Replacing 3spd manual, with 700r4

[RyanToms]

Anyone ever replaced a 3spd manual with a 700r4?   I have a 78' w/ a 208 transfer case.   Have a buddy with a 700r4 tranny to play with.  Can I get a tail shaft adapter to bolt this to my transfer case, with the swap, or modification, of the tailshaft.   What else, as for at electronic to cable conversion do I have to do on this newer tranny?   Lock-up on the torqe converter? 

Am I wasting my time, should I just find a TH350?

[HAULIN IT]

Ryan, Are you sure you have a 208? If you do someone put it in there. Is the transfer case Aluminum or cast iron? Let us know & we will proceed from there. Lorne

[Blazin]

Agreed, it should be a 203 or 205.

[RyanToms]

No, I'm not sure, was going off of memory.  It's not full time, I will check soon and let you know.  Has 4hi, 4 lo, 2 hi , but no 2 lo

[Mike Phillips]

I've driven my 75 Jimmy on one 200 mile trip since converting it from a 4-speed to an automatic using a 700r4 tranny and the Jimmy came in at 13 mpg.  This is with a brand new engine, (8:1 compression), 4:11 gear ratio and 31" tall tires.

If memory serves me correctly, my 71 3/4 ton Chevy truck with a 396 and 4:11 gears and a turbo 400 and 44" inch tires got a solid 11 mpg for the 12 years I drove it.


If gas mileage is important to you then do the work it takes to install a 700R4 tranny.  If gas mileage isn't a factor in your decision then whatever works best is best.


At this point, I think having a big block is worth the extra torque in trade-off for the mpg as far as usability goes for a daily driver.

Another way of saying that is compared to my 1971 Chevrolet 3/4 ton 4x4 with a big block 396 engine, the 1975 GMC Jimmy with the 350 small block moves out like a turd in a bowl of oatmeal.  (Old Drag Boat lingo when talking about Jet boats you just blew out of the water).

FWIW & YMMV

Big Blue


Future Big Red



Owning and driving things with big block Chevy's kind of spoils you and taints you at the same time.

[Blazin]

I agree there ain't nothing like plowing with a big block. As long as the tires don't spin you are making forward progress with little to no effort.

[RyanToms]

I'm new to knowing what to do with the TV cable and any other modifications needed to get this 700r4 to work.  Lock-Up switch on the torque converter.   I can get the physical parts taken care of, shaft, adapter, and mounting, but not good with the with the internals.

[HAULIN IT]

Ryan, I'm not sure what you mean by "internals".  The lock-up portion has had a couple different plug connectors, but the function is the same. What is best in your case I feel is get a lock-up kit from one of many available for the installation into a vehicle that did not have an original lock-up transmission. The TV cable is critical to the operation of the transmission. The arch on the carb must be correct to pull the valve in the tranny the correct amount, the bracket must be strong enough not to move around. What carb do you have? Post up & we'll help you through it. Lorne

[RyanToms]

not sure which carb, will find out.  Cab is body lifted, so should have enough room between, right?   The lock-up switch is all electronic, correct?  What does the TV cable do, what controls it, and what does it actually do to the tranny, control the shift points right?

[RyanToms]

What about the issue of using a 2wd 700r4?  As I said earlier, I know nothing about tranny's.  Looks like that output shaft has a bolted housing (4 bolts).  Can I take that off and bolt my transfer case adapter to that, either directly or through a special adapter?

[Captkaos]

you cannot use a 2WD transmission on a 4wd application.  The output shaft is not the same length.  You would have to tear a 2WD completely down to swap the output shaft to the 4x4 style...

[Blazin]

Plus the dust shield on a 4x4 700R4 is cast aluminum, & structural. It has to strut type rods that run from the bottom of it up behind the motor mounts. A 2x dust cover is made out of tin.

[RyanToms]

Is it only an issue of shaft length though, or is it a different shaft diameter and spline count?  I'm a confident I can model/design up an adapter to be fabricated that will allow for the existing shaft length, while also adapting the bolt pattern at back of transmission to front of transfer case.  I just need to know if length is not the issue, will the output shaft of a 2wd tranny sleave into my transfer case, will the splines and diameter match?  If so, I'd be happy to make, supply drawings of the part for anyone else who'd like to do the same, after I can test the success of it of course.

Thanks for all your guys help.

[HAULIN IT]

Ryan, Three speed manuals are far from my strong point, however I will offer a few words. The three speeds I have seen all had coarse (10?) spline, the 4 speed manual has 10 spline & can't see them making a different T-case input for an oddity like the 3 speed. As was mentioned, the 2wd output shaft is going to be way long, yes you may be able to mate the two up somehow, but you will have to either move the engine ahead or the transfer case back. Both ideas have their own set of problems. I feel you should get the right "tool" for the job, either a 4wd TH350 or 700R4 & the correct T-case (likely the most cost effective) or the proper adapter & move on. Lorne