HMMWV Transmission Trouble

[simoncrk]

Hey Guys
I bought an 85 HMMWV M1038. When I get on the highway it takes a while to shift. The motor really winds up tight, shifting into 2nd at 28 mph and 3rd at 47 mph. There isn't a tach so I don't know what RPM's. i changed tranny filter, the oil pan was clean as whistle. The control module with the cable going up to the throttle works as well. it's a 3L80 which is close to a turbo 400 with out park and it shows to have 11,000 miles on the speedomoter. any help would be greatly appreciated.

 

[tm america]

check vacume to the modulator with a guage it should have at least 20 inches of vac at idle and drop when the gas pedal is pressed .other than that it could be the gov sticking or you might just have to adjust the modulator

 

[simoncrk]

I thought about the vaccuum line. but I was told since it was a diesel there were no vac lines. I looked any way and couldnt find any. How do you adjust the modulator valve?

 

[tm america]

the modulator is no the pass side at the front of the pan rail it has a vac line going to it pull the line off at the bottom check vac with a guage first if vac is good there is a little screw where the vac line goes on to the modulator if you use a small screwdriver and turn the screw out to make it shift earlier you can tak it all the way out if you need to shift points should be 15-20 and 27-35 under normal driving

 

[Westech]

mm... the 4l80 is a 4 speed and does not have a vac control. and its computer controlled. the shift points sound a little high.. buy my 1150 sure sounds likes its going to take off before it shifts. You can try adjusting the throttle position sensor on the side of the injection pump

 

[tm america]

4l80e is a 4 speed he said he has a 3l80 which is a 400 same thing the technical name is 3l80

 

[tm america]

also his truck is an 85 they didnt start making the 4l80e till 89

 

[Westech]

well the 3l80 still is not vac controlled, My M998 has no vac pump.

 

[tm america]

ye sit is ive been building transmissions for 18years ive built probably 1000 of em and they have a modulator the controls shift timing and firmness and a kickdown soloniod that is for kick down

 

[simoncrk]

It is a 3L80 with out park. can the shift pattern be adjusted? I looked all over it for a vac line couldnt find any where. what do ya'll think? is it internal damage? the oil pan was clean...

 

[tm america]

look on the pass side right at the front of the pan the round thing with the line going to it is the modulator some vac pumps are belt drivin and some are electric or run off the injection pump ive seen it different ways depending on the year

 

[tm america]

its ussually a metal line

 

[tm america]

post a pic of your trans it should have the shift linkage on the driver side a 4 bolt cover on the pass side near the tailhousing and a round modulator with one bold holding the bracket just below the cooling lines the later hmmvvs had a 4l80e in them which is computer controled it has a round plug on the driver side behind the linkage and two speed sensors on the driver side as well

 

[simoncrk]

Is it the cable that goes up to the top of the engine that connects to the throttle? I took it off and the plunger is working.

 

[tm america]

what do you see on the right side of the trans just below the cooling lines

 

[simoncrk]

Its at my shop right now. or I'd send a pic. but I do remember a four bolt cover on the driver side at tail housing. is the adjustment in there?

 

[Westech]

its a 3l80e in the hummers....... no vacuum your right on the 3l80 they do have the vacuum control.. but the military uses the 3l80E

 

[simoncrk]

what do you think i should do? Im afraid to drive it... might blow motor or tranny...

 

[tm america]

probably still a 3l80 but they could use something in place of the modulator post a pic of the pass side of the trans please

 

[Westech]

your cant rev it past 3000 RPM.. that's what the military sets the governor in the injection pump. you will be ok. You can try to adjust the governor springs in the transmission to lighter ones to lower the shift points.