720 transmission confusion

[Madkaw]

It’s been days of reading to see what options I have for my trans on my 1983.5 4x4 . It is a 71b trans and it is bad - metal pieces. So it’s a shorty -12” extension I believe I read. So when I shop for used trans in the yards or web sites they show listings for 2WD with short and long extensions and 4WD with short and long extensions . With a divorced transfer case wouldn’t the 2WD and 4WD with the same length extension be interchangeable if they both were used on the z24 motor?

Also read that the 85 and 86 were bit hardier trans , but the C is even better . Once again - it needs to be a Z24 motor for a direct swap - correct?

I was quoted 1000$ to rebuild my B, so not sure what to do now

[datzenmike]

71B

Shorts are 26"

Longs are 31.5"

 

Yes the short 4x4 and the short 2wd transmissions will swap but best results if 2wd into a 4x4 rather than 4x4 into the 2wd. This is because the 4x4 speedometer is mounted in the transfer case and the 4x4 transmission is not machined to take the speedometer sleeve. If using a 4x4 transmission in a 2wd you won't have a speedometer.

 

The '85 and up transmissions have an improved counter bearing in them.

 

'86.5-'88 D21 Hardbodys use a 71C transmission but are around 30" long? and may not fit. A 71C and a modified driveshaft length is likely much, much less that $1,000 for a rebuild. BTW $1,000 is almost twice what a rebuild is worth. 

[Madkaw]

That helps. So I, better off with a swap since I have a 4WD and a transfer case , so Speedo will work. So there was two different length trans for the 2WD’s? So when I search 2wd trans and they say 16” extension , they are referring to the C trans which is 30”?

So it’s possible to take 4” off the shorty DS and it still works ?

Rebuilds must be pricey in the Midwest - I think it’s going rate, but I’ll check around.

The other possibility is other 71c trans from other engine types( vg30) if I swap front case

[datzenmike]

I missed you had the 4x4 so a 2wd trans will work for you.

 

720 trans are short and long at 26" and 31.5". Just match the length to what you have and you're good to go. 

 

The 71C is a different lengthy again  would need the driveshaft shortened. The shifter is also different placed and farther back.

 

 

BTW... there were 4 speed 71B transmissions so watch out.

[Madkaw]

Damn -just when I think I have it figured out - I get the old - shifter in the wrong place - problem. I have the short console so I’m betting I have the shorty trans.

So the C trans are different lengths that are different than the B trans. So the C trans has a short and long , but not the same short and long as the B

[datzenmike]

Yes. The D21 truck is close to the 71B long.... but only close

[Madkaw]

I don’t mind shortening or whatever to a DS , I just don’t want some funky shifter arrangement in the cab. I figured a C trans from a Napz truck would put the shifter in close proximity and be clocked the correct way- I can deal with that to get the better trans and save $$

[Madkaw]

And thanks again for the info and your patience

[datzenmike]

The 71C from a Z24i or a KA engine will both work. They share the same mount to engine bolt pattern. That's a lot of trucks to pick from

[Madkaw]

Well I will be carrying my bad trans around with me when I go hunting the salvage yards so I can match up things .

 

I guess a later year B trans 85-86 is also decent choice because they started to improve them from what I read . Not sure if there is a way externally to tell the difference between an early and a late though

[datzenmike]

If already out you can. The 7 bolt cover plate directly behind where the clutch would be has a larger bulge for the larger counter bearing under it. That's the one to the bottom of the input shaft. It's not much but easy enough to see if you have your transmission with you.

[Madkaw]

Good stuff Mike - thanks