(Solved) M923A2 Right rear brakes grabbing

[kendelrio]

Diaphrams

FYI you can chock the wheels.

Hook an air line from the front emergency gladhand to the front service gladhand and it will engage the brakes for you to find leaks on your own if you have no soldier b

OK bud, I've researched the methods behind changing diaphragms and a couple questions:

1. Should I do the parking brakes as well?

2. I take it this is the diaphragm I'll need?

Those Mikitary Guys Service brake Diaphragm

 

[simp5782]

DP12 and DP16 at napa or oreilly RB-D-12 and RB-D-16

Service chambers are size 12 hence the DP12. You need 10 of them for the whole truck.

Spring Cans have no resistance so you can't cage them.

You need 4 of the DP16s for the spring chambers.

The caging bolts should be on the spring cans. There is a holder on them.

If you don't have any in the holder then they are Oreilly part # RB008.

If you want the caging bolts socket it is oreilly # LIS 49000 or use a 3/4" wrench

 

[charlesmann]

Ken,

I too am running into this issue with my rear rear left side, left front and forward rear right side. i knew the left rr chamber was leaking from the spring side, and even though i ordered new diaphragms to rebuild ALL cans, i also ordered a new svc/emerg chamber from memphis. when i installed it, i was leaking air out constantly out of the intake stack. after talking with memphis, i got that leaking issue fixed. as wes said, the auto adjuster might be the cause, so while i had it apart for the chamber replacement and adjustment, i tore the whole mess down, minus removing the spider assy, cleaned and lubed everything, replaced the adjuster/idler plunger seals, reassembled and took it for a drive to put some black gold in the tank and unfortunately, the dragging issue is not fixed.

I was also having a dragging issue on the left front axel end, and after tearing it down, cleaning, lubing and assembling, it still wasn't fixed. I dug into the tm for troubleshooting and followed the procedures, and i am not getting the 90psi to the intake side of the svc chamber, and it tells me to check a valve under the radiator, but i haven't gotten that far yet. with the tee installed on the exhaust side of the svc chamber, where i had a psi gauge, i left it open to the atmosphere, with a filter installed, i noticed i wasn't dragging. i took the tee out and back to dragging.
So, i have stopped at that point in troubleshooting as well, but need to figure out where the exhaust line goes along the frame rail.

 

[kendelrio]

I was leaking air out constantly out of the intake stack.

I'm leaking air there too. What was the issue?

 

[simp5782]

Q2 Valve in the front is a culprit most folks have.

However a bad brake diaphragm causes air to go by the pancake and it goes our the vent line which Even from the rear axle it still vents to the stack

There is a block on the frame rail. Beside the transmission. Drivers side. Has about 5 lies going into it. That is the vent lines where everything Meets. You can remove each line one by one to find out which section its coming from. Your brake pedal, rear axles, front axle meet there.

 

[Elk1111]

One aspect of this whole thing you guys might not be considering is if the diaphrames are bad and leaking then the air pressure goes down and the spring brakes engage and drag.
Diaphrams are fairly inexpensive and the Q2 is less than $100 also. Both can be done in half a day and probably should be changed anyway. Start simple an inexpensive then go deeper if you have too.

 

[simp5782]

One aspect of this whole thing you guys might not be considering is if the diaphrames are bad and leaking then the air pressure goes down and the spring brakes engage and drag.
Diaphrams are fairly inexpensive and the Q2 is less than $100 also. Both can be done in half a day and probably should be changed anyway. Start simple an inexpensive then go deeper if you have too.

There was no mention of air loss with the pedal applied till the video posted today.

 

[kendelrio]

There was no mention of air loss with the pedal applied till the video posted today.

In my defense, I couldn't very well check it while rolling g down the highway!


Seriously, though, it was the advice on this thread that got me to that point. Thank you all so much!

 

[charlesmann]

I'm leaking air there too. What was the issue?

As discussed during our call, it was due to me plumbing the new svc/emerg chamber like the oem chamber. I had to plug one port on the svc side instead of plumbing in to block atop of the axle.

One aspect of this whole thing you guys might not be considering is if the diaphrames are bad and leaking then the air pressure goes down and the spring brakes engage and drag.
Diaphrams are fairly inexpensive and the Q2 is less than $100 also. Both can be done in half a day and probably should be changed anyway. Start simple an inexpensive then go deeper if you have too.

I would agree with the diaphragms being bad, if i hadnt replaced the svc/emerg chamber with a nib chamber. Granted, the rubber could be bad in that one too, but im thinking it may be something else. As for the Q2 valve, i would say yes, that is a failed/failing part.

 

[simp5782]

In my defense, I couldn't very well check it while rolling g down the highway!


Seriously, though, it was the advice on this thread that got me to that point. Thank you all so much!

Hitting your brakes should only cause a 8 to 10psi drop when applied. The dead giveaway should have been the gauge dropping.

 

[kendelrio]

Hitting your brakes should only cause a 8 to 10psi drop when applied. The dead giveaway should have been the gauge dropping.

This is a situation of "Not knowing what you don't know". I truly appreciate you and your knowledge. Thank you.

 

[kendelrio]

OK all-
Mis-diagnosis time on my part...

After sleeping on it, I realized the brakes AREN'T grabbing. What I experienced was the torque bar being off of the back axle. As I accelerated, the rear axle was driving forward into the forward axle, causing the tires to rub, which caused the smoke and loss of power I was associating with brake issues. The truck lurching to the left was the axle actually driving the rear of the truck right, causing the front of the truck to slew left.

I am lucky this is the extent of the issue, as bad BAD things could have happened.

I take full responsibility for not doing a proper pre-trip inspection and am ashamed for not doing so. My "justification" was that I was "only" driving three miles to pick up my spare. Lesson learned: proper pre-trip EVERY TRIP EVERY TIME.

Mea culpa.

I will be testing all of my bushings and diaphrams when I get home and replacing them.

 

[Steelreaper80]

Nothing is shared between right side together.

The T that supplies air pressure to the spring brake cans per axle sends pressure equal to both sides.

If one side has enough air to release then so does the other.

Auto adjusters are probably just sticking and with all the moisture this time of year the rust in the shoes is an over adjust and it can't back itself off. They only auto adjust up not off. So the first time you hit the brakes it adjusted up too much

Another issue could be that 2 brakes aren't working and 2 are stuck cause the spring brake yank isn't getting the full air system pressure. This happens the dual check valve sticking by the drivers step on the frame.

I had the exact same problem and Simp had me swap the valve under the driver's side steps. This completely fixed my problem. He has a video on how to check it on Youtube. It was invaluable! I ordered a good used take off valve from Boyce Equipment.

My rear brakes were also grabbing even going down the road with full tank pressure but the valve was not allowing the pressure to get to the spring brake cans.

 

[juanprado]

Air brake components are all hd truck stuff mostly haldex. Easy to find @ truck pro, napa etc.
I would not bother with a used takeoff as it is likely just as old as what you took off.