I read a lot of posts on here about this and the more I read the more confused I got.

If I have a 91 Firebird and use a TH350 with a 9" tailshaft, my present drive shaft will fit right?

If I buy the B&M 30229 conversion kit, do I still need a GM brace? If so what PN?

I would love to buy a Spohn adjustable torque arm but cant afford it. Can I use my current torque arm with the above stuff?

Are there any computer issues with the TH350?

Thanks

 

You will not have any computer issues with the 350. I think the brace just bolts to your tail housing, don't quote me on this but I think it comes complete brackets and all, but if you don't mind me asking why are you going to a turbo 350? Instead of a 700r?

 

You will need a crossmember from either an 82 or 83 Fbody or Spohn makes one. You will need a TQ arm mounting bracket or adjustable on Shohn makes the, B&M and a few others.
You will need a drive line from the same years 82-83. You will need to either get and aftermarket shifter or a shifter from 82-83. got an 82-83 thing going here.

I did this on my camaro it saw a 700R4 a TH350 and a TH400. My firbird has seen a 200c, TH350, 700R4 and T5. Out of all these transmissions I likes the T5 the most maybe you would too.

 

I decided on the TH350 because it is supposedly stronger and will hold up better to racing. I don't need the overdrive because the car is not a daily driver. I only drive it short distances to go to a car show or the track. It's also cheaper, like 1/2 price.

As far as needing all that 82-83 stuff, hmm. I was sure I read you could use a 9" tailshaft transmission and the stock 91 drive shaft. Is this not true? YOu actually have to change crossmembers? I thought the conversion B&M 30299 kit allowed you to use your existing crossmember. I didn't realize I couldn't use the stock shifter either. I guess I will go with a B&M megashifter if that is the case.

Dang, I wish someone would write a definitive tech article on this.

 

I just had the swap done. I used the B&M kit and one GM part. This was on an 86 Iroc and the driveshaft and all worked fine. I did have a Megashifter already so that was easy. Just make sure you get a TH350 with the 9" tailshaft.

 

I looked in the instructions that came with the B&M 30299 swap kit and it mention you need GM part # 10024028 or 10034259 depending on the torque arm.

 

If I get the 6" shaft, that doesn't effect the cross member positioning does it?

 

Twilightoptics

Mounting point on a turbo 350 is in front of the tailshaft on the transmission case. So a 6", 9" or 12" tailshaft transmission will have same crossmember mounting point.

See Trans Specs for dimensions.

Jeff

 

If you are replacing your 700R4 with a TH350 with a 9" tailshaft your existing driveshaft will fit.

 

Good. Thats what I was sure I had read. Now what about this additional part from GM? I plan on buying the B&M kit but how do I know which bracket to get from GM? 50/50 chance I guess. Also what about my speedometer and shifter. I was told I would have to buy an adapter to the tranny to send signals to the electronic speedometer setup. Where do you get that? I guess a B&M shifter will have to be bought. Lets see, Cheap TH350 but $80 for B&M Kit, ??$ for GM part, $200 or so for a B&M shifter (not sure of this price), $100 for speedomoeter adapter, hmm, I guess its still cheaper than a reguilt 700 r4

 

Yea a 9 might, I never tried a LSTH350 only seen a couple of them in my life so it was never an option for me.

 

The 9" tailshaft TH350 will work with the existing driveshaft from a 700R4 car. Larry when I checked on those GM part numbers only one was still available and that one worked on my car. I have an 86 so I didn't have to deal with the electonic speedo.

 

Hey Larry, we talked earlier. Unless there was a huge shifter change from 86 to 91 you can still retain use of the factory shifter, hell I raced mine that way last year and not until I totally redid the entire car this past winter did I finally install a B&M shifter-it is nicer slapping it than cautiously clicking so to speak. Find out exactly waht the GM part is gonna cost, again maybe 86-91 is different, but with my hurst kit it all just bolted up with no trips to any dealer/parts store. Speedo...you got me, that's why I went all Autometer gauges, though it would be neat to keep it original I guess. And your right, even buying all this extra stuff your stiull going to come is alot cheaper than trying to build a race ready 700r4-price their convertors once compared to PG/350/400's, which are lots easier to come by as well, heck thought I seen some at the 7-11 the other day with a whole section devoted to Chevy parts-gott keep these cars on the road somehow If I was really smarter than I thought I was I'd be racing a Rustang!!

 

I beleive if you use the BOP(buick,olds,pontiac) tailshaft on the th350 your existing speedo sensor will work. Only the chevy tailshafts had the small speedo hole. The stock shifter will work with the th350 too. My 87 came with a th350 installed.. stock shifter still workin. You just have to feel for the right positions. The shift cable transmission bracket wont fit the pan bolts. On my car they used a couple of washers under hte pan bolts at either end. That held the bracket securely but looked phony. Worked for 160k miles that way though.. So can't complain.