LMTV FMTV replacement or upgrade air dryers

[Suprman]

I get several pms every week from members looking for the upgraded lmtv air dryers. I DONT HAVE ANY MORE. Have not had them for some time. The air dryer you want is the Haldex purest type. The civilian model works fine it just has a 12v heater and the lmtv uses a 24v heater. It’s 3 screws on the bottom to change the heater very easy to do. There are several threads on this already. It’s a good upgrade to do the original finned air dryer does not do an adequate job of stopping moisture coming into the brake system.
Will

 

[simp5782]

There is also the Wabco air dryer as well that is pretty abundant on the ebay market for cheap. That can run a 12 or 24v heater it just has to be inserted. In the hotter climates you could just leave that cover on.

Wabco uses the same bolt mounts as the purest air. The fittings are just Boss threads instead of pipe. Is it around 1/3 the size of the Purest and stock air dryer on the LMTV and the weight is alot less. Filters are also around $12 each on ebay.

 

[scottmandu]

Is it around 1/3 the size of the Purest and stock air dryer on the LMTV and the weight is alot less. Filters are also around $12 each on ebay.

How does this size affect the replacement intervals on the cartridge? Smaller isn't always better.

 

[simp5782]

How does this size affect the replacement intervals on the cartridge? Smaller isn't always better.

Wabco calls for cartridge replacement every 2 to 3 years depending on compressor output and usage.

The cartridge is as big as what comes on the purest dryers. The unit body is smaller.

First post of my thread I attached wabco's maintenance schedule for it.

https://www.steelsoldiers.com/showt...abco-Series-1200-Air-Dryer-Install&highlight=

 

[Suprman]

Pretty much anything is an upgrade from the tube with fins that originally came on the truck. The tube came before the M939 (pure air plus) abs air dryer and the purest is the next model up from that.

 

[Amer-team]

The shop guy at our local Cummins dealer told me they recommend changing every 100,000 or so on the air filters.

 

[Suprman]

100k for a regular road going truck. Thats a lifetime of miles on a mil truck. I do my cartridge every 2 years.

 

[Amer-team]

That is a lot of miles on a military truck. If someone is going out swamping and mud bogging it every weekend, they should do more frequent maintenance, but it seems that there might be a point of diminishing returns. My 5T probably gets 3 thousand a year and is babied. So don't think it needs a new one every two years. But it may.

 

[No-0ne]

Hey everyone! Brand new to the forum. I think I may become a regular. There are so much knowledge on here I hope to learn from. This is a pretty old thread but I figured this is as good as any to get some help. I just picked up a 2005 SS M1088A1 rebuilt by ACELA in 2019. I bought it in North Carolina and was trying to drive it home to Utah. I should not have tried to drive a truck that’s been sitting for 5 years across the country. Oh well lesson learned. I’m stuck in Johnson City TN right now waiting for a transport to ship it home. I’m having 2 problems. One is a CTIS problem that I will find another relevant thread to ask for help on. The other question I have is Air Dryer related. The old Haldex N4253AB Air dryer started purging air and wouldn’t quit so the truck could air up. I got it to a mechanic and he swapped out the N4253AB with a Haldex 955300C. Should I have any concerns? Is this smaller unit able to handle the demands of this LMTV? https://www.haldex.com/en/na/air-dryer/air-dryers/all-makes-like-nu-air-dryers/wabco-ss1200/955300c/

 

[GeneralDisorder]

I would want a larger one myself just so the cartridge doesn't need changed so often. That's the smallest size they make......

You should likely rebuild the compressor cylinder head. There's a whole thread on that.

I do not see a 24v version of that Wabco SS1200 so I hope he didn't splice the heater to the 24v supply for the old heater.

 

[No-0ne]

I bet he did just splice it into the 24V. I found the old 24v plug with the wires cut and still plugged into the old air dryer. Should I unplug the new one and run it without a heater for now?

 

[GeneralDisorder]

I bet he did just splice it into the 24V. I found the old 24v plug with the wires cut and still plugged into the old air dryer. Should I unplug the new one and run it without a heater for now?

If you aren't in any danger of freezing, then yes I would unplug it. It may have already tripped a circuit breaker as a 12v heater would pull double the wattage on 24v. Probably popped the breaker already I should think since that heater runs anytime the ignition is on.

 

[GeneralDisorder]

Hard to find detailed specs on the WABCO SS1200 but the usual naming convention in commercial vehicle air systems is to name stuff or prominently indicate somehow in the part number the CFM (Cubic feet per minute) of the component. I assume the 1200 means 1200 CFM. The Compressor on our trucks is 1800 CFM so if that *is* in fact the case with the Wabco SS1200 then it is 600 CFM too small and the wrong voltage. I would feed that to the mechanic and find another dryer - maybe another mechanic too.

One thing to note about FMTV's that is often unfamiliar to civilian mechanics - many parts are 200% larger or higher capacity than they expect to see on a truck this size. The land of mil-spec is a universe that is governed primarily by "off-road" and "combat suitability". Things get weird and often that means overkill and oversized. But you don't want to restrict part of the system by introducing a bottleneck - back pressure on these compressors that are all highly likely to suffer exhaust valve spring issues anyway is a bad recipe.

 

[Ronmar]

Our air demand is probably less than some other trucks those are used on, so it should work fine usually a factor of how much leakage you have anyway... Since you have the old one, you can probably clean out/overhaul the purge valve, throw in a new cartridge in it and have a spare… don’t neglect the cartridge service, they can pop internally when they clog/fail, spreading cartridge media downstream into the system…

 

[GeneralDisorder]

Our air demand is probably less than some other trucks those are used on, so it should work fine usually a factor of how much leakage you have anyway... Since you have the old one, you can probably clean out/overhaul the purge valve, throw in a new cartridge in it and have a spare… don’t neglect the cartridge service, they can pop internally when they clog/fail, spreading cartridge media downstream into the system…

I don't like the idea of back-pressuring the 1800 CFM compressor that already likes to eat exhaust valve springs due to high discharge temps with a stock dryer. Asking for problems IMO. You want as little restriction as possible to lower compressor temps. The truck's consumption may be low enough, but the compressor is still trying to push 1800 CFM into the wet tank when it's loaded. Consumption (demand) only effects the duty cycle not the CFM being input into the tanks,

 

[No-0ne]

Yeah I think once I get it home I will replace it with the Haldex DA34100 PURest, but it’s a 12 volt heater also. How do I over come this? The first post in this thread Suprman suggests (if I’m understanding him correctly) that I can pull the 24v heater off the old dryer and swap it onto the new dryer with only 3 bolts? Am I understanding this correctly? Thanks so much for your help.

 

[GeneralDisorder]

Yeah I think once I get it home I will replace it with the Haldex DA34100 PURest, but it’s a 12 volt heater also. How do I over come this? The first post in this thread Suprman suggests (if I’m understanding him correctly) that I can pull the 24v heater off the old dryer and swap it onto the new dryer with only 3 bolts? Am I understanding this correctly? Thanks so much for your help.

The 24v heater is an option for the PURest dryer. They make multiple part numbers and take note that some have mirrored castings so do not have the ports where you want them. Haldex does sell the 24v heating element as a service part so if all you can source is a 12v unit you can use the old heater or buy a new 24v heater.

 

[No-0ne]

Thanks again! And thanks for your help with the CTIS issue as well!

 

[No-0ne]

One more thing, should I unplug the 12v heater on this wabco dryer? I don’t want to screw up anything else.

 

[GeneralDisorder]

One more thing, should I unplug the 12v heater on this wabco dryer? I don’t want to screw up anything else.

Till you know for sure, unplug it to be safe.