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1990 TC 3.0 with Overdrive issue


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I have a 1990 TC and the tranny shifts very well but at certain times it will downshift out of overdrive into 3rd and not upshift again. I installed both speed sensors and that didnt change anything. I noticed today that when it gets stuck in 3rd, if you let off the gas completely and hit the brake pedal a little bit, it will downshift into the correct gear. Seems like there is some kind of vacuum control to it. Cant figure out why it works right if you hit the brakes a little. Thanks for the help in advance!!

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having the same kind of issue... mine is in OD then downshifts suddlenly (once every 30 miles or so)... then will shift back and forth a few times... I just shift in manually back to drive, then after a few miles put it back in OD... I will let you know if I can figure out anything... I like your suggestion on something with a sensor... I was wondering if the motor was missing or losing power and so it downshifts...

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I realized I dont even have to let off the gas to get it to shift with the brake. I can just drive it normal and when it should usually shift on it own, I can just hit the brake for a second and it shifts normaly. Could it be the accumulator?? Thanks!!

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This is a typical issue when the transmission is replaced and the shop did not clip the wire to the transmission controller. Both Hemi and I have written articles in the TCA newsletter how to clip the wire to make the updated controller work properly. Takes about 5 minutes.

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You can find this info under ALLPAR.com. Once on the site, click on the the Tech /Engines box at the top of the page, then transmissions, then 4 spd automatics: repair info. It mentions the failure after takeoff and the missing ground path issues, as well as common issues with incorrect fluids. Good luck----the Dude Abides.

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Thanks, I'm not really interested in joining the club because I am going to be selling this car soon. I just got it because the person that owned it was going to cut it up and part it out but I bought it instead so I could fix it up to its previous glory. Its pretty nice but was being used as a daily driver and seems to have been neglected pretty bad. That being said, I dont think there is a problem with the tranny itself, I noticed driving it today that if you hit the brake at any time while driving at speed, it shifts gears. So if I'm in overdrive and I hit the brakes, it will shift down into 3rd and stay there (even if I give it gas) but if I hit the brakes again it will shift back into 4th and then overdrive. And it just goes back and forth like a switch every time I hit the brakes. I looked at the allpar site but they didnt say anything about that.

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Cut the wire in the wiring harness in cavity 49 of the Transaxle

controller

and tape it up so it does not make any contact anywhere.

You need do nothing more...

Back in 2002 I asked the same question on Yahoo groups. Hemi Anderson, a member of the TCA club provided me with this answer. I still owe him a free lunch.

About the TCA. IMO. Some members feel one way to increase membership is to only provide information to other members. I am not that way. I feel the best way to keep all of our TC's on the road is to share information. Not to have membership in a club. I am a member to support the club and help keep it alive.

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  • 4 years later...

what wire is it you cut?

You have most likely installed a rebuilt transmission controller, ( I have not read all the messages above) Anyway, you have a unique situation if that is the case.

Some people find this rather convenient, that you can downshift/upshift by tapping the brake pedal.

If you wanted to retain this option, just remember to do the brake tap.

If you like, you could install a push-button that could do the same thing just as some cars have on the shift lever knob, and eliminate the brake pedal from this function. Think about it a while.

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