63 rear end gear ratio options

[Daniel T.]

Hi, I'm trying to understand what gear ratios were available in 1963 with which engine/trans options and also if it was different for G81 posi. The chart attached is from Noland's book referring to the posi option. Was that not available on T10 equipped early cars? Was the L75 limited to a 3.36:1 ratio where the lower gears were for the higher HP motors only? (or was that only with posi?) I'm a bit confused and the judging manual didn't have much info on it either. thanks! Dan

[Harry S.]

Re: 63 rear end gear ratio options

If you have the NCRS 1953-1972 Pocket Spec. Guide, Look at page 41.

[Daniel T.]

Re: 63 rear end gear ratio options

thanks, I don't have that guide unfortunately, I'll have to get one but in the mean time could you share that page (picture of it etc?) thanks! Dan

[Harry S.]

Re: 63 rear end gear ratio options

OK, here you go...

IMG_2693.JPG

[Daniel T.]

Re: 63 rear end gear ratio options

thanks. wasn't sure the way Noland's book had it written if they didn't offer all the ratios with the hydraulic lifter motors, but by that chart it doesn't show any motor based limits.

[Jack M.]

Re: 63 rear end gear ratio options

This June 1963 Power Teams chart may be easier to understand:

1963-Corvette-Power-Teams-01.jpg
1963-Corvette-Power-Teams-02.jpg

[Daniel T.]

Re: 63 rear end gear ratio options

Jack- thanks, so by that it was 3:36 or 3:08 for my 327/300hp (L75), which is more inline with what I had heard but been unable to confirm. The car currently has a 3.70 coded center in it but with 4:11 gears and when I take the rear suspension apart this winter for the next part of the restoration I'd like to find a correct rear setup for it. I'm not ready for ncrs judging yet but trying to learn here and do things right as I work on the car since the rest of it seems pretty unmolested and numbers matching motor/trans.

So now to find a late 62 dated CA/CB 3:36 housing...

thanks! Dan

[Dave S.]

Re: 63 rear end gear ratio options

I have an original drivetrain L75 (300 HP) with a T-10 and 3:36 rear end. The chart mentions a first gear of 2:54 for 300 HP cars. I always thought BW T-10 transmissions were all 2:20 first gears. Can someone clarify that.??

[Jack M.]

Re: 63 rear end gear ratio options

The Chevy charts may be inaccurate, but the 1963 Finger-Tip Facts seem to confirm the ratios.
Perhaps someone else has some better information & practical/hands-on knowledge.

1963_M20-01.jpg

[Dave S.]

[Duke W.]

Re: 63 rear end gear ratio options

There is no such thing as a M-21 T-10 in 1963. The four-speed transmission option was M-20, period, and with the 250/300 HP engines you got a wide ratio and a close ratio with 340/360 HP engines. Wide ratio and close ratio were determined solely by the engine. The customer could not choose. This was also the case for '62 and '62 is also the first year for the WR version T-10.

The same applies to Muncies from late '63-65, and L-78 was CR.

The first year for the M-21 option was 1966. This is because the customer could order either WR or CR with the L-79 and L-36 engine options. M-20 became the option code for the WR and M-21 became the option code for CR. Each had a different standard axle ratio and a specific set of optional ratios.

The base 300 HP engine was only available with M-20 and M-21 was mandatory with L-72.

Powertrain charts that list all engine, transmission, and axle combinations are in the NCRS Specification Guides, AMA specs and Sueed's Finger Tip Facts a page of which jack uploaded in his prior post.

Duke

[Dave S.]

Re: 63 rear end gear ratio options

There is no such thing as a M-21 T-10 in 1963. The four-speed transmission option was M-20, period, and with the 250/300 HP engines you got a wide ratio and a close ratio with 340/360 HP engines. Wide ratio and close ratio were determined solely by the engine. The customer could not choose. This was also the case for '62 and '62 is also the first year for the WR version T-10.

The same applies to Muncies from late '63-65, and L-78 was CR.

The first year for the M-21 option was 1966. This is because the customer could order either WR or CR with the L-79 and L-36 engine options. M-20 became the option code for the WR and M-21 became the option code for CR. Each had a different standard axle ratio and a specific set of optional ratios.

The base 300 HP engine was only available with M-20 and M-21 was mandatory with L-72.

Powertrain charts that list all engine, transmission, and axle combinations are in the NCRS Specification Guides, AMA specs and Sueed's Finger Tip Facts a page of which jack uploaded in his prior post.

Duke

Duke,
Thank you for the clarification and explanation.

It is interesting what experimentation was happening back in the 63 model year.

Installing a 4 speed with a 2:54 first gear in a 300 HP small block Corvette with the standard 3:36 rear end was not the best decision.

[Thomas B.]

Re: 63 rear end gear ratio options

I too am confused on this. I have a 340hp 4 speed with a posi 3.70 axle, coded CX129. Shouldn't mine be coded "CD" or can you have "CX" with option G81 added which makes it a posi? Also, what do the numbers 129 after CX mean?

[Harry S.]

Re: 63 rear end gear ratio options

I too am confused on this. I have a 340hp 4 speed with a posi 3.70 axle, coded CX129. Shouldn't mine be coded "CD" or can you have "CX" with option G81 added which makes it a posi? Also, what do the numbers 129 after CX mean?

From memory, isn't CX a Service Replacement rear replaced under warranty?

[Thomas B.]

Re: 63 rear end gear ratio options

CX is in the NCRS pocket guide as a 3.70 with 4 speed close ratio.