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Technical Ford 9" gear setup?

Discussion in 'The Hokey Ass Message Board' started by Dunk67, Sep 19, 2021.

  1. Dunk67
    Joined: Sep 19, 2021
    Posts: 6


    First time installing gears, setting up in a Ford 9". I've got a set of Yukon 3.50:1 gears that I'm having a difficult time getting a good pattern centered between the root and top of the teeth. No matter what I do there is a long sharp line at the root on the drive side, which I think is an indication more pinion distance (more shim) is required. The line isn't as long after moving the pinion farther out, but when the line at the root starts to get shorter, the pattern is approaching the top or even running off the top a bit. I made fairly large changed up to .038", which I think is too far, then back to .030" which I think is closer to where it should be. Backlash is ~.008" +/- .001" for all of these. Any input on these patterns or what to try next?

    .021" -

    .027" -

    .030" -

    .032" -

    .038" -
    Deuces likes this.
  2. dumprat
    Joined: Dec 27, 2006
    Posts: 3,157

    from b.c.

    Are these used gears?
    .032 looks the best but the pattern is a little high on the heel of the gear and a strange shape.
  3. saltflats
    Joined: Aug 14, 2007
    Posts: 10,934

    from Missouri

    What backlash setting?
  4. Relic Stew
    Joined: Apr 17, 2005
    Posts: 1,147

    Relic Stew
    from Wisconsin

    Did you align the timing marks?
    3.50 is a non-hunting ratio. Each pinion tooth will mesh the same 7 ring teeth over 2 revolutions. There should be marks to align the teeth that were lapped together. Could be paint, or punch marks, depending on manufacturer.

    3.00, 3.25, and 3.50 are the common factory ratios for 9" that need to be timed. There are others in aftermarket sets. Check the tooth counts for a common divisible factor.
    Last edited: Sep 19, 2021
    Truckdoctor Andy likes this.

  5. Dunk67
    Joined: Sep 19, 2021
    Posts: 6


    These are new Yukon gears (3.50:1, 10/35 teeth). Backlash they call for is .006"-.010", I've been getting it to .008", give or take .001".
    I did not notice any timing marks on the gears, but I'll look more closely though.
    I don't know how much of pinion depth is how the gears are made vs how the housing was machined, but the original gears in this had a .025" pinion spacer which from what I've read is getting toward the upper end of typical for a 9".
    The pattern does look odd compared to many I see online, particularly that the hard line at the bottom doesn't go away even at .038" when it looks like the pinion distance is too much since the pattern runs off the top of the tooth. Should I try somewhere between .032" and .038"? Try changing backlash to tighter or looser end of spec at .032" pinion spacer if that looks best otherwise?
    Last edited: Sep 19, 2021
    Deuces likes this.
  6. Dunk67
    Joined: Sep 19, 2021
    Posts: 6


    I don't see any obvious markings on the pinion for timing. Toward the end of a tooth on the top of this picture there is a mark, but it looks like part of a line across the end of the pinion. This could be from handling at the factory, or from when I pressed the inner pinion bearing on. Nothing look like I'd expect for a timing mark... Either a punched or scribed mark or a paint mark.

    Attached Files:

  7. Dunk67
    Joined: Sep 19, 2021
    Posts: 6


    .033" at .010" backlash:

    One notch tighter on the carrier bearing adjusters brings backlash to ~.003", so .010" it is for a .033" shim.
  8. That’s along ways out on the heel, the pinion needs to go in.

    I would run it where it was with the 0.021” shim if it were me. Set the backlash at the minimum it’ll increase a little as they wear in.
    Deuces and Desoto291Hemi like this.
  9. I think the nominal shim on a 9” is 0.015”. Have you tried less then 0.021”?
  10. Dunk67
    Joined: Sep 19, 2021
    Posts: 6


    It gets far toward the heel on the drive side, as I shim to bring the pattern between the root and top of gear. My understanding is having the pattern centered between root and top of the tooth is more important than centered between heel and toe. The Yukon instructions also indicate that an acceptable pattern may run off the heel or toe, but is centered between root and top.

    I have not tried less than .021 pinion shim, since as .021 the pattern was so low toward the root. I believe spec for starting point on a 9" is .022", hence why I started at .021" (closest I had). This axle originally had a 3.00:1 open gear in it with a .025" shim. I'm putting 3.50:1, SpeedMaster Torque Worm, and replaced the pinion support with a Quick Performance nodular daytona support. So a few things have changed but it originally had a fairly thick pinion shim in it.
  11. Why are you worrying about root and top ?
    Get your pinion depth right,,,,,then the backlash.
    The pattern is just a guide to help with setup,,,,,the dimensions is what usually matter .
    Some gears will never pattern well,,that’s ,,just the way it is .

    I’m with Lane,,,,,the first pattern looked best to me .

    gimpyshotrods likes this.
  12. Dunk67
    Joined: Sep 19, 2021
    Posts: 6


    Everything I've read and the major gear manufacturer guides indicate that centered on root and top is the critical measurement, while heel and toe is preferable to be centered or slightly toward toe but can run off either end of the tooth and be acceptable. My understanding is that pinion depth is primarily to get the pattern centered between root and top of the tooth.

    With that in mind, that larger more centered pattern at .030", .032", and .033" seem more in the ballpark, despite being toward the heel. I'm inclined to run .032" with the tighter backlash I can get with that... But I may be mistaken as this is my first time setting up gears. Is is more important to have the pattern centered between root and top or heel and toe? Regardless of contact area? The contact area of this gear set at .021" is pretty small (and low) compared to even .027".
  13. I wouldn’t run any gear set that they run off the heel or the toe…..
    Desoto291Hemi and 427 sleeper like this.
  14. dumprat
    Joined: Dec 27, 2006
    Posts: 3,157

    from b.c.

    Two things.
    Backlash is just a fancy name for running clearance between the gears. Tighter is not better.
    Pinion depth is more important than pattern position. Less pinion depth equals less gear contact and will make for a weak set up that tries to chew itself apart.

    Put in a .019 shim and open the backlash to the max and see where you are at.

    I've seen lots of gears in jeep's break due to having the pattern way out on the heel.
    gimpyshotrods likes this.
  15. Large backlash leads to a clunk and the gear teeth slamming together, plus as the wear the backlash will grow…
    fauj likes this.
  16. For a gear set up novice...could someone explain what is meant by heel, toe, root and top. Please and thank you.
    fauj and Desoto291Hemi like this.
  17. Tedd
    Joined: Jul 7, 2007
    Posts: 122


    Are you applying additional pressure to the ring gear as you turn it to get the 'pattern'? Just free turning the ring gear can be misleading if not loading the ring gear with some pressure while turning the gear set by the pinion nut?
    fauj, Desoto291Hemi and saltflats like this.
  18. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,708


    Always pinion depth first.
    28rpu, fauj, 57 Fargo and 1 other person like this.
  19. dumprat
    Joined: Dec 27, 2006
    Posts: 3,157

    from b.c.

    Heel-the outer diameter of the ring teeth.
    Toe- the inner diameter of the ring teeth.
    Root- root of the gear tooth.
    Top or crest- top edge of the gear tooth.
    Backlash- running clearance of the gear teeth
    Pre load- bearing preload is needed to keep the bearing clearance correct under load. Which is commonly measured in pinion rotation inch pound torque. "Rotational drag"
    Last edited: Sep 20, 2021
    anothercarguy and fauj like this.

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