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Hello Everyone I am considering a swap to the turbo 400.I have an 85Vette Z51 package with a mildly built 350 , vortec heads, 58 mm BBK throttle body with Melrose long tube exhaust.Engine makes an estimated 300+ hp.
I installed the transmission in the fall of 17 and unfortunately probably didn’t have the correct amount of trans fluid. Drove the car for approx 4 months, put her down for the winter. In the spring I changed the trans fluid completely and noticed it was almost black. New fluid and the car was extremely hard shifting into 3rd and 4th gear.Checked fluid throughout the summer and everything seemed fine. But the car would rev high 3500+ then shift into 3rd. I really didn’t cruise much over 50mph so never thought about the overdrive.
In August I was planning on attending Corvettes at Carlisle but that trip ended rather quickly. At 70mph the car would not down shift into OD. So back home to the garage on out came the transmission.
The transmission has been repaired but I’m thinking of the swap for the following reasons;
1) I’ve read a lot of information on the 700r4 and it seems 3rd and 4th are consistently a problem.
2) I’m sure my computer is shifting at factory stock settings and with the new engine and modifications it is probably not shifting the trans at the optimum ratio
3) I need something reliable so I’m not looking at transmission problems in the future
4) I would like to eliminate the electronic aspect and go with a simpler hydrostatic pressure system.
What would you all do and why?
Do I only need to change the tail shaft to fit the torque bar and driveshaft?
What do I do with the computer after I put in the Turbo 400?
Who still works on these OBD1 Computers?
Any information you have would be greatly appreciated!!
I get people fear the electronics they don't understand but the 85 did not have any computer controls for the shifting. I have been running a Rossler built 700R4 with a good torque converter (PI) for several years and I am making 420 RWHP. I am probably looking at another rebuild since it has been a few years since mine failed and I take a ramp at WOT as much as possible. I think your issue is it breaks eventually. If you screw up the fluid level of any trans, it too will break. Stock, the 700R4 was not built to take any power more than stock. That said, if you build it up right, it will take what you are doing FOR A WHILE. More WOT runs, less life. I think what you need is a good builder. Sure, you are going to pay more TODAY but you might save more IN THE LONG RUN. Changing to a Turbo 400 is work you don't have to do at your level.
I also have a Rossler tranny; a 4l60e. I have close to a thousand 10 second passes on the thing and it has had no issues over the past 5+ years. A performance build of your 700r4 will suit your needs.
I agree with everyone who posted above ^^^^ The 700 is more than adequate if it is upgraded properly. The TH400 is a downgrade and an expensive one at that. You won't like its first gear ratio, either.
Beef up what you have, IMO. The electrical connector is for the TCC Clutch. Does not affect shift points.
No lock up 400s, lock up came with the 4l80e. A 400 has 2.48 first gear verse 3.06. You would want to change rear gear. The 400.is a great transmission, however not for your application. With the 700r4 it is important to make sure the shift cable is adjusted correctly.
Was there ever a lock-up TH-400? I know there was a lock-up TH-350, the 350C that came out in 1980. The TH400 was in production another 10 years after the 350, but I can't recall that there was ever a lock-up converter in the 400. Was there?
Not to my knowledge, no.. They all had a connector on the case and I have heard that misidentified very often as the TCC connector, but it's a kickdown solenoid. (It was electric in the 400's)
As you say, there was a 350C.. Late production that had lockup. But no 400 I've ever seen was equipped with it.
If you go TH400, typically a Gear Vendors OD unit would be attached to give you a 4th gear, which itself is pricey enough. There are people here who have it.
Was there ever a lock-up TH-400? I know there was a lock-up TH-350, the 350C that came out in 1980. The TH400 was in production another 10 years after the 350, but I can't recall that there was ever a lock-up converter in the 400. Was there?
I recall reading that a company had tried to make one but it was just too freaking expensive and the market was small compared to 4l80e availability.
Was there ever a lock-up TH-400? I know there was a lock-up TH-350, the 350C that came out in 1980. The TH400 was in production another 10 years after the 350, but I can't recall that there was ever a lock-up converter in the 400. Was there?
I believe the 1990 turbo 400 had lockup in the 454 ss pickups. Others may have I am just not sure.
I may be wrong, that was a small interesting piece of information I kept locked away in my head and I am not sure where I located that information.
I believe the 1990 turbo 400 had lockup in the 454 ss pickups. Others may have I am just not sure.
I may be wrong, that was a small interesting piece of information I kept locked away in my head and I am not sure where I located that information.
I don't think it ever happened. I have a th400(3L80) out of a 87 PU truck. It has the small output shaft like a th350. the 454ss did also. I would like to know if the 90 had a lock-up
It's not in the parts book, either.. But a lot of stuff isn't.
Guy I know has literally been doing this all his life. His father founded two of the largest transmission parts chains in the country. He says he built 400's that had a case which formed a full pan underneath. I forget the application... Isuzu truck maybe?
There's nothing like that in the reference material and nothing in any parts list I've ever seen. But if anyone would know what he was looking at, he would. So, I tend to believe him when he says that.
I've had calls about automatic transmissions adapted to light drilling rigs before. Who knows what the heck they did to them?
So there's some degree of transmission weirdness floating around out there..
The 400 uses a 32 spline output shaft there was a variant called a 375 which used the smaller 27 spline output shaft. It was used in some later 80s and 90s C10s. It still never had lock up. Electic kick down and in the 70s there was a "Transmission Controlled Spark" system which had switch in transmission. So there would be a 2 terminal connector one for detent the other for TCS.
09-25-2018, 10:00 PM
1985 Vette 700r4 swap for Turbo 400
