Aftermarket Over/Underdrive units for A727 / A904

[Kaitsu]

I red about these kind of "third planetaries" that come behinds the transmissions rear end, before the tail. Are these any good? The video showed that it works with electricity and can be set on/off with a button, which makes an overgear for all the gears in the tranny 1st, 1st OD, 2nd, 2nd OD and D, DOD. I´d like the idea of having 4th gear for my everyday highway trips to work, but dunno about the practical part of the extra planetary.

What is the ratio in manual OD 4-speed or the later OD Torque- Flites?

 

[kkritsilas]

.74 I believe. It comes out cheaper to get a an A500/A518 (42Rh/46RH( than the Gear Vendors overdrives. The Gear Vendors overdrives are about $2700 new, unless you get lucky with a unit out of a 60s-80s motorhome. You can get the overdrive torqueflites a lot less than that, even factoring in the fab'ing you would have to do, and the kit to make everything work seamlessly. This is noly true for the small blocks (both LA and Magnum), as the overdrive torqueflites only have the small block bolt pattern. The Gear Vendors overdrives are one way to go on a big block, or else something like a TCI 6X, which does dome in a version for a big block bolt pattern.

I don't know enough about the Gear Vendors overdrives to state an overdrive ratio, but I don't think it is as deep an overdrive as the Torqueflite overdrives.

Kostas