Turbo 350 Information and Facts

[HotRodPC]

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:
1st 2.52
2nd 1.52
3rd 1.00
Rev 1.94

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.

You must be registered for see images attach

You must be registered for see images attach

 

[HotRodPC]

Exploded Views of Turbo 350 Internals

View of Turbo 350 Internals.

Breakdown of Front Pump, Intermediate Clutches, Direct and Forward Clutch Drums.

Breakdown of SunShell, Planetaries and Low/Reverse Clutch Pack.

Breakdown of Case, Tailshaft Housing, External Componets, Valve Body and Lock Up Solenoid if Equiped on Turbo350C Model.

 

[HotRodPC]

Anyone know of anything I have incorrect, or any good piece of into worthy of adding, please let me know so it can be corrected. I'm a bit rusty on some of this, and sure don't want to be passing on bad info.

 

[89Suburban]

Damn!

 

[Swims350]

well the adapter or tail housing is the same bolt pattern for the th350 and the 700r4's.

In 4x4 applications, unless you want to move the crossmember and such you can buy an adapter/spacer that is around 1-1/2 to 2 inches thick, and the right length shaft to swap a th350 right in place of a 700r4 4x4. I've got it in my 88 k1500.

Without the spacer and the right length shaft, you'd need everything moved forward, and we all know the issues that cane cause.

TCI has this kit, northern auto parts has it, and another, it's around $150-200. it comes with the output shaft, spacer, bolts, washers, nuts, dust cover, dipstick, kickdown cable, and not sure if anything else.



Good point on the cable though, I hear guys argue o the 350's with no cable they will burn up, well my th350 aint got a cable, it's in a 4x4 with 3.42's and 30 inch tires and runs fine for over a year now. it is a ***** though.


Speaking of cables, there are 2 length cables.

The longest or one with the slot in the end fits the older vehicles and their manifold brackets etc.

The later style like for th350c's is shorter and has a clip like the 700r4, not a slot. The longer style cable will not fit and work if your bracket is for the new style cables.

You can buy a universal bracket, or buy the right cable for your factory bracket.

The way to tell is measure from the bracket that holds the clip portion and adjuster section of the cable, to the stud on the carb or tbi.

That same section or clip is the same as the 700r4 so the bracket for 700r4 or th350 should be the same, but the cable IS NOT, the 700r4 cable is thicker on the trans side and will NOT work for a th350.

 

[HotRodPC]

You're right Swims. I had intended on mentioning that about the T350 and 700r4 having the tailshaft pattern in common. To much info and I forgot to add it. So yes, Turbo 350 and 700r4 share the same Tcase adapters for 4x4.
And right again. The measurement from the front of the bellhousing to the end of the cases on the T350 and 700r4 are different. The T350 is 21 5/8 in length, the 700r4 is 24 in. So this adapter and spacer you refer to extends the T350 case 2 3/8in so that your driveshaft, and Tcase linkage stays the same. Or you can modify your driveshaft and Tcase shifter rod.

BTW, The trans being burnt up if the cable is NOT hooked up is on 700r4 NOT Th350. You can run the Th350 wo cable, just that your shift points will be early, and no passing gear. The Th350 does perform much better with it hooked up but no harm if it's not hooked up.

 

[Swims350]

yep, it's ok, it was just info I remembered from my swaps and work on them.

 

[HotRodPC]

yep, it's ok, it was just info I remembered from my swaps and work on them.

Thanks for the input. That is what's great about forums. I was doing this at 2:30am so I was pretty tired. I had it in my mind to add about the Tcase and kept thinking, what did I forget? I know there is something else I wanted in here. That was it. You get info like this put together, and other add a bit more, or share conversion experiences etc, next thing you know, you have more and better info than any book will provide all in one place.

 

[89Suburban]

You get info like this put together, and other add a bit more, or share conversion experiences etc, next thing you know, you have more and better info than any book will provide all in one place.

 

[Swims350]

couldn't have said it better, plus pure facts and experiences, not like asking questions and getting guesses or something.


Oh takes 5 quarts of fluid for a filter change/pan drop only.

12 quarts from dry torque converter and all, Give or take.

 

[89Suburban]

couldn't have said it better, plus pure facts and experiences, not like asking questions and getting guesses or something.


Oh takes 5 quarts of fluid for a filter change/pan drop only.

12 quarts from dry torque converter and all, Give or take.

Stick that info in there HR! Good **** guys!

 

[HotRodPC]

Stick that info in there HR! Good **** guys!

I did and also added a cutaway pic.

 

[HotRodPC]

Here are a few pics of differant Th350 parts you will come across. Same parts, just differant designs. Obviously anytime you can use a Torrington roller bearing instead of a thrust washer, you want to do so.

First is the front pump. Notice 1 has a thrust washer, and the other has a torrington roller bearing. You can still use selective washers behind both the thrust washer and the torrington bearing to acquire the correct end play measurement. You can actually simply buy the torrington bearing for this upgrade and replace the thrust washer as long as your end play is not to tight with the torrington. Some of the later pumps are machined down a bit further to make use of the torrington bearing. But there is always a good chance you'll be able to use the torringtin bearing instead and still be in proper tolerance.

 

[HotRodPC]

Next is the front planetary. One has the thrust washer, the better one usually found in later th350s has the torrington roller bearing. The planets do interchange with older models so if you see a roller type, hold on to it for the build you do that might have the thrust washer. The obvious difference here is less wear and less friction which means your transmission can last longer, run cooler and absorb less horsepower. Very minor, but using torring in 3 different places, the benefit does add up. If you don't have the torrington part, don't let it hold your build and use the thrust washer type. Its also strong. Just that rollers are better of course.

 

[HotRodPC]

Then there is the sun gear that is connected with the output shaft. Between the sun gear and rear planet there is the older design that uses a thrust washer between the 2, and the later design where the sun gear is machined out to make room for roller bearing.

If you have all the right OEM parts you can build a Th350 that has fully rollarized planetaries. There is also roller bearings between the drums and pump making almost the whole transmission rollarized. At anyrate, you have some pictures of what to looking for and holding onto when come across them.