Transmission / Overdrive: TH700R4 OD problem

[Corley]

A bit off the Studebaker theme, but since so many are using this trans now days,,,

I've finally started driving the Avanti around after installing the TH700R4 conversion (been busy with other things, so it has been a delayed start). The OD trans works a treat when cold/warm, but on super hot days (90+) it will not shift into OD after a while. (This has nothing to do with the converter lock up, I haven't even hooked that up as yet.) I've got the geometry right on the TV/carb link, and the shift points are good, nice kick down, etc. Everything is as expected unless it is a really hot day, then it works fine until everything gets hot, then it fails to shift into 4th (OD). One issue I have, is that the trans cooler in the radiator is not yet connected, but I have a rather large trans cooler in front of the radiator. I have not done any temp or pressure measurements so far.

Now, here is the strange part. I have a model A Ford with a 2.8L Chevy V-6 in it, and a TH700R4 trans. It has the exact same issue, on hot days it won't shift into 4th (OD). That one does have the converter wire connected, and again, it all works as expected when it is not hot outside. (By hot, I mean 90 degrees plus.) On the model A, at first I thought maybe since it is a small engine, and has a ton of wind resistance, perhaps my foot was just into it so far at speed that I'd reached the shift down point, but that proved not to be the case, after a careful analysis. Again, since there is not any trans cooler in the model A radiator, I have a large cooler under the model A in the air flow (no fan).

It just seems strange to me that I don't turn up a bunch of Google hits on this type of problem, since I have two vehicles with the same symptoms. I'm hoping there is a trans expert on here that has seen this and knows what is happening, or at least can give me some ideas. By the way, both of these transmissions are MM (men's mall) items, so not freshly rebuilt or anything, but both had hardly any junk and fresh looking/smelling oil when I pulled the pans to have a look (my only method for determining their condition).

Ideas from knowledgeable transmission people are appreciated.

[64V-K7]

Call someone at Bow-Tie Overdrive and tell this story to them. I'm sure they can diagnose your problem

[dynolou2]

As far as the external coolers for most vehicles,unless towing, the external should be enough. Did you put a oil pressure gauge on the line pressure port of the trans? Hint it is the 7/16" headed plug above the manual lever. Bowtie Overdrives has a blog on what to do. Line pressure MUST rise immediately with the throttle opening. One thing others have said that they don't have the lock up section connected, that it's OK not to. A little time on the transmission dyno will tell you that when lockup is applied cooler flow (pressure) increases by 15 or more psi at low throttle opening to as much as 100 psi at wide open throttle. Lou Cote

[Treblig]

I'm no expert but I know that:
3/4 shift valve could be sticking when the trans gets up to operating temp. OD is an application of the 2/4 band. Possible contamination in the valve bore.The valve body is aluminum & the valve is steel. Get it inspected by an experienced transmission rebuilder. Money well spent to have a proper diagnosis ,hopefully a low cost service of the valve body is the solution. If the pan is loaded with metal your SOL.


4th gear servo o ring could have been cut (often happens) during install.


4^th gear pressure switch could be overheating when trans temp get high enough.

treblig

[JoeHall]

No problems out of mine at any temp (knock wood). I wonder if your TVC needs tweaking? Might back it off just a hair, till it upshifts 1 to 2 to 3 a wee bit early, just to check and eliminate that possibility.
Joe H

[Corley]

No problems out of mine at any temp (knock wood). I wonder if your TVC needs tweaking? Might back it off just a hair, till it upshifts 1 to 2 to 3 a wee bit early, just to check and eliminate that possibility.
Joe H

Joe, I played with the TV cable some as a test, but it doesn't seem to affect the problem, however it really changes shift speeds. I don't like it shifting at too low engine speed, as it seems to me that there may not be sufficient pressure for a solid clutch engagement. But, what do I know, I'm not an auto trans man. When I get time to play with it, I'll check the 4th gear pressure.

