M932A1 loosing air when hand brake is applied - Steel Soldiers::Military Vehicles Supersite

rrrr · 12-09-2011, 14:34

The truck builds air great. Then when I take my hand brake off it starts loosing air out of the left middle axle brake assembly. Put the hand brake on and all is good. It is coming out of the brake assembly not the tube on the air intake.

Any ideas ?

I've looked through the TM and its not too helpful.

73m819 · 12-09-2011, 14:48

BAD Diaphragm, this is a spring brake, air on=release (off), air pushing AGNEST the spring so it RELEASES , no air=on, spring set, CAGE THE BRAKE POT BEFORE taking it apart to fix, there is ENOUGH spring tenson there to KILL you

rrrr · 12-09-2011, 15:15

I'll look through the TM's again. It makes sense what your saying !

rrrr · 12-09-2011, 17:06

OK, drained all air and caged the brake for the offending wheel. I pulled the clamp off and inspected the spring brake chamber diaphragm and it looks like it wasn't sealed well. The diaphragm looks very good. Tried to put it back together but the spring on the spring brake side is just too strong for me to push together and get the clamp back on. I tried to use a tie down strap but it would not track straight and the air brake assembly would just shift.

Is there a special tool for this ?

Do I need to pull the wheel and hub to get at the brake drum and relieve the spring pressure from there ?

The TM just is not very good for this or i'm missing something ? It just says to reassemble

73m819 · 12-09-2011, 17:23

If it is caged RIGHT, there should bo NO spring pressure

no need to pull hub, everything is at the pot

rrrr · 12-09-2011, 17:24

I'll go and check the caging and try to tighten a little more.

rrrr · 12-09-2011, 18:29

OK, got it back togehter and now air is leaking from inside the drum (maybe it was doing that all along)? The diaphragm that i pulled out looked almost new didn't see any signs of a problem but could have missed something. The diaphragm would have to be bad to allow air to exit from inside the drum assembly, right ?

Could it be something else ?

73m819 · 12-09-2011, 18:30

IF not together yet, take the diaphragm and and ROLL it tight, as rolling it side to side, then top to bottom, LOOK for a TINY crack, it does not take much to have a leak at 100+ psi, I would guess this will be your leak BEFORE just not being installed right

oops to slow in posting

73m819 · 12-09-2011, 18:39

there is 2 diaphragms in your system, the brake pot has one, the spring brake has one, would be NO air from the brake pot unless you step on the brakes, with the spring, the only air present is if the parking brake is OFF and air is releasing the spring brake, so if leaking with the spring brake released and NO brakes applied, it HAS TO BE THE spring brake diaphragm

if you want , call me, 703-389-6705

rrrr · 12-09-2011, 18:39

Quote:

Originally Posted by 73m819

IF not together yet, take the diaphragm and and ROLL it tight, as rolling it side to side, then top to bottom, LOOK for a TINY crack, it does not take much to have a leak at 100+ psi, I would guess this will be your leak BEFORE just not being installed right

oops to slow in posting

Thanks for all your help ! I'm really surprised at the lack of explanation the TM's have for the 9 series trucks. The Deuce TM's walk you through it; very detailed and easy to follow.

Its all togehter, I'll pull it apart tomorrow morning and see if napa or the local peterbuilt has the diaphragm. It will be much easier the second time around

I can't believe how much tension those springs have in the air brake pack !
You are so right that it could be a fatal mistake if not done correctly.

I will post up tomorrow about what I find.

Again, THANK YOU !