169stang

I posted this in a thread related to FRPP gears. I just wanted to field a broader audience with these questions.
Let's say the backlash setting for this excersise is .010. The pinion can be set at a certain depth and the carrier can be moved side to side with shims (as I understand it sets the backlash). For simple numbers for this exercise lets say the pinion is set at a depth of 1 inch and the carrier has a 1 inch shim on right side and a 2 inch shim on the left side. So...can you set the pinion at a 2 inch depth (closer to driveshaft) and have a 2 inch shim on the left side and a 1 inch shim on the right and still get the same backlash? I guess what I'm asking is...Does it matter where the pinion is set at. Do you tighten it as much as you can (crushing the collar) and just go from there to set the backlash? If some people are having an issue with whine and some are not, is there maybe a sweetspot for the pinion to be set at?

I know that the shims are quite a bit smaller than any inch increments and the pinion depth is never measured, as far as I know. I'm just trying to get my point across with this example. Short and skinny, can the pinion be set anywhere and still get the same backlash? Is there a way to place the pinion at a specific depth?

GM Refugee

I'll give a go at this. Just a disclaimer, my experience is with a GM 12 bolt. But I don't think that it's too different from the Ford 8.8. This might be a little long but should give you a good idea.

When I built up my 12 bolt I learned there were 3 critical measurements to be set:
(1) The pinion depth;
(2) The pinion bearing preload;
(3) The carrier backlash.
All 3 of these measurements had to be spot on to within a .001".

(1) Pinion Depth: The pinion depth is set with shims. The shims go behind the pinion bearing on the pinion gear. There are pinion depth measuring tools and I invested in one myself. It was a complete waste of money. The reason is that even when you set the pinion depth with the gauge, you still need to check the wear pattern on the gears with some marking compound. When rebuilding a new rear, it's best to use the original pinion shim(s) as a starting point. Then you can check the wear pattern and dial it in. I spent about 2 or 3 days when I built my rear swapping out pinion shims (a thousandth here, a thousandth there) to get the correct wear pattern. This is where experience really pays off. The wear pattern has to be correct on the coast and drive sides. Once pinion depth is set, you move on to the preload.

(2) Preload: Preload is set on the pinion bearing, usually with a crush collar/sleeve. I had to use an inch-pound torque wrench because the preload is so minimal. It takes a lot of torque to begin crushing the sleeve but you can easily over do it quickly.

(3) Backlash: The carrier backlash is set with the pinion already set and the carrier in the housing. Shims are used on both sides to set backlash. Backlash is checked using a dial indicator set on the housing. You rock the carrier back and forth, watching the dial indicator. I think for most new gear sets the backlash is around .010" I believe (I may be wrong, it was a while back). When setting backlash you usually leave out .005" on each side to preload the bearings. When your backlash reads right, you then insert the preload shims. Backlash requires the carrier caps be tightened down. This took me a while to figure out, but once I got the idea, it was really easy to get it nailed down.

Richmond sells a video for installing ring and pinions and was very helpful. You can visualize what all this is instead of just reading about it. All three measurements are critical to each other. You kind of have to do it in the order listed above (I learned this the hard way as I struggled to do backlash first without my pinion depth being set). I hope this helps.

EDIT: My 12 bolt used Motive Gears and handled the power of that 540" big block without any noise. Maybe beginner's luck?

169stang

I've watched it done twice, but just never really payed attention to the details. So, there is only 1 location for the pinion to be and one correct sized shims on either side of the carrier to have a centered wear pattern and the correct backlash. There is no various combinations to set the pinion and carrier and still get the same backlash? I'm just trying to figure out why some have whine and some do not and installing the gears is one part of that and the next part would be a bad carrier. I appreciate your info!

GM Refugee

There probably is only one ideal location for the pinion. Having seen them put it together you have some idea what I was talking about. Whine can come from a bad pinion depth usually, not so much from backlash (again I may be wrong here but believe that is correct).

I had a supercharged Nova that had a really poorly set up pinion that whined something fierce. When I pulled the cover the pinion was so far towards the carrier that it was grinding on the posi carrier and wearing into it. That is why pinion depth is so critical.

I know for instance that Richmond gears are notorious for making some noise, even when properly set up. I got Motive Gears because I had heard they were quality units and the noise issue wasn't as predominate as with Richmond.

I haven't heard of bad carriers causing noise before. That's interesting. I would presume it would be the bearings on the sides or an uneven lip for the ring gear.