Tow truck tranny issues, back again

[Kirk Morgan]

As a last thing to do you could get a stand alone controller for the transmission.

[BTR69]

Originally Posted by Kirk Morgan

As a last thing to do you could get a stand alone controller for the transmission.

Thanks. I've heard about this recently, but don't know anything about them. I'll be googling it tonight.. Haven't been able to make time for the truck recently. Tomorrow is looking good for me getting time to get back on it. Going to check out the speed sensor on the case that missed earlier on.

[Alan Roehrich]

Originally Posted by BTR69

Thanks. I've heard about this recently, but don't know anything about them. I'll be googling it tonight.. Haven't been able to make time for the truck recently. Tomorrow is looking good for me getting time to get back on it. Going to check out the speed sensor on the case that missed earlier on.

Why was it rebuilt to begin with?


Those are pretty reliable, I don't seem to have too much trouble with them. But then they get the Sonnax fixes, the Alto frictions, and a Superior valve body kit. That tends to eliminate further problems.


Order yourself the ATSG manual for the 4L80E. If you're going to work on it, you'll find that to be indispensable.

[BTR69]

Originally Posted by Alan Roehrich

Why was it rebuilt to begin with?


Those are pretty reliable, I don't seem to have too much trouble with them. But then they get the Sonnax fixes, the Alto frictions, and a Superior valve body kit. That tends to eliminate further problems.


Order yourself the ATSG manual for the 4L80E. If you're going to work on it, you'll find that to be indispensable.

After swapping out several parts that "could" cause it to go through 1-2 shift, then on 2-3 shift, it still falls back to low gear. Tranny shop I took it to has taken good care of me in the past and has a great reputation around here. The only thing left that they came up with was a rebuild. They did find a couple of internal issues that would end up causing me more grief and fixed those. I remember one having to do with a part that had been machined with too much tolerance from a prior rebuild. I'm taking their word on that. I know they upgraded it with the Sonnax parts. They kept it for a while troubleshooting and feel the ECU may be the problem. If I can find one in the junkyard, I may grab it, but have been told I'll likely need it flashed. The only other things that I can think of that haven't been changed out are the input speed sensor and neutral safety switch. Unless they did those and I'm not aware of it. Swapping those out tomorrow. If it doesn't work out, I'll look into the stand alone tranny controller. Looked them up this evening and seems like a viable option.

[Jeff Stout]

Input speed sensor sounds very promising

[Alan Roehrich]

A stand alone TCU is a waste. There's no reason to need one or go through the hassle.The stock stuff works fine, there's several million dollars worth of R&D behind them for reliability. Adding some stand alone controller requires more wiring harness and adapting/interfacing that just adds complexity, and does not guarantee a solution.



It's more likely to be a wiring harness problem than an ECU. The wiring diagram for your truck can be found online, probably for free.



There are two ATSG manuals that are good for that transmission, one is a dedicated rebuild manual, the other is a manual that covers it and the 4L60E, and includes the electronic/electrical diagnosis.

[BTR69]

Originally Posted by Alan Roehrich

A stand alone TCU is a waste. There's no reason to need one or go through the hassle.The stock stuff works fine, there's several million dollars worth of R&D behind them for reliability. Adding some stand alone controller requires more wiring harness and adapting/interfacing that just adds complexity, and does not guarantee a solution.



It's more likely to be a wiring harness problem than an ECU. The wiring diagram for your truck can be found online, probably for free.



There are two ATSG manuals that are good for that transmission, one is a dedicated rebuild manual, the other is a manual that covers it and the 4L60E, and includes the electronic/electrical diagnosis.

You make a great point on the TCU. I'll research the manuals you've referenced. Waiting on rain to pass here so I can get back under it and swap the input speed sensor. Thinking about swapping the neutral safety switch as well. I found a new one yesterday that had been picked up for another truck that has been sold. Nice to find stuff I had long forgotten about. As long as it's the same part from 95 to 98 anyways. I'm optimistic. I'll pull up wiring diagrams as well. Thanks for the info.

[Mark Ruset]

i was a GM service manager for many years, when we would see problems like this we usually found that the pin tension on the harness was not adequate for a proper connection. It is very important that you probe the terminals with the proper pin connectors, if someone used a test light or an ohm meter to check for continuity than they may have spread the terminals just enough to make for a poor connection. Make sure your shop has the proper tools to diagnosis this concern.

[BTR69]

Originally Posted by Mark Ruset

i was a GM service manager for many years, when we would see problems like this we usually found that the pin tension on the harness was not adequate for a proper connection. It is very important that you probe the terminals with the proper pin connectors, if someone used a test light or an ohm meter to check for continuity than they may have spread the terminals just enough to make for a poor connection. Make sure your shop has the proper tools to diagnosis this concern.

I'll certainly keep this in mind. Thanks.