Transmission or T-case issue?

[MR.E]

Having issues shifting between 4WD and 2WD.
When I shift into 4lo from 2hi with auto in park it requires a lot of effort on the shifter. Discounting this since I don't use it much. Returning from 4lo to 2hi is where the issues start.
4lo to T-case neutral - no issue
T-case neutral to 2hi - deep grinding. Feels like an unsyncronized shift in an old trany.
Humm....
Try putting the auto into neutral vs. park. Same deep grinding from T-case neutral to 2hi.
Put the auto back into park and new problem. Get a higher pitched grinding sound in park. Sounds similar to a starter grinding or a chain being pulled over the corner of a steel table.
Back to neutral.
Shut off the motor with auto in neutral and the shifting between 4lo, 2hi and 4hi is almost efortless.

I can use 4lo, 2hi and 4hi but need to shut off the motor to avoid the grinding between shifts.

Motor was just replaced (transmission/transfer left in place) not sure if this would affect anything.

Thoughts?

[More Power]

Your owner's manual would likely offer the best advice, but when the truck is sitting still, I usually shift the transmission into neutral when switching the transfer case from 2H to 4H or from 4H to 2H. No problem when the vehicle is moving.

If the txfer case grinds while shifting as stated above, the transfer case synchro may need to be replaced.

Jim

[JohnC]

This is from memory, and I didn't use 4lo often, so I could be wrong. Anyhow, shifting from 2wd to 4hi is a no brainer as long as you aren't spinning the rear wheels. You can do it anytime, any speed. I think GM recommends staying below 55.

4lo is the issue. As soon as the transfer case is in neutral the auto trans starts things spinning even if it is in neutral. The only sure way is to put the trans in park first, with the xfer case still in hi, so everything is and stays stopped. I suspect the noise you heard in park was the parking paw as the trans output shaft was spinning since the xfer case was in neutral. Once that happens you have to shut it off and start over.

IIRC...

[mitchedo]

I go between R and D and back and forth with very gentle pressure on the transfer case shifter handle until the transfer case slips into gear. This moves the gears in the transfer case enough until they mesh properly and drop into gear. You have to treat the transfer case as if you were shifting a manual tranny without the clutch. If you have one of those stupid electronic knob shifters, then that won't work.

Also, if you've driven the truck in 4WD on pavement, especially if you made a turn, you will find it easier to shift the transfer case if you go onto a gravel/dirt/grass or otherwise non-pavement surface.

It can be difficult to work the transfer case, especially 4LO, when on pavement. I spent most of my shifting into and out of 4WD with a Dana 20, which is a real bear sometimes.

[Robyn]

Tranny in N if your stopped and want 4H or do it on the fly.
Shifting into Low have the truck stopped or very nearly so and the tranny in N pull the lever all the way to low in one shot.

If you have the tranny in any position and the truck running and you stop the T case in The N position you will play hell getting it back into 4L or 4H without noise.
Dont do it, also dont throw the tranny in park at that point either as it can damage the parking pawl. Shut the engine off if you get it stuck in the N position.

As long as you are going slow you can go from 4L to 2 high with the tranny in N and it will shift fine.
If you try to shift the thing in park it may jam it up. Always shift with the tranny in N and it will do fine.

Good luck

Robyn

[mitchedo]

Tranny in N if your stopped and want 4H or do it on the fly.
Shifting into Low have the truck stopped or very nearly so and the tranny in N pull the lever all the way to low in one shot.

If you have the tranny in any position and the truck running and you stop the T case in The N position you will play hell getting it back into 4L or 4H without noise.
Dont do it, also dont throw the tranny in park at that point either as it can damage the parking pawl. Shut the engine off if you get it stuck in the N position.

As long as you are going slow you can go from 4L to 2 high with the tranny in N and it will shift fine.
If you try to shift the thing in park it may jam it up. Always shift with the tranny in N and it will do fine.

Good luck

Robyn

Robyn,

Is there some sort of synchronizer in the transfer case that allows switching in and out of 4 Low while moving? The only ones I've had apart are the Dana 20 and the Dana 300, neither of which have any kind of synchro gears in them.

