Brake question: New master cylinder needed?

efhughes3 · efhughes3's Garage

I've got a question on whether I need to replace my MC. I've bled my brakes no less than 4 times with my pressure bleeder (10-12 psi). I can't get the brake warning light to STAY off. The last time I bled, there was a small amount of fluid on the floor near the pedals. Is this a MC leak?

stormcrow · stormcrow's Garage

If you have brake fluid on the floor below the brake pedal it's time for a rebuild or new MC. Not a complicated job, just a PIA.

Steve

"A Porsche does more then just go fast in a straight line"

john70t · 05-26-2004, 07:37 PM

Make sure to prime it first: get a brake line that fits from a parts store, cut in half and loop back into resevoir, and pump until no more bubbles.
Makes install a lot easier.

aigel · aigel's Garage

Ed:

I take it you disconnected your battery to make the brake light go off in the first place, right? And then after you had it go off that way, it will come back on? After what time and use?

How do the brakes feel?

The switch may be faulty too.

George

efhughes3 · efhughes3's Garage

I've tried the battery disconnection. It will go off after bleeding, but the first time I hit the brakes, it comes on. They feel ok, but it's driving me nuts. The other thing was the brake fluid on the floor after the bleedings. My guess is this isn't s'posed to be

Stormcrow seems to confirm my hunch on the MC.

Jdub · 05-27-2004, 07:38 AM

A new MC if it hasn't been replaced is just good sense. Search on my name and MC to review my experience.

Consider that your brake switches might be bad. If so, you will spend up to $55.00 for two new OEM Porsche switches. Or, you might spend ~$12.00 for two VW switches which you will have to replace in two months. Finally, a new MC will include OEM switches so you are that far ahead of the game.

Also be sure to get a length of hose to replace the two hoses that go from the resevoir to the body of the MC. Yours will be old and cracked. Do not neglect this. I used fuel line from the local parts store.

Be very careful not to gouge any parts when removing the caps/hoses from the old MC body - you'll see what I mean when you get there.

Finally, check the Tech Articles section for a description of how to R&R your MC. Jim wrote it.

I did not bench bleed my new MC. It worked just fine. You will love the new harder feel of the brake pedal. That's what I noticed.

Really finally, consider doing the brake caliper rebuild and putting in new lines all around now. This will take some time, yes, but the final result is very satisfying and you won't sweat the brakes for another 25 years.

John

mwildt · 05-27-2004, 07:43 AM

Hi,

Before you get too far, check those brake switches first. A leak can very easily come from those guys. They are screwed right onto the MC. Some MC replacements can be avoided since the leak still was present afterwards due to faulty switches. Don't ask me how I know, it happened on my old SC.

Michael

efhughes3 · efhughes3's Garage

Thanks guys!

I'll look at the switches, but changing out the MC probably makes sense considering the age of the car. I'm pretty confident it's not been done. I did rebuild the front brakes last year, which wa a great improvement, this is actually kind of exciting in a wierd way to get one more item checked off the refurb list.

I'd been considering the braided lines, no time like the present!