I'm new to this forum, have seen this problem presented in other forums, never seen a conclusive solution on any thread

1996 ram 2500HD 4x4 rear antil lock system

History of fading brake pedal

- has slowly fading brake pedal when I bought it, installed new master cyl., same thing, now on 3d or 4th new master, all with same behavior

-in each case 2 qts of brake fluid used in repeated bleeding, this time for bench bleed got steel flare nut brake tubes routed into reservoir for bench bleed, air vanished quickly

-installed speed bleeders permitting one man bleeding

-also installed rebuilt vacuum assist unit because it was developing assist too slowly, checked vacuum delivery from pump, perfectly to specs, checked vacuum loss at new rebuilt assist unit, holds up after shut off with hose from pump clamped off very well as per factory repair manual.

-careful inspection of all brake lines reveals no leaking lines and there is no sign of fluid dripping to the ground ... or loss of fluid from the reservoir suggesting leak

- parked truck on up hill orientation, bled the system again since master cyl. is oriented downward toward the front while on level ground and could harbor air pockets in master, no imporvement

-rear brake shoes adjusted twice to verify proper adjustment

Converntional wisdom: bad master or leak in line somewhere. With one of the new master cylinders I removed steel flare outputlines , plugged out port on master, got a rock solid non sinking brake pedal.

Some say it could be the RWAL dump valve. Took it apart, cleaned very grungy pistons, no imporvement.

WTF?

Anybody been here before.??

 

Were you able to inspect the line that runs over the gas tank? That's a famous spot for leaking... but, as you aren't losing fluid......

Reinspect all lines, calipers, wheel cylinders. If the pedal is slowly sinking to the floor, you DO have something leaking somewhere. With no loss of fluid, that would indicate an internal leak the M/C. What brand are you getting?

Also, moving this to the tech section for ya.

 

Thank you for your obviously well informed response.

true: brake line to rear is inside frame next to fuel tank for most of its run in that area, then ends up on top of tank at rear. Numerous consecutive pushing brake pedal to floor with engine running shows no apparent loss of fluid at reservoir or dripping fluid from any leak. I'll see if I can feel on top of the tank (vs see on top) for potential pooling of leaked fluid.

If that section of steel line along rear portion is leaking, is it necessary to remove the tank to replace that part of the line?

 

You don't have to.... but, it sure makes routing that bit of line easier.

 

re: which brand masters

1- from auto zone, Fenco

2- from OReill, brake best

3- currently installed: Raybestos following trusted shops suggestion of quality unit

the raybestos sinks faster than the brake best

Is there a preferable type of replacement line, perhaps flexible (never worked with brake line replacement before so I don't know a lot about options …. especailly for install with no tank removal. Got 25 gal. diesel in there I'd have to deal with ….

 

I'm not much help, but my brakes NEVER felt right after I bled them or change pads. It always took a week for things to work themselves out. I tried a new MC at one point as well. No help. The only thing I have found to help is getting on your brakes hard. Jab them. Hard enough for ABS to kick in. I don't know if there is a connection with that. I also switched to Dot4 fluid. Check your three soft lines. If they are split internally or expanding, you could be losing pressure there without showing a leak. Check your rear wheel cylinders for weeping as well. Good luck!

 

Parts store will have line. You can bend it by hand... but, better to have the right tool for the job. (and they aren't expensive either.)

Are you going to replace the line just for giggles? Or did you find a leak?

 

The solution is a rebuild on RWAL valve

now it stops like a champ

the number of folks with this issue and the total lack of anyone who was on target to this as the solution amazes me…. especially the tone of finality and authority to so many totally wrong statements about this issue

 

that's what ya get from troubleshooting over the internet. At least ya got it fixed.

 

what ya get when forum participants are well informed is a bee line to a solution, I found nobody on any dodge forum and I scoured 'em

Good info happens more often on mercedes forums but you still have to use judgement about how you expend energy and money