Rear End:
-Ford 9" out of a 67' full size Ford car.
-28 spline
-New richmond 3.89 ring & pinion
-New auburn pro differential
-All new bearings, etc..


I'm trying to set backlash and I've been running into a problem. I set the one spot of the ring gear to .008" and as soon as I check 2 other spots on the ring gear, the backlash changes from .011" - .005". Why is this? I'm pretty positive this isn't normal... So I check the runout on the backside (machined surface) of the ring gear and come up with .002". Does anyone have any clue why this is happening? I'de like to get the car on the road tomorrow.

 

That's pretty normal, actually; although you have somewhat more than the usual amount, but not grossly so. .002 - .003" is real typical, you'll see that much most times.

You might want to try turning the gear 180° on the carrier.

IMO it's not so excessive as to be unusable or anything, even if that doesn't make it better. I'd open it up a couple of thou (to maybe .008 - .013 or some such) and run it. Better to have a litle extra in some places than too little, since the gears "grow" when they get hot, and then if there's too little, they try to occupy the same volume. Which as we all know, bad things happen when 2 pieces of finely machined heat-treated metal do that with each other.

 

Thankyou sofakingdom for the advice above.

I carefully checked every tooth's backlash on the ring gear. I set the lowest to .008" and the highest to .012". So that is .004" of tolerance. But I did notice something inparticular. For every 360* rotation of the PINION gear, the high area of .012" backlash occurs... So it isn't that thr ring gear is impropperly seated on the differential hub. I know this is OK to usu, but I would like to get it just a little more perfect.

Also, concerning the spanner (adjustable) nuts. I rigged and welded up a little tool so I can set the 25in lb of preload, using a tq wrench, on the carrier bearings. Is this Ok to do instead of the "tighten the RH spanner 1 notch, loosen the LH spanner 1 notch "approach? Tht approach just didn't seem to be logical to me... Opinions please.

 

Sounds good. I think I'd just run it and be done with it.

Can't see why you can't adjust it that way; as long as you get the preload and the backlash correct at the same time, it hardly matters how you did it!! Whatever is quickest and easiest. The book method assumes that you set the preload first (tighten/loosen both together), then move the carrier to one side or the other to set the backlash while maintaining the correct preload (tighten one / loosen the other equally).