Need help, at
your location,
with a rebuild
in Southern
California?

This website is
sponsored by a
General Motors
factory-trained
Chevrolet
dealership
transmission
rebuilder, who also
ran private automatic transmission shops
for 10 years!


Buick
Cadillac
Chevrolet
GMC
Oldsmobile
Pontiac



turbo350only.com

I don't sell
any parts
or supplies,




but will tell
you where to
find them!



350 specifications:
cast aluminum case,
iron valve body;
weight- 120 pounds
length- 21 3/4"


4 output shaft
extension
housing choices:
6", 9", 12", 4WD


Here is a 4WD,
the shortest
output shaft:




An output shaft
housing is what the
driveshaft plugs into.
It is aluminum and is held to the rear of the transmission case
with 4 bolts.





Above: example
of a 6" housing.



350 pan shape:



Has 13 pan bolts.
Use a 1/2" socket.



350 pan gasket:



Two types:
Cork and Fiber



There are three
main case patterns:


1) The Buick, Oldsmobile, Pontiac, and Cadillac engine-to-transmission
bellhousing bolt pattern is easily identified by the 'ears' at the top and by the valley
centered at the top,
(below):




2) The Chevy pattern
is peaked at the
top center (below):




3) The dual-fit or
multi-fit pattern case has both patterns built in, and fits any General Motors of those years. You can see both the valley and peak designs (below). The alignment pin holes and the lower bolt are the same.





The alignment of the 350 transmission is
done by two metal pins sticking out of the rear of the engine block; the 6 bolts hold the trans straight against the engine block.


Bolt 'tip/trick':
Removing the top 2
bellhousing bolts from
underneath the car is made easier when the rear of the trans is hanging down and then using a 9/16" swivel-socket on a very long extension.
Also: remove the
engine distributor
cap before
removing the
transmission.



QUESTION:

"Do I need to replace
the torque converter?"





ANSWER:

"Mechanically, most
old converters are fine.

BUT:

If your transmission
had any crud in it,
so does your converter,
and there is no way to
ever get it all out now.

Eventually, that crud will be pumped out into the new transmission.


Also:

-- check the shiny chrome part of it that plugs into the front of the transmission. Inspect for wear where it has been spinning in the pump bushing.

--stick a finger deep into the converter.
The gear you feel should turn only in one direction, not both.


If the trans died because a shaft broke,
and there is no clutch material or anything in the pan, maybe you can use the old converter.
Otherwise, it is usually best to replace the torque converter with a new one or with a properly rebuilt one.

Nobody guarantees
a rebuild when using
an old converter."



One way to tell
if a 350 is
'lock-up'
or is a
'regular'
is the
input shaft
(the part that sticks
out the front,
deep into the
torque converter)




lock-up, above
(weaker model
of 1980-1986)


regular, below

(strong model
of 1969-1979)




NOTE:
they use
different
torque
converters






350 forward clutch





350 speedo gear

(some use
'thin clips',
some use
'wide clips')


Different color gears
are different outer
sizes; use to adjust
a speedometer not
reading correct
due to a new
tire height




QUESTION:

"What's the difference between a 6-cylinder
engine turbo 350 and an 8-cylinder engine turbo 350?"


ANSWER:

"Internal only.
The direct drum and the forward drum from an 8-cylinder model have shorter pistons in them, allowing an extra clutch plate each, spreading the wear over more clutch material, making it more heavy-duty. It is easy to make this upgrade."







view from rear






350
accumulator
cover


(it is easy to
damage
its rounded
seal when
rebuilding,
causing
later leaking)



QUESTION:

"I installed a good
working 350
trans, and it now
won't shift past 2nd
(into 3rd/Drive).
What could I have
done wrong in the
installation?"



ANSWER:

"Assuming there
are no internal
issues, usually it
is one of 3 items
listed below.

1. Kick-down cable adjusted too tight

2. Not proper intake-manifold vacumn to modulator

3. Governor not
opening valve

"
(more to be
added here later)





QUESTION:

I'm done rebuilding
and I found this
piece left over--
what is it?




ANSWER:

Known as
a 350
'center-support
anti-clunk spring',


(more to be
added here later)

TORQUE
SPECIFICATIONS:


Pan bolts:
10 1/2 to 13 foot pounds

Converter to flexplate:
46 foot pounds

Bellhousing to engine block:
23 foot pounds

Rear mount to trans case:
32 foot pounds

Rear mount to x-member:
32 foot pounds

Pump:
13 foot pounds

Valve body:
13 foot pounds


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


General Motors
TurboHydramatic 350
1969-1979

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.

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!



turbo350only.com



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
  4. snap-ring pliers
  5. seal tools
  6. ratchet, 1' extension, 9/16" & 1/2" sockets
  7. 9/16" & 1/2" wrenches
  8. razor blade
(or use my tools!)


        

3 popular books for rebuilding 350s:


(left)
Turbo Hydra-Matic 350 Handbook
by Ron Sessions

(middle)
ATSG Techtran Manual 350/350C
by Automatic Transmission Service Group

(right)
Haynes General Motors
Automatic Transmission
Overhaul Manual 10360
by Godfrey/Haynes


Find them on Amazon.com 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!)



MODULATOR 'SECRETS'

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 parts have to go
back in using the correct order
.





Example of a rebuild kit




Where many installations go bad-
TORQUE CONVERTER INSTALLATION :

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 a 350 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


www.LearningByDVD.com



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





TO PAINT OR NOT TO PAINT
(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)




EXPLODED VIEW

To see an exploded view of a
Turbo 350 transmission , click here.



350 Governor

Found under a round cap on the driver
side of the transmission, just forward of 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)




turbo350only.com


Need to call me to discuss a 350?

Call
(Area Code eight-one-eight)
eight-eight-three, six-nine-six-nine

Ask for Peter




How about a FREE 8-page TH-350
parts catalog and exploded-view diagram?!


Our friends at Transtar have
one on this page that you can
click to download:
(it's about the 5th one
down the page center,
with the title '350/350C' ):

Click Here




Here are the 3 types of pan filters:

turbo 350 filters

brass ----- felt ----- nylon




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.


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


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