2008 H3 Alpha Drivetrain Slipping

[dscvdvr]

Greetings,
I am trying to isolate a problem with my 2008 H3 Alpha.
The first occurrence, I was traveling about 45mph in 4A and the engine revved as if put into neutral. I stopping and also noted in park it was rolling and had to apply the parking park. I was able to put it in 4H and drive home without incident.
I replaced the transfer case actuator and did a transmission filter and fluid.
Afterwards I drove about 100 miles with no incident, then the same think happened, driving and sudden engine revving like being thrown into neutral. I noticed when I put the transmission in park this time, there was a bit of light "gear grinding". I switched to 4H and it still freely revved, but after hitting the transfer case switches a few times, was able to travel in 4A. Since this, I have just parked it.
I tend to think it is the transfer case, but am just not familiar with the 4 Auto functionality of this case and hate to dig too deep into it and find out it is a transmission issue.

The H3 has 160k miles, btw.

Any advice on where to start trouble shooting?

Many thanks,
Dave

 

[Hawkeye__8]

I had a similar issue where it mine seemed like it slipped into neutral and had to put it in 4H to drive it home. It ended up being the front drive shaft, it would also grind when I'd put it in park prior to it being replaced. Hope this helps.

 

[alrock]

Could be a few places to look, including transmission, transfer case, front diff, front prop shaft.

I'd test it by putting it in 4H Lock with engine off and see how it does. If the front diff isn't working properly, i.e. spinning freely, all power will go there in 4 high unlocked. If you lock it, you'll lock in power to the rear and be able to drive.

You could also have issues in the t-case or even see issues with the propshaft, usually marked by a blown CV at the aft end and grease everywhere.

How was the transmission fluid when you changed it - was the color still good?

When my transmission failed it was the fluid pump - when it got warm the transmission would seem like it was in neutral.

 

[650Hawk]

Your symptoms are EXACTLY what I went through with my wife's 06 Tahoe, including the gear grinding. The problem was the transfer case encoder motor (actuator), shifting the transfer case into neutral while driving. I have to ask, when you replaced it, did you replace it with OEM or aftermarket (Dorman, perhaps)? I replaced the one on the Tahoe 3 times; first 2 with Dorman, kept having the issue. Finally, was told by a trusted mechanic that the Chevy encoder motor is one of those parts that ONLY the OEM will do; aftermarket won't last. That was almost 5 years ago and the OEM replacement is still going strong. Just an thought.

 

[dscvdvr]

Thanks for the feed back.

When we serviced the transmission, the fluid was like new with minimal material on the magnet, only a fine layer of grey material.

When we replaced the actuator motor, I used a AC Delco (new)

 

[USMC_315]

My dad had an issue almost exactly like yours. As soon as the truck shifted into 3rd gear, it revved up just as you described. Luckily I was driving it on 95 pulling off on my exit after a 5 hr road trip. He took it to AAMCO and they told him (I forget the issue) that it needed a full rebuild. He ended up just buying a brand new transmission from a company in Texas that builds new trans. Entire cost to get it replaced was just over 1200 I think. Not bad for a brand new transmission

 

[dscvdvr]

I am beginning to think it is a transmission issue. I want to drive it some more this week and try to isolate it to transmission or transfer case. Its a real nuisance how random the issue is.

 

[650Hawk]

The fact that it can be "fixed" by operating the transfer case buttons hints that it's not the transmission, but rather the transfer case. With my wife's Tahoe, I actually took it to Chevy and had them diagnose it first; they said it was the trans. So I replaced the trans (not at the dealer) and on the way home from the shop it did the exact same thing again! As I said, it turned out to be the encoder motor for me, YMMV. Maybe you got a bad OEM one?

 

[dscvdvr]

I just wanted to post a quick update to this. We did replace the actuator motor with no results. This was followed by a transfer case rebuild. We found the plastic forks virtually worn thru and the bearings in very poor condition.
After replacing the transfer case we had the computer flashed and the actuator calibrated.
Same problem, in 4A it drops into "neutral", pressing 4H gets it going down the road.
We drove it with a diagnostic connected and it showed that the computer matched the dash switch light.
At this point everything is pointing to either the control module or the dash switch. It looks like I will do the transfer case module next and see what happens.

 

[Burtor]

I'm curious about what you said regarding having the actuator calibrated.
My understanding is that the transfer case actuator motor has set points that it goes to, and they are not adjustable.
On my 07 there are several wires going back from the actuator, two for the motor power, and four for the position signal.
At each shift position (4H, N, 4H-Lk, 4L-Lk) one each of the wires would be triggered to indicate it had reached that position.
The controller would simply drive the motor in a direction until the next expected position was reached. Well, not exactly that simply, the controller seems to also be checking for the correct winding resistance and encoder signal sequence to determine that the actuator was behaving as expected. It would also send a "pulsing" signal in between certain gears, I assume to help "bump" it into position.

Anyway, that's all immaterial as you as still having your issue, but I could suggest one further test;
Start in 4H (normal) mode, then unplug the encoder motor and try to reproduce the issue. I drove for many miles with mine disconnected and there was no shifting out of 4H. There's a pretty mean worm-gear reduction from the motor to the gear which turns the shaft and I don't think you could back-drive it if you wanted to. This could help you determine if the motor is being commanded into the wrong position by some haywire electronics, or if the problem is something else entirely.

Let us know if you learn something more!