CRG Discussion Forum

Camaro Research Group Discussion => Originality => Topic started by: hihorse on December 30, 2007, 03:51:09 PM

Title: Gear reduction unit
Post by: hihorse 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?
Title: Re: Gear reduction unit
Post by: copo 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.
Title: Re: Gear reduction unit
Post by: hihorse on December 30, 2007, 11:43:23 PM
I found  a reducer with # 6476735 (1: .824). Would that work for my application?
Title: Re: Gear reduction unit
Post by: paceme 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.
Title: Re: Gear reduction unit
Post by: KurtS 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.
Title: Re: Gear reduction unit
Post by: Jerry@CHP 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
Title: Re: Gear reduction unit
Post by: paceme 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
Title: Re: Gear reduction unit
Post by: KurtS 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.
Title: Re: Gear reduction unit
Post by: paceme 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.
Title: Re: Gear reduction unit
Post by: Jerry@CHP 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
Title: Re: Gear reduction unit
Post by: JohnZ 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.
Title: Re: Gear reduction unit
Post by: Jerry@CHP on December 31, 2007, 07:57:43 PM
The 25 tooth gears are orange in color.

Jerry
Title: Re: Gear reduction unit
Post by: hihorse 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#?
Title: Re: Gear reduction unit
Post by: paceme 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.
Title: Re: Gear reduction unit
Post by: hihorse 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.
Title: Re: Gear reduction unit
Post by: paceme on January 01, 2008, 04:14:11 PM
I believe 22 tooth Driven Gear will work with that adapter.
Title: Re: Gear reduction unit
Post by: KurtS on January 01, 2008, 06:17:40 PM
And I think that with an 9 tooth drive gear, the car doesn't neet the adapter at all (like John's car).
Title: Re: Gear reduction unit
Post by: paceme on January 01, 2008, 07:03:03 PM
And I think that with an 9 tooth drive gear, the car doesn't neet the adapter at all (like John's car).

That would be my guess as well. I don't have any data on 9 tooth drive gears utilizing a reducer. Each transmissions has a part# tag that designated its build configuration. If 9 tooth drive gear transmissions did not need adapter/reducer in high numerical gear applications then why wouldn't they install transmissions configured as such based on the part# tag. Assuming that the pn tag/brass tag in fact provided a configuration/BOM for the trans.
Title: Re: Gear reduction unit
Post by: JohnZ on January 02, 2008, 06:37:05 PM
My original VIN-stamped M21, dated P9B17B, has the steel tag embossed 3946798, as shown in the A.I.M. in M20, Sheet A1 for use with M21 and Z28 or L-78.
Title: Re: Gear reduction unit
Post by: NED on February 13, 2008, 03:24:00 AM
Reguarding the 15 inch tire issue. I have a 67 Z with 4:56 and it does have the transmission speedometer adapter.
Title: Re: Gear reduction unit
Post by: red67l78 on November 29, 2010, 09:02:33 PM
This is a old thread but i have a reduction with part number 6479236. Is this for camaro or for what?  Ratio is  1: .950
Title: Re: Gear reduction unit
Post by: bertfam on December 01, 2010, 05:27:25 AM
Quote
This is a old thread but i have a reduction with part number 6479236. Is this for camaro or for what?  Ratio is  1: .950

Finally finished moving and was able to dig out my books. That P/N "appears" to be for a 1970's car, so it's not correct for a 1st gen Camaro. Most of the 67-69 Camaro adapters are 6476xxx numbers.

Ed
Title: Re: Gear reduction unit
Post by: JoeC on December 02, 2010, 02:37:07 AM
there was also a straight one and an offset

the offset  is stamped 666F U1 and 1.2020 X
the straight is stamped 777  then under that is 5000

Title: Re: Gear reduction unit
Post by: BillOhio on June 06, 2014, 01:14:22 PM
I was looking into if my car needs the adaptor and found this. My car has the same tag number as Johns. Z28 with 4:10. Should I also have the 9 and 25 combination? It appears when the 4:88s were installed my driven is the brown 18 tooth. I need to recount the driver I thought it was a 6 tooth. Good time to change before I have the transmission in! Are all drivers the same color?
Title: Re: Gear reduction unit
Post by: luv2sixty9 on June 06, 2014, 01:24:52 PM
My 67 Z28 with 4.88 gears has the reducer # 6476735 (1: .824).
Title: Re: Gear reduction unit
Post by: BillOhio on June 06, 2014, 01:30:37 PM
I should have added, got tired of engine screaming so the 4:10s are back in. What was interesting, the 4:88 gears were gym and dated end of 68, looked like the correct date for my car anyway
Title: Re: Gear reduction unit
Post by: firstgenaddict on June 07, 2014, 01:02:31 PM
going through a list of Window stickers in Jerry's book I found the following (probably a few more out there) I have listed what model they came in although there may be overlap none of these showed it.
Would the ECL codes indicate the different transmissions? 
3 ECL codes for the M20.
One used with the Z28 3.73 to 4.10
One used with a L35 3.07
One used with a L48 3.31

there were 2 for the M21
one with the Z28 3.73 -4.10
one with a L78 F70 14's 3.55

2 for the M22
One used with a L72 F70 14's and 4.10
One used with a Z28 and 3.73's
Title: Re: Gear reduction unit
Post by: BillOhio on June 09, 2014, 10:40:40 PM
I counted my driven gear again carefully and its a 7 tooth. I would say it appears to be white