Rear end gear replacement

[dbenamati]

I posted a few months ago about my truck and its very slow speed and improvements I can make to move a little faster without replacing the whole axle and transmission. A guy told me tday that I can simply pull off the differential cover, pull the axles apart and replace the gears to what I want or find in the wrecking yard. Is it that simple? My truck is a 68 3/4 ton and tops out at a whopping 55 mpg. In theory, can I find a rear end gear from a different truck and replace the one I have without getting in to a whole new project. I have never tried this before and whould have someone in a garage do it but I have to know what Im talking about first. Thanks,

[palallin]

It will be MUCH easier to replace the whole rear end than the gears: our Spicer and Dana rear ends require setting the gears up in proper mesh--contact pattern between the ring and pinion gears. Failing to do so--i.e. "simply pull off the differential cover, pull the axles apart and replace the gears to what I want or find in the wrecking yard"--means quick rear end destruction. 'Tain't simple: you have to pull out the pinion shaft and swap the pinon; you have to bolt the "new" ring gear on the carrier (incidently making sure that you have the right carrier for the gear if you don't get the whole thing at the yard); you have to shim correctly--a matter of trail and error with a stock of shims and the proper instruments--and you'll probably have to replace several bearings and all the seals. And your junk-yard gears may well be ready to break anyway.

Swapping in the whole rear end will be much easier: after jacking up and supporting the truck, un-bolt the drive shaft; remove the nuts from the u-bolts holding on the axle housing (The hard part--figure on heat, penetrating oil, and a lllllooooonnnnnggggg breaker bar), disconnect the brake lines, and swap.

[dbenamati]

ok...since it is a 3/4 ton and I have to find an 8 bolt wheel pattern, do or have they ever made a rear end in a newer truck that has the gears I require, for example a newer 3/4 ton chevy or GMC. Like I said I'm not out to win races, just go the speed limit. Thanks for your help so far, I need ideas.

Dave

[palallin]

First: find the rear-end ratio in your current rear. There were options available in our years; you may be able to avoid retro-fitting.

Sure-fire way to determine: pull rear cover. Count ring gear teeth (R). Count pinion teeth (P). R/P = Ratio (the math is left as an exercise for the student ).

I don't know which you have, but I'd bet there's a rear-end on a truck somewhere near you with a higher set.