Upgrade Master Cylinder?

[Chiragp]

I am having real bad pedal feel, and takes almost 1/2 the pedal before I get any real initial bite. Mercedes tech suggested the 400E calipers might need a bigger master cyilnder then the stock 190E 2.6's. Would this be a simple swap? Should I be looking for a 92 400E master cylinder then? I thought I was told they don't need changing. Any Ideas?

[Mervyn]

I do not think that MB designed their cars to underperform, especially the braking system. Hence I dont recommend you spend the extra $$ on a 400E master cylinder. Get the unit originally suited for your car.

Maybe you'll want to know my experience with bad pedal feel. I'd this problem and it gets dangerous at times, when the brake could not bite sufficiently in time. Braking efficiency was pretty bad, almost like 50%.

I changed all four rotors and brake pads, with the front two rotors being the cross-drilled and slotted type. Changed the sensors too. Still, the problem persists.

Next, I changed the master cylinder. Got slightly better, and I thought this is the best I could do. So I left it at that.

About 2 months later, my car started to want to stall every time I was at the lights, and the RPM needle fell to a new low. The car was shaking too. Then when the lights turn green, and I lifted my foot off the brakes, the car got back to normal. I thought I had a lower than usual idle setting, and so adjusted it higher. However, it did not help as when I was at the lights again, the phenomenon occured again!

I related this to my mechanic, and guess what? He traced the problem to the brake booster pump!! (the huge drum-like thing found near the master cylinder) So I got the booster pump replaced, and guess what again? Not only was the near-stalling problem solved, my pedal feel and braking efficiency improved by LEAPS and BOUNDS!! I was amazed, and very glad!

I supposed it could have been the booster pump giving problems all along, and I could have saved tons of $$ from the rotors, pads and master cylinder. Then again, I now have my braking system entirely replaced (except the callipers and brake lines), and my heavy W126 stops wonderfully quick. I'm amazed........

Hope this helps.

Mervyn
1983 W126 (280SEL)

Oops, re-read your post, you have 400E calipers on the car? If so, then I think you do need to use the 400E MC. The symptoms you describe (long pedal travel) are what would be expected if too small a MC were used.

[Edited by Brian K on 06-15-2001 at 01:41 AM]

[16vwannabe]

Well, he's got 4 piston calipers on there now. I'm not sure of the piston size, but I would imagine the surface area is much bigger than stock 190 calipers. This might warrant a larger bore MC to move more fluid. My pedal seems fine with the 400E front brakes, maybe the MCs were different between the years?
Darryl

[Tobias MB]

I've also got the 400E front calipers on my 1984 190 and am using the original (1984) master cylinder with no problems.
The few extra CCs of fluid needed to work the front calipers is very insignificant compared to the OE units.
Previously had 124 (300E)calipers on with no problems. You may have a defective vacuum booster, check the vacuum side for leaks.
Good luck,

TobiasMB
4 MBs