Hello Corvette gurus. My overdrive toggle button in the top of my shifter is nonfunctional. The overdrive works exactly as intended, but I cannot manually toggle it on or off which is pretty annoying. I'm assuming the switch or the wire has worn out and likely could use some solder to give it some more life.

Before I start blindly ripping apart my center console and shifter, I'd like to know what to expect might be involved in this little repair. Would anybody mind sharing their tips on working on this part of the car?

Thank you!

 

I recently repaired the switch in the shifter on my 86.

My symptoms were the opposite of yours, suddenly the OD would not engage at all. Luckily my car is in track mode...stripped interior, so I could just look at the front of my shifter and spotted the problem. Once you get your console and stuff out of the way...

Pop off the shifter button with a small screwdriver. Pry up from the FRONT, as the rear is the hinge point.

Unscrew the t-rod counterclockwise. The shifter button presses down on the rod and the rod threads into a block that pushes the actual switch plunger. When removing, count the number of turns so that you can install it into the same position. This isn't critical, i.e., if it took 72 turns to remove it and you installed with 70 it will likely still function...but your button will be just a little higher/raised in the shifter than before.

Loosen 8mm nut on the switch. You may have to grind down an open end wrench to make it thin enough to get in there. The first wrench I tried was too wide, but Craftsman wrench did just fit. Wrenching in this little area was tedious, so I just loosened enough to get the switch out (did not remove the nut all the way).

BE CAREFUL when removing the switch, as there is a narrow spring in the bottom of the plastic block...don't want that to fall into the abyss. When you are re-installing, use a small screwdriver to hold the spring up in the block then slip the switch assembly into the shifter.

Then you can follow the wires to a connection in the rat nest of wires behind the climate control panel.

I found that a small piece of the switch housing had broken away, letting a wire separate from the switch. Again, your symptom is that the OD engages, but you can't disengage to direct mode...the switch may not be your problem.
https://www.corvetteforum.com/forums...1&d=1619738618

Close-up of the broken area.
https://www.corvetteforum.com/forums...1&d=1619738801

I removed a little more of the housing to better observe and learn about the switch...it was not necessary. The wire should be flush with the bottom of the switch housing and be TOUCHING the contact piece inside the switch. The circuit is designed to be closed/on by default and when the switch is pressed, the circuit is temporarily open/off. At this point you can test the continuity with an ohm meter: should have continuity by default and not when the plunger is pressed...you need to press the plunger all of the way down to hear a CLICK and you should be able to observe the contact inside the switch move up/away from the wire contact. I carefully applied Gorilla Glue to hold the wire piece in-place...without getting anything near the contact surfaces inside the switch. Then just put a small piece of electrical tape to cover the opening.
https://www.corvetteforum.com/forums...1&d=1619738801

Then I ordered a new one from Zip Corvette
https://www.zip-corvette.com/85l-88-...ve-switch.html

Looking at my FSM, there is a trouble shooting chart of condition, probably cause, and correction.

Condition "Overdrive in All Gears"
a. Solenoid Plunger Stuck - Replace Solenoid
b. Solenoid Exhaust Hold Plugged - Clear exhaust passage
c. Shift Valve Stuck - Free up shift valve or replace valve body (this part makes me want to ask...are you keeping the fluid clean?)

Condition "No Direct Drive"
a. Sprag Clutch Damaged - Replace Sprag Clutch

 

Before deciding to go for the switch, you could first do a continuity check on the wires from the switch. The wires from the switch run forward from the shifter and then connect to the main harness behind the radio/climate control.

On my car, which again...I'm the third owner and it has been "racecar-ified"...the connector you are looking for has just two wires, both are black on mine. The side that comes from the shifter button will be wrapped circular plastic loom to protect it from rubbing between the center console and the trans tunnel...that should help narrow it down a lot. The other side of the connector goes to collection of several black wires and two orange wires (these black wires and orange wires were taped together like a minor segment of the loom.

Hope this helps. You could disconnect the connection (holding in my fingers) and test continuity with an ohm meter.

 

Wow, excellent information here! Thank you so much guys!

Based on the information contained in this graph, I believe the solenoid and shift valve are working as intended, so I think it's the switch or wire. The overdrive works exactly as described in the linked graph for a 1986 car. If I give >60% throttle in first gear it'll turn off overdrive until the next time I start the car, and if I provide a lot of throttle in the higher gears it'll kick down and upshift as intended. The only thing that doesn't seem to be working properly is the actual button itself on the shifter.

If I do give >60% throttle in first gear it'll completely turn off the overdrive system, which is a real annoyance when leaving the gravel driveway at work onto the highway. Then for part of my commute home I'm stuck in a higher gear ratio until I can pull over, shut off the car, and restart without giving much throttle.

 

You can confirm it's the switch by checking the continuity via the wires under the dash. You'll probably need a helper to push the button while you hold the leads onto the wires...it's a small connector.

 

How do I identify the correct wires under the dash? I've got the panel removed under the steering wheel and it's such a rats nest of wires, I don't want to screw with the wrong stuff.

Sorry if that's a stupid question, which it probably is.

 

Thought I would post a better pic of the connector to look for. This pic I put a facial tissue as the backdrop...easier to see the wires involved. The orange wires are for the power seats, then there is the two black wires going to the desired connector. Again, in my car, the previous owner was obviously in this area and it is possible that he taped all of these together himself.

But hopefully the two orange wires will be easy to spot and then you can find the shifter button circuit nearby. :-)

The connector is black, long-thin rectangular, and has a grey piece too.

 

Mine went under the HVAC panel on the driver side. As we mentioned earlier, it will likely have circular plastic shielding around the section that comes from the center console.

Look behind the HVAC panel area, check driver side first I guess.

Other wires that come from the center console (going off of memory because I don't have one now) to spot that should be nearby are the orange wires for the power seats.