700R4 won’t stay in overdrive

[LukeDM]

Howdy all. I have a 91 suburban with a 700R4 transmission that i have a few problems with. Also it may be designated as a 4L60, not positive about that.

My main problem is that it won’t stay in overdrive once it warms up. After about 20 miles of highway driving, i can ease off the throttle and get it to shift into OD but any acceleration kicks it back down into third. I know it’s not a lockup issue because i can shift into D and it doesn’t change my RPMs. My transmission fluid level is correct and I’ve adjusted my TV cable. It works flawlessly until it gets up to temp. I’m beginning to wonder if my 3-4 clutches are damaged or burnt.

It also doesn’t stall correctly and wants to lurch while sitting at a stop light, but I suspect this isn’t connected to the OD problem.

Reverse seems very weak but I’m wondering if that’s not just how this transmission is. It doesn’t slip but you have to give it more throttle to get going than I’m used to.

Any thoughts? I’m tossing around just having it rebuilt but it would be nice if it was a simple problem. Also, if I do have it rebuilt, are there any upgrades you’d recommend? Not racing but I’d like to tow 3-4,000 lbs with confidence. Thanks!

 

[NickTransmissions]

You're correct. The 3-4 clutch is going out. Drop the pan to confirm (and to drain the fluid) . If you see burnt clutch material, put the pan back on with a few bolts and yank it out for overhaul. Install a new torque converter as well.

Upgrades for towing include:

- Transgo Jr shift kit
- Corvette servo
- Wide 2-4 band
- New reverse input drum
- Sonnax TV plunger and sleeve kit
- .472 or .500 boost valve / .300 reverse boost valve
- drill the spacer plate per Transgo's instructions

I have a 700R4 info thread with more details -link is in my sig line

 

[LukeDM]

You're correct. The 3-4 clutch is going out. Drop the pan to confirm (and to drain the fluid) . If you see burnt clutch material, put the pan back on with a few bolts and yank it out for overhaul. Install a new torque converter as well.

Upgrades for towing include:

- Transgo Jr shift kit
- Corvette servo
- Wide 2-4 band
- New reverse input drum
- Sonnax TV plunger and sleeve kit
- .472 or .500 boost valve / .300 reverse boost valve
- drill the spacer plate per Transgo's instructions

I have a 700R4 info thread with more details -link is in my sig line

That’s fantastic information, thanks for the fast reply. I’ll be reading through your thread. I’ve seen some people recommending to install additional 3-4 clutches, do you think that’s worthwhile or even viable?
I’ve also considered installing a larger intercooler, is that worthwhile for normal driving and light towing? I won’t be hooking it to anything heavy, I have other vehicles for that.

 

[NickTransmissions]

That’s fantastic information, thanks for the fast reply. I’ll be reading through your thread. I’ve seen some people recommending to install additional 3-4 clutches, do you think that’s worthwhile or even viable?
I’ve also considered installing a larger intercooler, is that worthwhile for normal driving and light towing? I won’t be hooking it to anything heavy, I have other vehicles for that.

Yep - run the 4L65E Alto 3-4 clutch and steel module. Has seven friction dics and six steel plates vs six and five for 700s and 4L60Es; you'll need the 4L65 apply and backing plate. Additionally, run the 4L60E 97+ bonded apply pistons and 2nd design return spring in the forward drum. Larger cooler is always a plus. Lastly, upgrade the sunshell to the Sonnax Smart shell - best on the market.