8 3/4 gear set up help

Transmission and Drivetrain Tech

  1. dusterdragracer

    dusterdragracer Drag Racer

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    I know this has been addressed before, any new help would be great. I am pulling my hair out.
    I bought a set of new Motive gears 3:55 for my Chrysler 8 3/4 diff.(489 case)
    I have had the carrier in and out 2 times, and apart atleast 30 times.After the last adjustment, I get a whine at 40-50 mph gas half on, half off (sort of coast).Lower and higher speeds, it is pretty quite, but still there. Before the last adjustment it was at 30-40 mph.That was at plus .012 pinion out .042 total shims)
    I have all the correct tools,pinion depth finder, dial indicator, and digital calipers.I have done diffs before.I am using prussian blue to check the pattern.
    Starting with the correct depth of 2.767 on the pinion, I have tried every depth at .002 intervals all the way to .030 behind the pinion (total of .052 shims). The best spot I have found was .050 (+.028 additional from 2.767) . I have the back lash at .009 which seems to be the best (Motive gear wants to see .008-.012 BL).
    My pattern always shows heavy to the tow, but with this last set up (.050), I got the coast pattern centered in the middle of the ring gear, and the drive still a little low towards the tow.If I went any further (pinion deeper .052) I get the drive going deeper to the tow.
    Man, what is up with this? Any help?I know this isn't rocket science!
     
  2. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    Are you using the crush sleeve or the eliminator? When I set mine up I used the factory shim, set my backlash to .010 and the crush sleeve. I should have gone with the eliminator but didn't. Mine is perfect, no howl at all.

    I have also heard/read that some gears are just noisier than others. I used the Motive gear set (3.55) as well and no issues.
     
  3. dusterdragracer

    dusterdragracer Drag Racer

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    OOPS Left that out.....crush sleeve eliminator, set correct.I know, it shouldn't be that hard. I have slambed together lots of other diffs,with no issues many times.My 742 /spool 4:30's race car, no issues, got it right away.
    Based on the internet, everybody has had gear noise with whatever gears.Everybody has a different opinion (pun intended)Friends run Motives with no isuues.
    Thanks for your input.
     
  4. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    How does the side to side adjustment affect your pattern/backlash?
     
  5. dusterdragracer

    dusterdragracer Drag Racer

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    Not much, I went from .005-.015 stays close to the same.I feel like .050 under the pinion is way too much, but then any less is worse. both sides drive and coast move toward the tow. My Aussie friend Ray will be here today, he has an Ebody Cuda right steer over there (I've driven it at the drags etc.) and he is good with this stuff. I have a hoist & tall stands, I can recover the oil, and have it out in less then 10 min.Gasket is glued to carrier, so it gets saved too.Just hate the smell of gear oil!
     
  6. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    It almost sounds as though you're on the high side of the pinion gear. I would start with the original shim, if you have it, and go from there.
     
  7. dusterdragracer

    dusterdragracer Drag Racer

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    That is what I was thinking.Actually, the original shim puts the pinion in the exact correct spot 2.767.......go figure.
    Last round with it out, I did go negative .007 and it went nuts, so I went back to .042 and went up and down from there.
    I am beginning to think I got a bad set of gears, but not ready to say that yet. It seems unlikely.
     
  8. Map63Vette

    Map63Vette Well-Known Member

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    Is there a chance the case might just have some kind of warp/defect in it? Maybe the carrier bearings aren't seating right or the place where they mount is somehow out of tolerance?
     
  9. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    My guess is you should be able to pull it in where you want it with the original shim. Mine worked out perfectly drive and coast side.

    Set the original shim in and set the pinion as best you can, set the chunk in and set your backlash to.010 and see where your at.

    Did you by chance mark your caps so they are on the same side/same orientation?
     
  10. Supershafts

    Supershafts Well-Known Member

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    It sounds like the pin is way too deep.
    Try the bl at .008 and after you pull the pin out some, like try removing around all the depth you have and just add .019 and then .008 on the bl and see where you're at, you are right now as it sounds (sight unseen) definitely way way to far deep
     
  11. rmchrgr

    rmchrgr Skate And Destroy

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    Since you didn't mention it, how are you measuring pinion depth?

    Sounds like you are using the measurement on the gears, putting it together and then using the pattern to check where you are.

    IMO, the only real way to take the guess work out of it is to measure pinion depth off of the carrier bearing races. That way you will get the exact relationship of the gearset to the case which is what pinion depth is. You need to verify that before you start adding or removing shims.

    Also, there is a specific baby-shit yellow marking compound used for checking gears. Prussian Blue is more of a machining/valve seat reference, might be the wrong consistency to get an accurate pattern. I could be wrong on this but I've never seen blue used for this purpose. Every gear set I've dealt with comes with a package of that yellow crap.
     
  12. Supershafts

    Supershafts Well-Known Member

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    I never use the blue, like you said thats for valve and clearance issues.

    I personally hate the mustard yellow also and use the white marker.

