Trouble Shooting Brakes

[Anthiron]

Hi Guys and Gals

First post for me.

Recently had a touch up spray job done on my 85.5 NA 944. When I picked up the car the brake pedal was a bit spongy and traveled further than usual. while the car is running if i depress the pedal I hear a hissing sound like air escaping coming from the area where the pushrod enters the booster in the passenger seat foot well ( australian delivered RHD Car) There seems to be no fluid loss.

With the engine off if i pump the pedal a few times it will hiss a couple of times and then the pedal will firm up and the hissing will stop. If i then start the engine with the pedal depressed it will drop a couple of inchs and the spongyness is apparent.

My only idea is that when the car was baked to set the paint it somehow weakend the diaphram in the booster.

Does this mean that my booster is shot? or could there be another issue?

The car still stops well.

any input is appreciated.

In case it matters, the booster is an ATE 944-355-025-03.

Regards

Nicko

[Cocacolakidd]

Check also the brake booster check valve - If it is broken or defective it can make the same noises and have the same symptoms...

[John_AZ]

Check for brake fluid up under the dash by the drivers toes.
Look for moisture dripping from the brake pedal to master cylinder.
Air hissing? Are you sure you cannot see any brake fluid moisture?

You might just have air in the lines.
When did you last flush the brake fluid?
Every 2 or 3 years is recommended by Porsche. Brake fluid collects moisture.

Use a DOT 4 brake fluid--comes in blue and amber color.

I just replaced a MC on my '88-Girling.
I went rebuilt. My pedal goes to 1 1/2inch travel and stiffens hard. No air hissing.

Check for fluid around the brake cylinders by the wheels. Are the rubber covers cracked?

Check with Clarks-Garage.com for information on brakes.

GL
John

[John_AZ]

Good point on the brake booster check valve.

I replaced the brake booster on my Jeep Cherokee when the booster --not the check valve--would hiss (ssssssssssssss) when I applied the brake.

Just another idea.

John

[Anthiron]

No fluid around pushrod. Ie- none leaking out of booster. No leaks at calipers. Definate sound of air hissing which on an American car would be in the drivers side but in my Aussie car is in the passenger footwell. The noise is not coming from the check valve as it cannot be heard in the engine bay, only inside the car however I will take out the valve and inspect. Would a faulty valve cause air to escape the diaphram into the car?

If I have a leak of vacuum when I apply the brakes why does my engine not run rough?


Brake fluid is a year or so old. I am familiar with the hydroscopic nature of brake fluid. The system has not been open however and these symptoms (aside from this hiss) would make me think air in the lines except this could not happen in such a short period and there is still the matter of the air escaping hiss sound.

[mytrplseven]

I'd recommend taking the vacuum system schematic in Clarks Garage and follow each line religiously to see if there's a bad fitting. I used 7 to 10 psi of compressed air injected into the J boot (2" PVC cap w/air fitting screwed in) and soapy water solution sprayed everywhere. You'll quickly find any vacuum leaks. Focus around the brake booster and any fittings around the periphery of the engine compartment that the shop may have moved unintentionally (or not).

[John_AZ]

Originally Posted by Anthiron

. The noise is not coming from the check valve as it cannot be heard in the engine bay, only inside the car however I will take out the valve and inspect. Would a faulty valve cause air to escape the diaphram into the car?

and there is still the matter of the air escaping hiss sound.

When my brake booster went out, the hissing was inside from under the dash.

Try a simple test of the brake booster...
with the engine running--press slowly on the brake pedal.
If the pedal slowly goes down ....usually the booster is bad.

Search for other tests on brake boosters--Brake booster troubleshooting.

GL
John

[Anthiron]

If I slowly press the brake pedal whilst the engine is running I do not get any apparent assistance from the vacuum Booster. The pedal only moves with the movement of my foot. If I pump the pedal to solid with the engine off and start the engine with my foot on the pedal, it drops a few inchs when the engine starts. (This is the test the haynes manual suggests, It says it should drop a little but mine seems to drop too much)

Looks like the booster is toast.


Who has done this job on a 944 before? I have rebuilt a master cylinder before on my VW Baja Bug and bled plenty of brakes. but never power assisted.

The haynes manual makes it sound pretty simple however I am wary of simplified manuals sometimes.

Thanks for the suggestions so far.

Nicko

[xsbank]

Sorry, brakes - are those Oscars on your front bumper? Great lights, but an expensive park assist!

[Anthiron]

Ha ha. That's actually an old shot from
When I bought the car. They were the first thing I removed. They look good on the roof bar of my Baja bug though.