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HotRodPC
02-24-2011, 03:09 AM
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.
http://www.gmsquarebody.com/forum/attachment.php?attachmentid=1513&d=1298534920

A nice cutaway view of a Turbo 350. This give an idea of what a Th350 looks like insdie when assembled.
http://www.gmsquarebody.com/forum/attachment.php?attachmentid=1605&d=1298963012

HotRodPC
02-24-2011, 03:25 AM
View of Turbo 350 Internals.
http://www.gmsquarebody.com/forum/attachment.php?attachmentid=1514&d=1298535816

Breakdown of Front Pump, Intermediate Clutches, Direct and Forward Clutch Drums.
http://www.gmsquarebody.com/forum/attachment.php?attachmentid=1515&d=1298535839

Breakdown of SunShell, Planetaries and Low/Reverse Clutch Pack.
http://www.gmsquarebody.com/forum/attachment.php?attachmentid=1516&d=1298535857

Breakdown of Case, Tailshaft Housing, External Componets, Valve Body and Lock Up Solenoid if Equiped on Turbo350C Model.
http://www.gmsquarebody.com/forum/attachment.php?attachmentid=1517&d=1298535864

HotRodPC
02-24-2011, 03:27 AM
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
02-24-2011, 11:01 AM
Damn! :popcorn:

Swims350
02-24-2011, 11:23 AM
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 pussy 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
02-24-2011, 12:39 PM
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
02-24-2011, 01:08 PM
yep, it's ok, it was just info I remembered from my swaps and work on them.

HotRodPC
02-24-2011, 01:18 PM
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
02-24-2011, 01:22 PM
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.:High 5:

Swims350
02-24-2011, 01:41 PM
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
02-24-2011, 02:02 PM
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 shit guys! :High 5:

HotRodPC
03-01-2011, 02:13 AM
Stick that info in there HR! Good shit guys! :High 5:

I did and also added a cutaway pic.

HotRodPC
05-30-2011, 04:11 AM
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.

http://www.gmsquarebody.com/forum/attachment.php?attachmentid=2916&d=1306743102

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
05-30-2011, 04:20 AM
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.

http://www.gmsquarebody.com/forum/attachment.php?attachmentid=2917&d=1306743588
http://www.gmsquarebody.com/forum/attachment.php?attachmentid=2918&d=1306743603

HotRodPC
05-30-2011, 12:30 PM
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.

http://www.gmsquarebody.com/forum/attachment.php?attachmentid=2071&d=1300866525

http://www.gmsquarebody.com/forum/attachment.php?attachmentid=2750&d=1304455934

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.

89Suburban
05-30-2011, 02:12 PM
:popcorn:

Swims350
05-30-2011, 02:54 PM
awesome info dad's trans case I got laying outside has the roller bearings.

davbell22602
05-30-2011, 05:48 PM
Recommend this to be a sticky.

CerroCowboy
09-17-2011, 09:10 AM
could you take some pics of where the vac lines hook into the transmission?

HotRodPC
09-17-2011, 09:27 AM
It only gets one vacuum line off the vacuum modulator. Rear of trans case on passenger side.

WHEELMAN
09-17-2011, 05:47 PM
what about the steering column..for the 700r4 you need the over drive on the column there is an adapter-i think the name is lokar.com so you do not have to change your steering column if you do not want too

WHEELMAN
09-21-2011, 01:51 AM
i watched a utube video.they changed out a 350 trans for a 700r4..and you do not have to change the column you will not be able to shift down in to one..no manual shifting..drive shaft has to be cut and rebalanced

davbell22602
03-03-2012, 08:45 PM
I thought this was a worthy addition to this thread. Pics of Dave's recently purchased 4x4 Th350 trans with the very short output shaft.


Bought this today for $50. Here's the ID numbers on it C4E111485

http://i938.photobucket.com/albums/ad228/davbell22602/GM%20Squarebody/0303121620.jpg

http://i938.photobucket.com/albums/ad228/davbell22602/GM%20Squarebody/0303121620b.jpg

http://i938.photobucket.com/albums/ad228/davbell22602/GM%20Squarebody/0303121620a.jpg

http://i938.photobucket.com/albums/ad228/davbell22602/GM%20Squarebody/0303121621.jpg

davbell22602
03-04-2012, 05:06 PM
I heard today a np208 will work on this also.

bucket
03-04-2012, 05:26 PM
I heard today a np208 will work on this also.

You either heard or were told wrong.

82chevy350
01-10-2013, 02:06 PM
Ok i got a guy that wants to do some trading for my dirt bike.. Hes got a 350 010 nickel block and a thrbo 400 trans thats short shaft he said he pulled it out of a 1 ton. I currently have a long tail turbo 350 in my 82 longbed. I know ill defiantly have to get a turbo 400 yoke swaped out on my drive shaft. Now my question is will i have to have the shaft shortened or lengthened. Im trying to round up a trans that will hold up to my 383 im building. I do plan on rebuilding the turbo 400..

68post
03-06-2014, 10:47 PM
One minor detail which doesn't matter in a th350 thread is that the th400 and the Muncie M22 (Rockcrusher) share the same yoke , but not the th350 and the M22 as was mentioned as being the same.

M20 and M21 - yes, same as a th350. I'm old but do remember that.

HotRodPC
03-06-2014, 11:40 PM
One minor detail which doesn't matter in a th350 thread is that the th400 and the Muncie M22 (Rockcrusher) share the same yoke , but not the th350 and the M22 as was mentioned as being the same.

M20 and M21 - yes, same as a th350. I'm old but do remember that.

Very True. M22 is fine spline input shaft and finer splined 32 spline and thicker shaft. I'll see where I put that and make that correction.

1low4x4
03-12-2014, 12:05 PM
How do you tell a regular 350 trans form a 350c?

And I'm assuming th 350c has a lockup converter and regular th350 doesn't?

HotRodPC
03-12-2014, 04:13 PM
How do you tell a regular 350 trans form a 350c?

And I'm assuming th 350c has a lockup converter and regular th350 doesn't?

Yes, you're right.

Th350 = No Lock Up (No Electrical Plug-in on the Driver side)

Th350C = Lock Up (With Electrical Plug-in on the Driver side usually harnessed to a Vacuum Switch on the Firewall)

If the trans in mounted in the truck, you can ID a Th350C from a Th350 by this connector. Sorry, bad pic, but in the grease, you can see the black connector on the driver side of the case.
http://www.gmsquarebody.com/forum/attachment.php?attachmentid=18349&stc=1&d=1394655941

Out of the truck, you can easily ID the Th350 from the Th350C. The Th350C input shaft looks more like a clutch alignment tool.

1low4x4
03-12-2014, 04:54 PM
Thanks for the Info

tiredtiretodd
07-28-2014, 12:32 AM
I'm going thru my SB and trying to identify my tranny and transfer case. here's a pic of my t case to start.

HotRodPC
07-28-2014, 01:33 AM
Looking like an NP203 full time case to me.

marks86
07-28-2014, 08:11 AM
http://s15.postimg.org/z6t7subcr/np205_1.jpg (http://postimage.org/)
upload png (http://postimage.org/)
heres a np205 see the difference
I can tell by the little plate with three screws in the middle

tiredtiretodd
07-29-2014, 03:33 PM
http://s15.postimg.org/z6t7subcr/np205_1.jpg (http://postimage.org/)
upload png (http://postimage.org/)
heres a np205 see the difference
I can tell by the little plate with three screws in the middle

Thanks marks86, I am looking into a NP205 that a buddy has laying around. I think he said I could have it for about $50 if I came and got it out of his yard.