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Can I live with this pattern? First two pics are the drive side and the third is the coast side. I am as deep as I can go with the pinion gear, no shims, and backlash is set at .008 - .010. The last is the old pinion gear, 5 broken teeth, which, believe it or not, was still driving the ring gear, but noisy, and only one very small chip on the ring gear. This is in my 1993 K3500, 250,000 miles.
HH,
No you can't live with that pattern. The pinion depth is wrong. The pattern you have in the pictures you posted are what you get when the pinion is too close (deep) to the ring gear. Also, for clarity, the convex side of the ring gear is the drive side, not the concave side as you indicate.
The original shim as set from the factory rarely needs to be changed as long as the housing and pinion bearing retainer are original. If the replacement pinion is not a nominal pinion, then you would add or subtract the amount marked on the pinion to compensate.
Ideal backlash is .005" to .008", with a min of .003" and a max of .010"
The picture I attached shows what pattern you are after.
I agree! The pattern shown in the photos is not good. This will be noisy and probably lead to premature failure.
OK, Thanks. I will go back to square one and start with the orginal shim in the pinion housing. The housing is orginal and the new pinion gear has a +1. Not sure what the original shim thinkness is, measures about .020 with my vernier caliper, plus or minus .001.
Thank you for the clarification on the coast and drive sides, that will make a differance at what I am looking at.
If I question it I will post pics again. Thank you for the input.
The small tab that sticks out on the shim (passenger side) will have the thickness stamped on it. If it hasn't gotten rusted, it might be still legible. It is a light stamping, so don't be surprised if you can't make it out anymore. A mic will give you a more acurate reading here, if you can get your hands on one to measure with.
When the housing is measured for the pinion shim, it is based on the dimension between the centerline of the axle tubes to the rear inner pinion bearing race surface. This may be done differently at the factory, not sure on that. This dimension is designed into the tools used to measure it and the reading is taken off a dial indicator. The reading is directly used for a nominal pinion, as I mentioned in my earlier post. Since yours is a +1, it needs a shim .001 thicker than the one you now have, assuming your old gears were nominal. (This is the opposite of what you do with a pinion shimmed between the gear and bearing, btw)
The nice part about using the marking compound as you are, you can tell if you are getting the desired results.
How does this set-up look? Stock shim was .024, but the pattern was toward the outside of the ring gear. In the below photos, I took out .003 from the stock pinion shim setting, the backlash is set at .004. The carrier adjusting nuts are near where they where on the old set up, about 1 hole differant.
That's a lot better, but it still looks like the pattern could shift toward the toe some more.
The pinion you are installing was marked with a plus 1 marking. This means for your situation that you will likely need a 23 thousandths shim, one thousands thinner than the one you originally took out. These gears are a hypoid type gear, because of the way that they mesh. The interesting thing about them is that while you would expect that changing the pinion depth would change the gear heel and toe mesh. (I included an edited picture of your gear with the terms added so we are all on the same page here.) What it actually does is it influences the depth that it engages the gear teeth far more. Changing the backlash is what moves the gear pattern in a heel/toe direction. Decreasing the backlash moves it toward the toe end of the gear tooth. The precision machining process used in the manufacture of the components in the axle means that unless it was incorrectly set up to begin with it, you will most likely find the bearing adjustments very close to original. In your case, it was good enough to get you a 1/4 million miles. Also, I can't tell from your updated photos the pattern that you now have on the coast side. This would still be helpful.
You are definitely making progress, however
If I am at .004 for backlash, how can I decrease it more, to get closer to the toe? Should I remove .001 in shims (currently at .022) and then set the backlash as low as possible? If I understand right, if I remove a shim I will move the pattern slightly to the outer edge, and it will also increase backlash slightly, and then I can reset the backlash as low as possible on the spec, (.003). Does this sound correct? Thanks for the help.
If I am at .004 for backlash, how can I decrease it more, to get closer to the toe? Yes, but you can only go to .003”. Should I remove .001 in shims (currently at .022) and then set the backlash as low as possible? Possibly, but read my comment below to clarify. If I understand right, if I remove a shim I will move the pattern slightly to the outer edge, and it will also increase backlash slightly, and then I can reset the backlash as low as possible on the spec, (.003). Does this sound correct? Reducing the shim thickness will decrease backlash slightly, but when you have the pinion depth nearly correct, the change you see the most is the bias difference on the 2 sides of the gear. Refer to next paragraph. As I mentioned earlier, a hypoid gear has an interesting mesh compared to most gears. There is a significant amount of sliding that occurs as they mesh. This requires a different lube formula than more traditional gears do. This type of meshing is why they are as quiet as they are. Thanks for the help. You’re welcome!
I had better clarify my previous comments. While changing the backlash moves the toe/heel pattern, and the pinion depth moves the tooth depth; both of these certainly affect the other. If you take a look at the first photos you posted, the drive side pattern is biased toward the heel, but still contacts a long portion of the tooth. The problem, of course, is that the pinion teeth are only contacting on the tips. Looking at your most recent photos you can see that the heel/toe bias isn’t that much different than before, except now you have more even contact across the entire surface of the tooth.
The next step is to examine the coast side. If the bias is about the same, this is as good as you will achieve with your adjustments. If the coast side bias is toward the toe, the pinion depth will need to be moved closer to the ring gear, and vice versa if heel biased. Remember that the drive side is the most important, as far more torque is applied. I prefer to get this as good as I can, and not sweat the coast side, within reason of course. They seldom show perfection on both sides as in the illustration I posted earlier.
If you feel like posting photos of both drive and coast sides, I can give you a better idea of what I think of your pattern.
Here is a photo of the coast side of the gears, it appears to tend more toward the toe side. Have a good new year.
The pinion needs to be a little closer to the ring gear. Since you have gone -.002" from the original, another .001" or so should get you where you need to be. No exact formula at this point, let the pattern be your guide. Normally you wouldn't need to go this far from the original shim thickness. I'm thinking your are using aftermarket gears, they don't seem to follow the guidelines I mentioned earlier regarding being able to use the same shim. This is not an issue, just takes a little more finessing is all. I believe you mentioned the pinion was marked with a +1, as you can see, you will be farther from this when you are done. Another possibility is that the gears aren't original, and the shim was changed in the past.
Happy New Year.
Thanks for the help. The diff appears to work well and does not make any noise above what I am familiar with in other vehicles. It has been a good learning experience.