3800Pro Forums banner

need help 99 buick ultra supercharged

805 Views 2 Replies 3 Participants Last post by  DAHL
hello I have a super bad problem my transmission failed and due to covid my money was very limited. so a friend of a friend said he would help. he found a transmission online for 500.00 dollors used. I scraped up just enough money to buy and for him to install. everything went well and a couple of weeks later it was doon. I was out of town when he finished so I got back jumped in and no gears worked! I will skip what happened next but my problem is the donor turned out to be a external shift control and car is not!! please can j somehow wire in controller because money is long gone. thanks
1 - 3 of 3 Posts
Short answer is no. You'd have to dig into the side of the case and convert various internal parts/wiring to make it work. You should be able to find an appropriate transmission at a local yard for $200-300 on www.car-part.com and possibly recoup something from the other one via classifieds/marketplace/etc.

Good Samaritan work sometimes isn't perfect, and these things happen. Every week I have to remind people here that just because it bolts together doesn't mean it'll fire right up without accounting for the difference in years/models on certain things.

The tag on the back of the transmission is the key for this, and if you post a picture of your old one's tag & the replacement's, in conjunction with the year/make/model of your car (I see it in the title), it helps more clearly communicate what you need.

Some info here, although it takes time to understand the details:

EDIT - after skimming the FastFieros link, I can clarify what your car came with...


RPO: MN7 (4T65e-HD version supercharged cars get)
Model: 9FCB
Platform: C (Park Ave's were called "C" body due to legacy from '91-'96, but was essentially a G-body from '97-'05 like the Riviera/LeSabre, etc.)
Carline: B (Buick)

Looks like the only version that year to come with the Internal Mode Switch (more and more 4T65e's got it in later years, until they all got it by ~2003, along with some other internal updates that year). You could basically swap in any '98-'02 transmission with the IMS, but note that fittings for the transmission coolers started changing to the "quick-release" style in 2000-up cars.
See less See more
I am not an expert on the situation but from what I understand, the 97-02 transmissions will interchange while the 03-up 4T65eHD transmissions will not. The PWM signals that shift the later transmissions require a different PCM. .
1 - 3 of 3 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.