porsche924

I had posted a thread earlier asking about bleeding the hydraulic systems on my car and soemone mentioned that if i see a lot of blackish stuff in my brake fluid resevoir that it might be a good idea to replace my master cylinder. Well the first thing i noticed when bleeding my brakes was wow, the fluid is really dirty and has all this black junk in it. Does anyone know of a way to test the master cylinder to see if it is still good? I have a vacuum tester kit with a gauge and everything if anyone know how i can test it with that. Also does anyone know where i could get a rebuild kit for this and also how you rebuild it if i can find a kit?

thanks
bobby

Ed944-968

Bobby
I have the Factory 944/951 manuals in front of me and they do NOT list any method for testing (even though they do go through the rediculous task of rebuilding one yourself).

My gut feeling is to replace the master cylinder if you are getting all sorts of black gunk out of the system. It's cheap insurance for your brakes and your life.

Here's some more information I've acquired over the years

1 - Tools-
If you are going to remove/install or loosten/tighten any of the hard steel lines get flare nut wrenches first, otherwise you could vert easily "round out" the little brass nuts with regular wrenches (even vise grips and those "miracle wrenches").

2 - Testing the Master Cylinder-
When I used to work in a service shop that serviced primarally American cars we tested the Master Cylinder by getting into the drivers seat (engine on) and slowly pressing the brake pedal down to its limit (hard pressure). Then let up on the pedal very slightly (not anywhere near all the way off) and apply hard pressure again.

3 -If it's dead buy a new one, don't try to rebuild it (huge pain in the ***)-
Essentially, if you can get the brake pedal to keep going down after you have reached what you think is the bottom of the pedal travel (or if the darn thing just goes to the floor on the first try) then the master cylinder seals are going bad (or shot if you hit the floor). From personal experience, they are not worth rebuilding, buy a new unit.

3A - Buy an OEM Porsche part, not a knock off whenever possible. I've gotten screwed too many times by supposed "companies that make parts for Porsche" . I think it's usually only a little more in the case of master cylinders (I've done 3 on 944/951s all with Porsche parts).

4 - ALSO IMPORTANT - The total brake system capacity is one liter when totally full. Make sure that you get more (DOT 3 or DOT 4 rated) than one liter of fluid when you do the job. Buy smaller jars so you can return what you don't use (maybee 1.5 -2.0 liters or so?).

5 -The shop manual says that the brake fluid should be replaced at least once every 2 years due to water moisture infiltrating the system. bleed the system until the funky colored fluid is totally out.

That's about all I can say regarding the master cyl' issue
I Hope that this helps
Ed

Hans

There is no way of testing them, they either work or are dead.
The black / dark goo you found may very well be overaged fluid.
Try a good flush first, dont forget the clutch!!
I second ED above: if brake master goes, replace with OEM.
If clutch goes, replace both master & slave AND the hose along the fire wall.
TakeCare

porsche924

How do i flush out the clutch fluid? Also what is the best way to flush the entire brake system, i have tried just overbleeding all of my calipers, i did it twice and it was all clean the first time, did it again and it was a little dirty. Any help is appreciated.

thanks
bobby

Hans

Goes the same way as the brakes, but this time the valve is on the slave cylinder, so car needs to be lifted for access.
Level in the brake fluid container is critical now.
It should NEVER during this action be below the top level of the hose mounted to the side of the fluid container. One split second below this level and you have air inthere....
TakeCare