Sprag?

[FMJ]

When (year) were Sprag's no longer used on the Deuce?

 

[acetomatoco]

Not sure which contract when the Air Shift xfer case was made standard. The various rebuild programs added air shift to many early trucks thru the years, and even on the local level like the AR and NG CSMS were doing them on a one off basis with a kit which included, the MF engine and a new LF fender and a Overdrive tranny along with the new xfer case. I have found early gas trucks converted to MF and keeping the sprag case with a new nose and the air shift kit. and the sprag linkage just left hanging off the back of the tranny direct drive and all.. They saved the new trannys and the new fenders to fix other trucks. I remember them putting new bodies on M151A2s at Fort Devens in MA at about the same time as the Deuce conversions during the 80s when the budgets were lean. After all this I have not answered your question. Sorry...

 

[DDoyle]

US Military vehicle procurements and specs are rather like a large ship - once they are on a course, they are slow to change.

The air lock transfer was tested by Reo Motors and Aberdeen in the early 1950s (the tests, by the way, indicated that the air unit offered no improvement over a PROPERLY ADJUSTED sprag unit. Nevertheless - the sprag unit requres periodic linkage adjustment - and certain of the officers liked the "feel" of having a "manual" contol (the same group didn't like automatic transmissions and CTIS either). Eventually, the decision was made to go to the air lock transfer case - and IIRC, the first contract that this applied to was the 1970 contract.

Some one else may chime in with their information at their fingertips - my files are not, and that is the best my memoory can do.

HTH,
David Doyle

 

[FMJ]

Ok, I have a 67 KJ M35A2, it does not have air shift, I have a M109 parts donor with air shift, I was wondering if it was as simple as it seems to me, swap the air shift off the donor truck? or is there more involved?

 

[DDoyle]

If you swap the entire transfer case (and control) - no problem.

DD

 

[ems4ty]

Removed Comment....

Thanks,

T

 

[FMJ]

If you swap the entire transfer case (and control) - no problem.

DD

The part number on the 67 KJ transfercase is T 136 21

I'd really like to not have to swap t-cases, is this one not compatible with air shift?

 

[DDoyle]

The transfer cases are substantially different internally - if you are asking if you can just move the air valve from the dash and the air solenoid on the case between the two vehicles - the answer is no.

Sorry to bring bad news.

David

 

[paradeduty]

I think mine is an original 1968 M46a2c (I Think?) when i got it the front winch was still in burlap and the front seats were still in black plastic but does not have turbo - seems like early issue original (no turbo) anyways, mine does have the air shift transfer case but no turbo (sure seems pretty early in the air shift era. truck was never painted - no numbers except tire pressure and i think fuel tank level on the original paint - think it was never issued for use at a base, etc.

 

[FMJ]

The transfer cases are substantially different internally - if you are asking if you can just move the air valve from the dash and the air solenoid on the case between the two vehicles - the answer is no.

Sorry to bring bad news.

David

Thanks David,

So I'm also guessing that tire sizes (tread height) are important, as in making sure the fronts are as close to the same amount of tread wear as the rears so the rotational speeds are the same?

 

[BKubu]

FMJ: As I am sure Bjorn will chime in, it is always a good idea to run matched tires (that is, tires that have the same amount of tread on them). With that said, running mis-matched tires is LESS of a problem with the airshift front axle.

 

[gringeltaube]

So I'm also guessing that tire sizes (tread height) are important, as in making sure the fronts are as close to the same amount of tread wear as the rears so the rotational speeds are the same?

Not so important. Usually "new" (=taller) tires should go on the front anyways.
In the worst case scenario tire size tolerances + difference in tread wear combined makes for approx. 4%. With the referred sprag-TC the sprag clutch engages and starts driving the front axle after reaching a speed difference rear to front output of -7%. (100 *33div22, *21div34 = 92.6)
The only way the front axle could end up dragging the rears (not desirable when loaded, on paved ground!) is in tight turns, with smaller tires up front.
And than it all depends on the static loaded tire radius, not the outside diameter...!

Confusing enough?

G.

