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  1. #1
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    HR Diff Review..... kinda

    So I finally got time to build two new bulkheads for my merv - New HR bulkheads and two new HR differentials. After building up the diffs with the required Traxxas bevel gears, CVD outdrives and new Avid bearings, I was pretty shocked to see there was a TON of lateral slop - something in the neighborhood of .050 !! (at least) No way. Unacceptable. Trying to shim that would shove the bearing right off it's journal.
    Obviously, not gonna run that so I shot emails to both HR and Liquid RC - we'll see what happens now, I hope I will be able to report on their outstanding customer service...
    Comparing the width of the diff carrier to the Traxxas unit I hoped to replace revealed it to be .023" narrower measured "inside" the bearing journal and .028" narrower measured "outside" the bearing journal. (overall width) So, add that to the four shims it took to get the Traxxas diff carrier properly shimmed and my original estimate was not far off.
    I had read of others having to use large numbers of shims with these new Diffs but this is a joke. I just hope I can somehow get this straightened out because looking at a 70 dollar piece of useless junk on my workbench really makes me mad. I am NOT a happy camper.
    There are lots of ways to do that. Most are wrong.

  2. #2
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    I used 5 and it works fine. Much nicer than stock diff.

  3. #3
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    You were luckier than me, five would not even take out half of the slop in mine! Your diff must have been considerably wider than the ones I got. (they both measure the same)
    I used four shims to get a new Traxxas Diff in OK (Looks like that's what I'll have to run)
    There are lots of ways to do that. Most are wrong.

  4. #4
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    Not sure what's going on with their QC, I had to return some hr items last week for a popular crawler due to poor fit. Hope you do in fact report back on great customer service, I was fortunate that the lhs I ordered with thru amazon gave me no grief.

  5. #5
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    Quote Originally Posted by robl45 View Post
    I used 5 and it works fine. Much nicer than stock diff.
    are you using the HR bulkhead or the Traxxas ones -

    I had to add one addtional shim to both the front and rear on my car when I went to the HR bulkheads from the stock ones - I was using the stock differentials however -

    If the HR bulkheads are a bit wider than stock and the HR diffs are a bit narrower than stock this could explain the extra shimms needed by photon

  6. #6
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    Quote Originally Posted by RZSmerv View Post
    If the HR bulkheads are a bit wider than stock and the HR diffs are a bit narrower than stock this could explain the extra shimms needed by photon
    These two dimensional differences add up to nearly .050 !! That's a little more than a bit, it renders the hardware combo unusable - there's nearly nothing left to support the bearing, it's journal is only about a eight inch wide - maybe less
    There are lots of ways to do that. Most are wrong.

  7. #7
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    I agree - I was just wondering if the people who are saying they are getting the HR diffs to work are using the HR bulkheads - I am thinking no

  8. #8
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    I'm using stock bulkhead. With stock diff it was Like 2 or 3 shims so definitely more with hr, but I definately had enough for the bearing to be fine. Maybe photon can shim both sides so one side isn't taking all the shims.

  9. #9
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    That's not quite how it works. the goal is to obtain maximum pinion engagement so, unless shimming the ring gear side is driving the ring too deep into the pinion (which does happen but it's usually very minimal in comparison when it does) there's no reason to shim the opposing side. If I was to say, split the shim stack, it would reduce gear engagement and defeat the purpose unfortunately.
    There are lots of ways to do that. Most are wrong.

  10. #10
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    Quote Originally Posted by therealrsr View Post
    Not sure what's going on with their QC,
    Sadly, I have some theories....
    This is off by so far, I'd almost guess it to be a code error on the NC combined with a sell-em-anyway business philosophy.
    Programed properly modern machines should be able to easily hold <.005 tolerance - this exceeds this by 10X !
    I should have an answer to my email inquires any minute now........
    There are lots of ways to do that. Most are wrong.

  11. #11
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    Quote Originally Posted by photon_trap View Post
    That's not quite how it works. the goal is to obtain maximum pinion engagement so, unless shimming the ring gear side is driving the ring too deep into the pinion (which does happen but it's usually very minimal in comparison when it does) there's no reason to shim the opposing side. If I was to say, split the shim stack, it would reduce gear engagement and defeat the purpose unfortunately.
    I don't have the aluminum bulkhead so I don't know whats going on with that. Personally I think the diffs should have had seals, that would probably make the difference in the thickness.

  12. #12
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    The HR diffs dont have seals?!?!?!? Man no seals and the tolerances out of whack,,,this does not sound like a good set up to me.
    BlindMan Racing
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  13. #13
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    Aluminum or plastic, the set up logic is the same. There are recesses for O-rings on the end caps (for the outdrives) but not the carrier end OD's - a good machined surface may be enough to contain the heavy oil we run... I may never know.
    There are lots of ways to do that. Most are wrong.

