TLDR:
Symptoms: torque converter locking and unlocking randomly. And then later unable to hold gear. Transmission will successfully advance from first only under no load. With any load it will drop back to first but keep trying (unsuccessfully) to shift to correct gear.

Hello! So I will give some quick backstory - Bought used. Has an aftermarket trans cooler probably about 14" x 8" x 2" thick. Everything was good. After 2 winters the transmission started acting weird. It would buck (torque converter lock/unlock randomly) At about 40 mph on short trips but if I gave her time to warm all the way up it would go away. At one point it got so annoying that I cut the torque converter lock wire coming out of the tcm and installed a switch so I could control when it had the ability to lock. The switch had 3 settings (Lock - torque converter wire to GROUND, Unlock - torque converter wire floating, Trans - torque converter wire to tcm) I ran with an open converter on surface streets and locked her on the highway. It was annoying at first but then it was second nature. At one point the physical switch wore out so I just crimped the wire back together while my new switch was on order and volia my bucking problem was gone. Almost like hard locking/unlocking cleaned out the solenoid because that halfway pwm **** probably rarely got the poor little plunger moving. Anyway about a year after that the bucking started coming back but I didn't worry too much about it.

One day shortly after the wife and I were on our way back from Dennys when all of a sudden the transmission went from 3rd gear all the way back to first without warning. We slowed down for a stoplight and when trying to speed back up it would try to shift out of 1st but it would just slip back down whenever there was any load applied. 1st gear can get you going pretty fast in that sucker so I would get up to 40mph and then it would shift down like it was in 3rd but as soon as I gave it any gas it slipped back to first. The car has been parked for a while since then because no money to fix it but recently I took it for a drive to see the status. I wanted to see if temperature affected anything so I started early in the morning. Temp outside was around 35f. She started right up and drove like normal shifting through all the gears fine for about 10 minutes but as soon as she was a little warmed up (trans temp read 85f) it started acting the same as before. Couldn't hold a gear.

So that brings us to now. I have her up on my lift ready to do whatever I need to do to her. But I am not sure what the best course of action is. The way I see it I have 2 options.

1) Rebuild

• Theres a shop down the road from me that has quoted me $1800 for the rebuild. He has alot of guys making above stock power going to him and he is willing to work with them so that says something.

2) New transmission

• Detroit transmission has 4t65ehd listed for $1600. I messaged them and they said that every tranny is built to vin. Afaik I am making stock power so that shouldn't be a problem. they also offer a 3 year warranty.

If it were as easy as just taking the tranny apart and changing out some solenoids I would go for it but I have never been inside one of these and I don't know what I am getting into and looking at the rebuild manuals I get only a couple pages in and they are already using words I don't understand and have mentioned like 16 bajillion special tools that you need.

I know pretty much every option has me removing the transmission so in the meantime I will work on getting her out.

What do yall suggest? Does the issue sound like something mechanical or something on the control side? Would you have the shop rebuild it or would you just go for the ebay swap in?

 

Not sure what your preference is. I just wound up going with a junkyard one and will finally add a cooler, after mine basically died the same way at 142k. It's in the garage now to pull for engine gaskets and the swap. I'd probably go for the guy doing the rebuild over the generic shop response, but there might be other info that'd sway me the other way. Good luck.

 

4T80e

its not a true bolt in, but it will last once setup properly

 

My 2 cents is that $1800 for a trans rebuild sounds too cheap in order to guarantee that ALL the available upgrades to the 4t65 will be addressed... doing so at least would significantly minimize the chance of this happening to you next time. Milzy's alone offers one part for $2000... a 1" chain upgrade selectable in 1 of 3 available final drive ratios. So... $1800 to me sounds like at least something will be omitted assuming you are trying to create a long term car. You should floor this car at least 65% of the time you are driving as a rule. But sad news... You sound like you are having a serious failure right now, and, thus you should decide whether you are either all in, or not. Not sure who Detroit Transmission is, but $5000 would likely get you a transmission upgrade you could at least brag about at car shows. That's the minimum target budget for a rebuild imo plus you have to get the thing in and out of the car too that's costly. $5000 should be more than enough though I would think.