Topic: Swapping a TH350 with a 700R4 - issues?
in Forum: C3 Driveline Components
Good Morning,You might consider going with a 200 R 4 trans instead of a 700 R 4 as you will have to do a bunch of work getting the 700 to bolt in place of where the Turbo 350 sits. The 200 R 4 is the same length as the 350 trans and will not require and cutting of drive shaft as you would have to do with the 700 R 4.I have researched this for my '80 Vette and have concluded that the 200 R 4 is the way to go and has a high gear ratio for 4th (.67-1) lower RPM at higher speeds.
| Trans | 1st Gear | 2nd Gear | 3rd Gear | 4th Gear | Reverse |
| Powerglide | 1.76/1.82 | 1.00 | --- | --- | 1.76/1.82 |
| TH350 | 2.52 | 1.52 | 1.00 | --- | 1.94 |
| TH400 | 2.48 | 1.48 | 1.00 | --- | 2.07 |
| TH200-4R | 2.74 | 1.57 | 1.00 | 0.67 | 2.06 |
| TH700-R4 | 3.06 | 1.62 | 1.00 | 0.70 | 2.29 |
| 4L80E | 2.43 | 1.49 | 1.00 | 0.75 | 2.07 |
THM200-4R[edit]
For the 1981 model year, the 200-4R (sometimes called 200R4) was introduced. The components which were prone to failure in the THM200 were improved, and this transmission was used with high-power applications — primarily the Buick Grand National. The 200-4R was configured with several different torque converters and gear ratios depending on the vehicle application.
Unlike the 700R4, most 200-4Rs have a multicase bellhousing for use with Chevrolet, Buick/Olds/Pontiac (BOP), and Cadillac engines. However, 200-4Rs share mounting locations with the TH-400. Since the external dimensions are similar to the TH-350 (overall length, drive shaft yoke spline count/diameter and general size), 200-4Rs are often swapped in place of TH-350s in older vehicles to provide an overdrive gear.
Early models had PRND321 on the cluster, while later models had PRN(D)D21, with the left D identified as the overdrive gear by a square or oval ring.
The THM200-4R can be found in the following vehicles:
- 1981-90 B-Bodies
- 1981-84 C-Bodies
- 1984-88 G-Bodies
- 1985-90 D-Bodies
- 1981 Pontiac Firebird (with 301cid engine, non-turbo)
- 1989 Pontiac Firebird Trans Am Indy Pace car (with Buick V6 and a Turbocharger)
The THM200-4R was phased out after 1990; its final usage was in the GM B-body vehicles.