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68 firebird transmission swap help

3K views 7 replies 5 participants last post by  Dano68 
#1 ·
I have a 68 firebird 350 automatic turbo glide, I installed a posi in the rear end. The gears on the posi are 373. This makes high rpms when just cruising. Any suggestions on what transmission I can switch to to help with this problem? thanks
 
#2 · (Edited by Moderator)
Yep, you can switch to a well built, beefed up 200R4. But there are 2 problems. They ain't cheap.
And they require the use of a TV cable hooked to the throttle linkage, which must be adjusted exactly right for the tranny to function and survive. I think there are a couple of guys on FBN who can give you more details about the fit and function of the OD trannys.

It would be much cheaper to change out your gears for for a numerically lower number. 3:42 ? or maybe even 3.23, if you do a lot of high speed cruising.

One other alternative is to go with 3.08's and a tight 10" converter, with 2400-2800 stall, to maintain decent off idle WOT acceleration.


http://www.ebay.com/itm/FTI-ESR3380-9-5-2400-2600-RPM-Economy-Performance-Converter-Turbo-TH350-TH400-/151362235633?pt=Motors_Car_Truck_Parts_Accessories&hash=item233de46cf1&vxp=mtr

http://www.ebay.com/itm/TH350-TH400-10-HP-Torque-Converter-2600-2800-Stall-/171306175710?pt=Motors_Car_Truck_Parts_Accessories&hash=item27e2a4ccde&vxp=mtr
 
#3 ·
I went with a 2004R tranny. I have the same gears in my car and it dropped the highway cruising RPM from around 3200 to 2100 RPMS at around 60 MPH. Much more tolerable. There was a post on this, do a search for 2004R.
 
#5 ·
1128761[/URL]']
Yep, you can switch to a well built, beefed up 200R4. But there are 2 problems. They ain't cheap.
And they require the use of a TV cable hooked to the throttle linkage, which must be adjusted exactly right for the tranny to function and survive. I think there are a couple of guys on FBN who can give you more details about the fit and function of the OD trannys.

It would be much cheaper to change out your gears for for a numerically lower number. 3:42 ? or maybe even 3.23, if you do a lot of high speed cruising.

One other alternative is to go with 3.08's and a tight 10" converter, with 2400-2800 stall, to maintain decent off idle WOT acceleration.


http://www.ebay.com/...de46cf1&vxp=mtr

http://www.ebay.com/...2a4ccde&vxp=mtr
 
#6 · (Edited by Moderator)
200 r 4 is the way to go is a direct bolt in ... but yes the tv cable has to be adjusted right ... find a tranny shop that knows what they are talking about and its simple. there is much debate on the ability of the 200 to handle any power ... however there are many Pontiac 455+ using them and i have known them to live behind other powerful engines such as the grand national, and 572 Chevy
 
#7 ·
Well, for the most part it is a direct bolt in, the 2004R does bolt up directly to the pontiac engine, but if you currently have a 350 tranny, than you will need a Th-400 crossmember, you cant use the 350 crossmember and the crossmember will have to be moved back to the Th-400 crossmember position. I actually used an after market crossmember that allowed for better tranny oil pan removal, than the stock th-400 crossmemeber. If I remember correctly the length of the 350 driveshaft should be good, but if you have a Th-400 the driveshaft will have to be cut down. I had a drive shaft built for me because I had cut the driveshaft down once already because I put in a 8.5 rear end with the 3:73 posi and the snout on those stick out further than the 8.2 rear ends and I didnt want to cut it down a second time. And yes, the TV cable is a slight pain in the rear, but doable.
 
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