doug nash 4+3 help please

Hi all, have an 87 convertible with the manual 4+3. When I press the button to activate the OverDrive, the light comes on the dash but it doesn't engage. The RPM's stay where there at. Also, while slowing down in second
gear the tranny pops out of gear occassionaly?? I seriously doubt the previous owners ever changed the transmission fluid.. the car has 41k miles on it... any thoughts as to what might be the issue and how to correct? Any help would be greatly appreciated.
thanks wolf.
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Check the wire connector on the side of the OD. If the connector is tight I would check the wire for voltage with a multimeter in various switch positions. You could run a wire under the door to check operation when in motion or test on a hoist(CAREFULLY). If the wire is functioning correctly you will need to test the solonoid but I do not know how to do this. Good time to find a real GM manual, ask at a Vette dealer.
If you mean that the 4sp trans is popping out of gear, this is not a good sign. I would suspect (aggressive shifting caused) worn thrust washers in the tranny or damaged shift rings but would want to check the adjustment of the shift linkage first.
I would also want to change the oil in the trans (save the oil in a clean container and search for metal both with a magnet and visually after straining with a coffee filter. Do the same change for the Dexron fluid in the OD. If the trans seems overfilled suspect the input driveshaft seal of the OD leaking into the main trans. This happened to mine at 70,000 miles.
My current (1987 Z51) OD problem is with too easy kickdown. The OD kicks down under part throttle when I want it to stay in high gear. I am considering rewiring the OD switch to operate full manual with no auto kickdown. I also suspect it may be an adjustment issue with the throttle position sensor. If anyone has done the switch rewire to full manual or throttle sensor adjustment I would appreciate guidance.
It has been suggested that the best fix is a new Richmond 6 speed trans as the OD is expensive to repair. In my case the reseal job was not expensive and it was good that I removed the tranny because the clutch was down to the rivets but was not slipping.
Happy trails to all.
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thanks private.. I'll check the wire and connector.. just bought a tranny kit for the OD..

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The TPS MUST be in the proper position and working correctly for kick down to occur right. You should test the TPS at idle. It should be exactly 0.54 volts. Are you having idling problems? I have a scan tool which tells me the TPS voltage, but if you look in your Helm manual (you have one, right?) it will tell you which wires to probe.
I REALLY recommend NOT rewiring the OD. I did, and I suspect it's one of the reasons for early failure. The OD is not designed to be run in first gear, and rewiring it would let you do that. If you insist, you're going to replace the OD switch with a manual toggle on/off (it's a momentary switch right now), then you would route the signal from the switch from the ECM to the relay. IOW, the switch right now goes into the ECM. You would bypass the ECM altogether.

I put the Richmond in mine in August 03. I love it, but this year 6th gear broke. Sent the tranny back to Richmond and they fixed it for free, although it did cost $135 to ship the thing.
http://www.areddy.net/vettetrans
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wolfgang wrote:

I would think the tranny pop could be solved with a rod adjustment.
As far as the OD, change the oil AND FILTER right now, and do it every year. Couple be a couple of things with the OD. Here's how it works:
When you press the button, it's a momentary switch that sends a signal to the ECM telling it to toggle the current state of the OD. The ECM determines if it should be on or off, and sends that signal to the overdrive relay. When the relay energizes, it energizes, the light comes on the dash, and it energizes a solenoid in the valve body of the transmission. A valve body is just hydraulic "switches" that open and close to route the transmission oil to the proper path to put it in the gear required.
Since the light is coming on, we know the switch, ECM, and relay is working. The question is: Is the signal getting to the solenoid. If yes, is the solenoid switching? If no, then there could be debris in the solenoid that is preventing it from moving. The solenoid is just a piston in a cylinder (it's only about 1/2" in diameter, if I remember right), that is spring loaded.
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