Ford Mustang Forum - View Single Post - 1966 c4 is not shifting well from second to third
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post #6 of (permalink) Old 08-17-2019
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When you overfill, and there's a lot of foam, any transmission will have trouble shifting. The fluid becomes 'springy' because of the air in it, and when the hydraulic actuators try to clamp down on the bands, etc., they can't deliver full pressure. If your transmission has been rebuilt in recent history, the friction materials don't care about whether you use Type F fluid too much, but that specification has a lot of anti-foam properties which is nice too.

If it calms down, and drives normally now that you got the fluid levels right, then good - but if the friction material's gotten damaged due to excessive slip, then it looks like a good time to do one. Thankfully, the C4 is pretty simple inside compared to most transmissions.

A shift kit will allow for firmer shifts, and that helps the friction materials last longer. (If that sounds counterintuitive, just think about what happens to a clutch when you slip it too much. Same thing.)

Anyway, let us know how it all turns out!

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