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Performance th350

We have an excellent track record with our TH350’s. Deep into the 10’s without failure, they have proven to be a very tough unit for a reasonable price. We feel they are a very good choice in cars up to 600 HP/TQ but capable of up to 800 HP/TQ especially in lighter cars. The limiting factor is the stock planetaries. There are aftermarket planets available to make them live at even higher power levels but we usually recommend a TH400 for a dedicated 600+ HP application. Our goal is to provide long term reliabilty. Our base model TH350 has lived at over 600 HP reliably.

General motors turbo hydramatic 350,TH350,turbo 350, help you build,turbo350,thm350. General Motors Turbo-Hydramatic 350. Need help, at your location, with a rebuild in Southern California? I can come to you, or give help by telephone! This website is sponsored by a General Motors factory-trained. Automatic Transmission, Forward Shift Pattern, Automatic Valve Body, Chevy, TH350, 4WD,1982 and later 208NP Transfer Case, Each. Part Number: TCI-311700.

As with all Jake’s Performance transmissions they include all new friction clutches, bands, steel plates, soft parts, filter, modulator (if applicable), as well as hydraulic upgrades, and other modifications depending on power level. All TH350 transmissions include a new pan.

Our base model TH350 has lived at over 600 HP reliably. As with all Jake’s Performance transmissions they include all new friction clutches, bands, steel plates, soft parts, filter, modulator (if applicable), as well as hydraulic upgrades, and other modifications depending on power level. All TH350 transmissions include a new pan. The TH350 transmission was first mass produced in 1969 for both 2WD and 4WD vehicles and remained prevalent through 1982. The transmission was standard for most V6 and V8 vehicles. The Th350 transmission can be identified by its’ 21-1/2' long one piece aluminum case. The transmission has an integral or non-removable bellhousing.

Stage 1 TH350 is reliable to over 500 HP/TQ. It’s a very tough unit. It has several key modifications that increase it’s strength. Increased line pressure and lube flow. Additional bushing area, close attention to bushing clearance, blueprinted pump assembly, select cores used, and other areas that our experience has shown other shops and builders are not paying attention to.

PriceBuild #Build Description
$1700TH350-1AAuto shift
$2050TH350-RMVBTBReverse Manual Valvebody with Transbrake

This is our Stage 1 TH350 build with a heavy duty K case core and using a reverse manual valve body with engine braking for rock-crawling or off-road use.

PriceBuild #Build Description
$2200TH350-RCARockcrawler build
$2550TH350-RCRMVBTBReverse Manual Valve Body with a Transbrake

Our Stage 2 TH350 includes all the features of the Street model plus a 36 element sprag and drum upgrade, special retaining ring on the sprag, and a deep aluminum pan standard. 750 HP/TQ capable.

PriceBuild #Build Description
$2200TH350-2AAuto shift
$2550TH350-2RMVBTBReverse Manual Valvebody with Transbrake

Stage 3 TH350 will add a billet 300M input shaft making it good for 800 HP. Typically at this power level we recommend a TH400. Please let us help you with selecting the unit that best suits your needs.

PriceBuild #Build Description
$2450TH350-3AAuto shift
$2800TH350-3RMVBTBReverse Manual Valvebody with Transbrake

Upgrades are available. 4340 or 300M input shafts, fully rollerized with lightweight parts for competition applications, low gearsets for heavy cars or truck applications. Call for additional quoting.

Shipping is $200 within the continental United States.

(shown as one very long page to allow you to
quick-print the whole thing for reference)

More than 25 million were produced;
used in cars, vans, trucks, and motorhomes.
Buick - Cadillac - Chevrolet
GMC - Oldsmobile - Pontiac
The number-one choice in GM-powered hotrods.
Can teach you. Build yours yourself, with help!
I am a retired rebuilder and can assist you with
your bench (rebuilding) job, at your location in
the San Fernando Valley or the Los Angeles area.

It is far easier than most engine guys think it is.
I can quickly help you or teach you this knowledge.
Build it yourself, you know that
there were no shortcuts taken.

And it is FUN!
I will help with the real 350s of the years above,
but NOT with the weak '350-C' models that followed.
(The 1980 to 1986 'C' electronic lock-up
models were introduced to supposedly improve
fuel economy, but the modifications also lowered
the reliability & strength of the transmission.)

TRIVIA: most of the vehicles that came
with TH-350s had chrome bumpers!

Rebuilding steps:
  1. disassemble completely
  2. steam-clean case, rear housing, and pan
  3. obtain rebuild kit and any needed hard-parts
  4. rebuild all components
  5. reassemble

Tools needed:

#2 (left), #3 (right)

  1. pump-puller
  2. clutch-drum compressor
  3. 350 rear-piston tool T-0151
  4. snap-ring pliers (Snap On's srp1cp)
  5. seal tools
  6. ratchet, 1' extension, 9/16' & 1/2' sockets
  7. 9/16' & 1/2' wrenches
  8. razor blade
  9. shift seal tool T-1001
  10. accumulator cover tool
(or use my tools!)

3 popular books for rebuilding 350s:
Turbo Hydra-Matic 350 Handbook
by Ron Sessions
ATSG Techtran Manual 350/350C
by Automatic Transmission Service Group
Haynes General Motors
Automatic Transmission
Overhaul Manual 10360
by Godfrey/Haynes
Find them on or with Google.

