700R4 high RPM shift problems

[madcatter]

Starting from the beginning:

I changed the fluid and filter last March just for normal maintenance.

In June we moved and I pulled a pretty hefty load down the interstate and overheated the tranny (yes like a fool I was trying to hold it in OD). I pulled over to let it cool for about an hour, I lost a LOT of fluid but everything still worked. I pulled into the first town, topped it off and nursed it the rest of the way on 2 lane roads without problem. It appeared to have blown out of the vent on top as I couldn't find a leak source anywhere else. Everything has been fine since until the last month.

I've always had lockup issues in OD. With no load against it, lockup works just fine but a gradual hill or headwind will cause a vibration. A touch more OR less on the pedal and it goes away. This has been normal operation for close to 10 years.

About a week ago I started the truck and let it warm up as it was pretty cold out and took the kids to school but it wouldn't shift under 3000 rpm at any throttle position. It was the same for 1-2 and 2-3. OD shift didn't happen at all until I was over 10 miles down the road under light load.

All shifts felt proper. Firm but not harsh, same as it's always been. No slipping. The last time I drove it it was closer to 4000 rpm when it would finally make the shift, both gears. OD still took several miles but finally engaged at normal speed.

I bought a new TV cable and I've gone back and forth between it and the old one and nothing changed. Both have been properly adjusted twice. There's smooth tension against the cable so it FEELS like it's functioning as it should all the way down to the valve body.

Today I removed the governor and I could see nothing wrong with it either, the gear is in perfect condition and the mesh with the drive gear felt correct when I reinstalled it.

The fluid is pretty ugly again, brown and burnt but I've seen dozens of transmissions run on far worse. I know I need to change it anyway but I'm sure this isn't the problem. I can't tell if my lockup in the converter is working since it barely gets into OD before I've arrived at work. I only have about 4000 miles on the truck since the first fluid change in March and I've only driven it a couple times since it started failing.

My next step is obviously dropping the pan but what should I be looking for? The fluid shouldn't be so burnt already. Could the converter be causing this somehow? Is there something in the valve body that could be the culprit? I'm stumped.

The truck is a 1990 K1500 with just over 200,000mi on a presumably original tranny.

-N8

[j cAT]

So after the june overheating did you flush out the old fluid ? if not I would expect you now need to replace the torque converter and disassemble the transmission for a complete rebuild and cleaning/inspection.

If the fluid used was dexronIII this turns to acid and degrades with temps above 220 deg f quickly. since the fluid was boiling in the june overheating that could have been 500 deg f ...

[trannyman52]

The throttle valve in the valve body needs a return spring installed,,this will require valve body to be removed though,,,,,this condition is the start of letting you know that clutch failure is starting,,,,getting rid of that "acid forming" dextron III will not solve the problem....700-R4 JR shift kit from transgo is what you want to install,,has new throttle valve and springs ,,,,,but will not solve clutch issues.......gbaum

[madcatter]

I haven't put a lot of time into automatic transmissions since college 13 years ago. I know I'll be rebuilding before long anyway but the plan was to get a donor, rebuild that and swap it in.

I know I'm prolonging the inevitable but that's really my goal. I'd like to have this thing through the winter, it's our back up vehicle for when we have problems with one of the other 2 high mileage CK's in the driveway!

This situation literally happened overnight so there should be something glaringly obvious that just suddenly failed. Should I be looking for a broken return spring or is this an upgrade for something that wasn't originally there?

-N8

[trannyman52]

this would be considered an up-grade,,,engineering of the trans shows the valve will go to "nuteral" position with system oil pressure,,,,in the real world,,,doesn't work that way,,,this problem was addressed by the aftermarket about a year after the trans was introduced 1981,,,,,,I would NOT rebuild////repair without installing this kit,,,,the TV valve in the kit works slick as snot....can install in a half broken trans with good results,,,not to mention the other up-grades in this kit...i have repaired a-lot of these units,,,,,the transgo kit gives very good results,,,,because of the tv valve that comes with kit........gbaum