Hi Lock and Low Lock Actuation

[Shamrocker1]

My 90 model M998 6.5 will not go into 4 wheel Lock position. Anybody know how this works and what I should be checking first? All help is appreciated! Tx again, Sham

 

[gcbennet]

Like, grinds and won't engage, or physically won't shift even with the truck switched off?

 

[Wire Fox]

I guess some good questions to get the 'experts' started....

1) The vehicle is full time 4 wheel drive, so I assume you mean the "High Lock" position. Can you confirm?
2) Has this transfer case position you're trying to select ever worked since you took possession of this HMMWV?
3) Is the shifter physically unable to go into the gear position, or does it go into the position, but the gear never actually engages?
4) Is the transmission in neutral when you go to shift the transfer case?

 

[Shamrocker1]

It shifts fine sitting still, running and off and makes no noise at all. It just isn’t engaging. Tx

 

[Shamrocker1]

Yes, it is a full time “all wheel drive or 4 wheel drive with differential”. I am strictly asking about the Hi and Lo LOCK condition. I have not made it work since I have owned it. The shifter shifts fine with no noise. Come to think of it, I’m not sure I have tried it in Neutral as embarrassing as that sounds. I’m having a new half shaft put in the RR and I asked the mechanic to check out the locking mechanism. Just called him to try the Neutral Lock. I’m a true newbie! Lol I’ll reply with the results as soon as he tests it. Thank you very much.

 

[Action]

you said the lever moves with no noise. I would check ghe linkage underneath to see if one end came loose.

 

[NDT]

If your transfer shift linkage is working properly, fixing the interaxle differential lock involves pulling the transfer and splitting it. Make sure you have a proper diagnosis, block up both front wheels in the air; unlocked the wheels will spin, locked, the truck will move and fall off the blocks.

 

[Shamrocker1]

My mechanic put it on the lift just before leaving for the day. He was also unable to get it into the “lock”modes, hi and lo. He did so in Neutral as well so ruled that out. Also checked the linkage, no problem.

 

[Shamrocker1]

Geez, I really hope you’re wrong! He will be working on it tomorrow and I’ll know for sure what it is. Does anybody know if the mechanical linkage is all that puts in lock? He seemed to think there could be a vacuum or hydraulic line going to the transfer case but doesn’t know for sure yet. If I have to pull the transaxle, it’ll likely never work with me as the owner. Too much $$$. Thanks for the reply, Sham

 

[Action]

Geez, I really hope you’re wrong! He will be working on it tomorrow and I’ll know for sure what it is. Does anybody know if the mechanical linkage is all that puts in lock? He seemed to think there could be a vacuum or hydraulic line going to the transfer case but doesn’t know for sure yet. If I have to pull the transaxle, it’ll likely never work with me as the owner. Too much $$$. Thanks for the reply, Sham

This usually happens when you take s humvee to a mechanic and dont do it yourself. They have no clue what they are working on. You just pay someone to figure it out.

 

[Wire Fox]

Geez, I really hope you’re wrong! He will be working on it tomorrow and I’ll know for sure what it is. Does anybody know if the mechanical linkage is all that puts in lock? He seemed to think there could be a vacuum or hydraulic line going to the transfer case but doesn’t know for sure yet. If I have to pull the transaxle, it’ll likely never work with me as the owner. Too much $$$. Thanks for the reply, Sham

There is no vacuum system or external hydraulic system on that transfer case. The hydraulic lines you see coming in and out of that transfer case are purely for cooling purposes, tie into the transmission's cooling loop, and finally ties into the radiator stack in its own radiator core.

The mechanical linkage is purely what controls its ability to go into lock position. I would probably try some more voodoo magic of putting the transfercase in lock position, and then shifting the transmission into a forward gear or reverse gear and trying to slowly "roll it out" to get lock engagement. Going into reverse to get out of lock position is an official procedure due to driveline torque build-up that can occur...but who knows? Might help you get into lock.

 

[Shamrocker1]

My mechanic, who is a friend and a 4 wheel drive fanatic, his tried everything you guys have offered and he has discovered that the “Lock” works fine in reverse but not in forward. He says the transfer case is a very common item used in many 4WD vehicles. He says that the slider fork for the transfer case that engages the “lock” position has nylon bushings on it that can wear and could possibly be the cause of the reverse working but forward not. He isn’t ready to give in to that assumption and is still looking at different possibilities. I am relaying all of your ideas to him as they come in. If you have any more to offer with these new details, please let me know. Tx, Sham

 

[NDT]

Sorry, the interaxle differential lock is either locked or it isn't, forward/reverse has nothing to do with it. Repeat the test I described in Drive and Reverse to verify for yourself.

 

[gcbennet]

Dude, these trucks are maintenance pigs and will keep you busy. You can spend hours merely troubleshooting gremlins. Unless you're planning on taking out a second mortgage on your home to pay for someone else's labour I'd suggest getting intimate with the TM's and the inner workings of the truck itself. It's mostly old school. Hopefully you're mechanically inclined and know your way around a multi-meter.

 

[Wildland]

Oh I got a great one here for ya. Just now hooked my 07 1097R1 to a water buffalo trailer (400 gallons) so put it in L lock. Truck pulled it around my property perfect but noticed mt temp gauge pegged to 240 right off but thermfan didnt come on. Also didnt want to come out of L lock. I tried the back n forward twice and it shifted back to H and by golly my temo gauge popped back to 160 where it should have been! So L lock somehow affects temp gauge!

Sent from my SM-A716V using Tapatalk

 

[Mogman]

Oh I got a great one here for ya. Just now hooked my 07 1097R1 to a water buffalo trailer (400 gallons) so put it in L lock. Truck pulled it around my property perfect but noticed mt temp gauge pegged to 240 right off but thermfan didnt come on. Also didnt want to come out of L lock. I tried the back n forward twice and it shifted back to H and by golly my temo gauge popped back to 160 where it should have been! So L lock somehow affects temp gauge!

Sent from my SM-A716V using Tapatalk

Could be there is a switch in the transfer case that lights up a lock light down by the shifter, it could be shorted or miss wired, try testing it again in low lock or high lock to be sure that is what is causing the gauge to read wrong.
sometimes getting out of LL or even HL is a challenge