Setting up a new 8.5 gear set and carrier...

Discussion in 'Got gears?' started by sporty-to-GN, Nov 10, 2017.

  1. sporty-to-GN

    sporty-to-GN Well-Known Member

    The new pinion is scribed 309. That doesn't seem likely to be the pinion depth reference measurement?
    The old and new pinion heads are 1.690 thick from the shim surface to the face. Old pinion had a .035 shim.
    I'm using Ratech tool stamped 3.136 and a honed bearing to check initial pinion depth. I can get fairly consistent measurements and calculations but I'm not understanding what to do with the results.

    .5xx is ratech to the housing saddle is 3.136 minus the above measurements

    No shim = .500. 2.636
    .010 shim = .510. 2.626
    .045 shim = .545. 2.591

    What number am I shooting for?
    I think I'm supposed to take a baseline measurement of the original pinion with the ratech and match that, right? Or is there a number that is the standard pinion depth for an 8.5?

    I've always used the trial and error paint method, just thought I'd try to do one the 'right' way for once...smh
  2. BrianTrick

    BrianTrick Brian Trick

    Forget about anything scribed on the pinion head,of any brand. Just make sure the pinion matches the ring.
    Pick a pinion shim. That.035” is a hood start. Do a mock-up with the new pinion and that shim. You can leave the crush-sleeve out for mow. Install the carrier and shim it to achieve .008” backlash. Now check the pattern. That is what tells you if it is correct or not,or which way to go with it.
    techg8 likes this.
  3. sporty-to-GN

    sporty-to-GN Well-Known Member

    Yeah, that's how I've always done it. I was just hoping to get some use out of this ratech tool.
    I guess I was supposed to measure the original pinion with the original cups and cones and use that as the baseline.
  4. wovenweb

    wovenweb Platinum Level Contributor

    How did it turn out?
  5. Bens99gtp

    Bens99gtp Well-Known Member

    I have used those tools several times b4 on other gear set. There is normal a number on the bottom of the gears........and ratech has clear instructions.......if you don't have a checking depth to measure too then you really can't use it.

    The way it works is you measure the distance down from that tool to the pinion head, subtract that number from the number on the tool.......then you compare that number you can up with to the number in grave on the pinion .....the difference should in theory be the shim you need to use. Several times even after getting g that number spot on, I had to change shims cause the pattern told me it wanted something other that what should be by the tool.

    Keep in mind those are only 30 dollar tools and rely on how well you can center it on the gearing eyeball at best. Normally I measure 5 times when using it and average cause I never get the same measurement twice.

    One thing I have seen b4 with those tool is the plastic pin in them to center on the pinion center..... sometime that pin will keep that tool up off the pinion head...if that's the case tap the pin up till the tool does sit flat on the pinion head
  6. BrianTrick

    BrianTrick Brian Trick

    That is exactly what I recommend NOT to do.
    I have had countless customers contact me about repairing their rebuilt rear because it makes noise. Then you usually tell me that their guy “set it up right on the numbers.” I immediately know why it is wrong. Those numbers are merely a reference point. A place to start. The pattern you get is what really tells you if it is correct or not. I have all of the tools and fixtures,but I have not use the pinion depth tool for almost 15 years. I pick a pinion shim to start with,then shim the carrier to achieve about .008” backlash,then I apply the compound and run the pattern to see what it looks like. I know which way to go from there.
  7. sporty-to-GN

    sporty-to-GN Well-Known Member

    The diff turned out fine, not my first rodeo. As I stated in the original post, I have always relied on the paint method and I just wanted to try what some may consider the "right way." Turns out the Ratech tool is, at best, inconsistent. The directions are clear regarding taking a measurement but there is no mention of measuring the old pinion as a reference point, I assume that is the case. As far as I'm concerned, the Ratech is not money well spent. Good thing it's cheap.
    I'm gonna stick with mic'ing the pinion gear face to bearing seat thickness, figuring the difference between the old and new pinions, selecting shims accordingly, then checking with paint.
  8. sporty-to-GN

    sporty-to-GN Well-Known Member

    IMG_20171214_224438.jpg I don't really have green compound, just messing with editor settings. Almost went with the mirror imaging.
    Last edited: Dec 15, 2017
  9. Bens99gtp

    Bens99gtp Well-Known Member

    Too bad I was going to ask where you got the green from, it shows up well. I do agree as I posted the rate tool isn't the best, and have seen personally it not match what the gear set wants by the painted pattern.

    But if your someone with a bare case, no old parts with almost no rear end experience, it is a cheap way to get you in the ball park. Not the in the ballpark works for a gear set....but hopefully it gets ppl close enough to have an idea where they need to go. It is only a 30 dollar tool
  10. monzaz

    monzaz Jim

    That Pattern will run. I like to throw a bit more oil on the teeth and I like to see yoiu use more compound all the way around as you really should check every tooth... I had gear sets where one tooth never touched...Defective...they cut it NOT a laughing matter but I showed the manufacture/seller and they were ' wow we never see that before..' RIGHT.... ok.
    What is the back lash setting and what pinion shim did you end up with on this setup with the pictures?
    Also if you already have a good running rear...try to use the original shim to start with...most manufactures TRY to reference the same as the factory... they do not always succeed... but they try. Jim

    J D
  11. sporty-to-GN

    sporty-to-GN Well-Known Member

    .035 shim with .009-.010 backlash across 9 locations

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