Upgrade to Aftermarket Transfercase

[tucker79]

Im thinking of installing a Profab or SCS Transfer-case in my M818 WW. Just installed 1600s and after going through 2 stock T cases on 395s I hate the idea of swapping in another unknown case.
Has anyone done it???
If you could pick any gear ratio what would it be to run comfortable RPMs at 50 to 60 MPH???GEARING AVAILABLE FROM 3.8 UNDERDRIVE TO 2.73 OVERDRIVE
Some benefits I see with running one of these cases is some come with a 2wd/ 4wd option. They use them in Monster, Mega, Mud, Racing, pulling trucks with 2000+ HP and many are running 2.5 and 5 ton Rockwells so yokes is not a problem and there darn near indestructible. Also they are more compact 9.5 in flange to flange and would allow for some different transmission options if wanted. Much lighter. They come with quick change gears so your not stuck with whatever gears you start with. Come in all different lengths of drop. They run 2 to 3k
Reading OPCOMS thread on the T138 to T1138 http://www.steelsoldiers.com/showthread.php?59654-M818-Transfer-Case-Upgrade-T-138-to-T-1138
Seems one of these aftermarket cases would be a great way to go with similar cost if not less and you can buy the mounting/ install plate n cut way down on fab work. Still would have to retube drivshafts to get the lenth rite but other than that looks good in my head.
http://www.scsgearbox.com/wp-content/uploads/2015/11/10.66-Drop-Case.pdf
I am not affiliated with any of these co.s Just trying to BEEF UP my M818 as much as I can.
Anyone see any downsides or issues that may arise????

 

[farmerboywyotech]

I'm no expert but it appears to be full time engaged does it not. That would be a bummer and probably hard of milage and driveline components. Unless I'm all wet and missing something.

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[red]

You can get the T-1138 tcase from the m939 series for about $400 nowadays if you want better highway gearing.

How are you breaking the T-138 so often?

 

[tucker79]

You can get the T-1138 tcase from the m939 series for about $400 nowadays if you want better highway gearing.

How are you breaking the T-138 so often?

1st time I think my air shift got hung up 2nd one never seemed quite rite & now is stuck engaged all the time. I added a air dump & that does work but I'm waiting for the day it doesnt. I don't think the lockers help. These after market t cases do come with 2wd option but it comes with a cost

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[red]

Gotta clarify a few things on your tcase.

The T138 (stock for the m809 series) is not an air shift, its a sprag. It uses air to engage the sprag in either forward or reverse, and the sprag determines when to engage the front axle. It's known to be a very strong tcase.

If you want 4x6 capability with that tcase you can install an air switch to disrupt the air supply running to the transmission. Cut the air supply and the sprag defaults to neutral disabling front wheel drive, supply air and the sprag will engage. There are no lockers for the tcase if thats what you are referring to. Have read about some people pulling the sprag out and welding it up but I don't know the details on that.

If the air solenoids are sticking pour a little air tool oil into the line and work it back and forth slowly. I'm guessing this truck is used for mudding going off your location so the air system is inhaling extra water (humidity, splashes, ....) and the air solenoids are probably a bit gummed up.

Also how fast are you shifting from a forward gear to reverse or the opposite?


Not being harsh (realize my post may come across that way) just trying to clarify and help fix the issue.

 

[tucker79]

Gotta clarify a few things on your tcase.

The T138 (stock for the m809 series) is not an air shift, its a sprag. It uses air to engage the sprag in either forward or reverse, and the sprag determines when to engage the front axle. It's known to be a very strong tcase.

If you want 4x6 capability with that tcase you can install an air switch to disrupt the air supply running to the transmission. Cut the air supply and the sprag defaults to neutral disabling front wheel drive, supply air and the sprag will engage. There are no lockers for the tcase if thats what you are referring to. Have read about some people pulling the sprag out and welding it up but I don't know the details on that.

If the air solenoids are sticking pour a little air tool oil into the line and work it back and forth slowly. I'm guessing this truck is used for mudding going off your location so the air system is inhaling extra water (humidity, splashes, ....) and the air solenoids are probably a bit gummed up.

Also how fast are you shifting from a forward gear to reverse or the opposite?


Not being harsh (realize my post may come across that way) just trying to clarify and help fix the issue.

Yes I realise it's a sprag case that is shifted from forward to reverse sprag via air shift cylinder. Yes I tried air tool oil. Yes I now have a completely new air cylinder that I now realise had o rings instead of correct seals. Yes I have the air dump mod on this case. If I don't dump the air this case seems to stay in 6x6 and not stay disengaged until rears start slipping 10% or whatever. Seems most of you are happy with the stock case I am not so far it's been the weak link in my truck.