  14. #14
    Marshal Dadx2mj's Avatar
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    a good machined surface may be enough to contain the heavy oil we run
    I would have to see that to believe it. One of the biggest issues all sealed diffs have is keeping the fluid in them even with the use of seals. Trying to keep diff oil in a diff with no seals is like hoping a screen door will work on a submarine IMO.
    BlindMan Racing
    Rusty - MERV - Pede 4x4-Alias
    SPC Lipo Power

  15. #15
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    Yes, I agree, my statement was probably overly optimistic
    There are lots of ways to do that. Most are wrong.

  16. #16
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    Well mine seems to be holding the oil. I'm using 50k with the orings in the ends.

  17. #17
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    UPDATE...
    Ok, I Hobby Etc responded to my inquiry (Vendor was not Liquid RC as I was in error in my first post) they have been pretty helpful through multiple emails I will say. So here's the bottom line - the "factory" has confirmed they made the width of the diff undersized on purpose.... here's their quote:

    "As I understand from the factory due to the HR diff is a spiral bevel diff gear the size had to be different from stock with such a big variety of gear case on the market they did make it under size"

    Makes no sense to me at all. To shim a Traxxas diff it took ~.020" of shim, 5 shims. No problem, I can (and will) live with that. To shim the new HR diff it took .048" of shim (!) that means the bearing on the ring side is pushed almost 40% off it's boss. Maybe you find that tolerable but sorry I don't - to me it spells piece of junk. Another big issue which I never got around to discussing with them is that the pinion gear is cut short, meaning it has a TON of slop in the front to rear direction. Not that big of deal, it can be shimmed, but if it is not it has a HUGE impact on how the gears mesh.

    The factory's logic in making this dimensional change escapes me. I have never seen or heard of a bulkhead that was too narrow. I wish it was a Mfg. screw up so I could just get a correctly sized replacement. Oh well, these things are a write-off as far as I'm concerned - maybe they will work fine with .05 of shim IDK. personally I'll pass and take the refund they offered.
    There are lots of ways to do that. Most are wrong.

  18. #18
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    How about putting shims on each side of the bearing (some between the diff case and the bearing and some between the bearing and the bulkhead) so you don't need to move the bearing that far out of the recess?

  19. #19
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    You would need a shim with an OD the same size as the bearing OD but you'd be pushing the bearing inboard out of its bore. That's just splitting difference for the sake of running poorly designed hardware. I might try that had someone given me a set of HR bulkheads and diffs (it would still bug me anyway) but since I paid good money, they have no place in my world
    There are lots of ways to do that. Most are wrong.

  20. #20
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    If the machining is true the diff would seal with a little Silicone no problem. No updates on how the HR diffs are holding up?
    Those who forfeit liberty 4 security get neither

  21. #21
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    I'm running Traxxas Diffs in HR Bulkheads -
    I sent the HR junk back and was refunded long ago and, until I can see the dimensional issue has been resolved, personally, I'll never run em.

    This and other issues have definitely turned me away from HR (like a ton of other people)
    They just have zero quality control and as for customer service, there's none of that either (as in zero)
    Strike two, you're OUT !
    If you like em, good, maybe you were lucky. I'm done with 'em.
    There are lots of ways to do that. Most are wrong.

  22. #22
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    Quote Originally Posted by photon_trap View Post
    I'm running Traxxas Diffs in HR Bulkheads -
    I sent the HR junk back and was refunded long ago and, until I can see the dimensional issue has been resolved, personally, I'll never run em.

    This and other issues have definitely turned me away from HR (like a ton of other people)
    They just have zero quality control and as for customer service, there's none of that either (as in zero)
    Strike two, you're OUT !
    If you like em, good, maybe you were lucky. I'm done with 'em.
    I'll take your word for it, and buy stock stuff. I'm just have slightly rounded gear teeth on my stock diffs. And want to explore all my choices. I'm still frustrated that the stock diffs did this so soon.
    Those who forfeit liberty 4 security get neither

  23. #23
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    Quote Originally Posted by USA1 View Post
    I'm still frustrated that the stock diffs did this so soon.
    I suggest aluminum bulkheads, they definitely help!
    There are lots of ways to do that. Most are wrong.

  24. #24
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    HR makes a lot of garbage. I bought a set of shock bodies for the Merv and the threads were terrible. Also tried one of their shock towers for my Rusty and it was a pain in the you-know-what to make it fit. It wouldn't let me tighten that top plate down all the way onto the bulkhead. People talk bad about Integy but HR has been worse in my experience.

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