I just bought a 79 vette and have been looking at the Gear Vendors overdrive system to add to the back of my 4 speed. Does anyone have any experience with this product? Will it require any mods to put it in (other than the driveshaft)? I like the idea of a semi-automatic 8 speed. It should give great acceleration (super close ratio) andd I should pick up a few mpg to boot. Any experience for better or worse would be appreciated.
I have a th400 with a Gear Vendors unit. The th400 is a 3 speed auto unit, just in case you didn't know. I love my setup very much, no not that much. I don't know how much of an advantage it would be for your 4 speed tho. In practical driving use I don't think you would be splitting all your gears. It would be just too tedious. I think you would find you would only use it for the overdrive on 4th gear. It your 4 speed has a 1:1 ratio in 4th then yes you would possibly see lower rpm's and better fuel economy by using the GV to get a .78:1 ratio. As far as what's needed to put one in I think it wouldn't be that tough for a C3 since you have a cross member to support it. The guys at Gear Vendors were top notch to deal with. I could always call them up and ask them questions and they were very helpful. Good luck.
I think they would have the adapter fittings to attach it to your 4 speed. They do say you have to push in the clutch when activating/deactivating the Gear Vendors when it is attached to a manual tranny. I guess it is because when you push the button to engage it it hits pretty hard and locks in so they don't want to break things I suppose. And coming out of o/d it downshifts hard too. That's another reason why I don't think you would use it between all the 4 original gears. You would get a tired leg. I think just overdrive on 4th on the highway would be all you would use it for.
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