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No reverse 84 El Dorado with only 39K miles


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I bought a pristine condition 84 El Dorado. Everything worked perfect. On way to docks to ship back to the mainland, reverse stopped working. Now shipper will not ship car without reverse. All other gears work fine. Big problem, or little problem?

I know worst case scenario is R&R tranny, but is there possibly another way to check? Car is in driveway of my brother in law's home. Plan to drive it (very carefully) to a shop next week to get checked out.

Please tell me there's a cheap way to fix (solenoid, linkage,etc?)

Any help highly appreciated


Lihue, Kauai, Hawaii

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That transmission is the THM325-4L, used in the 1982-85 Riviera, Eldorado, Seville, and Toronado. It's a THM-400 derivative, but the parts spin in the opposite direction of those in the longitudinal transmission.

Two possibilities occur to me: low fluid, and a neurotic vacuum modulator. Be sure and use the factory recommended procedure for checking the fluid. The vacuum modulator is a throwaway part that tells the transmission how much manifold vacuum is happening, and strange things happen if it sticks. If it is shifting very slowly, or abruptly, even occasionally, I would change the vacuum modulator. Be sure and put new vacuum hose from it to the proper port on the fuel injection throttle body.

Another thing to check is the kickdown switch/solenoid. The switch is on the throttle body and it hooks to a terminal on the transmission and operates a solenoid that moves a valve inside the transmission. If it sticks, the transmission may think that the throttle is depressed and inhibit reverse. If you operate the switch with your hand and hear a click, the switch and solenoid are working. You can operate the switch repeatedly with your hand and free up the solenoid sometimes.

The low mileage probably means that it isn't a wear or breakage problem. The low mileage combined with the age tells me that it is probably cobwebs, i.e. something sticking. I would try having the transmission flushed, then serviced, in that order.

Others here may suggest that you try a transmission additive for sticking valve blocks, hard seals, etc. That's worth a try, I suppose, but someone else will have to suggest what to use.

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The only thing that should be flushed is a toilet. No way would I EVER let someone hook up a transmission flush machine to my car.

There is most likely a damaged component in the trans. that is preventing the reverse gear from operating.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Thanks Jim and Kevin. Gives me a little hope. Will find out after I take it to mechanic. Unfortunately, there is only on shop that specializes in transmissions on the island. But I'll take it first to a mechanic I know and see if he can diagnose.


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