need some help on this one. i have a 92 w250 the break pedal falls preaty much to the floor befor it build any braking presure. i have replaced the master with brand new one no rebuild. i have bleed all the lines 3 or 4 times and still see no inprovement. the pads drums are all almost new. 1 new wheel cyl. 2 new calipers in the front. 1 thing i did notice was the abs vavle thats up in the rear frame rails was bypassed by some one befor me. with the truck off i can pump the breaks up and they feel real nice but as soon as i start it i lose all presure. any ideas i dont know what to replace next. please help

 

No visible leaks? If the ABS dump valve is bypassed we can rule that out as a possible problem.

Does the pedal feel good with the truck off?

 

no leaks that i can see.yes it does you can pump it up and build a nice pedle.

 

i had the same problems with mine to be honest. and just got around to fixing it 2 days ago, i had to replace ALL the vacuum booster lines, it didn't seem like any had a leak, but the way to tell is to start your truck up, let it run for about 30 seconds, let the truck then sit off for about 10 seconds, unhook a vacuum line real quick and if you don't hear it make a hiss when you do that then you need to replace your vacuum booster lines. if that doesn't solve it by replacing the lines then you need to rebuild the pump or get a new one.

 

Apples and oranges....here goes anyway.
Check your rear drums,Ma's (2000 ram 2500) brakes were not self adjusting anymore,so I adjusted them,parking brake now functions,brake pedal right up at the top...easy way to do it with outboard brake drums is just to make em tighter till the drum sorta drags when installing it,then back it off a bit.
Her ABS light was on too,till after I fixed em'.
If you've tryed that allready then it must be something else.

bad brake boosters make the pedal go near the floor?
Mine have allways just made the brakes suck.
thats gas rigs though,so...

 

Will that nice pedal stay up as long as you feel like holding it, or does it drop slowly?

Tell me your bleeding procedure.

 

the breaks will stay nice when the truck is off. the rear drums are adjusted right up. right rear left rear right front left front

 

Sounds like a problem with the booster, probably the pushrod is adjusted too long. Did you replace the booster with the master?

 

yea no i didnt i jsut replaced that master

 

My first question is did you accidently pour power steering fluid in the brake system? I have seen it happen many times because the hydroboost uses PS fluid it's mistakenly put into the brake system. That will ruin it in a hurry. Second question did you bench bleed the master cyl.? If not then you need to. Also, when you bench bleed a master cyl. you have to be very careful not to push the piston to far in. If you do the compesating port can tear a cup causing the fluid to bypass the cup internally. In other words, no real pressure can be built up. There is only enough reserve in the accumulater for a couple of strokes after the truck is turned off which causes the pedal to get hard. When you start it back up the PS pump is running and pressurises the hydroboost causing the pedal to drop. Anyway, hope this helps. E