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So I am finally installing the US Gear Stealth/Lighting gears in my 9". I need help with the pattern. I have worked this thing for a few hours and below is the best pattern I've been able to achieve so far. This is with .020 backlash, which is way out of spec. Spec is .008 to .012 for street use per US gear. Pinion is shimmed .010. I'm happy with the drive side but the coast side is towards the toe. From what I understand, face hobbed gears require different adjustments than milled gears. I've been following page 3 from this guide (http://www.canadawideparts.com/downl...th_pattern.pdf) for face hobbed adjustments but the pattern doesn't seem to change much at all no matter how drastic the pinion depth adjustment.
When I bring the backlash into spec, the pattern moves down to the toe.
Thoughts?
Last edited by 98cherrySS; Apr 1, 2020 at 10:06 AM.
Never done these, however you can't run with that little backlash so there is no point in running a pattern with one critical setting so incorrect. Remember, there are lots of acceptable gear patterns, not just the picture perfect centered ones.
Never done these, however you can't run with that little backlash so there is no point in running a pattern with one critical setting so incorrect. Remember, there are lots of acceptable gear patterns, not just the picture perfect centered ones.
Correction, backlash was set at .020, not .0020. I just edited the original post. Thanks for chiming in. Another issue is that the high polish on the gears prevents the marking compound from rubbing off well. I have to make about 10 passes to show any pattern. I think I am pretty well centered between the root and the top land. My goal here is a quiet setup and I read somewhere that the closer the contact pattern is to the toe, the more it will make noise/whine.
Does anyone know what is more desirable, tighter back lash .060-.080 or looser backlash .090-.012? I assume that loose backlash will translate to looser feel on and off the gas, between shifts. Is one or the other quieter?
Most gears I setup recommend like 7 to 9. I generally shoot for 6 to 7, so on the tighter side. I'd have no problem running say 10, not saying its wrong, i just have developed preferences over the years of doing them. I will say, changing backlash "usually" doesn't change pattern much, within reason obviously. I would however start with appropriate backlash as step 1, before any pattern in run, and that's how i always do it.
I try to always try to shot for the average of the low to high tolerance if everything is new parts. If it’s 6-10 then I shot for 7-8. If it’s used parts I try to go a little on the looser side 8-10 on the backlash. Also if the center section is aluminum I run them tighter because they flex more. But this is just generally speaking about rears. For your rear .010 back lash is good in my opinion
Thanks for the feedback. I tightened it up to 7 thou and have been playing with the pinion depth. The pattern will be low on the ring gear so I'm going to keep it centered between the root and the top land and run it. Planning on putting the car back together on Thursday and Friday.
Thanks for the feedback. I tightened it up to 7 thou and have been playing with the pinion depth. The pattern will be low on the ring gear so I'm going to keep it centered between the root and the top land and run it. Planning on putting the car back together on Thursday and Friday.
I myself struggle with face hobbed gear sets...they set up different that 5 cut/face milled sets. Back lash needs to be tight...2 cut sets seem to be tight VS 5 cut.
I reference this site for 2 cut sets.....yes its for fords but the same applies to all 2 cut sets....scroll about a 1/4-1/3 of the way down
I myself struggle with face hobbed gear sets...they set up different that 5 cut/face milled sets. Back lash needs to be tight...2 cut sets seem to be tight VS 5 cut.
I reference this site for 2 cut sets.....yes its for fords but the same applies to all 2 cut sets....scroll about a 1/4-1/3 of the way down
That is very useful info! Copying in below for other users. Face-Hobbed Gears
These include OE and replacement 8.8-inch gears.
This computer model of the ring gear tooth face illustrates a face-hobbed tooth form. Note that the tooth profile has a uniform depth across the entire face.
You want to have the pattern centered, and this diagram illustrates certain shift patterns. Changes in backlash (B/L) for a face-hobbed gear set are shown. Notice that the black arrows represent backlash increasing or decreasing. As backlash increases the pattern shifts toward the top of the tooth surface. The direction and slope of the arrows shows that the pattern moves slower up the tooth on the drive side as compared to the coast side. Also, the pattern moves faster from heel to toe with backlash changes on the drive side. This makes it easiest to concentrate on the drive side of the pattern, as the coast-side pattern moves slower with backlash changes.
This diagram illustrates how the pattern shifts with changes in the pinion mounting distance (PMD). The PMD is changed with the pinion head shim for the 8.8-inch axle (the 9-inch axle uses the pinion cartridge shim). As you increase the PMD, which is accomplished with a thinner shim, the pattern shifts closer to the top face on the drive and coast surfaces. At the same time, the pattern shifts toward the toe on the drive surface of the tooth and toward the heel on the coast surface.