As for getting stuck with the transfer case in neutral, I've used the R-D-R-D-R... trick with the transmission to get the tranny output shaft to stop spinning with good success, but only with my old Dana 20's and the 241C in my 91 Suburban. Shutting off the engine is easier, but sometimes the gears in the transfer case aren't fully lined up and shifting can be difficult -- unless there is a synchro. I've only shifted my new truck in and out of 4 low a few times, and I've used the same method. I've never had the transfer case stop in neutral, and I've never heard any gear clash.

I suppose I could RTFM for my new truck's transfer case shifting instructions.

[cowboywildbill]

I wouldn't go from 2 or 4 high to neutraul or to 4 low unless it is in park or neutraul. If it is in any gear it will spin the cluster in the t-case and if the t-case hits neutraul and doesn't engage right away it may not mesh. I sometimes go to neutraul when trying to go to 4 low or back to 4 high. But sometimes an automatic trans can spin the tail tailshaft a little when it is in neutraul. If it is too much it will grind. And be careful about spinning the trans in gear if the t-case is in neutraul also, it may grind or break the parking pawl when you try to place it in back in park. If it grinds I would turn it off and go to park and restart. The truck should not be moving when going from high to low or vise versa. 2 high to 4 high and back while moving is fine.
Sometimes the problem is that the front and rear running gears are torqued against each other or binded a little. If you back up and pull forward a little or dissengage it or while still on a slippery surface it may help.That takes the pressure off of the two rears. In the old days in a straight stick manual t-case we would shift to high and low on the fly kinda like a two speed box in a big rig by double clutching and or matching rpm. But now lots of things are all auto. Hope I didn't confuse you.

[Robyn]

On some T cases there are electronic synchonizers but most do not have anything.

If you stop the T case shifter in N with the tranny in any mode other than park the tail shaft and the input on the Tcase will spin up resulting in a grind.

The N position is only used for PTO operations and "almost" nobody any more uses a PTO on the family 4x4.

As long as you shift right through from 2H and into 4L in one nice smooth motion the little beast will stay quiet. This is also true coming back out of 4L and into 2H.

Going from 2H to 4H is a snap and can be done on the road rolling right along even at moderate road speeds.
Just let off the throttle and "Float" the drive train and pull the lever into 4H
To shift out of 4H back to 2H just shift the lever and the case will disconnect automatically when the pressure is off the gears.

4L is actually shifting a gear set and the speed difference requires that you be stopped or very nearly so 1-2mph no more and the tranny in N.

The secret is doing the pass through N in the T case quickly so the shafts cant spin up.
Now with this said, even the best of them may make a little tiny noise as they change gears.

If you stop in N you are going to have to stop the engine before trying to engage anything in the T case.

Just the nature of the beast.

Robyn

[JohnC]

Now that I think about it, what Robyn said is what I remember doing. Like others said, if you pause even for an instant in neutral, even if the trans is in neutral, things start spinning. The manual shift cases do not have any syncros, and once things start spinning the only way to stop it is shut the engine off.

I recall that puting it in park first and shifting with your foot off the brake also worked.

Don't go from 2H to 4H if you're turning or if you're spinning the rear wheels, otherwise it should slip right in.

[cowboywildbill]

Good point, if your spinning,stop the spinning before going from 2h to 4h. On our 07 I notice that it will bang if I am not careful when stopped or moving slow on slick stuff for my 2h to 4h. The front axels don;t engage as quickly as our 06 did. Maybe our 07 has closer tolerences on the splines than our 06 did. I hope they loosen up in time. I will back up a foot or two and ease forward, then they mesh in OK.

[Robyn]

The later GM systems with IFS are fussy and you really need to be carefull when engaging. Once the lever is in be sure the light on the floor comes on before allowing the wheels to spin. If the rears spin and the front end finally engages it can mess things up.
I always make sure the thing is in fully before I put power on the system.

Best

Robyn

[JohnC]

One day I was driving out my driveway in the '95. the end of the drive was a sheet of glare ice and slightly uphill. I couldn't get up it in 2WD, so I stopped and shifted into 4WD There came this god awful ratcheting sound from the front. It took a couple of seconds to realize what was wrong, but by that time it had locked in with a horrible clunk. Turns out the ice was so slippery that the front brakes were holding the truck and the rear wheels were still turning from the trans being in D. Note to self: Press brake harder next time...