Background:

I want to get this thing ready for a route 66 trip, Chicago to Santa Monica, in the next year or two. I need to install A/C in it before that, so need to make sure it likes hot weather and cools well. One next step is radiator rod out, as I've already pulled the soft plugs and pressure washed out a ton of rust from the block. I'll also be installing a new trans cooler in the radiator at the same time, since the old one is shot. Who's up for a month long route 66 run? (Not happening for a while, got to paint this sucker first. Crap, that reminds me, I've got some bubbles under the old paint to deal with. Wonder if I'll live long enough for all my projects?)

[dynolou2]

If you are not familuar with TV adjustment see my post about setting with gauge. The 4 gear switch only has to do with lock up apply, only when the switch is closed by 4 gear oil can lock up occur. Not really germaine to this situation. As others have said you may have an issue with your throttle valve, which the TV cable moves. The 700 R 4 has a cast iron valve body, the aluminum valve body came into use in the 4L60 E models. Lou Cote

[wittsend]

Ironically the 700R4 (at least the one I have - '92 version) has a temperature switch but it is designed to do the opposite of your situation (that being not to engage if it is too cold), and only with the lock up. I too run only an external cooler (Ford F-150 plate type). My car rarely sees more that 10 mile drives but I have never had a 4th gear shift issue. Are you sure the shift lever is allowing the valve body detent to move into place? If you put it in "D" and then release the linkage at the trans does it..., then click (fully) into place?

A notation on the 700RT4 and the 4th gear lock up. My neighbor is a local trans builder. And, not just a rebuilder, but a builder with a good reputation. He has told me that unless the trans locks up in 4th gear that it is not being properly lubricated. He states it is a long term issue but the point of too much too often is not clearly defined. Since I have a switch on my lock up his recommendation was to use 3rd gear for in town driving and make sure it locks up in 4th on the highway. Given 225-60-16" tires and 3.07 rear gears that it a necessity. While the car can handle 45 MPH in 4th, the lock up is just too much and the car practically idles down a level road at that speed.

[JoeHall]

Ironically the 700R4 (at least the one I have - '92 version) has a temperature switch but it is designed to do the opposite of your situation (that being not to engage if it is too cold), and only with the lock up. I too run only an external cooler (Ford F-150 plate type). My car rarely sees more that 10 mile drives but I have never had a 4th gear shift issue. Are you sure the shift lever is allowing the valve body detent to move into place. If you put it in "D" and then release the linkage at the trans does it..., then click into place?

A notation on the 700RT4 and the 4th gear lock up. My neighbor is a local trans builder. And, not just a rebuilder, but a builder with a good reputation. He has told me that unless the trans locks up in 4th gear that it is not being properly lubricated. He states it is a long term issue but the point of too much too often is not clearly defined. Since I have a switch on my lock up his recommendation was to use 3rd gear for in town driving and make sure it locks up in 4th on the highway. Given 225-60-16" tires and 3.07 rear gears that it a necessity. While the car can handle 45 MPH in 4th, the lock up is just too much and the car practically idles down a level road at that speed.

Speaking of rear end ratios with the 700R, with our 63GT, I first ran a 3.07 but it was a bit too tall. Later, swapped the 3.07 out for a 3.31, which is much better, but contemplating swapping in a 2.54, while doing a flanged axle upgrade. I probably should just leave the 3.31 alone, but just can't leave good enough alone, I guess. LOL

[Corley]

Call someone at Bow-Tie Overdrive and tell this story to them. I'm sure they can diagnose your problem

HA! I did better than that, I called on the Studebaker Bug Busters! What fun would consulting the experts be when I got you guys! HA!

[JoeHall]

HA! I did better than that, I called on the Studebaker Bug Busters! What fun would consulting the experts be when I got you guys! HA!

But when it comes to GM transmissions, most of us are novices at best

[Jerry Forrester]

Speaking of rear end ratios with the 700R, with our 63GT, I first ran a 3.07 but it was a bit too tall. Later, swapped the 3.07 out for a 3.31, which is much better, but contemplating swapping in a 2.54, while doing a flanged axle upgrade. I probably should just leave the 3.31 alone, but just can't leave good enough alone, I guess. LOL

I hope you mean 3.54 and NOT 2.54. (G)