M929 A2 Takes Too Long to Lock-up the Torque Converter Forward, Not Reverse

[aventurateutonic]

Folks,

I am hoping that the community can provide insight around an ongoing concern that I have for my vehicle.

When I accelerate forward, especially on a hill, the truck takes forever to accelerate. I notice that the engine needs to exceed 1,500 RPM before it even begins to move ( very slowly - 30+ seconds ). It is almost like someone winding up the rubber band before it finally decides to launch forward. In addition, I find that it does not have any issue locking up the torque converter quickly going reverse. In reverse, the truck moves immediately.

My questions:

1. Is what I described a 'normal' behavior/characteristic of the truck?
2. If this is not 'normal', what could be the issue, as it goes immediately when in reverse, but not forward?
3. If someone knows or has had the same issue, what did you do to resolve it?

Thank you for your help from North Idaho.

-Rolf

P.S. For those interested in seeing the truck at work, I have attached some photos.

 

[Elijah95]

Let’s ask some preliminaries:
1) Is the transfer case in Low, or High?

2) Motor oil or transmission fluid in the transmission?

3) Have you or anyone that you know of tampered with the injection pump to add more power?

If you’ll supply that I can be of better assistance


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[aventurateutonic]

Let’s ask some preliminaries:
1) Is the transfer case in Low, or High? [ The transfer case is in high ]

2) Motor oil or transmission fluid in the transmission? [ To the best of my knowledge it is transmission fluid, not motor oil ( why would one that? ) ]

3) Have you or anyone that you know of tampered with the injection pump to add more power? [ A stock truck, no tampering ]

If you’ll supply that I can be of better assistance


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[Jbulach]

Normal for an A2. The torque converter does not lock up when taking off, what you’re experiencing is the turbo spooling. The reason you don’t feel it in reverse is because reverse is so much lower geared.

 

[Elijah95]

As J stated, completely normal especially with a load in the bed, the 8.3 doesn’t have a lot of grunt off the line and flat out is a dog in 1st high until the turbo spools up and the boost builds.

Torque converter doesn’t lock in first gear at all.

Try shifting into neutral, drop her down in low, and drive with a load on. It’ll feel like a rocket ship off-road and more responsive, tranny temperatures will decrease. Do not use reverse in low due to risk of transfer case failure.

To answer your question about the fluid, all M939 series trucks ran 15-40 motor oil in the transmission while in service with the military, and people who transition over to using ATF in them typically end up with higher transmission slippage % and higher fluid temperatures as well.


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[aventurateutonic]

Normal for an A2. The torque converter does not lock up when taking off, what you’re experiencing is the turbo spooling. The reason you don’t feel it in reverse is because reverse is so much lower geared.

Thank you for the confirmation on the 'normalcy' of this behavior.

 

[aventurateutonic]

As J stated, completely normal especially with a load in the bed, the 8.3 doesn’t have a lot of grunt off the line and flat out is a dog in 1st high until the turbo spools up and the boost builds.

Torque converter doesn’t lock in first gear at all.

Try shifting into neutral, drop her down in low, and drive with a load on. It’ll feel like a rocket ship off-road and more responsive, tranny temperatures will decrease. Do not use reverse in low due to risk of transfer case failure.

To answer your question about the fluid, all M939 series trucks ran 15-40 motor oil in the transmission while in service with the military, and people who transition over to using ATF in them typically end up with higher transmission slippage % and higher fluid temperatures as well.


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Thank you for providing some clarity and background on this behavior. I will keep the truck in low when moving around the property in the future, as we have steep roads, often with 7-10 yards of gravel in the back.

As for low AND reverse, the previous owner of the truck was wise enough to prevent the ability to do both together. I didn't look to see how it was accomplished but will do so to understand it.

Thank you for the tip on the 'transmission fluid' vs 'motor oil' for the transmission--I will do more research on that.

 

[Elijah95]

Thank you for providing some clarity and background on this behavior. I will keep the truck in low when moving around the property in the future, as we have steep roads, often with 7-10 yards of gravel in the back.

As for low AND reverse, the previous owner of the truck was wise enough to prevent the ability to do both together. I didn't look to see how it was accomplished but will do so to understand it.

Thank you for the tip on the 'transmission fluid' vs 'motor oil' for the transmission--I will do more research on that.

Anytime! Some trucks had the low-reverse lockout MWO performed to prevent even entering reverse, regardless be advised unless the washer down below on the t case is removed 6x6 is enabled by default when the linkage moves and the washer flips the air switch until the truck locking the front axle.

The tranny fluid is usually easy to ID, the motor oil if in good health will look like oil out of a bottle, no dye. Whereas tranny fluid, well you know.


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