Is my M813 sprag sticking?

Fresh diesel, new injectors & new injector pump. All adjusted, engine runs good. I’ve driven this truck & had it in 5th chugging along to make sure tranny works, than back to 4th than 3rd. This truck flat out going down hill hit 41 mph, I was the chase vehicle & that’s what my speedo read. Could not maintain this speed, unless going down hill. Mostly on flat ground 30mph+/-!

Removed front drive shaft no change , checked all bearings and brakes for excessive heat there isn’t any . The truck is confirmed in high range and I have a m36a2 so I am familiar with the shift pattern . I pulled the sprag air cylinder apart and it wasn’t rusty or anything I put it back together . I’m going to try to cap off the air going to the sprag to hopefully put it into neutral will probably mess with it Thursday. I drove it in low range and it seemed smother but hard to tell at low speeds . Thanks to Floridiann for the assistance.

Not sure what else would make the truck sluggish , it also seems like the rear axles seem bouncing a bit thought it was cause of old flat spotted tires but could also be from sprag stuck i think .

comike27 said:

Not sure what else would make the truck sluggish , it also seems like the rear axles seem bouncing a bit thought it was cause of old flat spotted tires but could also be from sprag stuck i think .

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Drop the axle between the rears. Then only one axle is moving the truck.
Honestly it sounds like an engine issue at this point. If the front axle is off you've eliminated the sprag issue. How does it run? Smoke at all? What is max rpm that you can hit in each gear? If it's low in power or has a cold cylinder under load it could cause some low power and drivability issues.


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It doesn’t smoke and seems to run great , in first and second goes right up to 2100 rpms when I get into third gear it drops to about 1500 and takes forever to get up to 2100 I have only got it into fourth gear a couple times and it was low rpm . I have had it in all gears just to make trans is working.

As 162tcat says, the sprag only affects the steering axle so if you pulled the front drive shaft, you've eliminated drag from the steering axle.

You say that you aren't finding any hot spots anywhere which suggests that nothing is dragging. What happens when you step on the clutch and coast at 30 mph? Does the truck coast freely or does it feel like something is dragging? This is starting to sound more like a power issue than something hung up in the driveline.

I haven’t let it coast yet at 30 I will try that tomorrow. I have recently replaced the injectors and the injector pump dove the overhead adjustment and replaced the fuel filters . I’m going to recheck my injector adjustment I didn’t trust my torque wrench so I ordered a new one I did Ibc so only 6 inch pounds .

Now that the front is off, remove the back driveshaft and run it through the gears sitting still. My TC had shafts loose but this has a sound of the (3) shafts binding...aka too tight. Have you checked the lube in the TC (and tranny)?

Yes I have checked all fluids I haven’t flushed the transfer case but i added some fluid , the trans was empty it had a leak so it has 30 weight oil in it

Floridianson said:

The other air line is on the transfer case and the Deuce has the return spring on the air shift transfer case so just one line.
Yes the is a position where there is no engagement without full air pressure.


As for the drag yes if you lock up the sprag it will feel like something is dragging and it is.
I am waiting for a call from him now.

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Myself, I can't see how to get three positions with one air line and spring return (or why even have a neutral). Neutral in the TC is not in the sprag unit, it's in the TC gears. Why have a neutral that is redundant? I had my sprag out and don't recall a neutral, it either locks in one direction or the other.

If the sprag is locked in the wrong direction, the difference in gearing is like 16/1 on the front and 15/1 for the rear (internally in the TC). The rear going forward is always trying to over-run the front.... the sprag relieves the difference. That (not relieving the difference) will produce plenty of drag. It would also show up by near free-wheeling with the driveshafts off. The rear output will turn faster that the front drive (by the above ratio), but it will turn free without axles attached.

This condition will result in a lot of heat in the TC after running for a while but it would have to heat the entire TC for you to know it.

comike27 said:

It doesn’t smoke and seems to run great , in first and second goes right up to 2100 rpms when I get into third gear it drops to about 1500 and takes forever to get up to 2100 I have only got it into fourth gear a couple times and it was low rpm . I have had it in all gears just to make trans is working.

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In 3rd gear even with something slightly dragging you should have no problem hitting 2100+. This sounds more and more like an engine issue. When you rev, do the RPMs drop back down fast? If it floats before it comes back down your sucking air which would cause your reduced power issue.

Is the emergency cut off lever pushed all the way open? Was the fuel shut off solenoid replaced? Have you turned the thumb screw to make sure it's all the way open?

Facts:
Nothing is hot and if something was dragging enough to slow you to 1500 in 3rd it would produce heat.

It's been sitting since 2002 and it sounds like you've replaced or touched most parts of the fuel system. Could have inadvertently created an air leak.

The only odd thing is the bucking. What tires? Old NDT tires would feel "lumpy" forever. Newer tires should be smooth unless they have actual flat spots from dragging.


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Check your third members(differentials) for heat.

I recently experienced someones truck that the pinion shaft bearings failed and it caused serious drag.

After you try coasting, just check for high temps with your hand on top of the differentials.

It has 14/20 super singles on it I replaced the front tires I haven’t replaced the rear tires yet . When I drove it last week the tires seemed to smooth out a bit . I replaced the injector pump and it had a new shut off solenoid and it works . I’m not sure if the rpms flutter I will check on that tomorrow. What thumb screw if where the throttle hooks up it’s all the way adjusted . I’m planning on jacking up the rear axles and checking for drag after removing intermediate axle . What adjustment is screw is on the injector pump and how would I check for a air leak

comike27 said:

It has 14/20 super singles on it I replaced the front tires I haven’t replaced the rear tires yet . When I drove it last week the tires seemed to smooth out a bit . I replaced the injector pump and it had a new shut off solenoid and it works . I’m not sure if the rpms flutter I will check on that tomorrow. What thumb screw if where the throttle hooks up it’s all the way adjusted . I’m planning on jacking up the rear axles and checking for drag after removing intermediate axle . What adjustment is screw is on the injector pump and how would I check for a air leak

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If I'm reading this right, you replace the 1400s on the front but still have the duels on the back?


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I just TX him about that no all 14/20.

Floridianson said:

I just TX him about that no all 14/20.

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Thanks for clearing that up!


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When I changed my fuel filter it had disintegrated and was full of crude and had frozen water in the bottom . I’m going to pull the screen out of the injector pump and check for debris and check all the fuel lines . Possibly drain a little out of the bottom of the fuel tank and check for water and debris .

Good thinking. The little screen is cleanable but if it does not clean out well or you have trouble I have some extra and will mail you one.

Check the parking brake.. broken spring keeping the shoe(s) dragging/engaged.

I replaced the brake cable and the brake handle it is adjusted. With the brake off the truck rolls freely. I looked at it yesterday and all the springs are they and with cable off I can move the arm