m998 with no shift from 1st to 2nd

[WRFPD]

Looking for some help with a m998 hmmvee (6.2 with 3l80e). Unit has 7,700miles on new engine and trans. All fluid levels are at spec and clean. Unit has a complaint of: when last in operation ,transmission kicked down from 2nd to 1st to pick up speed. After that it has stayed in first when in drive.

 

[NDT]

Check function of the mechanical modulator. Maybe the cable inside snapped. Oh and welcome to the forum. More folks will chime in shortly.

 

[Action]

Did you have the trans warm after driving around for a while before you checked its level?

The "e" in 3l80e stands for electronic. I don't think you have that.

 

[WRFPD]

I did check the mechanical modulator and it looks to be working. Thank you for the welcome.

 

[WRFPD]

I have not checked it after driving around and it is warm. Then its not a 3l80e then. only has one wire going to what I think is the Detent Solenoid? on the left side

 

[NDT]

I did check the mechanical modulator and it looks to be working. Thank you for the welcome.

To me, checking this involves pulling it out of the transmission and verifying the plunger moves with the gas pedal. I am focused on this item because on a vacuum modulated TH400, it will also not shift out of first if not functioning.

 

[WRFPD]

I was also. I did remove it from the trans and manually pulled the cable it looks to be working. I also checked to see it the plunger inside the trans was moving, which it is

 

[NDT]

That tells me the issue is internal to the transmission. Hopefully member "rustystud" will chime in as he rebuilds these and knows them in and out. I don't.

 

[Action]

trans fluid levels should be checked on a freshly driven vehicle and cycled through all the gears....mine wouldn't even shift out of PARK until the fluid level was raised. it was full sitting cold in the garage, but after running, some of the fluid moves to the cooler and lowers the transmission amount. leave the motor running while checking it.

 

[WRFPD]

I'm by no means a transmission guy and have become very rusty with the smaller stuff. Any help at this point is good help. What is the switch on the passenger side of the pump used for, is that some kind of kick down switch?

 

[WRFPD]

trans fluid levels should be checked on a freshly driven vehicle and cycled through all the gears....mine wouldn't even shift out of PARK until the fluid level was raised. it was full sitting cold in the garage, but after running, some of the fluid moves to the cooler and lowers the transmission amount. leave the motor running while checking it.

I did have it running for about 40min and then drove it into the shop and had it running as I was checking the level. I would think that it would have been good to check at that point.

 

[Action]

I did have it running for about 40min and then drove it into the shop and had it running as I was checking the level. I would think that it would have been good to check at that point.

In post #5 above, you said you did NOT check it after driving. So, if you did check it after with the engine running, where was the fluid on the dipstick?

 

[WRFPD]

In post #5 above, you said you did NOT check it after driving. So, if you did check it after with the engine running, where was the fluid on the dipstick?

Your right I did say that, after your post I rechecked it after running it for 40min then pulled it into the shop and checked it with it still running. The level is still fine. I have no park only R N D 2 1. It will go into reverse and 1st without any hesitation at all or any need to wait after starting the unit.

 

[Action]

yeah, i have park on mine.
The 3 speed trans shifts are sometimes hard to feel or notice
how fast have you driven it?
The 6.2 gets very loud in these. like so loud that you need to let off the pedal to speak to someone when at speed.

 

[WRFPD]

yeah, i have park on mine.
The 3 speed trans shifts are sometimes hard to feel or notice
how fast have you driven it?
The 6.2 gets very loud in these. like so loud that you need to let off the pedal to speak to someone when at speed.

30 to 35 mile max @ what sounds like a very high rpm

 

[86humv]

Did you Manually shift it while driving ?

 

[WRFPD]

Did you Manually shift it while driving ?

It was in drive, all was good and working well, needed to speed up, put my foot into it due to traffic. It down shifted to 1st and now will not shift out of 1st. I have not manually shifted when driving

 

[TedG]

Could be bad valve body, stuck clutches, clogged screen, to to name few. Drop pan and get busy.

 

[WRFPD]

Could be bad valve body, stuck clutches, clogged screen, to to name few. Drop pan and get busy.

found myself time to dig into this problem today. I found as I was checking the detent solenoid resistance, that the connection was not good at the plug. I replaced the plug and took it for a test drive. It now works great, up shifting and downshifting like it should. I want to thank everyone for their help.