Topic: 1981 with RPM issue
in Forum: C3 Driveline Components
Already a Member?
Click Here to Login
Not yet a Member?
Click Here to Register for Free!
Former Member
Send PM
West Bend, WI - USA
Joined: 3/18/2010
Posts: 46
Vette(s): 1985 silver coupe & 1975 red coupe
Hello out there from the still somewhat frozen state of Wisconsin. I bought a pretty nice 1981 car last summer to play with but it has a few problems. The computer is not in the system anymore and on the hwy the torque converter isn't locking up because the RPM doesn't drop off. I have heard the thing can be wired with a switch inside for the hwy. How is that done? also, how much of an RPM difference should I see if it's working right? Any help you guys can give me would be great!! Thanks, Darrell
SPONSOR AD:: (Our Sponsors help support C3VR)
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20218
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Lock up on a 350 trans will only drop the rpm about 200 rpm. A few things can keep the lock up from working, starting with a blown fuse(no power to the trans connector), a brake switch that is bad, or not adjusted properly, or a problem with the solenoids, or pressure switch inside the trans.
First thing to check is if there is 12v AT the trans connector with the key on. If there is voltage there, then the problem is the solenoid, or pressure switch.
First thing to check is if there is 12v AT the trans connector with the key on. If there is voltage there, then the problem is the solenoid, or pressure switch.
Joel Adams
C3VR Lifetime Member #56 
My Link 
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20218
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Now that I have re-read the post....the lock up will not work with the ECM out of the mix....
The ECM controls the ground side of the solenoid to energize it. You should have 12v at the connector even without the ECM in the loop, so what you need is a ground, which you can provide either with a toggle switch(on/off), or by re-wiring the harness inside the trans. The trans has a pressure switch inside that closes at a specific pressure, which happens to correspond to a specific MPH. You would need to change the pressure switch to one that closes around 45-50 psi/mph, and then cut one wire, and run it to ground inside the trans, and then your lock-up will engage as soon as the pressure switch closes.
Sounds a lot harder than it actually is to do. I think I have a wiring diagram specifically for this mod somewhere. I'll look for it....
The ECM controls the ground side of the solenoid to energize it. You should have 12v at the connector even without the ECM in the loop, so what you need is a ground, which you can provide either with a toggle switch(on/off), or by re-wiring the harness inside the trans. The trans has a pressure switch inside that closes at a specific pressure, which happens to correspond to a specific MPH. You would need to change the pressure switch to one that closes around 45-50 psi/mph, and then cut one wire, and run it to ground inside the trans, and then your lock-up will engage as soon as the pressure switch closes.
Sounds a lot harder than it actually is to do. I think I have a wiring diagram specifically for this mod somewhere. I'll look for it....
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
This topic brings back memories.
I remember my father put a lighted toggle switch for the lock up converter on either his '81 or '85 Olds Gutlass Supreme. I believe he tapped into a wire off of or near the brake switch. It's been so many years ago I can't remember exactly. He put it in there because the lock up feature use to kick in and out once the car was around 45 mph. It was annoying. so for around town it remained off. Once on the highway 55 mph and above he'd flip it on.
TKO500 5 spd.
Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
in Forum: C3 Driveline Components
SPONSOR AD: (Our Sponsors help support C3VR)