Ford 3.91:1 gears

[c9zx]

I remembered that I had a set of 3.91:1 gears in my small stash of parts. They have no damage of any kind but are used. Ring gear is C8OW-4210-A, pinion is C8OW-4610-A. Has the  the manufacturing and heat treating process improved to the point where a new gear set is warranted or is it the other way around? Should I use the Ford set or move it along to someone doing a concours restoration. Thanks for any input. Chuck S.

[cleandan]

My opinion.
The Ford gears are good, use them if they fit your needs.
I don't think anyone will be worrying about the literal part numbers on the gears of a restoration because that is not an area any judge will ever inspect...if they can get factory gears in good condition they might use them, but I don't think anyone will be paying huge money to attain that type of restoration part because you can still attain 3.91:1 gears to complete a restoration
The same with differentials, bearings, connecting rod and main bearing cap fasteners, and other internal items nobody will ever see...as long as the part works properly, and functions the same as the factory part (think new Detroit Locker as opposed to vintage Detroit Locker) things will be fine.

The best scenario I see is you trading the factory gears to a restorer to make things "just right" for a good aftermarket set you can use in your non-restoration application.

Again, just my opinion.

[My427stang]

If not worn out, street car, I wouldn't be afraid at all.  Add slicks and a little wheel hop, probably need something with a little more give.

[c9zx]

My thanks to everyone. Use is 462 CID, pretty aggressive, 4 speed, Cal-Tracs, M/T ET R tires. 98% street use. Chuck S.

[pbf777]

      In this period, the O.E.M. gear sets 'are' superior to what is being manufactured today in the aftermarket, period.   

      But as referenced previously, are intended as a "Street Gear" in the power levels of the time, say something under 500 H.P. and not too good a chassis or tire, they're just too hard and will break under severe "shock-loading".  So if your making "big power" and your car "hooks", I'd suggest a more modern, and as intended, "softer" gear. 

      As far as for the monetary value of these, if truly in good shape, there are individuals whom in their restoration projects greatly value these O.E.M. units and will pay a premium to have them.   

      Scott.

[thatdarncat]

As I’m sure most are aware, there are many ratios that are similar, but are a different combination of ring gear to pinion tooth counts. That can affect the amount of teeth in contact & strength. Many look at that too in race applications. For example a 3.89 is 35-9, a 3.91 is 43-11. There are lots of examples like that.

Then you have “Hunting” and “Non-Hunting” gear sets too.