Service Brakes not Releasing

[M35A2-AZ]

rrrr, Thanks for more things to try. I have used the glad hands for trouble shooting on other trucks. I will try the air tool oil all so.
I got the truck from GL the first week of Nov. and it was rebuild 7/2010 by Fort Riley, KS. But it had a starter problem and a fuel problem so it did sit for I long time I am sure. All we live on a dusty road so that may be a factor also.

Will do a little trouble shooting this morning.
When the brakes lock up there is no air venting out of the rear most vent, I have seen that. The TM calls that the Primary Relay Valve. That relay vent and the Secondary relay vent have wires going to them and I can not find them on the Electrical System wiring Diagram. Are they for the ABS?

 

[rrrr]

I believe, as mentioned earlier, that there might be two vents. One for the truck the other for a trailer hook up. I'm not sure. Let me dig into the TM's and look. The 9 series TM's are awful for trouble shooting the brake system. After my air brake issue I feel for ya !

I'll post up after I look.

I think I might have bid on that truck !

 

[rrrr]

Those relay vents look to have the abs input as well. They work on the spring side of the air brakes. Each rear axle has its own unit. Its possible that they are not releasing air and are stuck. Try the air tool oil suggestion. Also once you have full air pressure try applying brakes, firm pressure, and hold for about 15 seconds to see if maybe the stuck valve/vent will loosen.

As a last resort you could try to remove the air line on the vavle and squirt a little air tool oil directly in the unit. Just be careful because there is an abs solenoid in there.

Does your abs light go out after you start the truck up ?

 

[M35A2-AZ]

Well did more testing.
Went out put air into rear emergency glad hand with a little air tool oil.

Rear Brakes are caged.

Pushed on the brakes a number of times and all worked fine. Air coming out of both Primary Relay Valve vent and Secondary relay Valve vent.

Started truck,, pushed on brakes a number of times, all was working the same.
Drove it a little pushing on the brakes about 5 times and I could hear the vents had stopped ventimng and the brakes locked up.
Front brakes are not locked up.
Let the air out of the truck and the brakes unlocked.

I do not think its the vents due to both stopped working at the same time.

 

[rrrr]

OK, disconnect the electical abs connector on the top of the relay vent and try again. Maybe the abs is closing off the vent for some reason ?

Or find the abs control box and completely remove power from it. Does your abs give a good check out on startup ? The light will come on for a 3 seconds then go out. You'll also here what sounds like two valves actuating. This is before you go to the start position.

 

[rrrr]

If none of these work you'll need to pull the relay vents apart and clean them. You mentioned that you live in a dusty environment. They have a tendancy to get dirty and not work. Also, you might want to change your engine air filter as well.

Keep us posted !

 

[stampy]

to stop the mud daubers thread up a exhaust air fitting with a screen.

 

[M35A2-AZ]

OK, disconnect the electical abs connector on the top of the relay vent and try again. Maybe the abs is closing off the vent for some reason ?

Or find the abs control box and completely remove power from it. Does your abs give a good check out on startup ? The light will come on for a 3 seconds then go out. You'll also here what sounds like two valves actuating. This is before you go to the start position.

rrrr, The abs light comes on and then goes off when you move the switch to run and you can here the valves (or relays) actuating.
I think I will unplug them or undo the power.

Do you know were the ABS control box is?

I will out of town for two or three days and not able to work on the truck, but I will get back on it when I get back.


Thanks,

 

[rrrr]

Relay valve repair is TM 24-3 page 4-591

No luck going through the TM's for the abs system. You'll need to trace the electrical connectors.

I would just disconnect the solenoid at the valve for each rear axle.

 

[M35A2-AZ]

Here is an update of the problem.

I think I have the brakes working again. HA!!
I put some air tool oil in the emergency glad hand(as SS rrrr had said to do) I also took the valves apart that are on the driver side step and cleaned and air tool oiled them. SS halftrack told me that he had a problem with the brakes and that valves ended up being his problem. They did have some white powder in them and looked very dry.

The rear brakes started working ok, I did a number of test runs and all was ok.
I did go ahead and replace all the valves on the step with news ones.

One of the problems tracking the problem down is that there is A 100 MILES of tubing under the truck and it is all painted GREEN.

I would like to THANK all the SS guys that helped with my problem and hope this helps others.

 

[rrrr]

Glad you got it taken care of. I'm still going to put some air tool oil in my emergency glad hand and manually service the air system to keep a little lube in the system. I've been driving my truck and it seems the more I drive it the better is works ! I've oiled it twice in the last month since getting it from GL. I will do it one more time and then probably every 6 months.