Transmission shifting a little wonky only in 4low!

[alia176]

This is a new development as of couple of months now. The transmission shifts perfectly normal in 4high, but in 4low, she tends to hang onto a gear a tad too long, then SUDDENLY, she shifts up. This is happening from 2nd to 3rd and 3rd to 4th.

I thought perhaps the throttle cable needs adjustment but wasn't sure if I should mess with it since she's shifting normally on 4hi. Figured I'd get some feedback before I check the throttle cable gap against the FSM.

Thanks.

 

[ajordan1975]

Is the power button on??

 

[alia176]

Is the power button on??

power button isn't on but for some reason, I thought in 4low, the TCU pretty much shifts the tranny as if the power button is on.

Good question though.

 

[Malleus]

I think the power circuit is disabled for 4LO and only the 2nd start function works.

What does your oil look like? I've had good success just changing nasty ATF when the age gets to be a concern. Eventually, it'll need clutches, if it's hanging in low range; that's where the torque load is the highest and where you'll see slippage first.

 

[alia176]

I think the power circuit is disabled for 4LO and only the 2nd start function works.

What does your oil look like? I've had good success just changing nasty ATF when the age gets to be a concern. Eventually, it'll need clutches, if it's hanging in low range; that's where the torque load is the highest and where you'll see slippage first.

I drain/refill on every oil change so my ATF is quite pristine!!

Again, this problem is more noticeable on 4low vs 4high, which is making me think the shifting logic changed. Maybe this is happening on 4hi but not as noticeable?

 

[Malleus]

I don't think there's a diffent shift panel for HI vs LO. I have to check.

 

[Comet]

I recall low gear violently putting me in my seat on every shift.

 

[-Spike-]

I don't think there's a diffent shift panel for HI vs LO. I have to check.

I believe that normally there is a different shift profile for 4low, but if he has OD in low (in the later model 80) then the sensor that tells the ECU that it's in low is probably disconnected or otherwise not functioning.

 

[ChaseTruck]

Check the connector on the transfer case.
We have ours disconnected - then you'll get the HI shift pattern in LO (a Tools R Us thing from back in the day...).
The '93 1-2 upshift with that connector plugged in is harsh, unplugged it's more bearable. Not so much of an issue on the '97. But on both it's nice to have overdrive available in LO.

 

[GeoEng]

See this thread: Making the ECT button useful - https://forum.ih8mud.com/threads/making-the-ect-button-useful.1118558/
I did this mod (shown in post #1) and made my shift points in 4low much softer. Its only for a 93-94. Post #31 talks about a similar mod on a 95-97. Cheers

 

[landtank]

There is a switch on the t-case that signals the ecu that you are in low. Mine was bad and only found it by checking it. There is 3 switches on the t-case and 2 of mine were bad. I changed all of them out.

 

[alia176]

I believe that normally there is a different shift profile for 4low, but if he has OD in low (in the later model 80) then the sensor that tells the ECU that it's in low is probably disconnected or otherwise not functioning.

Hmm, this is very interesting. I'm going to have a look today since the temperatures are going to be decent.

 

[80t0ylc]

Being a driver that for most of my life, I owned manual trannys in my vehicles, auto trannys frustrate me. My '94 has always shifted as you described in low range, @alia176 . My understanding is, like @-Spike- mentioned, the ECT shift points are active in low range, regardless of if ECT is selected or not. And my OD sensor must be non functional since OD is active on my '94 in low range. But that's fine with me, since when I'm towing my trailer off road, I'm often in low range. I once thought about doing the mod mentioned by @GeoEng , but realized it wouldn't help much functionally. I've gotten used to the "wonky" low range shifting.

 

[GeoEng]

The mod I did allows you to use the ECT shift points in low by pushing in the ECT button, just like you're in High. Cheers

 

[surfpig]

Being a driver that for most of my life, I owned manual trannys in my vehicles, auto trannys frustrate me. My '94 has always shifted as you described in low range, @alia176 . My understanding is, like @-Spike- mentioned, the ECT shift points are active in low range, regardless of if ECT is selected or not. And my OD sensor must be non functional since OD is active on my '94 in low range. But that's fine with me, since when I'm towing my trailer off road, I'm often in low range. I once thought about doing the mod mentioned by @GeoEng , but realized it wouldn't help much functionally. I've gotten used to the "wonky" low range shifting.

That's me. It's wonky, but mostly just between 1 & 2. Almost ten years with this auto tranny and I'm still learning how to use it.

 

[-Spike-]

And my OD sensor must be non functional since OD is active on my '94 in low range. But that's fine with me, since when I'm towing my trailer off road, I'm often in low range.

That is normal behavior prior to 1995, OD works in low range. On '95+ models, OD does not activate in low range.

 

[alia176]

That is normal behavior prior to 1995, OD works in low range. On '95+ models, OD does not activate in low range.

This is an interesting point, and I have heard this as well. However, in my case OD does in fact kick in four low, at least it used to! This always surprised my buddies.

 

[alia176]

Okay, I've been playing with this issue this morning. I pulled out the center diff lock limit switch which is on the nose of the transfer case, and it checked out pretty good. I would have expected complete continuity zero ohms when the switch is closed but it doesn't. It was something like xxx kohms.

I removed another switch from the rear of the Tcase and notice similar readings. After pushing the pins into both switches multiple times, the readings did improve a little bit. Still, not zero ohms when they are closed.

Unfortunately the switch from the rear is not compatible in the front position due to the slightly different plug connections. It's no biggie but I was really curious.

Now onto a more important issue, and that would be the sound of the CDL motor. She don't sound happy . When the CDL motor disengages, unhappy sounds emerge. Here, take a listen. New video by A. Ali - https://photos.app.goo.gl/dRWnf3tUBp2YQY6R8

I can totally rebuild the motor or replace it with another one, but breaking that FIPG sealant is a royal PITA, I tell you what! I haven't put MAPP gas heat to it just yet but may have to slowly head that direction

 

[alia176]

Couple of questions. My '94 FSM shows the TCM behind DS kick panel. I went through the thread you referenced and seems like you did the mod and commented it was easy. Was this where you found the module? Also, OP of that thread said the pins modified were on connector 'B'. The schematics in the back of my FSM show the pins to be in connector 'C'. Looks like according to the schematic pic of the connectors, there's 2 connectors - 'C' and 'D' that plug into the bottom of the TCM. The larger 22 pin connector 'C', and a smaller 12 pin connector 'D'. Does this sound like the same animal you did the mod on?
Edit: This is a pic of the TCM connector pinouts in my FSM
View attachment 3218247

Do you mind taking this out of my thread and perhaps use PMs?

 

[80t0ylc]

Do you mind taking this out of my thread and perhaps use PMs?

Sure. I was thinking you might also benefit from it. But if that's what you want, its gone!