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700r4 lockup under which throttle position

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Hello everybody,

As I'm trying to get the 700r4 lockup right in my 81 I think overhere is the best place to ask as the 700 is from a 90 corvette.

The problem I have is that on my original transmission TH350C the lockup was controlled by the transmission and a little by the ECM (ecm controlled minimum mph lockup activation and brake de-lockup.) The 700r4 from a 90 corvette I now have the lockup was almost compleetly controlled by the ECM. So I almost have the lockup wiring right with some extra switches the only thing I need is a vacuumswitch that connects the lockup above ...Hg intake vacuum. (sorry no I'm not interested in the standard lockup wiring kits)

The question I have. Can somebody tell me for how long the lockup will stay active in a c4. For example, at a steady speed it's normal the lockup to work, but at 1/4 throttle will the lockup be on or off, and at 1/2 throttle?

I test drove the vette today with a vacuum gauge next to me. Steady driving at different speeds and rpm in 3rd and 4th vacuum was about 12 to 15 Hg. With 1/4 throttle the vacuum never dropped under 10 Hg. Going more throttle then 1/4 the vacuum will drop below 10 Hg (example taking over a car on the highway). So I'm thinking getting a switch which closes above 10 Hg. Any opinions on this one?

As the C4 lockup is ECM controlled it's maybe in relation to the TPS position?

Greetings Peter
 
Are you trying to convert an 81 car to use a 90 transmission?

The 1990 transmission requires a tv cable that is attached to the throttle. That cable controls the shift points based on the throttle angle.

Here is a post that has some pictures of the TV cable and throttle mechanism that operates the tv cable.


http://www.corvetteactioncenter.com/forums/c4-technical-performance/129144-85-automatic-not-shifting-cant-go-more-than-30-mph-2.html

I
n this post there is also a sheet describing the method to adjust the TV cable.
 
The Tv cable works perfect but thanks for asking :)

Greetings Peter
 
I would think at anything approaching WOT and the lock up feature would be released.

This is what I wanted to know! :)
But if I'm right the converter also helps to accelerate a little faster, but if the lockup only releases when approaching WOT then the lockup would be "distorting" this proces right? Of course you need to find the middle between giving the converter as much room as possible but also that the lockup is not constantly up and unlocking.

Greetings Peter
 

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