M932A1 loosing air when hand brake is applied

[rrrr]

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]

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]

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

 

[rrrr]

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]

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

no need to pull hub, everything is at the pot

 

[rrrr]

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

 

[rrrr]

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]

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]

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]

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 !

 

[doghead]

I think they stopped making them rebuild-able, so less people get hurt. The last new set of Bendix chamber brakes I bought were not serviceable.

Just go buy a whole new unit.

 

[73m819]

You can get the Diaphragms for the older brake pots, most shops now send out the rebuildable pots to be rebuilt, the new non-rebuildable throw away pots are cheaper at first glance but in the long run a lot more EXPENSIVE because everytime some LITTLE thing goes bad, Diaphragm, a valve, seat, ect, ect. means a new pot.

REBUILDING these brake pots is easy if you know what your doing, if you don't stay away, you will screw up a brake pot along with the chance of getting your self really hurt

 

[kc5mzd]

Try releasing the hand brake after you have full pressure. then if you hear air from one of the brakes you should press the foot brake all the way to the floor for 15 seconds. usually this will seat the spring brake diaphram.
Be sure to check the tire inflation system if you have it. This might explain the air leak sound from the drum.

 

[Truckoholic]

This thread was scaring me! Many many people have been hurt very bad and killed by attempting to replace the diaphragms. You can replace the one that applies the brakes okay if you know which of the two clamps to take off. But taking the wrong clamp off sure can result in a majorly broken face, or neck, or upper body.

But yeah, that has been one of my major gripes about the Technical Manual's. They are not "Technical" enough. They should be called BM's for "Basic Manuals" because they are just so basic. I guess they are designed for a bunch of young 19 year old guys to understand, but it is very annoying how when you actually need to know how to do something a little more advanced, you are on your own.

[media]http://www.youtube.com/watch?v=EnGWLPYYTx4[/media]

[media]http://www.youtube.com/watch?v=HeM4Av2EKbU&feature=related[/media]

 

[73m819]

I just got done reading the 900 5t TMs, thay suck big time, the -10 talks about caging, but the -20 just refers you to the -10, NEVER in the -20 does it talk about caging in the maintenance of the spring brake. the -10 reference in the -20 can be very easy to miss.
The 900 5t TMs on a whole lack, lack, lack

 

[m16ty]

You should cage the chamber whatever side you are working on. DH is correct about the new chambers being non-serviceable on the sprig brake side. The ones I've seen still let you service the non-spring side though. I've been keeping all the old style chambers I can find because it's much cheaper to just replace the diaphragm.

I did run into a problem I've never seen before on a chamber I worked on recently. It was leaking around the shaft between the two air chambers. Took it apart and there is a bushing and a o-ring in there. Bushing looks ok so I think I can fix it with a new o-ring. I also found out that when it leaks between chambers the brakes will stay applied all the time and back feed air into the service line. This was on my M870.

 

[rrrr]

73m819 and I talked at length about air brakes. I am definitely the new kid on the block when it comes to these brakes. I've learned soo much today. Tomorrow will be interesting to see how easy it is to get new diaphragms locally.

There is no dought that the leak is on the hand brake side. I plan on replacing the normal brake side as well since I'll already have the brake caged. This was recommended by 73m819 and makes since because you stress the diaphragm on the normal brake side when you cage it.

 

[rrrr]

Problem solved. After replacing both diaphragms and still having the same problem we, me and 73m819 began trouble shooting. We disconnected the opposite line from outside the spring brake diaphragm that was having air come in and causing the air loss. The other side did not have this issue. So, looked at how the lines were connected up at the T fittings and what do ya know, they were reversed ! I verified this by looking at the rear T fittings. So I swaped the two lines at the brake assembly and problem solved.

Unbelievable ! I can't imagine how long this has been hooked up wrong.

This pictures below detail what was the issue.


The TM's were virtually useless in this case. No detailed drawings or explanations in them.

 

[73m819]

I would CHECK the brakes on the switched side, something was done to allow the wheel to turn instead of draging and sucking power, if the spring brake would not release, the brakes might have been backed all the way off

 

[rrrr]

Took the truck for a test drive no issues and everything seems to work great !