Posted by Traveler on March 29, 04 at 19:00:33:
In Reply to: Question - Front/Rear end swap for '91 1/2 Ton 4WD posted by Flea on March 29, 04 at 18:05:27:
I'm no expert on the pre-92's but have played with a few rear ends. Add'l info helpful:
Where is it under powered now? Low end?
Do you ever plan on towing?
What trans does it have?
Reason is if it's just low end and you won't tow, there is a possibility that a looser torque converter and huge trans cooler could do the job. As long as you maintain the lockup feature.
If you have the 4-speed TH700R4 and find the ratio is just too tall in every gear, then 4.10 or 4.56. Caution in that 4.10 is about as high as you can go in an 8.5" diff before the teeth are on the weak side. (what does this mean for the front diff??) I've found the 7.5" Camaro type diffs don't like lower than 3.73. (wallet damaged) The 12-bolts will go to 5.13 OK and then hi-nickel gears needed. The 14 bolt SF and FF should be OK with whatever ratio you choose. In all versions be aware that the diff case will probably need to be changed when you transition from the 3-series (out to about 3.90) to the 4-series (4.10 to 5.56) due to the difference in pinion diameter and ring gear thickness limitations. More incentive to transplant rather than swap R&P.
Another approach would be to look at 2500 8-lug axles to gain the add'l beef and also get a brake upgrade. This probably means changing the master cylinder and combo valve. A full hydroboost conversion is nice but is more than most want to mess with. An option if you will tow a lot.
There are also the 9.5" semi-floating 14-bolt diffs used on the "heavy half" on 7200 GVW pickups and diesel Suburbans/Tahoes. These will retain 6 lugs and add some beef. Brakes should still be the Vacuum boost. Have to be cautious when messing with different brake parts than what came stock tho.
The 9.5 SF will bolt right in on the mid 90's but not sure about '91. I know even less on the front diffs so diff gurus please chime in.