On Ford OE and replacement gears, face-hobbed ring gears do not have the tapered back face machined. Here, you can see the area between the differential case mounting flange and the ring gear teeth. Close inspection reveals that the beveled surface is rough and has been left as an as-forged surface. This is an obvious sign of the type of process that was used to produce the gear—face hobbing. (On a factory face-milled gear, this surface is machined.)
In this diagram, the pattern is toward the heel and root on the drive surface and toward the toe and root on the coast surface. Decreasing the pinion shim thickness allows you to move the pattern toward the top of the tooth.
In this example, the pattern is really close to correct as far as root to top of the tooth surface; it is just a little high. You just need to center it between heel and toe on each surface. Decreasing the backlash corrects this pattern.
Here, the pattern is toward the toe on the drive surface and toward the heel on the coast surface. The pattern is also a little low, or closer to the root on both surfaces. Increasing the backlash corrects this pattern.
I added a .007 shim to the pinion support and that helped alot. Still silent on accel and a slight whine on decel. I’ll add another .002 and see how that goes.
Added another .002" and it is very quiet now. I have an ever so slight whine on decel at 50ish and again at 20ish. It is very faint. I think one more adjustment of .001 and I'll be done.
Success! The 4.10 gears are now dead silent. The last .002” made the difference. In 10 years of ownership the rear end of this car has never been so quiet. It’s amazing. Thanks for the help. The best feature about the 9” is the removable pinion support. This makes adjusting the pinion depth a quick and clean process.
Last edited by 98cherrySS; Apr 19, 2020 at 11:29 AM.
Any pics of your final pattern? Just my opinion, try to use a little less paint. You dont want it squishing around to much. You want more transfer from ring to pinion and then what gets on the pinion gets transfered to a clean spot on the ring gear.
Any pics of your final pattern? Just my opinion, try to use a little less paint. You dont want it squishing around to much. You want more transfer from ring to pinion and then what gets on the pinion gets transfered to a clean spot on the ring gear.
I didn’t get a pic of the final pattern as I was adjusting the pinion depth via the pinion support with the center section installed. I did read a few posts suggesting less marking compound and I found that applying less compound on the polished gears, there was no readable markings. It was frustrating because I agree with the logic behind using less compound... just couldn’t get it to rub off.
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Face Hobbed Gear Pattern Help 
This computer model of the ring gear tooth face illustrates a face-hobbed tooth form. Note that the tooth profile has a uniform depth across the entire face.
You want to have the pattern centered, and this diagram illustrates certain shift patterns. Changes in backlash (B/L) for a face-hobbed gear set are shown. Notice that the black arrows represent backlash increasing or decreasing. As backlash increases the pattern shifts toward the top of the tooth surface. The direction and slope of the arrows shows that the pattern moves slower up the tooth on the drive side as compared to the coast side. Also, the pattern moves faster from heel to toe with backlash changes on the drive side. This makes it easiest to concentrate on the drive side of the pattern, as the coast-side pattern moves slower with backlash changes.
This diagram illustrates how the pattern shifts with changes in the pinion mounting distance (PMD). The PMD is changed with the pinion head shim for the 8.8-inch axle (the 9-inch axle uses the pinion cartridge shim). As you increase the PMD, which is accomplished with a thinner shim, the pattern shifts closer to the top face on the drive and coast surfaces. At the same time, the pattern shifts toward the toe on the drive surface of the tooth and toward the heel on the coast surface.
On Ford OE and replacement gears, face-hobbed ring gears do not have the tapered back face machined. Here, you can see the area between the differential case mounting flange and the ring gear teeth. Close inspection reveals that the beveled surface is rough and has been left as an as-forged surface. This is an obvious sign of the type of process that was used to produce the gear—face hobbing. (On a factory face-milled gear, this surface is machined.)
In this diagram, the pattern is toward the heel and root on the drive surface and toward the toe and root on the coast surface. Decreasing the pinion shim thickness allows you to move the pattern toward the top of the tooth.
In this example, the pattern is really close to correct as far as root to top of the tooth surface; it is just a little high. You just need to center it between heel and toe on each surface. Decreasing the backlash corrects this pattern.
Here, the pattern is toward the toe on the drive surface and toward the heel on the coast surface. The pattern is also a little low, or closer to the root on both surfaces. Increasing the backlash corrects this pattern.
