Hey all,
I just did the brakes in my 1985 6.9 (New Rotors Calipers, Shoes, hardware, wheel cylinders, etc.) and the brakes still feel spongy. I have bled the brakes on 3 different occasions and still cannot get the damn brakes to stop when they should. My last thought is that it has a bad brake booster and vacuum pump. Had anyone ever changed these? Where is the brake booster located and is it a pain the in the rump. Thanks
-Linny

 

Did the breaks on my 86 and they are still really bad. I don't know why but I think the breaks on these trucks are just no bueno.

 

That's' what I keep hearing, but I think there's a problem with the diaphragms in the booster and vacuum pump. It is a pretty common problem I guess that I found doing some research on the interwebs. It would make sense though seeing the truck is pushing almost 30!

 

One mod I'd like to do someday is called a hydroboost. From what I understand ( which isn't very much haha) is that it is or basic ly is hydraulic assist instead of vacuum. Lost more pressure in the system and works great for heavy towing. I have no idea how much or where to get one though. Check it out though.

 

check the vacuum at the brake booster, unhook the vacuum line and see how much it pulls.

If it has good vacuum ( had trouble with mine like this).... Mine ended up being that when i changed out the master cylinder, i didnt get the push rod the right length, it was too short which causes spongy brakes, almost like air in the system. get that the right length and the brakes will be much MUCH better........

 

Is the problem that the truck won't stop ??? Or that the pedal is spongy and not tight?
There is a replacement brake booster that is "supposed" to address a soft pedal. From what I remember it has a larger diameter diaphragm and gives you the solid feel in the pedal.
I found this out after changing the wheel cyclinders, calipers, booster, and master cylinder out on mine. the truck will stop but the soft pedal makes me nervous the way it feels... so me assuming I can't bleed lines properly took it to a shop and watched them do it... Same results... truck will stop fine... but pedal is still too soft.

Another option is a faulty abs control valve. ??