M998 6.2, 3 speed trans adjusting questions

[Glider]

My M998 shifts the same regardless of throttle position. It barely gets moving before it shifts into 2nd and then shifts into 3rd fairly quick. It will not downshift from pedal input. It will downshift when slowing to a stop as one would assume a properly operating trans should. When accelerating from a stop with average throttle and manually shifting starting from 1 position it accelerates much better without taxing the engine. I have read about the downshift switch on engine. I don't think it is working or is improperly adjusted. I'm asking questions now so when I get started hopefully I can find a bad part or properly adjust everything in one session. My question: What is the best order of adjusting and checking components? Is there an adjustment on the transmission? If this has been covered already I didn't find in my searches. I've seen threads about the downshift switch that I am assuming pertains to full throttle shifts. I want to fix that but would like the trans to hold gears longer at part throttle also.

Any input appreciated

 

[TOBASH]

You realize that these trucks are only meant to drive 0-45 MPH, and less if your gears are above 2.56

 

[Glider]

Yes I am aware. Like mentioned earlier when shifting manually at part throttle it accelerates as to be expected for 180hp. I'm inly looking to change the shift points.

 

[NDT]

Sounds like the cable operated modulator is snapped.
45 mph??? Army drove these with the needle pointing down …

 

[ehinlein]

Yes I am aware. Like mentioned earlier when shifting manually at part throttle it accelerates as to be expected for 180hp. I'm inly looking to change the shift points.

My HMMWV was one of the original old ones I redid prior to the current release so I’m a little behind the times, driveshaft e brake etc. 6.2 3 speed. I sourced the mechanical modulator at that time. It has cable linked to throttle cable which drives pin in modulator on side transmission. Usually these are vacuum in “normal” situations. If you’ve got that it could just be broken cable or disconnected, needs adjustment etc.

 

[Glider]

OK...Cable operated modulator. Ill check that first.

 

[Action]

Yes I am aware. Like mentioned earlier when shifting manually at part throttle it accelerates as to be expected for 180hp. I'm inly looking to change the shift points.

More like 150 hp.

 

[Retiredwarhorses]

You realize that these trucks are only meant to drive 0-45 MPH, and less if your gears are above 2.56

45mph ?? A bit more than that for a 3 speed truck

 

[TOBASH]

Military convoys typically travel at what speed?

 

[Coug]

Military convoys typically travel at what speed?

Depends on where you are at.
When I was in South Korea we had a 25mph convoy speed.
When 5 or fewer vehicles we could do 35.
When on our own we drove whatever speed we wanted to.

I was on Ammo detail a lot. One trip to the range center (over 100 miles away) I had the S-3 (a Major) riding in the HMMWV with me.
His only requirement was that I not jump the vehicle.
We made it in under 2 hours.

 

[Retiredwarhorses]

Military convoys typically travel at what speed?

depends on the convoy commander and what he sets as the speed….the lead truck sets the pace.

 

[Thumper580]

OK...Cable operated modulator. Ill check that first.

I have a brand new one if you need it......

 

[Glider]

Had time to work on the humvee. Turns out the throttle cable was poorly adjusted. The kickdown switch was not activating at wide open throttle. All that was necessary was to adjust out the slack. That allowed the throttle to be opened fully by the pedal. Its runs like a new unit! I might adjust the kickdown a little more to make the shifts happen sooner.

 

[ehinlein]

Had time to work on the humvee. Turns out the throttle cable was poorly adjusted. The kickdown switch was not activating at wide open throttle. All that was necessary was to adjust out the slack. That allowed the throttle to be opened fully by the pedal. Its runs like a new unit! I might adjust the kickdown a little more to make the shifts happen sooner.

It’s nice when you get an “easy fix”. Glad it’s working.

 

[Glider]

Adjusted the modulator cable. It is very easy to access thru doghouse. Can be done with 1 wrench and channell locks. Adjusted so housing moved to left in picture. Didn't hardly get my hands dirty. It made a big difference in shifting and makes truck feel robust rather than sluggish.

All in all. It was well worth it. Adjusting the throttle cable to fully open and engage kickdown switch,then adjusting modulator. Both of which are two easy to access usually clean areas. Only expense was time. I would venture to bet a large majority of m998 would positively benefit from those easy adjustments.

The photo is taken from passenger side looking into doghouse. The adjustment is at bottom of picture. I exposed more threads to the left of bracket.

 

[jpletsch]

I experienced the same issue with my M998. The M998 would not move a while pushing the accelerator pedal to the floor. It felt like a transmission vaccum symptom. It would shift erratically and accelerate as if the transmission was in limp mode. After inspection the 3L80 transmission's modulator cable assembly was not fully pulling the cable forward. I manually pulled the modulator cable forward and locked it from retracting with vice grips. The truck accelerated and shifted correctly after. The modulator cable should have 1.5 inches of a pull distance .