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Gear ratio question....yes I searched :) Please help while the cover is off

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by eripley, Nov 18, 2003.

  1. eripley

    eripley 1/2 ton status

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    I pulled the cover to my 12 bolt for Three reasons:
    To find out my gear ratio for 35x12.50 tires, to fix the leaky gasket, and to cheak for wear. Now I am more confused than ever reading old posts about how to determine my gear ratio.

    I have a 12 bolt rear end. No numbers stamped on gear that I can find to resemble anything listed in the forums. I counted outer teeth 5 times and came up with 34 teeth. Not 41 as everyone says are supposed to be there. The pinion gear has 10 teeth. I counted 5 times and could be off by maybe 1. It MAY have 11 but I think only 10.

    Whats my gear ratio?

    I bougtht RTV sealent. Should I seal both the housing and the cover? with the gasket sandwiched in between.

    For all those that care...no metal shaving or teeth in my drained oil!
     
  2. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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    3.42 with 10 teeth on the pinion

    3.08 with 11 teeth on the pinion

    Just use RTV on the cover. I dont even use a gasket.

    John
     
  3. kennyw

    kennyw N9PHW Premium Member

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    If you are going to use a NEW gasket, dont use RTV. If you are going to use RTV let it set up before installing the cover, then let it cure for 24 hours before filling the axle.

    I like to use a paper gasket with spray tack adhesive on both sides to help seal it quick and let me use it right away.

    34 divided by 10 is a 3.40 gear ratio /forums/images/graemlins/thumb.gif
     
  4. eripley

    eripley 1/2 ton status

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    Thanks guys. First off let me thank you for the speedy reply. Im going to put the cover back on!

    ....Im bummed. I cant even run the 31's I got on this truck according to the chart at 4lo.com!!

    Theres no way for 35's or even 33's.

    I got a 4" lift on here. Do you have any idea how funny this looks with 31's!! /forums/images/graemlins/frown.gif

    I was hoping I counted wrong. Is 34 teeth standard for a 12 bolt rearend?

    What does this guy mean:

    "OK, lets see if I can do better. The ring gear teeth count is identical on all GM axles, regardless of gear ratio. All ring gears (for GM OEM axles) are manufacturer with 41 teeth. The only difference is the ring gear diameter for the front and rear standard and heavier axles. For example, the standard rear ring gear diameter is sized at 9.5 inches (they may have an exception for the 4.56). The heavier the axles, the larger the diameter, up to 10.5 inches max. The front axles ring gear diameter range is 8.5, 9.25, and 9.75 inches (the Dana FF comes with 9.75). The way GM determines the ratio is to change the pinion teeth, i.e., 3.42 = 12 pinion teeth (pt), 3.73 = 11 pt, 4.10 = 10 pt, 4.56 = 9 pt. This same count applies to all their axles regardless of size (i.e., ½ through 1 ton). The math is simple: 41/12 = 3.42, 41/11 = 3.73, 41/10 = 4.10 and so on… Where are the GM engineers?"
     
  5. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    My rear 14BFF doesn't have stamped #'s on the ring gear either. I figure my rearend was rebuilt once with an aftermarket R&P that isn't labeled or did GM just not stamp some of them? /forums/images/graemlins/thinking.gif

    Not trying to hyjack.
     
  6. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I have yet to see a factory gear set that didn't have the numbers stamped on them. Grab some brake Kleen and spray the edge of the ring gear, then rotate it and repeat until it's gone at least one revolution. In that one single revolution you should see the numbers somewhere.

    3.42's is 41/12...not 34/10

    3.08's is probably not a 41 tooth gear set.

    Rene
     
  7. kennyw

    kennyw N9PHW Premium Member

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    [ QUOTE ]
    3.42's is 41/12...not 34/10

    [/ QUOTE ]

    Rene, I have a factory 3.40 12 bolt with 34/10. Came out of a late 70's 2wd pickup.
     
  8. eripley

    eripley 1/2 ton status

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    [ QUOTE ]
    I have yet to see a factory gear set that didn't have the numbers stamped on them. Grab some brake Kleen and spray the edge of the ring gear, then rotate it and repeat until it's gone at least one revolution.

    [/ QUOTE ]

    I can assure you its not there. I brake cleaned and castrol super cleaned. Its very shiny now. However there is no numbers. I have since put it back together.
     
  9. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    [ QUOTE ]
    I have yet to see a factory gear set that didn't have the numbers stamped on them. Grab some brake Kleen and spray the edge of the ring gear, then rotate it and repeat until it's gone at least one revolution.

    [/ QUOTE ]

    I can assure you its not there. I brake cleaned and castrol super cleaned. Its very shiny now. However there is no numbers. I have since put it back together.

    [/ QUOTE ] Me too, I cleaned mine all up before it went under the truck and no numbers. Aftermarket R&P?
     
