1999 e280 Rear Brakes (weird)

[gasket]

A little while ago i spoke how i could not get the brakes to bleed on my merc
well after a master cylinder change & abs unit change still no rear brakes!
but they do bleed.
What is odd is that no matter what i do even with a pressure bleeder I cannot get the air out it seems that air is getting in somewhere and I mean lots of it! not little bubbles & this is only on the rear.
strangely though if I leave the easy bleed on I get a good pedal and rear brakes.
I have looked at the pipe between master and the abs no fluid leaks what could it be?? its driving me nuts!

 

[Myros]

trying to be logical about it

if you have good pipe connections at the master cylinder and at the calipers, and there are no leaks in the pipework, then the remaining culprits have to be the caliper or the piston seals.
It looks like you might as well have them off and put new seals in. You can inspect the bores for cracks or chips at the same time. Wierd that you aren't showing fluid loss somewhere.
The only other thing I can think of that might do it is the brake force limiting valve thing, but I don't know where it is or whether it could produce these symptoms. I hope they'd engineer that to failsafe and still give you hydraulic feed to the rear.

 

[hardtop]

i dont know the model but on some cars esp est you might have a load sensor valve this gives more brake power to the rear when loaded & may be the prob

 

[gasket]

Well the air seems to come from the abs unit when I crack the pipe is is possible the abs unit can introduce air to to system??

 

[wireman]

I would be looking at the rear caliper pistons which could as suggested be tatty and sticky allowing air in when pressure is lifted from the pedal, a slight vacuum can be created in the system as the pedal returns to its stop.

Are the flexible pipes in good order? they can get spongy inside and block flow of return fluid making the master cylinder induced vacuum draw in fluid over a seal anywhere on the system.

You must bleed the rear part first or an air lock can form in the gap between the front and rear pistons of your master cylinder.

Use an eazi bleed and work the pedal whilst its pressurized to see if you can shift the air out. Take great care to not let the eazi bleed's cap blow off with too much pressure.