I experience an intermittent issue in 4wd only when reversing.

The first time this happened was this past May on a beach. I was slightly stuck but had been cruising very leisurely putting very little strain on the drivetrain. To get out of this hole I put it in reverse and gave it gentle gas. It seemed to not send power to the wheels and came with a sound that reminded me of gears slipping - perhaps not fully engaging.

It’s happened several more times since then. It only happens in 4wd and seems to be when I shift to reverse during a low traction situation. Today it was when backing up in a snow bank, another time it was when turning around on a trail.

It won’t happen in the middle of reversing. I will shift into reverse and it just won’t reverse at all and instead will rev and whine. If I shift to drive then back to reverse it will sometimes work or sometimes I will have to repeat that process.

I’ve tried searching around but can’t find any similar cases. I really hope it’s not transmission related. Since it’s only in 4wd it seems like it may be related to the front diff.

I don’t know enough about the inner workings though to know if a certain issue would only crop up sometimes in 4wd and only in reverse.

Appreciate any advice as always.


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That's really strange. My thinking on this is it's not likely to be the front differential. I would think a bound/binding front differential would cause too much strain on the transfer case and the transfer case would fail. I would try removing the front driveshaft and trying to reverse in 4wd in similar conditions and see what happens. If it still does it with the front driveshaft removed then that would eliminate the front diff.

Sounds like the tranny isn’t fully engaging reverse.
Does this happen when shifting into 4 wheel and reverse at the same time, or were you already in 4 wheel previously?

What year, auto I assume, ect...

It only happens in 4wd and has happened when I'm in 4wd for hours and shift to reverse, or if I just shift into 4wd then shift to reverse.

It's a 97' 3.4l auto with e-locker.

For some reason I didn't even think about the transfer case here. Does the transfer case reverse directions when you go in reverse as well? Would there be anything inside there that would uniquely slip in 4wd reverse?

Its always good to check the atf level also for burnt smell and color. If it only does it in 4x4 lo then transfer case not engaging in reverse . Could also be the shift solonoid going bad. Transmission pump not building enough pressure. when was the last time atf was replaced? sometimes just replacing atf will solve a bunch of issues.

Do you have any idea if the rear wheels are spinning and the fronts not turning during this event?

You say its only "low traction 4x4". Does it never do it in 2x and never in 4x4 when there is good traction?

I haven't wrapped my head around why reverse and 4 low. Maybe its a "only under heavy load" thing.

Are your shift lever bushings and shift linkage in good shape? Maybe your linkage isn't fully shifting it into reverse all the time?

It might be something simple, or not, but I suspect you need to get it fixed or you'll tear something expensive up if it isn't already.

Did a Transmission flush when I got it back around May/June 2017 (20k miles). Last checked fluid 2 months ago and the color is good, smells new.

That’s a good point though on 4WD vs under load. I have not specifically tested it in 2WD under load - I’ll try standing on the brake this weekend in 2WD reverse.

Re: Linkage - I’ve never checked it. I have not noticed any problems shifting into or using reverse in 2WD.

That said, the shift to reverse is not instantaneous - there is probably a 1/4 second delay. I do know that if I shift to reverse and give it gas immediately then it will slip briefly (no sound though) and then catch. This has only happened once or twice since I try to be very careful and let the transmission engage in reverse before giving it gas.

I will do some homework there and see if there are some things I can troubleshoot.

I think the first step is just recreating this reliably and figuring out if this causes just the front wheels not to turn, or all of the wheels not to turn. I will see if I can figure that out and make a video this weekend.


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If its never had the tranny filter replaced and the magnets/pan cleaned that wouldn't be a bad thing. At the same time you could inspect for metal shavings.

Its delayed going into reverse but is doesn't slip or hard shift into any other gears, and doesn't not shift up into second until higher rpms or several hundred yards when cold?

The tranny pan has been off before, not by me though. I can tell because there's red RTV globbed all over the place.

It shifts pretty well across all gears as far as I can tell and does not slip under any driving conditions that I've noticed.

Your last sentence is true for me - it does not shift into second until higher RPMs when cold. I read somewhere else here that that is normal - is it not? Is that indicative of a clogged or semi-clogged filter?

I wouldn't describe a noticeable increase in RPM and/or time to shift to second when cold as normal.
Pretty easy to find out about the filter. Drop the pan, clean the magnets and pan, replace the filter, and fill it up with Valvoline Max life, and see what she does.
You might try some Lucas Stop slip in it if the filter and fluid change don't help.

I don't know that any of that would be related to your reverse in 4x4 issue.
Might be worth a shot if your not just going to take it to a shop and have it gone through.

I don't think this is a transmission issue. It sounds like an ABS problem. You have a wheel speed sensor going bad, dirty, or not seated properly (usually due to rust). The grinding gears you are noticing is the ABS kicking in, because a sensor is erroneously indicating one wheel skidding

Strong theory there! The ABS sensor on the front passenger wheel is broken and my ABS light has been on for about 1.5 yrs. it looks like the PO broke the wire at the point where it enters the brake and had electrical taped it up.

I’ll see if I can pick up a sensor/wire from the dealership when I go to pick up a new trans filter.

I wonder why it would only happen in reverse? I’ve done a decent amount of wheeling with the ABS light on and never had this in occur in drive.

I will also say that it’s more of a screeching sound than gears grinding (there’s no click to it).

Edit - did some more research into what the ABS may sound like, it does NOT sound like this YouTube





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I wouldn’t expect the ABS to do anything when not applying the brakes.
I spin tires frequently and haven’t had the ABS activate when brakes weren’t applied.
But, my ABS is operating normally.

It was a nice theory.. And the ABS can absolutely activate when your foot isn't on the brakes. However, if you have a broken sensor wire and the ABS light is on, your ABS is deactivated. So, your problem is not ABS related. At least not this problem

Okay I did some more testing.

First - I was mistaken, it shifts from 1st to 2nd fine when cold, I just didn’t notice because it was so subtle.

So I went to a field and confirmed this happens in 2WD as well. I held the brake and gave it gas in reverse - here are 2 vids where you can hear the screech. Before the first screech there was a definite clunk.

Here at about :12

YouTube

And here at about :22

YouTube


Another thing that happens occasionally is when backing up for the first drive of the day I’ll get a squeak that comes from I think the pinion bearing area of the rear diff. I’ll inject some grease in the little gap where the driveshaft connects to the rear diff and that quiets it down for a month or so.

I think this may be related to the pinion bearing or rear driveshaft u joint related. I did try to grease the rear u joint about a year ago but one of the zerks was seized up and I couldn’t get it loose. Probably about due to swap it out.

Does this sound like a u joint to you?


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