How do I know what Tranny I have???

I have a 94 C1500 with the 4.3 engine and Im trying to figure out why at 55mph and higher it constantly wants to kick down into passing gear to maintain speed. I looked in my Haynes manual and it said something about a TV adjustment, but its only on 2 types of trannys, so then I noticed mine doesnt have that cable, and now Im trying to figure out what tranny I have so I know whether I need it or need to figure something else out. Does anyone know how I can figure out what tranny I do have? Thanks much.

A 94 with a 4.3 should have a 4L60E. The shape of the pan should be a square (or pretty close to a square).

Most likely, you are having TCC lockup issues caused by valve body wear. One way to test this is apply enough pressure on the brake pedal to make the brake lights come on but not enough to slow you down. This will cause the TCC not to lockup. If the problem stops, the valve body needs to be removed and repaired. Usually the TCC apply valve or TCC regulator valve is the problem.

//2000CAYukon

Is the 4L60E different from the 4L60? What is the TCC and can you tell me where abouts I can locate it on the tranny? Thanks for such a quick response.

And...My Haynes manual says on the "4L60" (No "E") that mine should have this Throttle Valve (TV) Cable. Is this something I should get and have on it anyway?

Is the 4L60E different from the 4L60? What is the TCC and can you tell me where abouts I can locate it on the tranny? Thanks for such a quick response.

The E stands for Electronic and all shifting is controlled by the PCM (Power Control Module). The 4L60E does not need a TV cable since the shifting is controlled electronically.

If you really have a 4L60, it could not work without a TV cable so I doubt you have a 4L60.

TCC is Torque Converter Clutch. When locked, the input of the Torque Converter is locked to the Output of the Torque Converter (i.e. no slipping). This was introduced to get better fuel economy. Without TCC lockup, there is normally some slipping of the Torque Converter.

When the TCC locks up, RPMs will drop 300-400 RPMs. To some this can feel like a gear shift.

//2000CAYukon

So if this TCC Valve or regulator is the problem, where is it located if I need to have it repaired or replaced. Have you done this? Is it a DIY job, or does it need to be done at a tranny garage?

So if this TCC Valve or regulator is the problem, where is it located if I need to have it repaired or replaced. Have you done this? Is it a DIY job, or does it need to be done at a tranny garage?

The solenoid is inside the transmission. It's under (above) the pan, ahead of the valve body and plugged into the front pump. You can replace it yourself if you're so inclined, but keep in mind that the 4L60E has a few solenoids in it. The TCC solenoid is usually the largest one in there. It's also of 'open frame' construction, meaning you can see the wire coil.

Replacing this is not likely to solve your problem though. How hard to you have to get on the gas to get it to maintain freeway speed?

When say going down a highway at 55-60 mph it will take it about 15 seconds to drop from 60 to 55 then maybe 15 more to drop to 50 mph. Once there, I can press the gas 1/2 way (Not down far enough to get the true passing gear) to get it to downshift like out of OD and then it will slowly build the speed back up. If I kick it into passing gear, it revs the rpm's up so high it sounds like its going to blow up. The tranny has no problem getting up to 60+ mph, just maintaining it.

I would suggest you have this scanned on a trans function scanner to check for slippage errors and solenoid functions, sounds like you may have lost one gear function here. Keep in mind poor engine performance issues can create the same symptoms, ie: low fuel pressure or blocked cat.

How does your truck drive when you leave it in D, and not OD? I drive in a somewhat hilly area at times so I leave my trans in D, and don't go to OD until it flattens out. My truck is a 350 though. If your truck had a TV cable out of adjustment you'd know it before you ever got to 60 mph, believe me. I doubt it has anything to do with an adjustment like that. It sounds to me like that 4.3 is straining under a load more than anything. That's my possible take on the matter, anyway.

I'm with Maxwedge on this - get that thing scanned to see any problems that might exist.

If I was to give a SWAG*, it would be slippage on the 2-4 band, either wear or a problem with the 2-4 servo assembly. When was the last time you took the pan off, and if you did, did you use RTV sealant (silicone, The Right Stuff etc) on the pan? There is a drain-back hole drilled into the pan rail under the 2-4 servo, and RTV can plug this hole, leading to issues with the 2-4 system on up to and including a burned band and warped drum.

* SWAG - a military term, meaning Scientific Wild Ass Guess.

The truck drives fine in either OD or 3, in 3 it just runs a little higher RPM's. This is all happening on straight roads, no hills or curves to speak of. I hate to take it to any of our tranny places around here as theyve been known to tell people stuff that isnt the problem. I was hoping it would be something I could fix myself.

Back back to the engine performance issue if this only happens under a load. That said, at no point should any trans down and " race" and go nowhere.

Truck has no cat converter, so I know its not that, and the engine seems to run great. If it was a engine problem, Im not sure where to start to see what it would be that would cause this.

You mentioned that it tends to 'go into passing gear' when it's in OD under load at freeway speeds. You also said that it wraps the engine up when you deliberately hit passing gear. Due to the propensity of the transmission to shift into 2nd during passing on highways, and it doesn't stay consistent under load at freeway speeds, this tends to tell me two things:

1. In passing gear, your transmission is slipping something fierce.
2. In OD, your transmission isn't downshifting, it's slipping.

That's why I stick by my diagnosis of a malfunctioning 2-4 band and related hardware.