Greetings,

http://www.americanmuscle.com/ford-3...arbondisc.html



I want to upgrade my differential in my truck. I read the write up on American Muscle that seemed to be incorrect and was curious if, "what I read was true"


The FAQ said nothing about having to check // re-shim the pinion gear when installing a new unit into the differential....


I want to reuse my old gears.

Reason why is the only tire that ever grips is the passenger side. I can feel the twist on that side when accelerating. Also no traction on take off during first gear. I have to take it easy and let it shift into 2nd gear. I hope that upgrading the unit will help. Thanks

Any thoughts?

 

Do you currently have an open/non traction aided rear differential?

Or could you have a factory Limited Slip unit that has been worn out?

An open differential will apply power to the wheel with the least amount of available traction (relative to the opposite wheel).

Any traction aided differential will make a difference in vehicles driving on slippery surfaces.

Installing a new/different differential will require some re-shimming for proper gear mesh.

 

You don't have to pull the pinion gear to install a new carrier. If your talking about carrier shims, in theory, the carrier should be the exact same size as your old one, whether it's an open carrier or worn out limited slip. Re-shimming comes about when you change your ring and pinion gear ratio. The thickness of your gears change with the number of teeth on your ring/pinion. Also ring and pinion brands maybe machined a bit different. When I swapped mine, I didn't have to run a pinion shim with my Richmond gear. If I was going to install one of these, I would not expect to have to re-shim, but I would check my backlash before and after just to make sure it's still very close. DONT swap OR flip over your carrier end caps. Your factory shims will just be one shim on each side, DONT swap these. DONT just beat them back in. Use a brass hammer and tap them back in gently. They are cast and can bust. Then your screwed til you can get some shims.

 

... but if that theory was always true you wouldn't need to reshim when you change gears either, because in theory they are all supposed to work with the same carrier (exception being when you go past a break point like 3.73:1 in a Dana 44 which requires a new carrier).

The problem is production tolerances. No two mass-produced parts are exactly the same, be it gears or carriers. Tolerances on carriers are pretty tight, so you frequently can get away without changing the carrier shims. And the original shim set would definitely be the right place to start. But as Ron said, check the backlash and I would add definitely check the gear mesh too before you cal it good. You might get lucky and not need to change shims. But it's not a guarantee that you won't.

The original pinion shimming is even more likely to work, because while production tolerances on the carrier can shift the ring gear from side to side, requiring diferent carrier shims to dial it in, a new carrier won't move the ring gear front to back. It'll stay on the axle center line. When you chack the gear mesh and backlash you'll be checking pinion depth too. But unless something is messed up in your gears now you shouldn't need to change your pinion shims.

 

[quote=Nothing Special]... but if that theory was always true you wouldn't need to reshim when you change gears either, because in theory they are all supposed to work with the same carrier (exception being when you go past a break point like 3.73:1 in a Dana 44 which requires a carrier)

Um, are you saying with my theory you can regear with a different ratio without reshimming? Cause I definitely didn't say that. That theory don't work, because different ratios have different numbers of teeth, changing the diameter of pinion and thickness of ring.

That's why I said it is a theory. And this theory is why they don't have you check your shims in that install write up. Also why I said check backspacing before and after. If it's within a few thousandths, run it. I would have a new cross pin shaft and retaining bolt on hand. They are fairly cheap, and when your old retaining bolt is broke, you will be glad you have them. Any wear on the cross pin shaft makes for dramatic slack and it's a good idea to replace them. I've broke a cross pin and slung it through the rear cover. That being a ford racing carrier, the chances are very, very good it's going right in. If the shimming and checking worries you and is to overwhelming, you have the option of a lunchbox locker. You don't even have to pull the carrier to install it. It's an hour install in the driveway if the retaining bolt isn't broke. If the bolt is broke, you CAN get it out with damaging anything. Lunch box lockers are known for being noisey, and use to not be very smooth. But the newer ones are suppose to be much smoother and a little quieter. I haven't ran a newer one... yet. That's a good price on that carrier.

 

My newest one has the spider gears inside. MY old one had the Clutch packs that I wish I never got rid of. Long story....It was worn out and the casing was cracked. 4.10's and a lot of highway driving. Pulled another one out of a junk yard that had 3.55's.


I rebuilt the newest one with new bearings seals ect.... Only thing reused was the gears and shims. There is nothing wrong with my current one other then traction issues.


The plan is to get that ford racing unit put new carrier bearings on it. Reuse every thing else except for seals and may be that really small bolt and the cross pin.


So in theory shimming should not be needed?

 

I'm saying that any gears or carriers that are made to be used together would be in the same place and would work perfectly IF all the parts were right on nominal. Yes, as you said, when you put new gears in you need to change the shims. And yes, that's because the gears are different sizes. But it's not that they are INTENDED to be different sizes, it's because no mass produced parts are exactly on nominal. Having to use shims isn't because the manufacturers intend to make the carrier be in a different place when you change gears. It's to adjust for the manufacturing tolerances.

Same thing with carriers, except probably on a smaller scale. It's likely easier to hold tighter tolerances carriers than on gears. So using the same shimming with a new carrier as was used on the old carrier is more likely to work than if you tried using the same shims when you change gears. But it's not a guarantee. Sure you can just check the backlash and hope that if it's close enough that the mesh will be too. But a safer bet is to check the mesh too. If it's good with the original shims, great. If not, at least you know it and can do something about it.

And by the way, it's probably not a bad idea to check the mesh before removing the old gears too. A friend of mine replaced a carrier using the old gears and he ended up not being able to get the mesh perfect. He decided that the gears must have been worn a little, and he got it as good as he could and buttoned it back up. But he always wished he had know what he had started with.

As I said, there's a reasonable chance that the shims currently in there will work with a new carrier. But it's no guarantee. At least check it.