Transmission (4L80E) First and Second Gear Only

[Cowracer]

Hi Tim,

My symptoms are a little different - no slamming etc. It drives normally but without reverse and won't shift into 3rd. It does sound like the sensors could be the culprit.

Did you have reverse?

Paul

Yeah, I did, now that you mention it...

Still and all, its probably a good thing to take them out and at least check them. I checked resisiance through both of them and found them vastly different. I cant remember what the resistance of the good unit was.

tim

[JohnC]

I'm voting with BobND. Reverse is purely mechanical, so no reverse is a mechanical problem.

First check for codes, but I'm betting you're in for some hard parts.

(sorry...)

[redbird2]

I would agree when we have one come in with no reverse we start by pulling the pan you will most likely find big pieces in the pan (NOT GOOD)

reverse mean hard parts failure it take comb of clutchs working togeather to make reverse.

I think its time for trip to trans shop or time to order a rebuild and install yourself, if it is a hard parts failure make sure you clean the lines out, I normally replace the coolers as there cheaper than the transmission to replace

good luck keep us posted

[danbenili]

Thanks for all the replies and suggestions. I now feel like I'm on a mission.

I pulled the valve body out today. Transmission is still in truck.

Tranny oil could use a change but still has a red appearance with no burnt smell. No metal chunks or slivers in pan, just small accumulation of "silt" on bottom of pan - gone with one wipe of the rag.

Everything looks clean, no junk in the passageways. Looking up through to other areas of the transmissions - the gears that I can see all look good - nothing missing - sharp distinct edges.

Looking at the "Powerflow Chart and Shift Solenoid Pattern". Looking at what reverse, 3rd and 4th(OD) have in common, is the "Direct Clutch"...

I'd like to rule out the "First and Second Gear Only" Condition outlined in the ATSG manual as it points to rule out electronic malfunction prior to pulling everything apart (aside from the 2-3 Shift valve - which I checked and didn't appear to be stuck - pulled the roll pin, slid it out-bounced it against spring).

I think the transmission electronics expect rpms on the input shaft before you can test, I tried with the system on, but engine offf and couldn't get voltages to change on solenoid's A and B.

Anybody have tips on testing the electronic inputs to the solenoids? I tested the solenoids by putting juice to them and they "click".

Thanks,

Paul

[BobND]

Be carefull randomly putting current to the tranny solenoids!

I'm not sure about the 4L80E, but MANY transmission solenoids have a diode built-in for voltage spike suppression, and if you power up the solenoid with reverse polarity, you'll blow the diode open, or short it out.

[Bnave95]

I would now be looking very close at the Trans. wire harness for any sign's of damage if you have checked out what Cowracer said.

[JohnC]

Have you checked for DTC codes?

Are you sure you have first? Default behavior is 2nd gear only, all solenoids off. If the PCM detects a solenoid fault during power up, it will default to 2nd gear only and set codes.