1969 Corvette with factory 4.10

[Joseph A.]

I have seen in posts that 4.10 cars had a speedometer reduction adapter. I have owned my car for 40 years and it is untouched and there is no adapter on the transmission. Just looking for clarification.

[Joe L.]

Re: 1969 Corvette with factory 4.10

I have seen in posts that 4.10 cars had a speedometer reduction adapter. I have owned my car for 40 years and it is untouched and there is no adapter on the transmission. Just looking for clarification.

Joseph------


1969 with 4.11:1 did not use a speedometer adapter. With 4.56:1 an adapter was used, though.

[Joseph A.]

Re: 1969 Corvette with factory 4.10

Thank you Joe

[Mike M.]

Re: 1969 Corvette with factory 4.10

Joseph------


1969 with 4.11:1 did not use a speedometer adapter. With 4.56:1 an adapter was used, though.

Joe: is the adaptor insert in the tail housing such that the speedometer cable inserts parallel to the long axis of the main case? I've got an old 39 chevy sedan deliver which could benefit from such an arrangement. thanks, mike

[Joe L.]

Re: 1969 Corvette with factory 4.10

Joe: is the adaptor insert in the tail housing such that the speedometer cable inserts parallel to the long axis of the main case? I've got an old 39 chevy sedan deliver which could benefit from such an arrangement. thanks, mike

Mike-----


Speedometer adapters were configured both ways, depending on part number. In other words, some had an input that was parallel to the transmission speedometer fitting (i.e. perpendicular to the transmission mainshaft) and some had an input that was 90 degrees to the speedometer fitting (i.e. parallel to the transmission mainshaft). However, GM did not usually offer the 2 different configurations with the same ratio. Several different ratios were available, though, some overdrive and some underdrive.

Adapters came into more widespread use in the 1971+ period. That's because 1971+ Muncies and BW-Super T-10 had only one speedometer drive gear which could only accommodate driven gears of up to 22 tooth (silver). So, any cars having rear ratios of 3.70:1 or numerically higher required an adapter. Of course, in those years not too many cars had such rear ratios.

The adapters used by GM were manufactured by either the AC Division of GM or Stewart-Warner. None of the adapters used on Corvettes remain available from GM. I understand that speedometer shops can supply them and also set them up for the specific ratio required. Adapters are often used on police patrol cars in order to have "certified" speedometers. In other words, through the use of an adapter a very precise speedometer calibration can be obtained.

[Joe L.]

Re: 1969 Corvette with factory 4.10

Joe: is the adaptor insert in the tail housing such that the speedometer cable inserts parallel to the long axis of the main case? I've got an old 39 chevy sedan deliver which could benefit from such an arrangement. thanks, mike

Mike------


Here's a 90 degree adapter which I think is what you're referring to. This one has a 1: 0.8834 ratio.

https://www.ebay.com/i/114478212993?ul_noapp=true