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Brake advice for 1985 280ge

1K views 3 replies 4 participants last post by  w123silver 
#1 ·
I recently removed a rear wheel brake cylinder from my truck. When I removed the brake line from the brake cylinder I was surprised that no brake fluid ran out-no even a drop. I then replaced the cylinder with a new one and bleed the entire system with eezee bleeder pressure system according to MB workshop manual. After bleeding the whole system and ensuring there was no air in the system I went back and opened the bleeder at the rear cylinders--again I found no brake fluid coming out--not a drop. Is this normal?
Also, I find my brake pedal to be low and spongee. I also replaced the master brake cylinder recently. What may be causing the low spongee pedal? Brake pads and shoes are almost new. I inspected the flexible rubber brake hoses for swelling under pressure but I didn't see any problems withn the hoses. Could a struck proportioning valve be cause of these problems?
Any advice or comments would be appreciated? Thanks inadvance!
 
#2 ·
No this is not normal at all!. You have blocked piping somewhere along the line. I would suggest you disconnect the hydraulic line to the brake cylinder and use the easy bleeder to apply presure - check if fluid comes out freely. It may also help to clear any contamination. You can also use the pedal to force fluid out. Just make sure you attach a hose to the line so that you may syphon fluid(if any) to asafe container. It could also be a faulty load presure regulator
 
#3 ·
Lots of times the flex lines fail internally. The inner layer of rubber separates from the line and can block the passage. Pressure from the pedal will force fluid through, but it won't flow by gravity. The usual complaint when this happens is of brakes dragging because the fluid can't return to the MC under just the return spring pressure.

A faulty or mal-adjusted rear proportioning valve is also a possibility, as is just enough crud in the lines to impede flow by gravity.

Brake fluid should flow through the system by gravity pressure. This is the first thing to correct before tryign to go further.

The spongy pedal is almost certainly due to air in the system, or a bad seal in the MC. One thing you can try for the air is a reverse bleed where you hook pressurized fluid to the bleed screw at the wheel and force it backwards through the system to the MC reservoir. This technique is used a lot on clutches which seem more prone to trapping air. But it works equally well with stubborn brakes.

Good luck, and let us know what you find!

-Dave G.
 
#4 ·
help needed

i am searching for old posts that could help me with my problem, but found none, so i will ask a question,

my 280ge, a manual, does not brake, lucky it happened when i was going slow, i actually just got it from the mechanic for the same problem, he said the booster leaked so he used some sealant and that the brake proportioning rod needed replacement so he removed it so i could use the truck until i get the brake proportioning rod,
just a few kilometers away.. no more brakes.. he does not know what the problem is..
should i replace the master cylinder? or is this some hose problem? the fluid does not leak by the way
 
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