Topic: 4+3 Trans
in Forum: C4 Driveline Components
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Minster, OH - USA
Joined: 9/6/2011
Posts: 17
Vette(s): Beautiful Original Condition 1987 C4 Convertible, Bright Red exterior, Red interior, 4+3 Doug Nash Manual transmission, with 62K miles. Garage housed and dry roads driven.
Fun to cruise along in, but always ready to go!
My 87 has the 4+3 manual transmission also. The OD was recently fixed, but the disengage switch on the shifter does not disengage the OD once there.
I need to downshift from 4od to 3, instead of disengaging the od (like downshifting from 4od to 4) from the column push button switch.
My info is that the standard disengage switch is no longer available, but a Radio Shack normally open (NO) mometary push button switch can be installed in its place.
Has anyone ever done this, and do you know of the RS model number needed?
Is the no availability info correct as well?
Thanks
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Duncanville, TX - USA
Joined: 3/18/2009
Posts: 2246
Vette(s): 1985 Coupe-L98/Auto,Bright Red/Carmine.
1974 Coupe-L48/4speed, Medium Red Metallic/Black Deluxe.
Are you sure the switch itself is bad?
There is a relay involved in the circuit that could be flaky, or a fuse, wiring, or connector issue. Did the button work before the trans was worked on?
There is a relay involved in the circuit that could be flaky, or a fuse, wiring, or connector issue. Did the button work before the trans was worked on?
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"
Hi Guys, I have the 4+3 in my '85 with 162,000 miles on it and it still works good..Changing the fluid regularly helps, and taking it easy when you know it will shift is most important.
When you want to get on it, leave it off, and around town in traffic too.
The '85&^ shifter switch is still availiable from Corvette Central, with the right size end and wires. Still a simple small on/off switch, like would come with an alarm for valet, I use one to bypass my antenna motor because I always use my XM Roady thru the radio.
On long highway runs it helps, because at those speeds the downshift is enough for most passing situations, and yes, it engages about 105 mph even when switched off.
A two speed O/D unit added after the trans, or rearend was popular in a lot of foreign sport cars in the '60s. Had one in my '63 Volvo P1800..
Chevrolet's was basically a poor idea thrown together in a rush to meet fed. regulations.
I like it, but a manually controlled, simple O/D would be better.
Really, does anyone who enjoys their Corvette give a sh.. about mileage?.
I bought my first 'vette last week. It's a '86 coupe (silver/grey) w/ the Doug Nash 4+3 and I have an issue with the overdrive.
The OD light kicks on in 2nd/3rd/4th gear as it should but the overdrive unit doesn't shift. I'm running 3k rpm at 70mph. Backing off the throttle for decel causes the unit to freewheel and engine speed to drop to curb idle while I'm coasting. Clicking the OD-off button on the shifter turns off the OD light and drops the unit out of overdrive where I then get engine braking.
I have no clue if the OD unit has ever been serviced. I'm going to do that first and then presumably, I'm looking at rebuilding/replacing the OD unit.
Any help from the Doug Nash gurus is greatly appreciated. I have the FSM ordered but it hasn't arrived yet.
As an FYI, if you want to defeat the OD and have it off all the time - remove the OD relay which is on the firewall. It is bundled with the fuel pump relay and sits on a bracket above the valve cover on the drivers side.
Very handy if you plan to drive on track or in autocross events.
There is no problem a little horsepower can't fix!
C4s: 1993 LT-1 coupe, 6-Speed, White w/black
1986 L-98 Coupe, 4+3 Trans, Satin Black w/red-black interior - SCCA Time Trial racecar.
C3: 1979 L-48 couple, auto, Red w/doeskin interior.
in Forum: C4 Driveline Components
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