DeSpline Questions

[acme66]

I have done a bunch of searching and could find some hard Duce numbers but can't seem to come up with any for the 939 5ton. Can someone with desplined hubs on a 5ton comment on what you have seen in the real world? MPG, tire wear etc? Have issues with bushing wear or? On road obviously but I do have questions about if the 5ton would waddle about on steep gravel roads or see axle hop descending. I have heard numbers for the 2.5 ton as high as 4mpg gain, if the 5ton saw half that that would be $1600 in fuel for my truck per season. Not sure if I can push it up/down the mountain with out axle hop on just the rears but I would be willing to try for another 2mpg. The Duce guys seem to like them, curious if the big boys do as well.

Ken

 

[73m819]

Depending on what 5t, a 939 would be a lot different then a 39/809 series, the 5t spindle has only one axle bushing, this is towards the rear of the spindle, the outer end is supported by the hub cap, on a 939, this will not be a issue BUT on the 39/809 series this will be a issue, the sprag will think the rears are spinning and will engage the front drive, causing the front axle to spin, that is a LOT of unsupported weight flopping around, something WILL were and break.

One way to handle this issue is to install a bushing in the desplined hubs, another way is to install the air cut off to the trans poppet valves and transfer MWO.

 

[acme66]

Sorry, edited to show that it is a 939.

Ken

 

[Scar59]

I have a pair that I swap out with my M925 and m936 when I'm head out on the high way. There is a fuel saving, however I haven't calculated down to the mpg. The big difference is no rotating mass up front in the axle. Feels a lot smoother in the steering wheel and no wear to the drive line. As for the exposed spline in the hub, no wear or even contact. I pack a little grease in them and bolt them on. As for my M813, I'm preparing to install a air switch to control the transfer poppet valve as Ron has described. Got the switch, sourcing air line/hardware, then I'll call Ron again to ensure I'm headed in the right direction.

 

[73m819]

With the 939s, the axle is not flopping around EXCEPT if you forget and engage the front drive, maybe come up with a safety cap that goes over the dash air switch like the safety cover the can go over a toggle on a toggle switch.

 

[acme66]

Front axles for me. I would like to know from those that have done it if desplining the front axles on a 939 gives similar on-road benefits as it does for the M35. Fuel mileage is of particular interest to me. The trailer discussion is interesting and to that end I would be tempted to simply set the back half of a 939 on some surplus trailer axles but I understand how that wouldn't look the part which I gather is also important to the builder. Again, I just want to know from those who have done it what effect a front despline has on MPG and tire wear as that is a large expense for our business. Even a mile or two per would make it very worth it to me but I would like to know hard numbers rather than being the test case.

Ken

 

[VPed]

I haven't done it to a 939 but I can tell you I got no where near 4 mpg improvement on the deuce. I got 1 mpg at 55-60 mph over 300 miles.

 

[Steelreaper80]

Old thread but interested if anyone has any experience they could share. 99.9% of my driving is on road. I would keep the splined hubs in the side box just in case they are needed but very interested in seeing at least SOME MPG improvement. A little would help a lot.

 

[74M35A2]

Old thread but interested if anyone has any experience they could share. 99.9% of my driving is on road. I would keep the splined hubs in the side box just in case they are needed but very interested in seeing at least SOME MPG improvement. A little would help a lot.

8.3? If not, get one. That doubles your mileage.

 

[Steelreaper80]

8.3? If not, get one. That doubles your mileage.

I have one. M925A2. But, I pull an M322 trailer with 14,000 lb tractor on it. Sometimes a skid steer with a forestry head. Same weight though. Getting around 5.5-6MPG now.

 

[simp5782]

About 1mpg better

 

[Steelreaper80]

About 1mpg better

Any mechanical problems that creep up from running de-splined hubs?

 

[simp5782]

Nope tap the outside so you can add grease as needed

 

[tobyS]

If you don't want to ruin a perfectly good spline hub, consider making a blank to cover the bearings.

Use the dished head to an air tank, readily available, and weld on a flange.