Noob question about 700r4.
Thread Starter
Instructor
Joined: Sep 2014
Posts: 243
Likes: 23
From: Vancouver WA
Noob question about 700r4.
So I am new to Vettes and during my research I have found the term "lockup torque converter" . I understand the principle of the lockup feature and as far as I can tell, the 700r4 (in my 92 coupe) has one.
So I am cruising along about 50mph in OD. If I push the gas pedal about halfway down, there is a slight but very noticeable increase in engine rpm that is definitely not a downshift into 3rd. Is this slight increase in rpm the lockup unit disengaging? Funny thing is, I've driven lots of AT cars and have never noticed that before. Is it just a Vette thing or is my tranny going out? Thanks a lot.
So I am cruising along about 50mph in OD. If I push the gas pedal about halfway down, there is a slight but very noticeable increase in engine rpm that is definitely not a downshift into 3rd. Is this slight increase in rpm the lockup unit disengaging? Funny thing is, I've driven lots of AT cars and have never noticed that before. Is it just a Vette thing or is my tranny going out? Thanks a lot.
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
You say "about 50". I believe the converter locks up at 50. So if you are going 45 you may see a bit of rpm increase without speed increase. You also can feel the lockup at 50 as it nearly feels like a slight gear change.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 413
From: WV
The convertor also unlocks when you hit the brake..
The convertor is the only electronic operation on the 700R4 trans , and it is also adjustable... If you have the knowledge to work on the cars tune/chip, you can go into the tune and change the speed/mph that the convertor locks up..When I installed my 383 engine with the larger cam , I changed my convertor to lockup at 53 mph, and unlock at 49 mph, which is much higher then stock.....
...WW
The convertor is the only electronic operation on the 700R4 trans , and it is also adjustable... If you have the knowledge to work on the cars tune/chip, you can go into the tune and change the speed/mph that the convertor locks up..When I installed my 383 engine with the larger cam , I changed my convertor to lockup at 53 mph, and unlock at 49 mph, which is much higher then stock.....
...WW
Team Owner
Joined: Sep 2003
Posts: 20,179
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
A don't forget a TC lock override switch can lock the TC at any speed, any gear cept first.
Very useful when using 3rd in the twisties.
Very useful when using 3rd in the twisties.
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
If I can get TunerCat operating, I will be happy to post the stock settings for those years.
My lock/unlock TC setting is likely what I set when the 393 was installed in 96. Too many years ago for me to remember.
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Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
Since the VSS doesn't know which direction the car is going, I have speculated that it would lock in Reverse at 40 MPH. I haven't tested that...
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
Your 92 uses a DA2 definition file. Here is a screenshot from a DA3 definition file. The latter is the Fbody and the former is the Ybody, but back in OBD1 days the information is virtually the same although is in different addresses on the actual 256k chip.
This screenshot shows the 2 tables and the section of the ECM Constants Tables that affect the Torque Converter.
This screenshot shows the 2 tables and the section of the ECM Constants Tables that affect the Torque Converter.
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
Now here is something that most folks don't know. Here is a jpg of a screenshot of the Constant Table on a 93 ZF6 Corvette bin file. Note it also contains all the info you need to control an automatic and its torque converter.
Racer
Joined: Jan 2014
Posts: 324
Likes: 7
From: Littleton Colorado
No, it will not, because there is no pressure on the TCC circuit in 1st or reverse.