 

[FMJ]

So I'm also guessing that tire sizes (tread height) are important, as in making sure the fronts are as close to the same amount of tread wear as the rears so the rotational speeds are the same?

Not so important. Usually "new" (=taller) tires should go on the front anyways.
In the worst case scenario tire size tolerances + difference in tread wear combined makes for approx. 4%. With the referred sprag-TC the sprag clutch engages and starts driving the front axle after reaching a speed difference rear to front output of -7%. (100 *33div22, *21div34 = 92.6)
The only way the front axle could end up dragging the rears (not desirable when loaded, on paved ground!) is in tight turns, with smaller tires up front.
And than it all depends on the static loaded tire radius, not the outside diameter...!

Confusing enough?

G.

YES,

Well, the reason I asked is, I replaced the fronts with new tires because the old ones had little tread left, and were dryrotted. The rears had more tread than the fronts before the changeout, so now the fronts are just a bit taller. The only problem I see/experience now is when backing, the approach to my shop is uphill and I parked the truck on this incline when I changed the tires. When I finished I put the truck in reverse and started to back up, down hill, noticed a little binding/jerking, when backing on level ground there is no problem, forward no problem. Just the partial load reversing. I'm going to read more regarding the Sprag adjustment. From what I've read here, letting a Sprag vehicle roll backwards is a no no, so I'm not sure if what I'm experiencing is normal or not.

Ed

 

[gringeltaube]

...The only way the front axle could end up dragging the rears (not desirable when loaded, on paved ground!) is in tight turns, with smaller tires up front.

Ooops! Just realized that my previous post is pure nonsense!

It is known fact and true that for the T-136-21 the rear propeller shaft and axles have to turn 7% faster before the front starts to engage (typical for slippery surfaces). On firm ground however, with equal tire radius all around everything will be turning at approx. same rpm.
BUT…. smaller front tires actually will make the front propeller shaft and overrunning clutch (sprag) turn faster than the rear! Same while turning; front tires will have to travel a longer distance, speak rolling faster for any given rear rpm. Which means even greater difference and less probability of engaging and/or binding.

Did I say confusing....?

G.

 

[gringeltaube]

.... The only problem I see/experience now is when backing, the approach to my shop is uphill and I parked the truck on this incline when I changed the tires. When I finished I put the truck in reverse and started to back up, down hill, noticed a little binding/jerking, when backing on level ground there is no problem, forward no problem. Just the partial load reversing. I'm going to read more regarding the Sprag adjustment. From what I've read here, letting a Sprag vehicle roll backwards is a no no, so I'm not sure if what I'm experiencing is normal or not.

Ed

There shouldn't be any binding if linkage is correctly adjusted and you shift from first into reverse before rolling backwards...!

G.

 

[FMJ]

Thanks, I'll see about the sprag adjustment and getting a pair of tires that more closely match the tread depth of the rears.

 

[m-35tom]

rolling backwards is fine as long as the trans is in rev. same for rolling forward trans should be in any forward gear.
smaller tires on front would be no problem except for more slippage of rear before lockup would occur. different size tires with a air tc would be a problem as binding would occur.

 

[JasonS]

rolling backwards is fine as long as the trans is in rev. same for rolling forward trans should be in any forward gear.
smaller tires on front would be no problem except for more slippage of rear before lockup would occur. different size tires with a air tc would be a problem as binding would occur.

I don't think that this is correct. I have freewheeled backwards with the tranny in neutral and had it bound up. This is because the forward sprag is still engaged. In fact, just because you have the transmission in reverse doesn't mean the the reverse sprag is selected. The linkage operates through a spring.

 

[familyxj]

OK I read earlier in the thread about swapping the sprag to air shift. I am currently doing this on a buddies 77. I know nothing about these either. He has a bunch of dueces and told me what he wanted so we found an air shift and dropped it out. Next we dropped the sprag. We took out the seats and used a cherry picker to lower it down with 2 cargo straps. (that made it pretty easy) We set them side by side and the only thing different about them was the drivers side brackets were completely different. We switched them and the air shift lined right up and bolted right in. This is a two man job for anyone thinking about it. Now we have to figure out the air lines and we will be good.