  10. bee32

    bee32 1/2 ton status

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    Factory R&P will have a stamp. Not all after market ones will. 3:08 have a 43 ring and 14 pinion. I just pulled some out so I am sure of that one. So that answers that question about all the ring gears having the same amount of teeth. I am not sure where he learned math. I am by no means an axle expert but I can figure gear ratios pretty well and I don't see where he was saying all ring gears have the same amount of teeth. Not to mention all the rears I have re-built in hot rods. But hey, I have been known to have been wrong. 34/10=3.4 in my calculations.34/11=3.09 and I don't think you step down. I KNOW YOU STEP UP. then again I could be wrong. /forums/images/graemlins/rotfl.gif But not likely /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
    Hope this helps some.
     
  11. 99firehawk

    99firehawk 1/2 ton status

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    [ QUOTE ]
    Thanks guys. First off let me thank you for the speedy reply. Im going to put the cover back on!

    ....Im bummed. I cant even run the 31's I got on this truck according to the chart at 4lo.com!!

    Theres no way for 35's or even 33's.

    [/ QUOTE ]


    I am very happy with my 3:08s my 3 speed and my 35s /forums/images/graemlins/laugh.gif
     
  12. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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    [ QUOTE ]
    [ QUOTE ]
    3.42's is 41/12...not 34/10

    [/ QUOTE ]

    Rene, I have a factory 3.40 12 bolt with 34/10. Came out of a late 70's 2wd pickup.

    [/ QUOTE ]

    I can back that up. I had one too.

    John
     
  13. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I definitely have not had every possible ratio in every common diff in front of my very eyes...3.40 is a new one on me. Then again so was the 3.75 ratio in Greg72's van 14 bolt.

    I should stop replying to gear ratio posts.../forums/images/graemlins/crazy.gif

    Rene
     
  14. 84_Chevy_K10

    84_Chevy_K10 Banned

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    12 bolts have some funny combos.
     
  15. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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    [ QUOTE ]
    12 bolts have some funny combos.

    [/ QUOTE ]

    They do.. I think it was because of the wierd 8.785 (i think) ring gear size. It made for some non standard sounding ratios. But they were close enough to work fine.

    and....


    Rene, your experience is always welcome /forums/images/graemlins/smile.gif Don't worry about it

    John
     
  16. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    I definitely have not had every possible ratio in every common diff in front of my very eyes...3.40 is a new one on me. Then again so was the 3.75 ratio in Greg72's van 14 bolt.

    I should stop replying to gear ratio posts.../forums/images/graemlins/crazy.gif

    Rene

    [/ QUOTE ]

    I started to read the replies and I was getting ready to say the same thign and then I saw your reply.
    I have seen thousands of ratios on many vehicles and it's the first time I see a 12bolt with that ratio.
    Well learn new things every day.

    But I have yet to see a ring gear set without the ratio or count stamped on it. It must be a really cheap set from a non reputable place.
    I wouldn't trust them.

    And I am fine with my 3.08 and 35" tires.
    I guess I should mention the diesel in the front though /forums/images/graemlins/thumb.gif /forums/images/graemlins/rotfl.gif
     
  17. eripley

    eripley 1/2 ton status

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    [ QUOTE ]


    But I have yet to see a ring gear set without the ratio or count stamped on it. It must be a really cheap set from a non reputable place.
    I wouldn't trust them.



    [/ QUOTE ]

    So what are you saying!? I said I could have counted wrong. This is a single owner truck with stock eveything. the first owner did no such transfers of ring gears!
     
  18. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    [ QUOTE ]


    But I have yet to see a ring gear set without the ratio or count stamped on it. It must be a really cheap set from a non reputable place.
    I wouldn't trust them.



    [/ QUOTE ]

    So what are you saying!? I said I could have counted wrong. This is a single owner truck with stock eveything. the first owner did no such transfers of ring gears!

    [/ QUOTE ]

    Well that's puzzling.
    Like I said I haven't seen, does not mean it's not possible.
    it is definitely weird that GM wouldn't stamp it though.

    Maybe at some point the ring gear was bad and under warranty the dealer replaced it with aftermarket set and in the 70's there weren't that many reputable aftermarket places for truck gears.
    All were into hot rods.
    /forums/images/graemlins/thumb.gif
     
  19. u2slow

    u2slow 1/2 ton status

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    I'll vouch for the 12-bolt 3.40 gear set also. I've had a set in my hands.

    I've noticed that some GM gears are "halfway" stamped. Like they almost missed with the number dies. Either that or the gears are stamped first, then machined - they just hadn't figured the ring gear would be so thin /forums/images/graemlins/crazy.gif
     
  20. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    The tooth counts are also stamped on the end of the pinion in some cases. Good info to know if your in a junk yard trying to find a specific ratio and can't turn the ring gear for whatever reason. Just shine a flashlight in there and look at the end of the pinion. /forums/images/graemlins/pimp1.gif
     

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