Supplies needed for a rebuild:
  1. assembly lube
  2. rebuild kit and any needed hard-parts
(kits are available locally quick; I do not sell parts,
however, I keep on-hand small clips and several
other things sometimes lost during the process!)

If you have an 'adjustable' modulator,
the shift-timing adjustment screw
is down the vacumn nipple, the
hollow tube at the left end above,
pointing towards the rear of the vehicle.
To make it upshift a little later (higher mph),
turn the screw in / to the right.
Slightly later shifts are popular for when towing
or carrying a heavy load, keeping the transmission
in the lower gears for a few extra miles per hour.
If you get a drop of transmission fluid when
you pull the rubber hose off of this left end,
the modulator is bad and it is letting trans
fluid be sucked up into the intake manifold.
This often explains why you
needed to add fluid occasionally yet
there was no leaking on to the ground.

If the modulator is not plugged into
proper vacumn, the trans will shift very late.
It goes to the intake manifold,
not to the carburetor.
With the engine idling in park, vehicle supported
safely, pull off the hose at rear of the modulator.
Feel for light suction from the hose end that
had been on the modulator. No suction =
no vacumn = will not shift properly.

A 350 rebuilding secret:
There are NO adjustments
made during a 350 rebuild:

simply, the right parts have to
go back in using the correct order

Example of a rebuild kit

Where many installations go bad-
If the torque converter is not 'in'
all the way (some use a '3 clicks'
method to determine this)
prior to
the bellhousing bolts being tightened,
the converter's hub can break the pump
gear, leaving the transmission useless.
A clue: if you can get your fingers in between
the bottom front of the trans case and the
torque converter, before the 6 bellhousing
bolts are in, it is not in all the way.

A trick: to keep the the torque converter locked
deep into the transmission pump while it is
wobbling on the jack or being lifted up to the
engine block, so it doesn't shudder out forward,
use a 3/8' wrench attached to a torque converter
dust-cover hole using a dust-cover bolt. Angled
correctly, it is like keeping a finger gently
pushing against the converter, lightly holding it in.
A tip: slowly pour a quart of trans fluid into
the torque converter before inserting the
torque converter into the transmission.
A reminder: one of the usually most-worn bushings
in a 350 is that in the pump body that the converter
hub fits into. Be sure to replace this bushing if not
using a new replacement pump body & gears.

See photos of a350 rebuild!
Want to see some outstanding photos of a 350
being rebuilt? These are not from me, but by a
knowledgeable builder in Texas. Here is a link
to a forum he has them all posted on: click here.

350 SHIFT KITS (coming soon)

On DVD: a 350 rebuild
GM Turbo 350 (1969-1986)
Transmission Rebuilding DVD

HEAVY-DUTY 350 (coming soon)
The most popular HD 350 parts:
--case-hardened intermediate clutch outer race
--heavy-duty sprag on the direct drum
--hardened input shaft
--metal pump-stator rings

(coming soon)
Paint causes heat-retention issues?

Emergency 350 rebuild-parts that I keep on-hand:
(things that don't come in a rebuild kit but often get
lost or damaged during a rebuild, or seals/bushings
that sometimes get damaged during the rebuilding)

  • front seal 44070 / 38151V
  • rear seal 44074/ MC248
  • pump-bolt washer gaskets
    44309 / 13268A
  • center-support anti-clunk spring
    / D61915
  • pump bushing 44034 / 8005
  • pump pressure screen 44012 /
  • governor screen 44014 /
  • steel 1/4' valve-body check balls
    / 13924S
  • detent wire link 44997-7
  • steel plates for forward & direct clutches
    44126 / 35100
  • thrust washer kit, complete set
    44200 / K35907
  • steel plates for low & reverse clutches
    44134 / 35101
  • speedometer gears (plastic)
  • speedometer gear clips,
    wide M463FB / 35226B and
    M463F / 35226
  • rear piston clip ring
  • speedometer latch
  • front planet clip
  • clip for direct-drum springs
  • pump-stator rings
  • Transjel assembly lube M465TJ
    to find parts in your area.


To see an exploded view of a
Turbo 350 transmission,

350 Governor
Found under a round capon the driver
side of the transmission,just forwardof the
extension housing,it often is a problem source.
It can be inspected with
the transmission fully installed.

The first 2 things to check:
--the plastic gear at the skinny end
--the moving valve inside the long shaft

(more to be added here later)
Need to call me to discuss a 350?
(Area Code eight-one-eight)
eight-eight-three, six-nine-six-nine
Ask for Peter

Need to read an 8-page TH-350
parts catalog and exploded-view diagram?!

Our friends at Transtar have
one here that you can
click to download:
(This is their main catalog;
go down to the 4th choice
(Domestic- GM),
click to download it;
then open it--
the Turbo 350 section has
pages numbered
at their bottoms
of 30 through 37,
with the title '350,350C' ):

Click Here
It shows every 350 part,
and it has their part numbers
so you can order them from Transtar.

Here are the 3 types of pan filters:
brass ----- felt ----- nylon

Th350 Transmission For Sale Craigslist

Here is your 350
'Tip of the day':

While the transmission is out of
the vehicle, inspect the flexplate.
It is bolted to the
back of the engine;
the starter motor turns
the large gear welded
to its outer edge.
Stress-cracks are very common
between the crank bolt holes
and the weight-reduction holes

or the torque-converter bolt holes.

Th350 Rebuild Kit

Breaks here are sometimes a
source of 'mystery clanking'.

Faster and cheaper to replace
the flexplate while the trans is out.

Th350 Transmission Seal Kit