2-Speed Rear Differential

[joihan777]

I've seen this idea from time to time, but I'm not really sure if the idea is feasible or not.

 

I wondred about this when I read the diff. gearing for the 2011 V6 regular vs performance package.

What would happen if the RWD differential had 2 gears, a low & high gear?

The gears would be 2.7 & 3.3 or something like that. That way you'd get plenty of grunt on take-off

but the 2.7 would kick-in on highway cruising.

 

Could this help mileage? Is it possible?

[theoldwizard]

IIRC, Ford actually sold a car in the 60s/70s (Cougar) with a 2 speed diff.

 

Heavy and expensive.

[Mad Hatter]

I guess 2-speed differentials lost justification when overdrives were offered. Don't know about a Cougar from the factory with one, but I recall an article in Hemmings Muscle Car about a man that owned a Torino King Cobra and a Mercury Cyclone Spoiler II. These cars were modded at Holman-Moody to compete with Charger Daytonas and the Torino had an experimental 2-speed.

 

Probably a better option is two overdrive transmission gears; maybe split the usual 70%.

[lfeg]

The expense (both cost and weight) needed to properly do a 2 speed rear for something like a Mustang is not worth the effort. A 6 speed automatic with a fairly deep first and a tall sixth is less expensive, lighter, less complicated, and smoother. And you do not have the shift sequence and NVH issues a 2 speed rear can bring. I can just imagine some poor fool trying to impress someone by splitting the gears in his Mustang, and dropping a shift to end up in neutral. 2 speed rears are not as popular in medium trucks today for the same reasons. A couple of more gears in the transmission and a wider gear spread is a better choice for most applications.

[Sixt9coug]

I have an issue of Hot Rod from 1969 that talked about that differential a bit and it's then use in the upcoming Cougar Eliminator. It of course, was never put into production on any Ford passenger car, but the two speed rear ends were used in some 9 inch housings in motorhomes and stuff.

 

It was known as the "hone-o-drive".

 

Here's a thread on the Cougar forums about it.

 

http://www.mercurycougar.net/forums/showthread.php?t=26940&highlight=speed+rear+end

[Sizzler]

A company called GearVendors sells either a overdrive or underdrive unit that bolts onto the back of common transmissions. It is a over/under drive for the whole transmission, or thinking of it another way, a 2-speed axle, just not attached to the axle.

 

It is a very strong unit, and has a good reputation. It fits in most transmission tunnels with maybe a little banging needed to fit. It turns a 4 speed automatic into a 8 speed, letting you shift from 2nd to 2nd+1/2 to 3rd...and even gives you two reverse gears.

 

Seems like it's a better idea. More flexible in installation, stronger, even adds its weight to the center of the car instead of out back.

[Ralph Greene]

As noted above....with 6 speed transmissions (and 7 and 8 in some cars now) , what is the point of a two speed rear. You can just do the same thing cheaper, simpler, lighter, and with more reliability in the trabsmission. Remember....just because a transmission has more forward gears, that does not not mean it contains a lot more parts than an older transmission. It's all about what cog meshes with another cog....done electronically.

[Donaldo]

We also have CVTs now with "infinite" gear ratios. No need for shifting at all! No maintenance required, either.