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[bigford]

I picked up used 138 for the bigford after backing up with the sprags in forward one day. "New" case seemed ok but resealed / gasketed it. It never seemed to release the front drive soI pulled it. In the front section where the front shaft rides in the front drive gear, I found the shaft had siezed at one time and then broke free. Probably the reason someone got rid of it. I found out this happens more than you think. After swapping the shaft and gear from my old one, all was well. When disengaged the front should free spin easily. It took a very BFW to turn mine before. Just thought I'd pass this on. Good luck with yours.

 

[wcuhillbilly]

The 138 is finicky sometimes, but overall it seems to be the stronger of the two, I agree I dislike the Sprague myself.... However, I am at a loss as to how your destroying them frequently. Unless severe gear jamming is occurring. IE: rocking fwd and rev in a mudhole... where the Sprague cant keep up with the forward reverse of the gear change and thus gets caught in forward when your dumpin the clutch in reverse.
Have you looked into the Civy market past the monster trucks. per say the Ashplundt trucks- powerline/swamp trucks that they clear right of ways with... last one I came across was running a civy Rockwell with Marmon Harrington axles and a mix of rock/marmon driveline.
Once you get your T case figured out, I would put money on the trans snapping next.
Personally I would start looking for a truck wrecking yard and find an airshift trans and t case combo from something that is a little more in tune with what your attempting to do... While your looking into that, I would look and personal driving habits and see if there is something there that may can change,,, I don't know you, but I do follow the motto- take care of your equipment and it will take care of you.

 

[gimpyrobb]

PM sent, I have an MRAP T-case if you'd be interested.

 

[tucker79]

I use this truck on the street 85 % of the time and I'm very aware of listening for the case to engage in proper sprag before I go after learning the hard way altho I wasn't ignorant of how it worked I may not have paid close enough attention to it. Altho I thought I had it working perfectly. It was one of the 1st things I fixed.
Yes I already have a bad vibration in the transmission so I'm looking at trying to fix it ALL once and for all and was hoping that I could improve on a 70 year old design. I don't mind the transmission even with the big hole it's flat down here and I don't pull any loads that come close to m818s capabilities. I love this truck and plan to keep it forever. I'd just like to not have to do any major repairs for a while on trans/t case. I worrie on long trips in the middle of nowhere

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[tucker79]

Now I'm having issues with new 1600s rubbing on Pittman arm. What do you guys think is the best fix. I can get a set of bridge truck spacers but that puts the front tires way out there or stack a 2nd rear spacer on the front with longer studs. Does everyone have these 1.5 U.N. spacers on the front already.???

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[tucker79]

The 138 is finicky sometimes, but overall it seems to be the stronger of the two, I agree I dislike the Sprague myself.... However, I am at a loss as to how your destroying them frequently. Unless severe gear jamming is occurring. IE: rocking fwd and rev in a mudhole... where the Sprague cant keep up with the forward reverse of the gear change and thus gets caught in forward when your dumpin the clutch in reverse.
Have you looked into the Civy market past the monster trucks. per say the Ashplundt trucks- powerline/swamp trucks that they clear right of ways with... last one I came across was running a civy Rockwell with Marmon Harrington axles and a mix of rock/marmon driveline.
Once you get your T case figured out, I would put money on the trans snapping next.
Personally I would start looking for a truck wrecking yard and find an airshift trans and t case combo from something that is a little more in tune with what your attempting to do... While your looking into that, I would look and personal driving habits and see if there is something there that may can change,,, I don't know you, but I do follow the motto- take care of your equipment and it will take care of you.

Thanks I'm almost OCD about checkn fluids n maintaining as much as possable especially before and after a long trip. Yes I can be hard on it at times but that's what I have it for. To do jobs my other trucks can't at the same time I'm not stupid about it cause I know if it breaks I'm screwed, stranded, parts hard to come by n a long walk to even find help with no phone service. I do everglades restoration, tree service & the occasional mud bogs/camping trips. I spend most of my time pulling out all the dummies that sink there HUGE trucks at the mud bogs n putting around

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[red]

Do you still have your old t138? If so maybe open up the sprag section of it and find out what went wrong. User Simp5782 has welded up a sprag on a t138 before, sure he would be willing to guide you through the process if you are interested. Much cheaper than buying a different tcase and addresses the weak link. (edit) After doing more reading welding up the sprag is a no go. Front output spins slightly faster than the rear output, would cause a major binding issue in the driveline.

For the wheels either the bridge truck spacers or a set of HEMMT wheels will take care of the tire rub issue. I wouldn't stack spacers because of safety concerns unless it was a trailer queen.

 

[162tcat]

Now I'm having issues with new 1600s rubbing on Pittman arm. What do you guys think is the best fix. I can get a set of bridge truck spacers but that puts the front tires way out there or stack a 2nd rear spacer on the front with longer studs. Does everyone have these 1.5 U.N. spacers on the front already.???

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HEMTT rims will take care of the rubbing issue.

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[tucker79]

Bridge truck spacer acquired. Hope these get my turning radius back

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