1965 speedo gear for 4.56

[Bill W.]

My 65 BB came with a 4.56 rear . It lost its orig. trans. some time before 1973 . I have a close ratio trans for it but it has a 4.11 speedo gear (24 tooth) I need a 25 tooth (4.56) and it seems nobody makes them . Does anybody know where I can get the correct gear ? How much will the 24 tooth change the millage & speed ?

[Wayne M.]

Re: 1965 speedo gear for 4.56

My 65 BB came with a 4.56 rear . It lost its orig. trans. some time before 1973 . I have a close ratio trans for it but it has a 4.11 speedo gear (24 tooth) I need a 25 tooth (4.56) and it seems nobody makes them . Does anybody know where I can get the correct gear ? How much will the 24 tooth change the millage & speed ?

Bill --- do I understand your car now has the original 4.56 ? The orange plastic gear has 25 teeth, and works with the # 3708145 drive gear, which it sounds like you have now (works with 3.70 and 4.11). To duplicate what your car's trans had from the factory, you'd need the 6-tooth steel drive and the 20 tooth driven (shown below). [3850479 / 3860329], but that requires tranny work.

So the orange gear 3860348 is best you can (easily) do. In fact, that's what's in my L78 now, as (for fun) I installed a '64 diff w/4.56's.







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[Keith B.]

Re: 1965 speedo gear for 4.56

I have a very gently used 25 tooth plastic gear I bought from Long Island Corvette. If you pay shipping and what ever you think it's worth you can have it

[Bill W.]

Re: 1965 speedo gear for 4.56

Keith .That sounds great . My Email is pondpeoplel78@gmail.com Send me a note with a price please .

[Bill W.]

Re: 1965 speedo gear for 4.56

Wayne I have a few gears and all of them are tan . I wonder if the service or aftermarket were color coated ? Long Island says the 456 rear takes a 25 tooth . They say a 20 is for a 3.36 ???? I dont know . My car came with a 4.56 when new and the rear was changed to a 3.70 when it was raced 1/4 mile and the 4.56 for 1/8 mile . we had both tracks here . I bought a NOS 4.56 with a 65 date that came out of a training center . thats what I have in it now . I have the 3.70 also .

[Joe L.]

Re: 1965 speedo gear for 4.56

Wayne I have a few gears and all of them are tan . I wonder if the service or aftermarket were color coated ? Long Island says the 456 rear takes a 25 tooth . They say a 20 is for a 3.36 ???? I dont know . My car came with a 4.56 when new and the rear was changed to a 3.70 when it was raced 1/4 mile and the 4.56 for 1/8 mile . we had both tracks here . I bought a NOS 4.56 with a 65 date that came out of a training center . thats what I have in it now . I have the 3.70 also .

Bill-------


All GM PRODUCTION and SERVICE driven gears I have ever seen were color-coded. In fact, all aftermarket gears I have seen were color-coded, too. The 25 tooth gear, GM #3860348, is color-coded ORANGE. It has been recently discontinued but it's easily available in the aftermarket.

A 20 tooth BLUE driven gear of GM #3987920 with drive gear GM #3708144 can be used with a 4.56:1 ratio IF adapter GM #3932220 (0.7773:1) is also used.

[Wayne M.]

Re: 1965 speedo gear for 4.56

Bill -- here's what I do. As I never trust speedometer calibration (and anyway, in Canada, and the rest of the world, speeds are in kilometres/hour). Knowing the rear end gears (4.11's, so I installed the proper 24-tooth yellow plastic gear) and the circumference of the tires I have on the car, I calculate the RPMs versus speed in both mph and kph. I keep the table in the glovebox for occasional reference. I then stick markers on the tachometer dial to correspond with the most important speeds, ie. to avoid tickets. School and playground zones are 30 kph, most city streets are 50 or 60 kph, and open highway 100 or 110 kph.