brakes
 

soft brake pedal 1990 300se.changed new master cylinder and both front calipers and pads.went to bleed brakes with pedal and had plenty fluid to front but,the back just dribbles.help

sounds like air,bleed rears first,till a stream,then fronts.

There's one master cylinder reservoir, but it has separate compartments front/rear. The rear doesn't fill until the front is completely full. So the usual answer is that you're pumping on an empty master even though it may look full. The way you make this work is to simply keep the reservoir topped to the brim until the rear brakes are fully bled.

Did you bench bleed the master cylinder when you changed it?

Yep.

Some may not agree, but I've been doing the following to my 300-SEL for the last 20 years.

Fill master cyl reservoir and keep it full throughout this entire process. Open all 4 bleeders - hose attached - other end in a catch pan/bottle

Start engine(if ABS) then start pumping pedal. You do not have to pump the pedal far - shorter strokes are better. Pump several times. This gets the fluid flowing. Continue keeping an eye on fluid level in master cyl reservoir - keep it full of fluid. Let as much flow out each bleeder as you like.

If any bleeder is not flowing - something in that circuit is clogged - bleeder/caliper/hose.

Once done - tighten all 4 bleeders.

You may need to either pedal bleed - vacuum bleed or pressure bleed all 4 afterwards, but in my case, the gravity bleed method I just outlined has never failed me when bleeding/flushing my 300-SEL. Nice firm pedal afterwards.

2x

I just do not see how you can do it with all four open. You start with the one farthest away from the master cylinder and then do each of the others. Have been doing this for 50 years and have never opened all four at the same time.