Is my transmission about to...

...crap the bed?

2001 GMC Sonoma, 4.3 4x4 Auto, 153k miles. Fluid is still somewhat red, doesn't smell burnt.

On mild acceleration, 1st will hang around 3,000 rpm, then shift HARD into 2nd. 2nd to 3rd seems fine. The part that really concerns me, though, is that it won't go into 4th/OD, unless I let off the accelerator. As soon as I apply even the slightest pressure, it downshifts to 3rd, even at 75-80 mph.

Do I just need a fluid flush and fill and new filter, or am I looking at bigger problems?

I may pick up a used transmission, to do a rebuild, in preparation for a V8 swap (383, maybe?). 8)

That is the expected lifespan on a 4L60E.... It just is tired and needs a rebuild. I may have 170k on the one in the Avalanche, but I've done tricks to it to make it live longer.

If it were an AOD I'd say your T/V cable was too tight.

I'm not too familiar with the workings of the 4L60E but I would assume there's a servo or sensor that controls line pressure and shift rpm, and it's on the fritz. Might need a code reader and/or reflash.

In that small of a vehicle and with that mild of an engine I would have assumed the trans would last a lot longer than that unless there has been a lot of maximum capacity towing.

In reply to The_Jed:

They reduce the number of clutches for the "reduced" power and capacity, but same hard parts.

My ex-wifes acted like that as well. The lockup converter was slipping in OD so the ecu raises the line pressure causing the hard 1-2 shift and it did delay going into OD as well. I did get a check engine light after a while, but forgot the code. A trans service seemed to help a little bit. We divorced before it got any worse so I don't know what was the outcome.

In reply to Ranger50:

I thought a 4L60E was a 4L60E, no matter what it was behind, with the exception of the Corvette (hence the popular "Corvette servo upgrade").

I've only had this truck for eight months, putting about 3k on it. I don't know the history of its towing life, but it does have a hitch.

I had the same issues with the 4L60E in my van. Scroll to the bottom of page 1 of my build thread for how I fixed it: http://grassrootsmotorsports.com/forum/build-projects-and-project-cars/lets-go-on-safari-1998-gmc-safari/86217/page1/

In reply to 81cpcamaro:

I have been getting periodic SES light, but haven't scanned it yet. I'll do that this afternoon.

In reply to RealMiniDriver:

Dollars to donuts it's code 1870

In reply to bgkast:

I forgot I had my scanner in the truck. I have two codes - 0751 and 0756. Solenoid A and Solenoid B, respectively.

Hmm, new solenoids came on the re-built valve body I installed. Might be worth a call to Ken at that link in my build thread. He seemed to know quite a bit about these GM transmissions.

when in doubt, change the fluid and filter.

That's about the mileage 4L60s E36 M3 themselves. Sorry.