6.2 Diesel Brake pressure

[COKE]

Good day all,

I changed the rear axle shoes and wheel cyls. and now the truck does stop,but i guess it doesn,t brake like it should.
It locked the wheels with 33´s tires on a panic moment and now it doesn,t
I have meassured the brake pressure using a gauge on the front caliper bleeder hole and it arrives to 1500 psi with engine running(It is a 6.2 with the hydroboost) and the pedal fully depressed.
Years ago when i bought the gauge i meassured it and it arrived to 2000psi or more if i recall correctly.

The brake light is off wich means the valve is centered and there is not a difference of pressure between both systems.I used a tool to keep the valve centered while i was bleeding the system. i also used a mytyvac for vacuum bledding.

Maybe the master cyl is not delivering all the pressure?It has been few days without fluid ,and i have heard that sometimes they used to die when this happens.

Thanks a lot for any input.

 

[diesel4me]

Not sure about the master cylinder possibly being wounded,but if your truck has the rear brake load proportioning valve thats attached to the diff housing and the frame with a linkage,if that is screwed up it could be restricting the pressure too much...its designed so it reduces the pressure to the rear brakes while the truck is empty to avoid rear wheel lockup,it has a linkage that adjusts the pressure as the truck gets loaded down,the heavier the load,the more pressure it allows to the rear brakes...I "deleted" the one on a few trucks I had,and just learned to brake more gently,I found it stopped much better without it...

 

[COKE]

No,it hasn,t it.
It is a 1/2 ton Blazer and it only has the combination valve wich is attached in the front of the frame.

Thanks

 

[80' 427]

Did you adjust your rear shoes up?

 

[scottystills]

Hey COKE I've got the same truck. Had the same problems and found that there was a small stress crack on my hydroboost, had to replace it was bleeding some of the pressure. I never would have seen it without another set of eyes on it... It was leaking just a touch around the edge of that cylindrical pressure vessel on the front of the assembly.

 

[COKE]

Did you adjust your rear shoes up?

I just left the shoes enough closed to mount the drum...

 

[COKE]

Hey COKE I've got the same truck. Had the same problems and found that there was a small stress crack on my hydroboost, had to replace it was bleeding some of the pressure. I never would have seen it without another set of eyes on it... It was leaking just a touch around the edge of that cylindrical pressure vessel on the front of the assembly.

Scotty ,did you have to replace the whole thing or just the golden cylinder?
Thanks

 

[80' 427]

If you don't adjust your drums up it will not stop as well. You need to adjust them out with a spoon or go to a parking lot and back up, brake, back up , brake until they are better.

 

[scottystills]

Scotty ,did you have to replace the whole thing or just the golden cylinder?
Thanks

I ended up replacing the whole thing. Reason was, I tried the wreckers' to replace just that cylinder but almost every time that thing was either missing or broken. I'm going to take a wild guess that it's not uncommon for its seal to break or the thing breaks itself. Got a full new assembly, remanufactured, for about $200. That's about a year and a half ago, and so far so good.

Just check around it, I dumped some water over it while the engine was running (messy ask I know) and could see it sputtering over where the pressure was escaping. If you're lucky it's where you can see it, if not it could still be along the bottom and it'll take a much more careful look.

 

[COKE]

Thanks Scotty,It does,nt show leaks when the pedal is depressed.It has a little film of oil& dust covering it but i suppouse that this is usual.

80´427 ,the spoon will not work here.
I doesn,t have a window in the backing plate for this.You need to remove the drum and turn the adjuster star with your fingers.

However today i have bleed the brakes again,and i have gone out for a ride.
I folowed your advises about to brake on reverse and drive and now i have a better pedal feel.Today is rainning and the pavement is wet so it locks the wheels .
What i,m going to do now is to change the front brake pads.They still have an acceptable grossor but they are 12 years old(I don,t use the truck very much) and maybe they could be a little hardened?...