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FYI, a couple years ago my tranni wouldn't shift into OD after replacing the dash harness. I tried vainly to trace the signal from the computer to the tranni. I thought I found it, but I couldn't see a problem with it.
Finally, a friend at a good shop printed out a comprehensive diagram for the OD circuitry from a website service that he subscribes to . Lo and behold, there is a +12volt side to it, wouldn't ya know. (What else would the ground be there for?) Lo and behold, the +12V runs through a brake pedal-acctuated switch, which I had mounted with the dash harness, but did not understand. (I thought it was cruise cancel.) It is the lower of the two brake pedal mounted switches, and it is OD cancel, not cruise cancel. Well, it might cancel cruise, too, for all I know. I removed all my cruise gear, so it doesn't matter.
Anyway, I had not properly adjusted the switch. It was too far away from the pedal, so it was as if I was constantly pushing in the brake pedal away from the switch, which is how it disengages the OD, by opening the +12V side of the OD solenoid circuit. Once I pushed it in all the way against the pedal, it began to work instantly. (The rest of the circuit, the return side, is sunk through the computer when it decides that you have reached at least 45 mph. Thus, with no brake, but no 45mph, you have +12V, but no ground, so no OD. No brake, 45mph, ground is made through the computer, OD hooks up as soon as you let up on the gas or reach 54mph. OD will hold all the way down to 37 mph on mine, but once I touch the brake pedal, +12V drops, and the solenoid pulls back, dropping the OD. Once below 37mph, the computer opens the ground circuit, and OD drops out.)
Live and learn.
Steve
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Thats some good info Steve! Thanks for taking the time to post this!
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
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What you are dealing with is the torque converter lock-up, not O/D...the 700 is all hydraulic shift, but the lock-up is electrical.
Everything else is absolutely right on...the converter uses the brake switch signal to un-lock the converter when the brake is pressed. The same switch also dis-engages the cruise control(when so optioned).
The trans has a few pressure switches(4th gear on all, 3rd & 4th on some) on the valve body that also must be closed(making contact) for the circuit to be complete. This is what un-locks the converter when you mash on the go pedal, and it downshifts. If the converter did not un-lock, the downshifts would be quite rough.
Glad ya got it fixed!!
btw...did I not send you a wiring diagram? The ones I have do show the lock-up circuit.
Everything else is absolutely right on...the converter uses the brake switch signal to un-lock the converter when the brake is pressed. The same switch also dis-engages the cruise control(when so optioned).
The trans has a few pressure switches(4th gear on all, 3rd & 4th on some) on the valve body that also must be closed(making contact) for the circuit to be complete. This is what un-locks the converter when you mash on the go pedal, and it downshifts. If the converter did not un-lock, the downshifts would be quite rough.
Glad ya got it fixed!!
btw...did I not send you a wiring diagram? The ones I have do show the lock-up circuit.
Joel Adams
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Tx, Joel. I keep mixing my terms. I knew that. I even know the name of the negative signal from the computer: "TCC," or Torque Converter Clutch. I was just happy to get the next shift.
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Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
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Joel Adams
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(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"
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A
A simple wiring diagram can be found here;
Lockup wiring post
CRAP!!! I couldn't get the Hyperlink to work. If you really want the diagram go to "C3 Driveline Components"/ Page 5, (11/06/07)/ topic, "700R4 dilema". It's on page 2 of that thread....
Dave
(fixed link)Adams' Apple 2008-08-22 19:04:43
Lockup wiring post
CRAP!!! I couldn't get the Hyperlink to work. If you really want the diagram go to "C3 Driveline Components"/ Page 5, (11/06/07)/ topic, "700R4 dilema". It's on page 2 of that thread....
Dave
(fixed link)
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#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
HERE'S the thread, and here's the diagram Dave produced...
+_____o o_________o o__________o o___________o////o________-
BSW1 VSW2 PSW3 LU sol
+_____o o_________o o__________o o___________o////o________-
BSW1 VSW2 PSW3 LU sol
Joel Adams
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A
Why can't I perfect a hyperlink here??? I ustacould....
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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
You made the link correctly, but the address had to many "http://" in it. I fixed it fer ya...
Joel Adams
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Thanks Apple!!
Dave
Dave
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in Forum: C3 Engines, Driveline and Handling
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