1970 ZR1 LOOKING for rare part

[Ronald R.]

1970 ZR1 Corvette speedometer gear reduction unit with 411 rear end. Anyone seen one of these? I had a L88 that had one, my ZR1 does not have one, thanks RDR

[Ronald R.]

Re: 1970 ZR1 LOOKING for rare part

If anyone has a picture of the correct unit please post! thanks RDR

[Terry M.]

Re: 1970 ZR1 LOOKING for rare part

If anyone has a picture of the correct unit please post! thanks RDR

Ronnie

Not hard to find a picture. Google is your friend:

https://www.google.com/search?q=speedometer+gear+reduction+adapter&sxsrf=ACYBGNQHL24qkio4WZMKcAgywtAgrtoE2g:1568821782070&tbm=isch&source=iu&ictx=1&fir=h89stGbgtrU6LM%253A%252CjJ9jhXVI7dx2jM%252C_&vet=1&usg=AI4_-kRa3MZeJVlM703FbA5MsV_ENH3meQ&sa=X&ved=2ahUKEwi_3KTI3NrkAhUGPK0KHQmHC_0Q9QEwBnoECAkQDw#imgrc=h89stGbgtrU6LM:

See the Stewart Warner item. Also the one for Camaro.

BTW: The same gear reduction unit was used on any Corvette with 4:11 gears. I would think a similar unit was used in other GM vehicles with 4:11 gears. I know the same looking unit (with different internal gears) was used for 4:56 rear end. If there are any speedometer correction shops left in the world they likely have a drawer full of them and the internal gears to adjust the speedometer for accuracy.

[Mike M.]

Re: 1970 ZR1 LOOKING for rare part

terry: u imply the gear reduction units were commonly used on corvettes. i've never seen one on a c-1 or c-2 although i acquired one in the Don Blatchley stash i received in the late 70's(u will recall ole doc bletchley bought grady davis's year old corvettes and ran them in scca. ) don had a 62, a 63, a 66 and lastly a 69. perhaps the gear unit was born with the 69. enlighten me regarding the usage of these units. thanks, mike

[Ronald R.]

Re: 1970 ZR1 LOOKING for rare part

Seems to be several Stewart and Warner styles, right angle and strait many of each. I have a poor picture of a 69 Camero 396/425/456 that is right angle thanks RDR

[Ronald R.]

Re: 1970 ZR1 LOOKING for rare part

The JM shows them only on the L88 and ZR1 with 411 or 456 axle ratios??? Thanks RDR

[Dick W.]

Re: 1970 ZR1 LOOKING for rare part

Seems to be several Stewart and Warner styles, right angle and strait many of each. I have a poor picture of a 69 Camero 396/425/456 that is right angle thanks RDR

Go to a HD truck salvage yard that has older trucks. They were used on many makes. If you find one and the ratio is wrong, I have a complete selection of gears and shafts. Just need to know the ratio you need

[Ronald R.]

Re: 1970 ZR1 LOOKING for rare part

Is this the style? thanks RDR

[Ronald R.]

Re: 1970 ZR1 LOOKING for rare part

or possible one of these? Or does anyone really lnow? thanks RDR

[Terry M.]

Re: 1970 ZR1 LOOKING for rare part

terry: u imply the gear reduction units were commonly used on corvettes. i've never seen one on a c-1 or c-2 although i acquired one in the Don Blatchley stash i received in the late 70's(u will recall ole doc bletchley bought grady davis's year old corvettes and ran them in scca. ) don had a 62, a 63, a 66 and lastly a 69. perhaps the gear unit was born with the 69. enlighten me regarding the usage of these units. thanks, mike

Mike
You know I know nothing of C1s or C2s. I don't even think of those when I answer here, but I guess I should limit my comments. Time to pack anyway; and stop this foolishness.

We see them on the chrome bumper C3s with those deep axle ratios I mentioned. It wouldn't surprise me to see them on other Muncie so equipped Corvettes, but I plead ignorance.

[Terry M.]

Re: 1970 ZR1 LOOKING for rare part

Is this the style? thanks RDR

You got it.

[Ronald R.]

Re: 1970 ZR1 LOOKING for rare part

I have found a guy thar owned a speedo shop for 40 plus years and he will have the correct one just need to know what correct is? thanks for any guidance RDR

[Terry M.]

Re: 1970 ZR1 LOOKING for rare part

or possible one of these? Or does anyone really lnow? thanks RDR

The one on the left in the first picture.

[Ronald R.]

Re: 1970 ZR1 LOOKING for rare part

This guys has several and the gears to make it work, thanks for the help!!! Ronnie

[Joe L.]

Re: 1970 ZR1 LOOKING for rare part

This guys has several and the gears to make it work, thanks for the help!!! Ronnie

Ronald------


According to GM the correct speedometer adapter for your application is NO ADAPTER. An adapter was not used for 1970 Corvettes with 4.11:1 axle ratio. Your application used a speedometer DRIVE gear of GM #3924097 and DRIVEN gear GM #3860348. The latter is a 25 tooth gear and orange color-coded. The 3924097 DRIVE gear was replaced by GM #6261795 in March, 1975. The latter was discontinued without supercession in March, 1999. The 3860348 DRIVEN gear was discontinued without supercession several years ago. I believe that replacements for both gears are available in the aftermarket.

If you had a 1971-72 ZR-1 with 4.11:1 rear gear ratio then different speedometer gears would have been used in conjunction with a speedometer adapter.

1967-69 Corvettes with 4.56:1 or 4.88:1 rear gear ratio did use a speedometer adapter. 1967-69 Corvettes with 4.11:1 rear gear ratios did not use an adapter.