Sorry to cross post, you can throw rotten ovals at me... but I'm thinkin' you diesel guys might be better people to ask than the 80-86 forum folks...

I am trying to find a solution for tall gearing for my upcoming truck rebuild and SWB chop project. Right now I have a narrow range T19 with Gear Vendor overdrive behind a 6.9L diesel, and 4.10 axle gears. The GV unit helps (0.78 overdrive) gives me a 3.20 final axle output, but I still feel like I need one more gear. I am trying to get a final ratio somewhere around 2.50-ish.

The obvious is a ZF 5 swap (double overdrive), but in my area it is extremely difficult to find used ZF's especially with the diesel housing and 4x4 configuration. I don't really want to pay $2,000 - $2,500 for a rebuilt one after core charge, not to mention I would still be lacking the clutch, shifter, cross member, master/slave cylinders, fork etc... $$$.

Plan B is to do a R & P gear swap, but I read up and found that the D 60 front axle can't take a 3.08 (which would be perfect) because the housing is too small for the big pinion gear. I did see mention of a 3.31 that came in some D 60's in the 70's and 80's. Does anyone know if this would work in the front 4x4 D 60 axle? Perhaps more important, does anyone know if these are still available anywhere? All I can find is 3.54 and 3.55.

The catch is that I have a sterling 10.25 rear axel, so I won't be able to get a 3.31 for it, but the local JY has plenty of rear D60's for cheap. If I could get the 3.31's it would be worth changing out the rear axel since I'm going to have to have a new drive shaft made anyway and the nose length of the housing won't matter. 3.31's with the GV overdrive would get me pretty close to where I want to be... 2.58 final output.

BTW, I'm not terribly worried about my low end, because my BW1345 transfer case is X2.74 in Lo, so first gear Lo is still like 36 to 1. Plenty low enough IMO. 1st gear Hi is 13.31, just about like the 2nd gear in granny T18's that I know and actually prefer over the narrow range T19.

 

Piston Auto Recycler, LLC USA-AZ(Yuma) 928-782-4399 / 928-782-3980

lists a 89 ZF 5 speed on Car-Part.com--Used Auto Parts Market for $700.
it is out of a superduty truck, but you should be able to unbolt the driveshaft brake and bolt on the transfer case mount if i remember correctly

 

Yup, you remember correctly...

 

I'd pay $700 no problem, but it's a risky 750 mile round trip if it's sold out from under me, not what they say it is, or has any problems. Even Phoenix at 400 miles round trip is a gamble... one that I have lost more than once chasing online used parts and craigslist ads I thought I had a for sure ZF 5 for $400 this weekend, drove 300 miles round trip to see an ancient Clark 5 speed that used to sit behind an 8.2 L diesel in a dump truck. Seller didn't say "ZF" but described it as aluminum and having the drive shaft brake when I talked with him on the phone (NOT... it was rusty and had a large yolk but no brake). *Sigh... I guess I really need to be more careful and less optimistic! I might find one yet, but a drive to Yuma does not fit my planner this week