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Old 05-23-2011, 08:40 PM
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7004r Transmission with Mechanical Speedometer

I am installing a 7004R transmission in a 1956 Chevy with a 400 Small block Chevy motor. Is it possible to use the mechanical speedometer with the 700R transmission? If so, how is that done and what components are needed? If not, what is the best solution for this circumstance?

Thanks for the help, StreetRodder37

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Old 05-23-2011, 09:10 PM
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i think all you would need is a speed-o cable the gears and cover for the trany and a mechanical speed-o i know the 86 camaro used a mechanical speed-o measure the length and compare
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Old 05-24-2011, 01:36 AM
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Should find neccesary parts & Info here:

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Old 05-25-2011, 12:43 PM
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What set up is on the transmission now? Does the trans have an extension housing on it?

I'll assume you bought a transmission that has no extension housing, and no mechanical drive gear, or hall effect sensor present on the output shaft.

If this is the case, you will need:
Extension housing for mechanical speedo
Drive gear to get pressed onto output shaft
Clip to retain drive gear once on the shaft
Driven gear housing & seals (o-ring around housing diameter & smaller o-ring that seals against the driven gear)
Driven gear
O-ring for driven gear housing to extension housing seal
Retainer, metal, to hold the driven gear housing in the extension housing
Bolt to hold metal retainer

I sell a lot of 700's and if a customer does not already have all of this stuff on their old trans, it can add up fast. Not to mention you will need to know what drive & driven gear you need (tooth count or color) to get your speedo to register the correct speed. If you know your rear gear ratio, and your tire size, you can look on-line at the charts before you order the plastic gears to be sure you get the right ones. Or, if your speedo in your car is correct at this time, you can count the teeth on those gears in your old transmission and get the same ones for the 700. Not sure but I think some of the gears will swap between the 700 & T-350.. Never tried it myself but if they will work, that will save you some money. Good luck on finding the mechanical speedo housings.

They are highly sought after where I live and when you find them, they want $50 just for the housing, and sometimes much more... Most salvage yards around here will not sell the housings separately from the transmission. I used to have a lot of the mechanical housings on hand and sold them on transmissions.. Now I'm down to 3 or 4.. No, I don't want to sell them! Ha ha..
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