Author Topic: Gear reduction unit  (Read 9621 times)

hihorse

  • Member
  • ***
  • Posts: 123
    • View Profile
Gear reduction unit
« on: December 30, 2007, 03:51:09 PM »
Would a 1969 L78 Camaro  with M20 and 410 rear come with a gear reduction unit? If so what is the part number?

copo

  • Member
  • ***
  • Posts: 73
    • View Profile
Re: Gear reduction unit
« Reply #1 on: December 30, 2007, 07:19:55 PM »
Yes, the part number is 6476736, stamped 1:.777, 6476736. This speedo adapter is extremely hard to find. I have only seen two for sale on Ebay and both had sold for more than $700.00.

hihorse

  • Member
  • ***
  • Posts: 123
    • View Profile
Re: Gear reduction unit
« Reply #2 on: December 30, 2007, 11:43:23 PM »
I found  a reducer with # 6476735 (1: .824). Would that work for my application?

paceme

  • Member
  • ***
  • Posts: 484
    • View Profile
Re: Gear reduction unit
« Reply #3 on: December 31, 2007, 12:20:36 AM »
Would a 1969 L78 Camaro  with M20 and 410 rear come with a gear reduction unit? If so what is the part number?

410 4spd cars with 14 inch wheels received speedo reducer.

Interesting to note that cars equipped with 15" wheels such as Z28's and 9737  (sports car conversion) did not.  The use of the reducer involved a couple of variables such as tire size and transmission shaft/speedo gear as well.
Steve Shauger
Vintage Certification™ Program, Providing Recognition And Status To Unrestored Vehicles. Website www.vintagecertification.com

KurtS

  • CRG Coordinator
  • *****
  • Posts: 3560
    • View Profile
Re: Gear reduction unit
« Reply #4 on: December 31, 2007, 06:41:07 AM »
It depends on the trans version the car received. If I recall the details correctly, the 4.10 could use either of two M20's (shown in the AIM). One was for the deeper gears and one was for the normal gear range. One required the use of the adaptor, one didn't. Which trans was used depended on availability in the plant.

I've definitely seen original 4.10 M20 cars without the adaptor.
Kurt S
CRG

Jerry@CHP

  • CRG Member
  • *****
  • Posts: 1455
    • View Profile
Re: Gear reduction unit
« Reply #5 on: December 31, 2007, 01:40:27 PM »
Another isssue that comes into play is the drive gear on the main shaft.  There are two, 8 and 9 tooth.  In my 35+ years of rebuilding Muncies, I have seen both used for the same model year application.

Jerry

paceme

  • Member
  • ***
  • Posts: 484
    • View Profile
Re: Gear reduction unit
« Reply #6 on: December 31, 2007, 02:45:21 PM »
Another isssue that comes into play is the drive gear on the main shaft.  There are two, 8 and 9 tooth.  In my 35+ years of rebuilding Muncies, I have seen both used for the same model year application.

Jerry

I agree with you and Kurt regarding the use of the reducer "The use of the reducer involved a couple of variables such as tire size and transmission shaft/speedo gear as well." (driven/drive gears)

The transmission drive gears you mention 8&9 tooth, was 16 also used?

I have a listing of reducers which shows it was possible to have one on a 373 gear car as well. Have you seen any used on any 15" wheel applications such as z28's and Yenkos?


BTW everyone have a safe and happy New Year
Steve Shauger
Vintage Certification™ Program, Providing Recognition And Status To Unrestored Vehicles. Website www.vintagecertification.com

KurtS

  • CRG Coordinator
  • *****
  • Posts: 3560
    • View Profile
Re: Gear reduction unit
« Reply #7 on: December 31, 2007, 04:30:15 PM »
Another isssue that comes into play is the drive gear on the main shaft.  There are two, 8 and 9 tooth.  In my 35+ years of rebuilding Muncies, I have seen both used for the same model year application.

Jerry
Yup, that's actually the same issue. Those are the two different part #'s the AIM shows.

Steve, I'll have to look into the 15" wheel question.
Kurt S
CRG

paceme

  • Member
  • ***
  • Posts: 484
    • View Profile
Re: Gear reduction unit
« Reply #8 on: December 31, 2007, 04:58:25 PM »
I believe I answered my own question "The transmission drive gears you mention 8&9 tooth, was 16 also used? "

The 16 tooth drive gear was used in the Turbo Hydramatic application.
Steve Shauger
Vintage Certification™ Program, Providing Recognition And Status To Unrestored Vehicles. Website www.vintagecertification.com

Jerry@CHP

  • CRG Member
  • *****
  • Posts: 1455
    • View Profile
Re: Gear reduction unit
« Reply #9 on: December 31, 2007, 06:08:22 PM »
Steve,

That's correct.  8 and 9 are for 4-spd.  Also remember that the speedometer could be re-calibrated w/o use of the reduction unit by using a different driven gear ranging from 23 to 25 teeth.  All of of the oriignal 3.73 rear Z28 transmissions that I've rebuilt over the years usually have the black 23 tooth driven gear. 

Jerry

JohnZ

  • CRG Member
  • *****
  • Posts: 4261
    • View Profile
Re: Gear reduction unit
« Reply #10 on: December 31, 2007, 06:31:08 PM »
My original '69 Z/28, built with M21 and a 4.10 axle, had no reducer and a 25-tooth driven gear.
'69 Z/28
Fathom Green
CRG

Jerry@CHP

  • CRG Member
  • *****
  • Posts: 1455
    • View Profile
Re: Gear reduction unit
« Reply #11 on: December 31, 2007, 07:57:43 PM »
The 25 tooth gears are orange in color.

Jerry

hihorse

  • Member
  • ***
  • Posts: 123
    • View Profile
Re: Gear reduction unit
« Reply #12 on: January 01, 2008, 01:59:24 PM »
Would a 1969 L78 Camaro  with M20 and 410 rear come with a gear reduction unit? If so what is the part number?
My car did come with the 14's, and L78/M20/410, just to recap what combination(s) of the following would it have from the factory?
1)Drive gear teeth?
2)Driven gear teeth?
3)Speedo adapter Part#?

paceme

  • Member
  • ***
  • Posts: 484
    • View Profile
Re: Gear reduction unit
« Reply #13 on: January 01, 2008, 03:32:43 PM »
The key is transmission drive gear teeth. If your transmission has a 8 tooth drive gear the following should work for
4.10 Rear Axle,  F70-14 Tires, 8 tooth Drive Gear (P/N 3924098), 20 tooth Driven Gear (P/N 3860343),  Adapter P/N 6476736. This is good for 3 or 4 speed transmission.
Steve Shauger
Vintage Certification™ Program, Providing Recognition And Status To Unrestored Vehicles. Website www.vintagecertification.com

hihorse

  • Member
  • ***
  • Posts: 123
    • View Profile
Re: Gear reduction unit
« Reply #14 on: January 01, 2008, 04:07:27 PM »
Thanks, would you know what the combination is for the #6476735 adapter as I don't have the other adapter.