Opinion please: Keep or replace stock ring and pinion?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Aug 6, 2021
Washington State
Ignoring cost, should I replace my stock ring and pinion with modern (e.g., Sierra) stuff?


- The diff is out and completely stripped down on my bench.
- The backlash was high (avg ~0.014"), but consistent.
- The runout was about 0.004".
- Paint pattern looked even but shallow. Given that the pattern didn't look all that bad to me, I'm thinking I should be able to get a good pattern with the right BL.
- Pinion bearing preload was very near zero, but no play. Bearings look good (will be replacing with new).
- Gears looked to be in good shape with no chips or discoloration on ring or pinion.
- The diff in question is from my 1980 40 which I believe to have 50K miles on it. There is still a bit of vibration in the rear drive chain (axles are shimmed and U joints freshly rebuilt, which eliminated 80% of the bad vibes) and some clunking in the rear which hasn't been positively diagnosed as coming from the diff (yet).
- This is my second diff rebuild and upgrade to ARB lockers.
- For the first one, I started with a diff I bought off CL, replacing the R&P with new Sierras (here). (I'm almost done installing this completely rebuilt axle and diff, so that may tell me more about where vibration and clunking is/was coming from.
- This second diff is the original off the rear of my truck which I am now rebuilding and will use to replace the front diff currently still on the truck.
- I have a couple of the old school type spacers and shims for the outer pinion bearing from both the CL diff as well as the original rear diff, and the two shims I have differ by about 0.010", so with some careful sanding, I can probably get to a correct PBP using the old school shims and spacers without having to source more shims which I understand to be hard to find.
- I have everything I need to put it all together, including the aftermarket solid spacer should I decide to go with new R&P.
- I have some fairly rough trail I plan to ascend when it's done, but I'm not a rock crawler... more of a "get me to the fishing hole" kinda guy.

So, it comes down to which is stronger, stock or aftermarket (e.g., Sierra) ring and pinions and should I care given my planned usage?

TIA for any and all o-pinions!
Well... if the stock stuff is better, and not worn out, maybe it would be better to keep it?

Here are some pics (gear paint was a bit runny... fyi).


AND! Since this will be on the front, it will see a lot fewer miles/year than the rear, which is almost completely new.
I'd probably run what you have if your not going to a different gear ratios. The gears appear to be in good shape. 1st I'd install the pinion at the same depth as the factory did. Set up the diff and see what you have. Most likely you should be good. Bearing dimensions are pretty consistent from one another. Pinion depth adjustments are required for the variations of the machining of the 3rd member case . Your 1980 pinion is fine spline, so it's strength should be good. Pre load is used to determine if the bearings and races are seated properly. Over time it dissipates as the bearings and races seat /wear in to each other. I would try to get the same ring & pinion pattern as they were originally setup. When you change the b/l it might change it slightly. These gears have been running together for 50k on that setup. Changing from the original pattern could cause whining or howling. Your clunk could be from the spiders. When load is applied to pinion the spiders slide outward on the center shaft and hit the diff case, that's why there are thrust washers. If your going to an ARB that might eliminate that.
I would keep the stock gears and get a full rebuild kit that includes shims. Might want to put in a solid spacer too.
I would keep the stock gears and get a full rebuild kit that includes shims. Might want to put in a solid spacer too.
Thanks @matzell, I'm leaning that way at this point. WRT the solid spacer suggestion, the original pinion has the shoulder for the original spacer and shims. I have a solid Nitro spacer for the '90 and older 9.5" diff, but it doesn't fit on the original pinion (I checked). I was planning on just re-using the original spacer and shims... is there another option for a solid spacer that works with the original pinions?
Just came across another advantage of keeping the original gears: Easy/no break in required! ARB doesn't seem to have a break in procedure... or?

Users who are viewing this thread

Top Bottom