Tranny not Engaging - 1995 TLC

[Polar_Pile]

I've done some researching on the IH8Mud threads, but don't have a clear answer on this problem:

My 95 TLC will occasionally not downshift at a stop sign or stop light, so when you hit the gas to go again, the engine revs as if in neutral. The rev'ing is only temporary as the tranny will then quickly engage and you can go again. When it engages, it doesn't bang or thunk more than expected, but the failure to successfully downshift is my very large concern.

I have seen threads on adjusting the Transmission cable (kick-down cable?). I plan on playing with this a bit, but would like some opinions from you weathered TLC owners.

 

[Pin_Head]

Do you have stripped drive plate splines? Try locking the center differential and see if the problem goes away.

 

[Polar_Pile]

As far as I know, the only way to engage the center diff lock is to go to Low Range. I have never experienced the problem in low range, yet can cause the problem at will (almost) in high range (normal driving) by not coming to a complete stop, but rolling and hitting the gas again. Do you still think stripped drive plate splines may be the culprit?

 

[scottm]

You can engage it in low, then prevent it from disengaging when you switch to high by pulling the "diff" fuse in the fuse box on the lower left of your dash. I wouldn't drive around like that on pavement, but it might help troubleshoot. Sounds like a stripped drive spline, pretty cheap and easy fix.

 

[scottm]

79,000 miles? Seriously? Your truck is toast, I'll come get it with a flatbed.

 

[Polar_Pile]

79K was 5 years ago. It just turned 100K this month - and it broke my heart. I absolutely love it - has served extremely well on some rough elk hunts - and still takes my wife and kids all over the place. If you show up with a flatbed, you will have to go through my wife first

 

[Pin_Head]

Do you still think stripped drive plate splines may be the culprit?

Yes.
If it doesn't do it with the center diff locked (low range) then one of the wheels is disconnected from the drive train. The most common reason would be a stripped drive plate, but it could also be stripped birfield or axle splines or other even less common possibilities. Jack up one wheel at a time and see if you can spin it.

 

[Polar_Pile]

I appreciate the responses. I haven't had time to 'test' per your recommendations, but will this week. Just a couple of questions:

1. If the drive plate splines are stipped, why would it not happen every time? I can get it to do it most of the time, but not always
2. If the drive plate splines are stripped, why would it engage at all and not just spin as if in neutral?
3. Also, why would it never happen going from park to drive and taking off? It is always from a down-shifting perspective
4. And finally - since I'm not a 'real' mechanic - where is this drive plate and what is its real name? I don't mind doing my own work - I just need a bit more direction before I dive in.

 

[Hilux]

Somebody donate me a video camera, and I'll make the easiest to understand "how AWD works" video that has ever been made...

 

[scottm]

If you pop the plastic center cap off a front wheel, you'll see the end of the axle. It passes through a splined hole in the drive plate, which is bolted to the outer hub. If you take the wheel off, you'll see the nuts in a ring around that plate. It's pretty easy to take off from there. After loosening the nuts, whack the drive plate edge adjacent to each stud 'till the cone washers pop loose, then take the nuts, washers, and drive plate off.

If the plate is stripped, you'll see the axle turning in the stripped hole. Yours might not be completely stripped, just getting there. Or you may have a transmission problem, or something else, but this is the easiest and cheapest possibility, and it's pretty common.

 

[Hilux]

Exactly what scottm says... but the Viscus Coupler will render that test (somewhat) ineffective.


two things will propel you even if your drive flanges are stripped. The VC and the TC locked in low range.

A slight 3 is what scott is saying. Not yet totally stripped splines in the drive flanges.

I would show you an AWD vid, where I can explain that ice and a stripped drive flange have THE SAME EFFECT on a differential... But all the ones I found are complex b/c they have traction control or some play on words name, or marketing term... just like "full time 4WD" of which there is no such thing.

AWD and 4WD are COMPLETELY different.

A drive flange.

 

[Polar_Pile]

Thanks for the detail, scottm. For this theory to hold, wouldn't both the front and rear axles have to be spinning in all 4 stripped plates since the cruiser acts like it is in neutral (no wheel is engaging)?

 

[scottm]

With all three diffs unlocked, any one wheel on ice or stripped will stop you. Locking the diffs will get you going.

Just found this pic, similar to already posted but the hammer idea. Note the lugnuts protecting the lug studs from my poor aim. An easy side-of-the-road repair, last I heard these drive plates were under $100.

 

[Polar_Pile]

Thanks for your patience, scottm and Hilux. You're finally getting it through my thick skull!

Why would it eventually engage after a brief spin in what feels like neutral (axle spinning in a stripped spline)? And it only happens when the cruiser is slowing down (downshifting), then trying to go again.

I'm slowly connecting the dots here.... but definitely catching on.

 

[scottm]

Why would it eventually engage after a brief spin in what feels like neutral (axle spinning in a stripped spline)? And it only happens when the cruiser is slowing down (downshifting), then trying to go again.

Yeah, that part, I dunno. We're still in the random guessing part of the problem solving matrix I guess.

 

[Ebag333]

Why would it eventually engage after a brief spin in what feels like neutral (axle spinning in a stripped spline)? And it only happens when the cruiser is slowing down (downshifting), then trying to go again.

Viscous coupler, perhaps?

The VC acts somewhat like a limited slip in the center diff. If your front and rear drive shafts are spinning at different speeds, it will lock up and cause them to spin at the same speed.

In your case, stripped spline in the front causes all the power to go to that one wheel. The VC engages because the front DS is spinning and the rear DS is not. Half of the power goes to each DS, and you're back underway.

 

[Polar_Pile]

Scottm and Hilux, either way I appreciate the explanations and the pics. This is something I can check easily this weeked.

If anybody else has some ideas, I would welcome them. I think there are some pieces of the puzzle that make me think tranny, still.

 

[Polar_Pile]

That is a good explanation, ebag333. I will check the splines this weekend.

 

[Pin_Head]

Why would it eventually engage after a brief spin in what feels like neutral (axle spinning in a stripped spline)? I'm slowly connecting the dots here.... but definitely catching on.

Sorry, I assumed you knew about the viscous coupler, but that is what it does: engages after a brief spin. After it cools down a bit it will slip again. It is better to fix this rather than relying on your VC as it could overheat and sieze.

 

[Hilux]

here's something to paroose through... Because you can't understand a VC without 1st understanding AWD.

This owner thought he had full time 4WD so he thought he could just add manual hubs and drive in 2WD... And save some gas.

Keeping in mind unlocking manual hubs has the same effect as stripped out flanges on the front axle. It's still disconnecting somewhere.... Unlocking a hub, a stripped flange... spinning a tire on ice or any other loose surface... all has the same effect on a differential. It will cause power to be lost on that side.

lock out hubs