    He is definitely in to far
     
  13. dusterdragracer

    dusterdragracer Drag Racer

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    Thanks guys, lots of good info. I am using the ritchard (sp)depth setter, that goes off the race. But you can also lay a staight edge across race, and measure down and they are both the same, I mean exactly to the thou.
    I am going to do what everybody says, go back.and start at correct pinion depth.Which I have done twice.I think it is too deep.I am going to work with back lash.
    Sure would like to find out what the yellow goop is, prussian blue is too hard to read. I also tried paint, and white grease with no luck..
    Thanks Guys
     
  14. mcode

    mcode Well-Known Member

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    GM,(there, I said it), part number 1052351 Gear vMarking Compound.
     
  15. 69MOPE

    69MOPE Well-Known Member

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    I would set depth to what the gearset is marked and drive it. I have had several new gearsets make noise until broken in. The pinion depth numbers on the gears eliminates the need to check tooth pattern. That number is the gear depth established by the manufactures run-in machine that determines the quietest setting.
     
  16. jughead

    jughead Member

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    ten years of working at chry. dealership for a start. 1966 chry. 5 times, 4 ring and pinions still had the noise between 42 -50 mph. had factory rep by my side for part of them. only got paid for one set-up so u know what we went through back then. about a month later chry sent out a bulletin to the effect live with it if the gear does go out in warranty we will replace it. said it was something about the machining that would be too expense to change.
     
  17. rmchrgr

    rmchrgr Skate And Destroy

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    Is this the tool you are using? Not sure how accurate it could be since you have to hold it with your finger while you insert the dial indicator. I've never used it myself so I can't say either way but it does not look like there's any way to firmly set it in place - that could account for a lot of variance. I could be wrong though, seems like a decent idea for a quick set up.

    I use this tool. Pricey, yes, definitely but dead-nuts accurate. The difference between the two tools is that the MW uses machined discs that mount in place of the actual bearings. The caps are tightened down so there is a full 360 degrees of clamping force like there would be when the bearings were in. Kind of like honing a block with a torque plate, similar principal.

    A gear set is of course a matched pair but it still has to be installed in the correct relationship to the case. Pinion depth has to be measured because of machining tolerances in the case, not the gears.

    Do yourself a favor and find some marking compound. I think things might be a little more clarified with the right indicator.
     
  18. SGBARRACUDA

    SGBARRACUDA ROY FABO Gold Member

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    I too use the MW depth tool and it is the right tool for the job. That said several years ago I had I bought a set of 3.55 Motive gears for a Mirada that I installed a 68 B body 8 3/4 in. And I too had a whine at 40-50 when cruising. After several atempts at resetting the pinion/BL, I just gave up and wrote it off to a poor set of gears.
     
  19. dusterdragracer

    dusterdragracer Drag Racer

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    You guys are awesome. I am confident the pinion depth was correct to start with, and every adjustment along the way.I agree with better marking goo. I disagree that the noise might go away, and that it is something I should live with. These are new gears, and now that I drove it some more they are very noisy. My old 4X4 van with 200,000 miles on it, sounds better. More later when I pull them out in a week. My aussie friends are visiting (Ray has an ebody Cuda with a 440 and 4:56 8 3/4 he is a mechanic, and says they are way too noisy for new gears.
     
  20. Supershafts

    Supershafts Well-Known Member

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    You pin depth is definitely your problem, and every adjustment after that has been the wrong way
     
  21. dusterdragracer

    dusterdragracer Drag Racer

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    Thanks super shaft, but i did go the other way, and it got worse.
     
  22. dusterdragracer

    dusterdragracer Drag Racer

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    The on going drama. I had a friend with a performance shop, give the gears another go.He set them up, and I saw the perfect pattern, guess what, they still whine like crap. So that completely verify's, Motive Gears suck, and they give you no help. Also remember,Richmond was bought out by Motive, so if you order Richmonds, you will get Motives.
    At least I know now, I had them right the 1st time, when I did them.
     
  23. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    That's what I run with absolutely no whine.
     
  24. fishy68

    fishy68 Tyr Fryr's Inc. FABO Gold Member

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    A lot of times if their not set up right the 1st time and break in with that pattern you won't ever be able to get the whine out. As far as Motive buying Richmond, hopefully they'll still make Richmond's in a higher quality like they've always been and sell the Motives as the lower cost alternative.
     
    • Like Like x 1
    • inertia

      inertia Well-Known Member

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      Back in the late 60's - early 70's, We had to refuse installing Zoom gears, becaue they were always noisy, and customers hated the noise, other brands .. no problem..

      Jughead

      I remember that memo,, "hatchet-marks"_ lol..

      did you go thru the "boxcar bearing" fiasco, ??

      Vehicles transported by rail, had flatspots pounded into the axle bearings.. you had to diss-mantle the bearing, without damaging it, to show the "flatspots" to get paid for warranty,, sheesh..

      Anyone remember crankshafts 1 and 2 thou. under from factory?? that'll blow your oil pressure all to he!! . .

      Oh Gawd ! ! ,, am I that old,,
       
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