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Hello, I have a 79 automatic Corvette, that has an unknown on/off toggle switch beside the air conditioning controls. I chased the wire to a plug into the driver side of the transmission. Does anyone have any idea on what this could be? Pictures added below.
No Torque converter lockup if OEM turbo 350 tranny. If it is a 700R4, easy to identify if the car has 3 (Turbo 350) or 4 speeds (700R4). If it is a 700r4, then maybe it is a switch for the TQ converter lockup to disengage that functiomn.
I'll take a stab at that switch being a manual on/off switch for the reverse lights to manually put the reverse lights on when not in reverse??
79 Corvettes did not have a turbo 350-C with lockup converter OEM..the only C3 corvette to ever have a lockup converter was the 82 with the 700R4 tranny....
My 81 definitely has the lock up converter. It has the wires going from the CCC to the transmission. A picture of the transmission pan would tell us what is in it. Quick blurb about it.
However, the most substantial improvement to the 1981 Corvette over earlier models was the introduction of Computer Command Control (CCC). Though not unique only to the 1981 Corvette, Computer Command Control used electronics to integrate the emissions and fuel systems in order to reduce smog and fuel consumption. Similarly, CCC was tied into the automatic transmission’s new lockup torque-converter clutch. This provided a direct mechanical linkage between the flywheel and the propshaft in second and third gears at steady-state speed, thus eliminating gas-eating frictional losses through the converter.
Last edited by MattoonVette; Mar 11, 2020 at 01:45 PM.
My 81 definitely has the lock up converter. It has the wires going from the CCC to the transmission. A picture of the transmission pan would tell us what is in it. Quick blurb about it.
However, the most substantial improvement to the 1981 Corvette over earlier models was the introduction of Computer Command Control (CCC). Though not unique only to the 1981 Corvette, Computer Command Control used electronics to integrate the emissions and fuel systems in order to reduce smog and fuel consumption. Similarly, CCC was tied into the automatic transmission’s new lockup torque-converter clutch. This provided a direct mechanical linkage between the flywheel and the propshaft in second and third gears at steady-state speed, thus eliminating gas-eating frictional losses through the converter.
Stand corrected! Thanks
Last edited by jb78L-82; Mar 11, 2020 at 02:53 PM.
........and that would be why I mentioned it, as I have an '81 and put just such a switch in my car to do just that, disable the lockup. Best thing I ever did, so much nicer to drive in town without that trans going into lockup. Really makes it doggy when engaged and not going at highway speed
Did a quick check for trans codes over at CAC's knowledgebase
79, 80 & 81 had only One OE auto trans: Non lockup THM 350
79 codes TB or WB --- 80 codes JC or TW --- 81 code 8JD
In the course of 40 some years, I can envision how lockup THM 350-C would've been swapped in for OE THM 350 ... especially when/if OE trans failed ... even a lockup 700R4 swap for that matter
Seems vast majority of CF C3 owners are not original owners.
81 did have the lockup transmission. It was a one year only that was controlled by the computer that also controlled the one year only computer controlled carburetor and distributor. It also has a speed sensor on the back of the speedometer.
Last edited by MattoonVette; Mar 12, 2020 at 06:08 AM.
Did a quick check for trans codes over at CAC's knowledgebase
79, 80 & 81 had only One OE auto trans: Non lockup THM 350
79 codes TB or WB --- 80 codes JC or TW --- 81 code 8JD
In the course of 40 some years, I can envision how lockup THM 350-C would've been swapped in for OE THM 350 ... especially when/if OE trans failed ... even a lockup 700R4 swap for that matter
Seems vast majority of CF C3 owners are not original owners.
Yeah, thats why its in the 81 brochures and service manuals that it does have it......
Thanks so much
OK, I don't have an 81 brochure or 81 service manual or an 81 anything for that matter But I'd like to KNOW
Best reference I have on this trans Q is CAC's knowledgebase; perhaps it's full of it (errors/omissions).
So, exactly Which lockup trans does your 81 brochure & 81 service manual specify is installed by OE ? I'd like to KNOW.
Above pan diagram can help others Identify which trans installed; whether OE or not.
The OP's picture of his 79's on-off toggle switch is clearly Not an OE switch
You are correct about the 8JD code for the 81. It looks like someone may have put the lockup trans in his 79 and added the toggle switch to control the converter. Definitely not a factory 79 install. Here is a picture from the 81 GM Service Manual of the inside of the lockup 350 valve body and TCC wiring harness. Just under the "More Standard Equipment" in the brochure, talks about the converter clutch feature.
Last edited by MattoonVette; Mar 12, 2020 at 10:26 AM.
You are correct about the 8JD code for the 81. It looks like someone may have put the lockup trans in his 79 and added the toggle switch to control the converter. Definitely not a factory 79 install. Here is a picture from the 81 GM Service Manual of the inside of the lockup 350 valve body and TCC wiring harness. Just under the "More Standard Equipment" in the brochure, talks about the converter clutch feature.
Thank You, sir for Good Info ! Clear from svc manual valve body pic the wiring's there for lockup while sharing same pan profile as non-lockup THM350. Brochure's reference as well.
Seems CAC's Knowledgebase trans reference for 81 deserves an addendum. FWIW, now I KNOW
79 corvette unknown toggle switch
