Kit for Master Cylinder

[ejsharp]

I would like to rebuild the Master Cylinder on my 1987 300E. Does anyone have a suggestion as to where I might purchase a kit to rebuild it?

[jeffsr]

Earl, replace it. They aren't that expensive (around $100 or so here at parts Shop). A rebuild kit will cost $25-$35 or so, if you can find one, plus the labor to recondition the MC bore. Cheap insurance for great peace of mind. Just my $0.02..

[ejsharp]

I just read in Alldata that the master Cylinder has a stepped diameter... whatever that means. Is the inside diameter stepped for some reason... possibly a safety feature in order to allow multiple chambers for a stepped piston?

Anyway I agree that a new MC is the wiser of the two alternatives. Now I have to diagnose the pedal slippage to determine if it is in fact the MC that is causing the problem. Are there any sub systems in the 87 300E that might cause pedal slippage? (So far no noticible fluid loss.)

[jeffsr]

Earl, stepped diameter means the bore of the MC has two or more different internal sizes. The emergency or high pressure bore is usually the smaller of the two. Possible causes for excessive pedal travel, worn pads, air in the system, blown caliper piston seal(you would be losing fluid however). One other thing comes to mind, but I am not sure if it applies to MBZ. A stuck check valve in the vacuum boost chamber.

[ejsharp]

Thanks Jeff... that may explain why the pedal can sometimes slip but then catch again.

The Check valve sounds interesting. I have not encountered that problem before. Therefore I'm not sure how to diagnose it. It seems to me that if it were a check valve then the vacume could not assist when foot pressure is placed on the brake pedal. Thus the pedal would remain high and not slip toward the floor. But then I'm only guessing about the function of the check valve.

[william rogers]

by all means put in a new one I just replaced mine on my 81 sd it was 63.00 from fast lane for a new ate ,bet they are three time that at the dealer for same part. It's an easy install make sure you bench bleed it well then bleed all four
calipers starting at the right rear which is the farthest away from the master cylinder then go to the next farthest an so on...............
William Rogers....








[Edited by william rogers on 07-02-2001 at 12:40 AM]

[jeffsr]

Earl, too much vacuum, makes the pedal too easy and travel too far. But, I don't know if this is part of the MBZ braking system.