4l80e Advice

[udidwht]

Crawl underneath and look carefully at the trans connector. Do you see any red fluid? You shouldn't. If so, the internal wire harness will needs replacing. Easy job (drop pan for replacement). There are milliamp volts flowing thru the connector any fluid in it will short it. If you do replace the connector you may as well replace the A & B solenoid valves as well. And turn the force actuator valve 1/2 turn up (clockwise).

The TPS (Throttle position sensor) is also tied to trans shifting issue as is the brake switch and ignition switch at base of steering column.

 

[DTrain]

Yeah, I’ll get under there and take a look. I was wondering how long it’d be till I’d have to take the cover off and take a look. This truck is going to be a trail truck, I’d like to do a manual shift on it. Might get all my ducks in a row for that before I drop the pan

 

[DTrain]

I haven’t gotten under the truck to look around too much. But I do have a new discovery. When I come to a quick stop, the truck will also stall then. Same issue as the reverse situation?

 

[Schurkey]

I don't think you have a trans problem. I think you have a "doesn't run properly" problem.

I'd connect a scan tool, look at the data stream. Also test fuel pressure, and the usual tune-up items--cap, rotor, plug wires, plugs, filters, distributor offset. I bet you'll find problems with the IAC, TPS, or some other sub-system that leads to an unsteady idle resulting in stalling.

 

[DTrain]

So I hoped under the truck today. Decided to eliminate the oil cooler lines, they were a mess. Sprayed some degreaser and hosed down the engine bay and under the truck to clear things up a little and start from new on the residues. Definitely had residual from the oil leak, but the trans itself looked good. I do have a leak in the transfer case somewhere that has some wires pretty wet. I’ll let my work today dry up and hop under again. The leak I found at the transfer case is right where a skid plate needs to come off.

 

[DTrain]

I did do plugs, wires, cap and rotor tight after I bought it

 

[DTrain]

I do need to hook up a scan tool I guess

 

[stutaeng]

Ditto on the scan tool. You have to make sure it's not some other engine sensor causing problems. Do you have any CEL code on your dash?

I've watched some 4L80e rebuild videos and there's actually not a lot that seems to wear out on these units. Seems like it's mostly the bushings that wear!

The reverse servo going out and the boost valve getting stuck are known problems. Apparently, if the boost valve gets stuck the pump is capable of generating fluid pressures of up to 600 psi, which can break things. I believe the Sonax kit has a way to mitigate this; there's hole that is drilled on the valve body for this.

Probably need to take it to a shop for proper diagnosing. At the minimum, a line pressure check is required (by a shop or yourself.) May want to read through this: https://www.sonnax.com/tech_resources/88-diagnosing-the-elusive-no-reverse-with-the-4l80-e

 

[DTrain]

I took the truck to a transmission shop down the road, which I know nothing about, I just tried because they were pretty much walking distance. He told me, through his front desk girl it needed rebuilding, but it didn’t look like it even moved from when I dropped it off. So I took that with a grain of salt.

Then I left it with a general purpose, all around mechanic I take stuff to and he said he thought the tranny seemed fine.

What the heck right?

It had just enough other stuff going on with it, that I just went ahead and traded it on another NV4500 truck.

 

[DTrain]

Which is originally what I would’ve preferred anyhow.