Yenko turbo 400 speedo adaptor

[JoeC]

I believe the reason for the Speedo adapter was to get correct Speedo reading within federal tolerance. Adapter use was not governed by the gear ratio but by the gear tire trans combo. If you go one tooth up or down on the speedo gear in the trans it is about a 5 mph change. With the Speedo adapter if you go one tooth up or down on the gears in the adapter it is an about a 2.5 mph change. Some tire trans gear combos needed the adapter to get correct Speedo reading. My Yenko Chevelle TH400 4:10 gear has original trans with adapter and the Speedo reads correctly.

[JBB]

You are right Joe, it is to give the proper speed on the speedometer. But the only way to achieve this is the use of the Stewart Warner unit, as a 4.10 or bigger speedo gear could not fit in the casing. This info is per a transmisssion specialist, who has been rebuilding transmissions since the early 60's............

[copo69]

Well, do all 4:10 or lower geared cars use adaptors or only 14" tired cars? Auto's different from 4 speeds?

[COPO]

Believe it is all 4.10 and greater got the adapter regardless of trans type. My 70 Z-28 w/4.10 also has the adapter and it came with 15" wheels.

[Kurt S]

No, not all Muncies hooked to a 4.10 got the adaptor. Depended on which Muncie model it was, there were two different size speedo drive gears.

[copo69]

Should the 9737 Camaro with 4 speed have the adapter? 9737 with auto?

[Ed Cunneen]

Yes

[Kurt S]

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Should the 9737 Camaro with 4 speed have the adapter?

[/ QUOTE ]
Maybe. Some 4.10 rears got them, some didn't. Depended on plant inventory. I have documentation on several Z's with 4.10's and no adapter. Tire size shouldn't be a factor, but Z's had 15x7's anyway.