Joined: 17 Jun 2005 Posts: 458 Location: Phoenix, AZ

The Y-piece was fit on the right way the first time I checked vacuum and it was about 13-14 and the same when connecting a T-piece between the intake and booster. The vacuum would decrease initially with throttle, then go up into the 20s when the RPMs would increase. I don't think I have a serious vacuum leak, if one at all, since the vacuum stayed the same with booster connected and booster not connected.

The back brakes will need adjusting, atleast one will as it is almost 1/4" from touching the drum, the other is slightly touching the drum so it is fine. I will go into both and get new adjusting nuts/screws though.

I am pretty much at a loss at to whether it is a bad booster, master cylinder, rear brakes needing adjustment, etc. or all of the above.
_________________
Rob
'80 931 (sold)
'80 924 NA (sold)
Former Omaha Crew

Ozzie · Posted: Fri Aug 19, 2005 8:40 am Post subject:

The straight leg on mine points to the back not the front.
It looks like it might have a venturi effect to assist the braking vacuum so would reduce if on backwards.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

isuras2 · Joined: 17 Jun 2005 Posts: 458 Location: Phoenix, AZ

That is how mine was installed. Now I have the booster hooked directly into the intake and the brakes are about the same as before. I guess I could replace all the lines going to the venturi tube and see if that helps...those are the ONLY vacuum hoses I did not replace.
_________________
Rob
'80 931 (sold)
'80 924 NA (sold)
Former Omaha Crew

Paul · Posted: Fri Aug 19, 2005 1:27 pm Post subject:

Fix and adjust your rear brakes (make sure you check the wheel cylinders).
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