First a little info about Turbo 350 Transmisisons.
Turbo 350's Come in 2 Differant Bell Housing Configurations.
#1 Chevrolet Bolt Pattern
#2 Buick, Oldsmobile and Pontiac Pattern. aka BOP Patten. (also most Cadillac )
***NOTE*** There is also such a Turbo 350 Case that is a universal BellHousing, where it has both patterns and will fit most (Not 60* V6/4cyl) Pre LS GM Engines.
Turbo 350's come in NON Lock Up and Lock Up Versions Turbo 350C designates, Converter Lock Up.
(Very Important, Pumps, Input Shafts and Torque Converters are NOT Interchangeable between TH350 and TH350C.)
Year Models Used (Approximate)
1969-1979 Turbo 350
1980-1986 Turbo 350C
Turbo 350 is a 3 speed non overdrive transmission. Gear Ratios as follows:
Turbo 350 is manufactured in 4 Differant Output tailshaft dimensions.
#1 6in. Usually found in Passenger Cars and 69-72 Trucks
#2 9in Usually found in Squarebody Trucks, Suburbans and 2wd Blazers.
#3 12in Usually found in 69 to Early 70's Vans and is uncommon these days. (Many are not aware this 12in
exists and refer to the 9in as long shaft, when its actually an intermediate shaft)
#4 4x4 Output shaft used to marry Turbo 350 to Tcase with proper adapter.
(Apparently, there may be 2 different 4x4 Output sizes. 1 for NP203/NP205's, and maybe 1 for NP208. New Unverified Info to Me that I was unaware of)
Turbo 350 Dimensions
Front of Bell Housing to end of Trans Case - 21 5/8in (Not including Tailshaft Housing)
Overall Length with 6in Tailshaft - 27 5/8
Overall Length with 9in Tailshaft - 30 5/8
Overall Length with 12in Tailshaft - 33 5/8
Turbo 350 Fluid Specificatons
Fluid Type - Dextron ll or Better. (Some Shift Kits recommend use of Type F fluid, although Dextron ll works well also w/ Shift Kits)
Fluid and Filter Change while installed in vehicle - Requires 5 quarts of fluid. (Considiering use of OEM standard pan)
New TH350 Install with New Torque Converter - Requires 12 quarts of fluid. (This can vary depending on depth of pan, and Torque Converter Type or Size)
Other Turbo 350 Facts
Turbo 350 Uses Same driveshaft yoke as 700r4, 2 Speed Powerglide, Muncie M20, M21, and Saginaw 4 speed manual transmissions as well as others.
Turbo 350 uses a Detent Cable (aka kickdown), Vacuum Modulator and Governor to control shift points.
Turbo 350 Detent Cable must be hooked up to have kickdown passing gear function, and proper shift points. However, unlike the 700r4, the detent cable is NOT a TV (Throttle Valve) cable that regulates fluid pressure although their functions are very similar, but a Turbo 350 will not be harmed by driving without the Detent Cable connected but shifts will be very early.
Turbo 350 Non Lock Up Torque Converters and Vacuum Modulators Interchange with Turbo 400. Both TH350 and TH400 use the same part #'s in TC and Vac Modulators.
Turbo 350 to 700r4 Conversion & Vice Versa
Turbo 350 with a 9in tailshaft, which is most common used in Squarebody trucks, is only 5/8in longer in overall length of a 700r4. Also using the same spline count on the outputshaft, in many cases, a Turbo 350 equipped truck can be easily converted to 700r4 without even modifying the driveshaft provided the driveshaft lengtih is the right size to allow for 5/8in compensation in the yoke. Cooling lines are also in the same location as is the shifter linkage to the manual valve for gear selection. Also works in reverse, if you wish to convert from 700r4 to Turbo 350.
Just to prove they exist, Here is a photo of a BOP Turbo 350 with a 12in Tailshaft Housing. This is a true Long Shaft Turbo 350, where most refer to as the 9in tailshaft transmission commonly used in Squarebodies as a Long Shaft.
A nice cutaway view of a Turbo 350. This give an idea of what a Th350 looks like insdie when assembled.