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'77GMC 3speed 305 V8 2 barrellong bed

E

Excarguy08

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I want to covert my 3speed to R 400 automatic.What's the best way to get the transmission so I have the right bell housing and match up for the rear end.
A friend suggested I get and old Pontiac station wagon or similar wreck and take the whole transmission and rear end assembly.
 
Do you mean a Turbo 400, or a 700r4? If you plan on doing a transmission swap You might as well get a the 700r4 as it has overdrive. You can get one out of your body style truck, blazer, burb, or van etc. I think anything after 81 had them, and the bell housing/ transmission is one piece. Get the cross member and drive shaft with it, if you find a donor out of a long bed pickup like yours you won't have to have drive shafts made. Depending on what gears you have in the rear end and what you want out of the truck will determine if you should swap out the rear. I guess you mean you have a 3 speed manual (with granny), so you can decide how you want to fill in the hole in the floor but you will still have the high hump unless you want to change all that too. Also you will need the auto pedal assembly (or just remove the clutch pedal), steering column, shift indicator/ gauges, and the longer speedo cable. I hope this helps.
 
700r4 Swap Q

Does the 700r4 simply bolt up in place of the old Turbo Hyromatic three speed slush box ? .

I'm piqued .

TIA ,
 
th400 (turbo 400) - 3 speed auto - typically used behind high hp/torque motors
th700r4 - 4 speed/overdrive auto - light duty, but better highway fuel economy

Like Roadhazard suggested, I would get the transmission, crossmember, and driveshaft from a donor truck.

For the shifter, you can get an auto steering column or buy a floor shifter (Hurst, B&M, Lokar, etc).

There's no need to change the rear end if you don't want to. If you have a 2 piece driveshaft you might be able to get away with using the front half on your old rear half (I'm not sure if there are any differences between the years at the slip joint).
If that won't work, you can use a conversion u-joint at the axle. Your truck should have a 12 bolt rear which uses a 1310 yoke/u-joint. You can get a conversion u-joint to S44 (700r4/10 bolt, '83 and newer 1/2 ton rear) or 1350 (th400/14 bolt 3/4 - 1 ton rear) depending on what trans you are getting and what axle it had behind it.
 
Yes, the 700r4 uses the same V8 engine bolt pattern as the th350 and th400.

Forgot to mention the 700r4 also uses a throttle valve cable to shift, make sure you grab this and you will need a bracket to attach it to the throttle on your carb. Without this properly set up, the trans will burn up very quickly.
 
Bolt Patterns

O.K. , here's my real question :

Will it bolt to my L6 ? .

TIA ,
 
' Slushbox ' Vs. ' Speeder ' Trannies

Yeah , I had the same attitude 40 years ago when I was spry and could easily operate a clutch pedal...... :rolleyes: .

Now , by force not choice , I have to have Slushboxes in my entire fleet :( .
 
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