Air Dryer Issues On '86 AM Gen M934...

[archmark]

My '86 AM Gen started as usual this morning and I let it warm up while I loaded a few things. When I climbed back in, the low air pressure warning light was no longer blinking and both air pressure gauges showed +/-90 PSI and I assume were climbing to the usual 125 PSI.

I backed about half way out and stopped to retrieve something that I'd forgotten and when I got back in, the low air pressure warning light was blinking and the gauges were showing +/-30 PSI and falling. I stopped the truck, did a brief walk around and then started it again and found that the brakes were locked.

Checking the air drain valves, #'s 1, 2 & 3 from the top had very little to no air pressure coming out and #4 seemed to have the normal amount of air pressure.

There's a very slight low pressure air leak coming from the bottom of the air dryer unit and another very low air pressure leak coming from some kind of valve(?) at the upper front passenger side of the engine next to the upper bent radiator hose This valve(?) has 2 small holes in the front of it and an air hose in the top of it that comes from a grouping of air hoses located on the driver's side firewall. Other than that, I don't hear any other leaks.

What gives? Any help in solving this would be GREATLY appreciated as the M934's back side is sticking half way out into the drive lane and I need to get her back inside to make any necessary repairs. Is there anway I can pressurize the M934's air tanks so I can unlock the brakes and drive it the necessary 20 feet.

Thanks guys, now I'm headed to the TM's...

Mark

 

[dilligaf13]

Could be the air dryer expello valve sticking open. It's the dump valve on the bottom of the unit. Try to pull it closed with some pliers and see if you can work it up and down. A picture of the other air leak would help. Sounds like fan actuator valve. In the picture below there is a black button on the far right. It's an air brake over ride. Once you push it in you'll have no brakes what-so-ever but you'll be able to move the truck. Be extremely careful and good luck....

 

[porkysplace]

You can also "cage" them but make sure you have the wheels safely choked.

 

[juanprado]

the front valve sounds like the LQ2:
http://www.steelsoldiers.com/archive/index.php/t-92788.html

The bottom of the drier is notorious for sticking and indicates your drier needs to be replaced or rebuilt.
When mine used to stick I used spray silicone lube(rubber o ring safe) and a screwdriver to push the piston upwards to close it. I have since completely rebuilt the drier and no more issues.

good luck

 

[archmark]

After taking dilligaf13's advice and using the air brake over ride to get the beast back under cover and out of the drive, I crawled underneath and removed the cup from the air drier. What I found is shown in pix 1 & 2:



There was no moving the spitter either up or down, even after a liberal application of Kroil, so I guess tomorrow I replace the air dryer unit with a new spare that I bought shortly after I got the truck, just in case, which I guess was today.

In the lower right hand corner of picture 3 & a close-up in picture 4 shows the valve? that has 2 small holes on the end, at least one of which was also leaking air. I've got no idea what it does and if it is supposed to occasionally bleed off air. I never noticed it doing it for the 1st few months that I owned the truck and it started probably 2-3 weeks ago. I could hear it when I shut off the truck or feel it while the engine was running when you put your hand up to it. Somebody please enlighten me as to it's purpose and if it needs to head to the scrap heap also.



So, for what was planned to be a productive 5-ton, 3 day weekend where the oil was going to get changed, a spin-on oil filter adapter added, the cooling system flushed and new coolant added and Westfolk's spin-on fuel filter setup installed, will probably turn out to end up being just getting the beast moving and stopping under it's own power, hopefully. I guess the rest of what could have been some productive time will get wasted on the couch. ****, I hate that.

Again, thanks for all the help guys...

Mark

 

[porkysplace]

That looks like the fan actuator valve .
M923 air leak
$92 shutterstat fan clutch actuator

 

[dilligaf13]

You can still do all those upgrades this weekend. The air dryer replacement takes about an hour. There's a thread on here about fan actuator rebuild. Not sure on the time for that one but none of it will preclude the other upgrades and PMs.

 

[archmark]

dilligaf13, your 1st piece of advice was greatly appreciated. Your 2nd piece, I'm not so sure about. I'm thinking (hoping?) that the air dryer replacement may cause some back discomfort that will require getting horizontal on something considerably softer than the ground!

 

[archmark]

A partial victory, BUT I'LL TAKE IT!!! After some good advice and motivation from several members, I went ahead and changed out the original air dryer with a NOS unit that I purchased shortly after buying the M934. The new dryer must have been a "one size fits all" unit, as I had to drill 3 new 9/16" holes in the truck's original mounting bracket to bolt it up to the dryer's triangular shaped mount.

Sure enough, with the new air dryer installed, the air pressure built right up to 120 PSI and starting spitting just like the good old days. It's hard to believe that the air dryer seems to the main PITA on these trucks and that Uncle Sucker hasn't demanded a better and more reliable system. I guess I'll start looking for a rebuild kit for the dryer so that I'll have a spare when, not if, needed.

I still have the leak from the fan actuator but at least now the truck is drivable and the compressor can keep up with the air being lost. I'll get a new actuator and replace it when I do the coolant flush and then try and rehab the old one also. I'm sure starting to collect a lot of used rebuilt spares!

Thanks for all the suggestions and help...

Mark

 

[dilligaf13]

I've always used working air dryers from parts trucks, so they bolt right up. The biggest weakness with the air dryers is they don't like long periods of inactivity. All the more reason to drive your truck more often. Glad it all worked out

 

[porkysplace]

A partial victory, BUT I'LL TAKE IT!!! After some good advice and motivation from several members, I went ahead and changed out the original air dryer with a NOS unit that I purchased shortly after buying the M934. The new dryer must have been a "one size fits all" unit, as I had to drill 3 new 9/16" holes in the truck's original mounting bracket to bolt it up to the dryer's triangular shaped mount.

