Thinking about UD/OD gearbox.

[David Morton]

Question: If somebody wanted to have the best of both worlds and install a gearbox on the end of their transmission, similar to one of these (http://www.atiperformanceproducts.com/fallsale/fs_od.htm), and could choose overdrive or underdrive, which would be better; to get an underdrive that will give them the 4.10 - 4.88 effective ratio and keep the stock rear end gears, or to change the rear end gears to that 4.10 - 4.88 and get an overdrive to bring back the effective 3.55 or even lower?

My thoughts are going along these lines; I could get a switch chip and program the chip for the two different ratios, also connect the servo for the gearbox so that everything happens with the flip of one switch. Position one - 3.55 and "economy" program (yeah, right), speedometer reads correctly. Position two - 4.88 and rich program, speedometer reads correctly.

More to the point of what I'm really trying to find out, don't the 4.10 or higher ratios make the rear end run hotter? And if so, since a rear end cooler can be installed, would that be more desireable because the 3.55 rear end is susceptible to breakage from the massive amount of torque coming out of the gearbox when in underdrive?

I like this idea. I'm going to pursue it next year, if God allows and the creek don't rise.

[FordNut]

They're heavy and take a lot of space in the driveshaft tunnel. Will probably require mods to the floor pan. Rather expensive too. I'm quite pleased with my 4.10s.

[RF Overlord]

More to the point of what I'm really trying to find out, don't the 4.10 or higher ratios make the rear end run hotter?

David, AFAIK you're the first person to mention this...I can't believe they run so much hotter as to create any problems, but that's what synthetic 75W-140 is for... ;)

[gpfarrell]

One disappointing downside... more gears = more friction, so you'll lose some ponies to friction. Entertaining concept though!

[MENINBLK]

Why do that when you can just do this ???
http://www.gearvendors.com/installation.html

Or just replace the 4R70/75W with this !!!
A new FORD TREMEC T56 6-speed Manual from Rockland Standard Gear !!
http://www.rsgear.com/
They are featured in the NEW PRODUCTS section of the January 05 Hot Rod mag...

Just think a 6 SPEED MARAUDER... :eek: :burn:

[Zack]

I researched the Gear Vendors Under/Overdrive a few months after i bought the car. Turns out they only offer the unit for the 4r70w out of pickup trucks. This means some internal trans modifications will be in order because the truck output shaft is much longer. And to top it off, like Fordnut said, Trans tunnel modifications will be necessary.
This may sound far out, but I want to have an adapter plate made up so I can bolt a Turbo 400 up to the motor, then put on a Gear Vendors UD/OD and slap a reverse manual valve body in the trans. Now that would be cool.

[David Morton]

This may sound far out, but I want to have an adapter plate made up so I can bolt a Turbo 400 up to the motor, then put on a Gear Vendors UD/OD and slap a reverse manual valve body in the trans. Now that would be cool.That is far out! But you're preachin' to da choir there brudda. I built many a TurboHydramatic 400 and for HD use you can't get much better for the size.

Putting one in a Marauder though...seems like "Guess Who's Coming to Dinner". I like the T/H 400 but I wouldn't want my daughter to marry one. (Yes, I think of "Quicksilver" as my little girl. I only want the best for her.) :D