700R4 Conversion Driveshaft Length

[gbkwork]

I just purchased a 700r4 for my '72 C10 Longbed with a mild 383 and would like to know if anyone can tell me how much the driveline (2-piece) should be shortened. The TH350 I am dumping was original.

Also, I have 3.08 gears in the rear and know that I will need to swap. Any advice on 3.73 vs. 3.42?

Does anyone have advice on a limited slip or posi unit? I figure I should saddle-up now to install when I have the ring and pinion replaced. The rear axle is a stock 12-bolt. What should I expect to pay for labor to do the rear-end if I buy the parts?

Thanks in advance for the help. This MB has been a tremendous help in this project.

[qksilver]

Just an idea, instead of going thru all that, why not swap in an SS Impala rear, it would have the right gears, posi and disc brakes with the correct wheel bolt pattern.
When you change the ring and pinion you would probably want to replace the outer axle bearings then you might need axles..........on and on.
Swap the Impala rear, about all you would have to do is have mounting brackets welded on it and make sure the pinion angle is right

[qksilver]

plus then talk to who is going to make the new shaft/shorten the old and ask them how to measure it properly

[gbkwork]

So the Impala SS axle is the correct length?

This is a great idea as I am in the process of redoing the brakes with a hydroboost set-up.

[qksilver]

I have never done it personally but others have, the width is jsut about right and everything else is what you want.
You would have to redo the barke lines anyway and this way you would aslo have emergency brakes.
I am not sure who did it but I am sure they will speak up

[nate68]

i would recommend 3.73 gears. i was running 3.50 gears (ford 9 inch) and it was a little too tall in OD. i switched to 3.90s and it's perfect

[Greubin]

I installed a 700R4 this past spring. I measured the distance from the rear flange ( where splined shaft exits the tail housing )of the tranny to the front of the yoke on the rear end. Take this dimension and driveline to your local shop to be shortened and rebuilt. They should be able to tell you over the phone how to measure as well.

[SactoJim]

I got lucky!

A number of years ago, I swapped in a TH350 for my (3 on the tree). The tranny I got was a long tailshaft TH350 (9" vs 6".....someone correct me if I'm wrong). When I recently swapped in a 700, the driveshaft fit just right. Seems to me when I did the first swap, it cost about $80 to get a drive shaft shortened and balanced.....and that was 15 years ago....so this was a nice surprise.

Measure your tailshaft.....ya never know.

[nate68]

the 350s and 700s are supposed to be the same length

[8696steve]

Would a gear like a stock 3.07 cause problems with a 700r4 with tcc?

[Green Machine]

Try to find the front half of a driveshaft from a 6 banger, should be about three incher shorter than the V8, might close to what you need.

[gbkwork]

Well, I think I am just going to do this the old fashioned way...eyeball it with a tape measure and take it to the shop.

It looks like the driveshaft shortening is the cheapest part of this project ($100), but my eyes bled when I looked at the quote to rebuild my rear axle and do the ring and pinion swap ($1,200). That is without a ltd. slip.

So, how technical is rebuilding a rear-end. I'm not a complete idiot, just don't want to be driving down the road with a metal mill in my rear-end.

What are your thoughts...should I tackle the rear axle rebuild or not????

[incoma]

Bring the axle to a pro. most shops around here quoted me 750 to do the rebuild (including Eaton ltd slip). I'd get another quote. If you don't set up a rear axle just right it won't last very long.

[nate68]

fortuneately i know a few ppl who know how to set them up and don't charge me much. they make it sound hella easy.

[rfmaster]

There are two (commonly found) different tail shafts used for TH350 6 or 9" - just measure distance from flange to flange distance of the tailshaft. If it is 9" inch then overall length of TH350 should be around 30 11/16 vs. 30 3/4" for 700R4. The 350 yoke can be used with 700R4. Also, early 700R4 (82-87) used 27 spine input shaft - very weak. There are also different lengths 700R4 - Corvette was shorter.

I am in the process of putting all parts together to perform a transplant in my 75 C20 (TH350 to 700R4)