View Full Version : Ot Th700-r4

08-08-2007, 12:09 PM
I've got a 3/4 ton chevy truck (1989) with a 700-R4 in it. The truck was a farm truck and was rarely out of first gear. Its only got 52,780 miles on it. Everything looks great, no rust etc but the transmission no longer shifts properly. I learned to drive on this truck and then it worked great, but in the last year it hasnt been shifting. I found two stuck valves and ran some crockus paper over them and it worked good for a month or so and now its doing the same thing again.

So far i've run emery cloth over any valves that felt like they had any possibility of sticking, (except the ones that have the tapered roll pin retaining them like the line bias valve, but they all move freely when i poke them with a scribe), installed a B&M shift improver kit for heavy duty/towing, new filter, new gaskets, new valve body spacer plate, new filter, and 75,000 mile plus fluid. I don't suppose the fluid really matters; it said it was good for reconditioning old seals and i figured, even though it only has 52,000 miles, it had old seals!

Nothing has helped so far. I just realized that this time, after installing the kit, i did not adjust the TV cable so maybe that is the cause of the problem. Second gear does not shift well into third either, it holds until about 4500 or 5000 rpm. Any advice or help is appreciated!

<edit> just for the sake of argument say the TV cable wasn't the problem... then what should i do?

08-08-2007, 02:09 PM
"Shift improver" kits are different depending on the application. My understanding is that those for performance use reduce the band slippage (potentially improving band life),but cause a hard shift that may be hard on the rest of the drive line. I put one in my GTO and it will shift hard under high throttle. This is supposedly the opposite of what happens with the "RV/towing" kits where a hard shift with a big payload could really tear things up. I wonder if the shift kit has slowed the pressure buildup (which is what determines shift rates) to the point that you are having more stiction problems (with old seals) than you might otherwise have.

If you are shifting way high, it may not be anything sticking. I know the old TH400's used a vaccuum actuator on the side. A high shift point was often a result of a vaccuum leak in the hose/hard line that fed this or the actuator itself.

Perhaps someone else will have a better idea.


08-08-2007, 02:16 PM
Hmm... according to the instructions the RV/towing package was supposed to increase fluid pressure to the clutch packs and bands so they were less likely to slip, and they said it would generate "noticeable" shifts while the performance set up was "hard, neck snaping shifts". The procedure for the two are almost identical except that a smaller spacer is used in the accumulators and the line bias valve doesn't get a spacer for the RV/towing package.

It may be that the shifts are slower but that they ultimitely achieve a higher pressure than stock ... ?

The 700-R4 doesn't have a vacuum modulator or any vacuum lines going to it, but does the computer read engine vacuum to deterimine shift points? Its not techincally an electronic tranny, but it does have a considerable amount of info being fed to it.

08-08-2007, 03:24 PM
Fasttrack, it definitely sounds like the TV cable is the first and easiest place to start. The TV cable adjustment is critical for the proper shifting and operating parameters of the transmission, without setting a baseline here first, nothing else matters. The symptoms you describe are certainly TV cable related.

I would start with the cable adjustment first and then carry on from there in a methodological order. A factory shop manual is a great help in situations like this because they describe the procedure to follow as far as diagnosis protocol. I find the Chilton and Haynes manuals very lacking, they don't hold a candle to the factory manuals, they'll let you take something apart to a certain level and then they leave you hang there.

Baring a factory manual try Googling "TH400 700R shift diagnosis" or something along that line, there's a lot of info out there on those tranys, I'm sure you aren't the only one that has had the same symptoms.

Have a look here for a start....

edited to add...some more info....http://purplesagetradingpost.com/sumner/techinfo/700R4p1.html
Good Luck...Willy

08-08-2007, 05:49 PM
I've got the Haynes manual it does suck!

I've adjusted the TV cable - which was a rather big ordeal because the plastic clip broke in the process and the ratcheting mechanism didn't want to work worth a darn. I had to do it by hand. I basically just slid the cable a little bit forward (like one "click") then checked to see if the throttle would go to the stop and kept doing that until i got it there. I'm going to go look at it again and make sure its ok.

I took it out for a drive and it seems to sorta work. When i'm doing 25 i run at about 2000 rpm and i feel engine braking going from [d] to d but there is no engine braking from d to 2. From 2 to 1 there is noticeable engine braking.

Somethings not right ... it doesn't really feel like its taking off in first most of the time and it doesn't shift up even at 45mph with an rpm of about 3500 or 4000. What should i do?

08-08-2007, 06:40 PM
Did the problems surface after the shift kit installation?

I'll give you another link where you can download two pdf's that are copies of the factory manual for service diagnosis and operation of the 4L60-E transmission which is very similar to the 700R-4.


Near the top of the page download #'s 5&6, go and study these sections, I'm sure you'll find the answer there. You will have to register to get more info from them. Only you know the exact sequence of the transmission performance degradation and with a little bit of detective work and a lot of thinking you will find the answer.

08-08-2007, 07:04 PM
Just wanted to add that the biggest factors affecting shift quality are, valve body, tv cable adjustment and freedom of operation, and the governor, in that order.
You have to be meticulous and thorough in order to eliminate problems.
It's not rocket science but you want to stay focused.

08-08-2007, 07:39 PM
Thank you so much for all of your help! Transmission work can be kind of intimidating and scary, but i think i'll get it working well again.

The problem exsisted before the shift improver kit, and i adjusted the TV cable a bunch - just minor adjustments over and over and i got it to were it shifts great but then it slowly resets itself to the normal posistion where it doesnt shift. Is it possible that the automatic adjuster isn't operating correctly?

Anyway i'll go study those pdf's for a while. Thanks again!!

08-09-2007, 01:26 AM
Sounds like leaking seals, 2-4 servo sticking or a bad pump. Have you checked the pump pressure? That thing has five clutch packs and a bucket load of seals. I've never had much luck using "liquid fix" methods.

08-09-2007, 11:47 AM
Sounds like leaking seals, 2-4 servo sticking or a bad pump. Have you checked the pump pressure? That thing has five clutch packs and a bucket load of seals. I've never had much luck using "liquid fix" methods.

Yeah ... me neither but i keep hoping :D