How to properly check gear pattern on a used gearset

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84hurstolds
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How to properly check gear pattern on a used gearset

Post by 84hurstolds »

Question- while this question specifically pertains to an 8.5" 10-bolt corporate open rear end, my question is sort of general in that if you use a good, used gear set to change ratios, how can you effectively get a good contact pattern in the paint on the drive side? Since the gears have worn together so-to-speak, wouldn't the gear pattern be harder to distinguish? Or is there a cool trick we should know about? I tried a search here on this and came up empty. I was told that coast side pattern may can be used, but I believe the coast side pattern 1) isn't quite as important as drive side contact as long as it's not crazy, and 2) doesn't always correlate to what you're getting on the drive side. But since I don't know, I ask the question.
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monzaz
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Re: How to properly check gear pattern on a used gearset

Post by monzaz »

You are correct ...Use the coast side especially if you have a compromised drive face .

it will be a valley to peak swipe and as far across the gear you can get...remember you do not have 3000-4000 pounds of weight and torque of the drive line to get this swipe. so be reasonable as to how much swipe your going to get. Too deep in the valley sharp hard line at the base of the tooth all the way across and like a sunrise pattern on the the teeth is likely too deep.
Just the opposite for too shallow swipe hard at the top of the tooth across the complete peak and reverse mirror of sunrise will be too shallow add more pinion shim.
try to always keep your backlash consist as pinion depth changes are done. usually over .005 your going to need to change the side shims to bring your backlash back to spec again.

Yellow or White compound grease paint to help see the pattern then mix it with a few drops of gear oil mix it and the compound will go further and spread cleaner to see the contact pattern
If you use a rag to create drag on the ring and spin the pinion yoke in both directions, this will help the pattern come through better too.
DO NOT just paint a couple gears you should try and check the entire 360 degrees of the ring to be sure you do not have any contact pattern run out...Which will show in the pattern also. Dial indicator in 3-4 different spots will also check run out too. (meaning backlash will increase and decrease as the running gear is spinning around).
dirt / debris under the ring can cause this ....or dents in the carrier mating face of the ring gear to...might be from a hammer disassembling or shipping.

Hope this helps.
Used gears can be a bit tricky ...but if you take your time user the pattern and FEEL of the mesh being smooth and keeping the backlash in .007-.010 for 5 cut gears and 2-4 in 2 cut gears ...you should be good.
Remember the gears are used and will not normally run in the spec of a NEW gear set...all depends on the mileage and how sloppy the gear got over that mileage as to how forgiving your used gear backlash will need to be for a quiet running gear.

IT is even possible you can have a gear that LOOKS entirely good but just will not set up good. Those are the flip for the coins you get with unknown used gears.

Hope some of this helps....
good luck!
JD Race
Jim Mitschke
J D Race
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