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I was pulling my car out of the garage yesterday my foot barely on the gas pedal when all of a sudden the car accelerated out of control in reverse and I did not get it to stop until it hit the wall of my garage damaging by driver's side door. The car just did the same thing in drive-again I was barely able to get it to stop while burning rubber. Does anyone know what I should look at for this? My car has been converted to a GM 700r transmission for reliability I have never had a problem like this before.

Sounds like a missing or broken throttle return spring.

Agree...or something laying across the linkage that should not be there. Ernie in Arizona

It does sound like the linkage return spring might have broken or become disconnected and is not returning the linkage to the idle position. The spring could be in one of two places or, in some cars, both places.

Originally a single spring was positioned under the floor board pulling on the pivot mechanism at the bottom end where the accelerator pedal pushes a rod thru to the pivot piece. Later another location was used in the engine compartment where the spring was mounted vertically, one end on a piece of linkage on the firewall at the rear of the engine and the other end thru a hole in the welded flange toward the bottom of the firewall where pieces of sheetmetal are joined. In some cases a spring was added so both places were used.

Another possibility is since you have the GM transmission, instead of a rod for throttle linkage the GM trans uses a flex cable connected to the accelerator linkage to work the throttle and kickdown mechanism inside the transmission. It is also possible something has happened to the cable or whatever piece was fabricated to attach its end to the accelerator linkage and cable is somehow binding and not letting the accelerator linkage return to the idle position. Depending on how the cable was attached, positioned, or clamped, make sure it did not kink or get damaged by being too close to a hot manifold.

Excess heat can cause a modern cable to stick.



Another possibility is an engine or transmission mount that has separated. In such a situation, the engine can shift and bind the throttle linkage, causing a situation like you experienced. Sometimes, a car with a separated engine mount will stick the throttle when power is applied, and release it if the engine is shut off, after which the engine may start and idle normally, and respond normally to the throttle until the car is put in gear and throttle applied, whereupon the linkage will bind up again. The left side motor mounts are more likely to separate on some cars, but any issue with motor or transmission mounts can cause the problem.

How did this go undetected while the car wasn't in gear???

Probably because he tapped the gas pedal once he was in gear 🤔

Thanks for all the replies and advice I admittedly scratching my head over what could have went wrong. Many times on the forum I have stated how pleased I was with the conversion (bendtsens) since it was done almost 10 years ago. it is a mystery to me. Has anyone else who installed a GM 700r in their Packard had this problem? Even if you had the conversion (and it proved to be trouble-free) I would like to hear from you.