My BIG M925A2 Project Truck Is Home - Page 29 - Steel Soldiers::Military Vehicles Supersite

steelsoldiers · 11-08-2009, 22:14

It was a beautiful day to work on the truck! The sun was shining and there was a nice breeze all day.

The first thing I did was go rob some more parts off of the A2 parts truck. I needed a brake wedge assembly and a set of shocks. Once I was done fighting that mess I went to work on the front brakes on my truck. I got both of the wedge assemblies, the actuators, the fittings, and the air lines installed. After that, I installed the front shocks.

I spent about 20 minutes drilling a hole in the pivot for the transfer case shift linkage. It was rusted solid when I got it, but I have been working it back and forth with Kroil. After I got the hole drilled I started shooting Kroil in it over and over. Once I get it moving smoothly, I will tap the hole and install a grease fitting.

I also swapped out the muffler. The whole bottom had rotted out of the one on my truck. That made it tough to work on it with the engine running. The new muffler went on smoothly and made a big difference in sound and smoke direction!

Jason Peecook showed up about the time I was starting to work on the muffler. He was picking up some stuff from John and stuck around to lend a hand. We retrieved an 817 dump to slave my truck off. Once we got it started I crawled underneath to try and track down the air leak. After disconnecting several air lines under the truck, I was able to isolate the leak to the rear relay valve. It won't stop dumping air out of the vent line. We hooked up a gladhand air hose to the 817 and I used a blow gun to blow out the valve over and over. It still just kept blowing down. I used the blowgun to pressurize the brake system on my truck and at one point the expeller valve on the air dryer opened and it dumped a bunch of water out of the system. At least I know that it works.

I messed around with the relay valve for about half an hour. It was starting to get dark and Jason had to take off for Richmond. I decided to just yank the valve and bring it home with me. The air fittings came off really easy, but the two little rusty 5/16" bolts about killed me!

I finally got those off and packed up my stuff to head out.

I am going to split the relay valve open and check the guts out. I am guessing one of the valves is corroded and is stuck open.

No, the truck didn't move. I was tempted to try, but my throttle linkage is still rusted solid and I couldn't build any air pressure to get the spring brakes to release. Maybe next time!

jwaller · 11-09-2009, 00:29

good luck with the air system. I've been trying to get mine to hold air for about 8 weeks now. seems that when I fix 1 problem, 4 more spring up right down stream.

I too had a rear relay blowing down and after airing it up and stepping on the pedal several times it finally shut.

my spring tank fills first front gladhand and I can release my spring brakes with the dash valve.

cranetruck · 11-09-2009, 06:59

You keep mentioning how this truck was used near the ocean, have you seen any other (other than the relay valves) evidence of "internal" corrosion? The compressor must have sucked a lot of salt laden air in that environment.
Is your parts truck free of this kind of corrosion?

I'm looking at an air line diagram from TM 9-2320-272-24-4 and see a lot of valves....why is a "limiting" valve used for the front brakes and "relay" valves used for the rear, they seem to serve the same purpose? The system is very different from the 100% air system on my 8x8, so I'm just wondering.

steelsoldiers · 11-09-2009, 12:56

Quote:

Originally Posted by cranetruck

You keep mentioning how this truck was used near the ocean, have you seen any other (other than the relay valves) evidence of "internal" corrosion? The compressor must have sucked a lot of salt laden air in that environment.
Is your parts truck free of this kind of corrosion?

I'm looking at an air line diagram from TM 9-2320-272-24-4 and see a lot of valves....why is a "limiting" valve used for the front brakes and "relay" valves used for the rear, they seem to serve the same purpose? The system is very different from the 100% air system on my 8x8, so I'm just wondering.

Bjorn, the air system looks pretty clean for the most part. I may end up replacing the air dryer since the parts to rebuild it will cost more than buying a NOS one.

The truck has definitely been in and out of salt water, but the air compressor draws air from the intake manifold on this truck. It is actually pressurized when the turbo is making boost. This helps to keep up with the demands of the CTIS system. That also means the air to the compressor travels through the intake stack, filter housing, intake plumbing, and turbo before entering the compressor. It should be pretty clean by then.

The parts truck is also a rusty hulk of a navy truck, but it seems to have a little less salt intrusion in places. I may scavenge the relay valve off of it if I can't get mine cleaned up and working right.

The rear relay valves work just like an electrical relay. There is a large supply line that takes air from the primary air tank to the front-rear axle and rear-rear axle relay valves. There are two output lines from the relay valves that supply air to the service and spring/service actuators on either side of the axles. Then, there is a small line that runs from the treadle valve to the service port on the relay valve. When you step on the treadle pedal, that signal line energizes the relay valve, which supplies the actuators with air from the primary tank.

The front limiting valve drops the air pressure to the front axle to prevent locking the brakes up on the steering axle. It is similar to a proportioning valve on a hydraulic system.

Quote:

Originally Posted by jwaller

good luck with the air system. I've been trying to get mine to hold air for about 8 weeks now. seems that when I fix 1 problem, 4 more spring up right down stream.

I too had a rear relay blowing down and after airing it up and stepping on the pedal several times it finally shut.

my spring tank fills first front gladhand and I can release my spring brakes with the dash valve.

John, I'm glad I'm not the only one that has had this kind of fun with the air system! Sounds like you have some weird stuff going on there. Hope you get yours figured out.

Westech · 11-09-2009, 12:59

Dont put a muffler on it! just stack it!

Floyd · 11-09-2009, 13:14

Hey Chris: For one person working with limited time you’re doing a fantastic job. This is one of the best threads on the site, good reading.

Floyd

Cucvnut · 11-09-2009, 13:55

We need pics of the the on new tires !!!

steelsoldiers · 11-09-2009, 19:44

Floyd, thanks for your support!

cucvfreek, there are some pics of the new tires back in the bowels of this monster thread. Just keep flipping pages until you find them. You'll find a lot of great info and photos along the way.

I took the relay valve apart today to find out why it wouldn't stop exhausting all of my air. I soaked it in Kroil last night, which made it really easy to get apart. It's amazing that stuff can creep all the way down a tightly threaded bolt!

It is a pretty simple device inside. The service side of the relay has a large piston surrounded by a rubber o-ring. When the treadle valve is actuated, the piston is pushed in toward the middle of the relay. The service piston has an actuator rod on the end that pushes on a floating valve assembly. The valve is made up of two washers with a spring in the middle that rides on a tube and o-ring seals. The valve allows air to be transferred from the supply line to the delivery lines when the brakes are applied and then from the delivery lines to the vent line when the brakes are released.

The problem with my delivery valve is the lower washer in the valve assembly was made of un-coated steel and it had rusted in the bore. I removed the washer, sanded off all of the rust, cleaned the bore, lubed all of the sealing surfaces with white lithium grease, reassembled everything, and shot a coat of black GCI paint on it. It should work like new now.

Bjorn, there was no evidence of salt corrosion in the valve body, which was cast aluminum. I think that's a good sign. I will probably take the other one apart and clean it up too just to be safe. I would hate to have it stick open going down the road!

Here are some pics, of course!!

scooter01922 · 11-09-2009, 20:03

Easy to see why that wasn't working, keep up the GREAT work

beezer1424 · 11-09-2009, 22:12

I was considering purchasing a restored MV, but after reading this thread how can I possibly trust that the one I purchase is restored with as much effort and attention as you are putting in! Very impressive.