Technical Questions - M35 Air Shift Xfer vs Sprag

[Miltrucks]

Luckily, in working with all of my trucks, I have never really had any Xfer case problems so I haven't had one of these cases apart.

Can anyone explain if a sprag Xfer case can be converted over to an air shift case by swapping out some parts?

Off hand, I am guessing the front plate and the air valve, but nore sure if there are other parts needed, or if it is possible.

I believe there are kits out there to convert, but are they as strong as the original parts? any drawbacks with the kits?

I've heard a lot of people looking for Air Shift cases to replace their sprag units, and stories of they can and cant be converted. Just wondering if anyone had some specific details?

 

[Recovry4x4]

Long and short of it is yes and no. You can convert the sprag to an air shift but it's not as easy as just swapping the entire fron assy. The front output shaft is different between the two but it too can be changed. What was once thought easy, became undoable, then became doable with extra effort. This is actually hearsay from some first hand experiance right here on the forum. I intend to attempt the swap here in the future just to settle some different opinions and photograph the facts.

 

[gringeltaube]

I did that conversion once, but only because at that time there was no air shift around in our whole country! I would not recommend this to any one living close to places where you can buy a good air shift takeout or even rebuild one for less money than what this conversion would cost.

It is NOT possible to convert the sprag TC by just swapping in the front output subassembly from the air shift TC because the rear output shafts are also totally different. And to exchange those you need to pull everything apart, find a complete airshift unit anyways and a lot of time and pacience, too!

To make the sprag type T-136-21 work like the air shift T-136-27 you need to fabricate/exchange 3 parts inside and connect a small air cylinder to the shift shaft.
It is not necessary to remove the complete TC, just pull the front section out.
Take a look at the schematic drawing below: it shows the stock gear/teeth distribution of the sprag TC. To have both front and rear output shafts turning at equal speed the (red) drive gear #22 (red circle in 2nd pic) needs to have one more tooth (21->22) and the (blue) driven gear #9 (blue circle) one less (34-> 33). Both gears had to be fabricated new, no other (cheap) gears could be adapted or modified. The clutch assy. or double sprag unit (#15, green circle) was replaced by a solid piece with same dimensions but only one row of teeth. The shift collar # 10 remains the same but flipped. Everything else goes back into original position. To actuate the spring loaded shift fork from outside, a short single action air cylinder with 1” diameter and 1” stroke was installed between cross-member and shift shaft. To engage front drive it needs to push the shaft in (backwards) 3/4 inch, compressing the internal spring. A small industrial grade air switch with discharge was mounted under the dash.
I had this home made setup working well for years until I had the opportunity to swap the complete transfer case for a brand new air shift.
That kit is still in use in a friends truck.

Gerhard

 

[Miltrucks]

Thanks for the feedback guys. I had teh opportunity to pick up a rebuilt sprag case and thought about keeping it as a spare for the air shift.

Based on what was provided, I think I'll pass on it. Those were the details I was looking for!

 

[BFR]

want to pass along the info on the rebuilt sprague?

PM me

 

[Miltrucks]

Sure - feel free to Emal or PM for the details.

Have a guy that has a M46 chassis (the long wheel base one) - stripped down to the cab and chassis only. Fenders and front sheet metal gone. Non turbo multifuel is in parts, trans is believed good. Sprag Xfer still in red oxide paint - looks to be a recent rebuild. (Rear PTO has been removed) Axles and driveshafts in place.

Can probably get it for $1500. I'm stealing a bit of front wiring off of it and one of is getting the rear PTO setup. I was going to purchase the whole thing, but not really worth it for me once I found out it wasn't an air shift case.

It's located in Columbus, Ohio.

 

[joeM62]

Luckily, in working with all of my trucks, I have never really had any Xfer case problems so I haven't had one of these cases apart.

Can anyone explain if a sprag Xfer case can be converted over to an air shift case by swapping out some parts?

Off hand, I am guessing the front plate and the air valve, but nore sure if there are other parts needed, or if it is possible.

I believe there are kits out there to convert, but are they as strong as the original parts? any drawbacks with the kits?

I've heard a lot of people looking for Air Shift cases to replace their sprag units, and stories of they can and cant be converted. Just wondering if anyone had some specific details?

Thanks you just answered my question I had been wanting to take my sprag out for a air shift