Has anyone done a gear change on a 91 f250? Any info on what this involves and can it be done by a novice mechanic. Im not sure wich rear end i have the tag on it reads V121C L55 10 2 OH29 The sticker on the door reads C9N

 

I just had the gears in the rear end of my 84 f350 crew cab changed. there wasn't a tag on the diff. so i had to open it up and count the ring and pinion teeth. once i had that info i divided the ring gear teeth by the pinion teeth: 43-14=3.07 then i went to a diff specialist and had 4.10 gears with positraction put in to the tune of $850.00. it took about 3 hrs and they work like a champ.

 

Form 84 to present the Ford 3/4 and 1 tons have been equipt with the Sterling 10.25 rear axle.They are very very good axles,they are almost indestructible.I have never even heard of someone breaking one,unless it was through neglect. The 1st question on how hard it is to change,I would strongly suggest that you have a pro do it unless you are very mechanical.You will also need a dial indicator,micrometer,torque wrench & bearing puller,along with all your basic tools.The back lash and pre load must be adjusted almost perfectly using a dial indicator and the shims provided in a Master Rebuild Kit.You may have to remove the carrier and pinion several times to get it right. One trick is to take the orriginal bearings and races and grind them down a few thousands and use them for the set up procedures,)the bearings and races should be measured 1st to make sure they are same size,(they will be if you use quality components),then install the new bearings races and seals after you are dialed in.It can take anywhere from a few hours to all day depending on how well the ring and pinions match up,and how lucky you get durring the shimming process,(make sure to measure the shims coming out of the orriginal set up),and use that as a starting point. The cost is about $250 for a quality Ring and Pinion, $200 for a Master rebuild Kit,(buy a good one or you will end up having to reuse items like the oil slingers and seals,Genuine Gear,and Spicer are very good).A qulity limited slip(positraction)or locker will cost between $300 and $500 and will come with its own carrier and gears. Available for the Sterling are Dana Trac Lok,(Factory style,Limited Slip Device,LSD),Detroit Locker(very aggressive off road Locker),and ARB air lockers. The only gear ratios available either from the factory or aftermarket are 3.55, 3.73, 4.10, & 4.56:1 . Installation is usualy about $300 to install the ring and Pinion and usualy not extra to install the LSD or Locker since they would be doing the same work either way.
Jeff