Excessive Brake Pedal Travel
 

I just swapped out the front rotors and steering stabilizer on my '92 300SE in an attempt to get rid of the under-braking shimmy I was experiencing.

Didn't swap the pads as they are practically brand new, from what I could tell.

Discs are MB OEM. Shimmy is gone.

Before the work, pedal travel to get "real" braking was what I call excessive - probably at least 1" or more. After the work, same thing.

I bled all of the brake lines using brand new DOT3 fluid. I've since been told that I should have used DOT4 and flushing that out will restore the brake pedal to a more reasonable functioning level.

Far as I can tell, the car is more than capable of stopping quickly when required, I just don't like having to press so far on the pedal to get it to do so.

Any suggestions, or is the DOT4 change the solution to my problem?

does the pedal feel firmer if you push once and right away push again ?
more over, given you have new parts, when the car is parked and ON, press on the pedal firmly and keep pressure on it for half a minute or so. repeat that three to four times. that will bed in the distance in the new pads with the calipers etc.

if the first scenario is present where the second push is always firmer, then open up the callipers and clean/grease the calliper sliding pins as well as the calipers inside where the pins slide. that ought to do the trick :)
keep us posted and good luck.

DOT 3 is just fine. no need to change to DOT 4. and bleeding isn't always the cure either. try the above first.

I don't believe that there's any difference with a rapid reapplication of the pedal, but I'll check.

I'll check the sliding pins on the rear - the fronts are 4-piston units, so the calipers don't slide (at least I don't think they do).

I didn't figure that there would be an improvement between DOT3 and DOT4. My understanding is that the main difference between the two is boiling point. Several people offered that there's a difference in the "compressability" of the two fluids (from what I remember their comments being). Far as I can remember, within the parameters of a hydraulic system such as found on my car, you can't compress a fluid - period.

Thanks for the input.

1" of travel seems about right to me.

tom w

1 inch seems a bit excessive, I can lazily brake my 300D if I see a traffic light coming by barely touching the brake pedal. If you are talking about a neck snapping stop then 1+ inches sounds right, but it's hard to quantify what real braking is :confused:

free play is free. it shouldnt take any more for an easy stop than a hard one. once the free play is gone, the rest of the travel is bending of the pedal arm and whatever else there is to bend. the brake fluid shouldnt give at all nor the disc nor the pad.

so total brake travel shouldnt vary much whether the stop is hard or easy.

tom w