Sure enough, with the new air dryer installed, the air pressure built right up to 120 PSI and starting spitting just like the good old days. It's hard to believe that the air dryer seems to the main PITA on these trucks and that Uncle Sucker hasn't demanded a better and more reliable system. I guess I'll start looking for a rebuild kit for the dryer so that I'll have a spare when, not if, needed.

I still have the leak from the fan actuator but at least now the truck is drivable and the compressor can keep up with the air being lost. I'll get a new actuator and replace it when I do the coolant flush and then try and rehab the old one also. I'm sure starting to collect a lot of used rebuilt spares!

Thanks for all the suggestions and help...

Mark

Servicing the air dryer should be the first thing done to a auction truck , it is not a design flaw it is a lack of maintenance. As dilligaf13 pointed out they don't like sitting and the major cause of failure is neglect. They should be serviced on any auction truck before hitting the public roads.

 

[archmark]

I'll second all of the above. I knew the air dryer was troublesome and that's why I bought the new spare but it's kinda funny how something can go from 100% to 0% operational overnight. Of course it could have just been my trucks way of saying that I needed to slow down and not plan so many things to do to it over the Labor Day weekend.

So maybe this weekend it gets the oil changed, next weekend the fuel filter setup swapped out and the coolant flush the weekend after that. That'll teach me to be so industrious...

Mark

 

[JohnnyBM931A2]

A partial victory, BUT I'LL TAKE IT!!! After some good advice and motivation from several members, I went ahead and changed out the original air dryer with a NOS unit that I purchased shortly after buying the M934. The new dryer must have been a "one size fits all" unit, as I had to drill 3 new 9/16" holes in the truck's original mounting bracket to bolt it up to the dryer's triangular shaped mount.

Sure enough, with the new air dryer installed, the air pressure built right up to 120 PSI and starting spitting just like the good old days. It's hard to believe that the air dryer seems to the main PITA on these trucks and that Uncle Sucker hasn't demanded a better and more reliable system. I guess I'll start looking for a rebuild kit for the dryer so that I'll have a spare when, not if, needed.

I still have the leak from the fan actuator but at least now the truck is drivable and the compressor can keep up with the air being lost. I'll get a new actuator and replace it when I do the coolant flush and then try and rehab the old one also. I'm sure starting to collect a lot of used rebuilt spares!

Thanks for all the suggestions and help...

Mark

Sounds like you bought the "updated" version used on newer MV's? Most of the air dryers that I see listed on places like eBay are (supposedly) the updated version. It does mention in the listings that new holes will need to be drilled.

 

[archmark]

Yep, I think the seller referred to it as the new version, I think he said off of an MRAP, but I'm probably mistaken about that. It's pretty much identical to the old one when placed side by side, except for how it mounts and I did have to swap put one of the air fittings from the old one to the new one. Other than that, and drilling the 3 mounting holes, it was pretty much "plug and play". I think I paid in the neighborhood of $119 for it on the big auction site. Now I need to find the necessary rebuild kit for my old one and I'll be set with a spare...

Mark

 

[The HUlk]

Now I need to find the necessary rebuild kit for my old one and I'll be set with a spare

I have heard that you can purchase the new version air dryer for less than the cost of a rebuild kit for the old style. Also heard that the new version is more reliable than the old version fwiw.

 

[archmark]

I have heard that you can purchase the new version air dryer for less than the cost of a rebuild kit for the old style. Also heard that the new version is more reliable than the old version fwiw.

I've read the same thing here on the forum and as soon as I find the necessary parts I'll be able to decide if it's worth it to rebuild the old. I'm hoping that the new one that I installed is good to go for as long as I own the truck and then some...

 

[archmark]

I have heard that you can purchase the new version air dryer for less than the cost of a rebuild kit for the old style. Also heard that the new version is more reliable than the old version fwiw.

Should you be interested, here's the item number from the big auction site for the new dryer unit that I purchased: 191419423518. Looks like he's raised his prices a bit, but he has sold 58 of them...

 

[The HUlk]

Should you be interested, here's the item number from the big auction site for the new dryer unit that I purchased: 191419423518. Looks like he's raised his prices a bit, but he has sold 58 of them...

Thank you, I already installed the new type soon after acquiring the truck a couple months ago. The expel valve was sticking and it was 5 years old.

 

[Bandit02]

My air dryer stuck open and drained all the air last summer when I was hauling down a hill out in the sticks soon after I bought it. I pushed it up with my finger and it built air again, purge off and stick open.

I replaced with a rebuilt Bendix AD-9 with a 24v heater element. Still common on todays trucks. Not alot (at all) of places to find rebuild/new anything for the Haldex dryers up here for me

 

[mustang1928]

Had the same problem with my M931A1, air hissing out of the air dryer and couldn't build pressure above 60psi. Bought a "NOS" one off Ebay. It said Stewart/Stevens on it but bolted right up, except the three bolt mount design to the frame plate. My pressure however now builds to 130psi++ and climbing. I pumped the brakes to bleed off the system down to 115psi and watched it build back to 130psi+ again. I remembered that the old unit would purge at about 125psi. Background: My truck is a Red River zero time truck(90 hours/500 miles). I assume the air pump is new and putting out max performance. I don't want to blow the tanks/system and don't know if the NOS air dryer is a bad unit too. I don't want to experiment/test pilot to find out what the max system pressure is. Anyone know if a high air pressure(130psi+) is OK, and what the system limit is other than the 150psi on the air gauges themselves?