2 Speed Rear End

[fasterthanu]

Is anyone out there running this? Do they make it for corvettes? What ratios do they come, and does anybody have a link?

 

[BeaterShark]

I've never heard about a multiple speed rear end. Do you mean an auxillory transmission? I've heard of a Doug Nash 2 speed that (I think) bolts to the tail housing of a tranny, but I don't know the details.

 

[yakatak76]

i've run 2 speed rear ends in my grain trucks all the time, never heard of an application for a car tho...

 

[Bob Chadwick]

This appears to be along the lines of what you are talking about. It originated in this post originated by 69MyWay on changing out to a Richmond 6 speed.

Gear Vendors Overdrive Unit.

Get the best of both worlds. You have your original equipment and a 28% reduction in any gear. That would drop your rpms to about 2160 at 70 mph. It'll cost some $$ but you'll get to keep your original tranny. Also, the unit can be removed if you want to transfer it to another shark later on.

Russ

 

[fasterthanu]

actually, no, that is not what I am referring too. A company called Columbia does make 2 speed rear end for cars. I have heard of vettes that have had them custom installed. yakatak76 was right, they are in some trucks. They were never stock on cars, but I do know that there were people with them.

 

[Culprit]

My grandfather's dump truck that we used to haul the back-hoe around with had a 2 speed differential. Basic idea was to get super low gearing when the dump truck (or grain truck) was fully loaded, but still have regular gears when empty, or when you (finally) get up to speed.

Sounds like just the ticket for someone who likes to launch fast from lights, but still wants a daily driver to commute to work on the highways. I've never heard of them in cars, but apparently somone out there is doing it.

Culprit

 

[Stallion]

I don't understand how this two-speed rear would work. How could you change gears in the differential? Wouldn't there have to be a clutch of some sort? :confused

 

[fasterthanu]

Honestly, I wish I knew... Trying to find that out myself. The idea is great, just want to learn more...

 

[MaineShark]

I'm curious how it works, but I think that might be a little bit of excessive modification, for one of these cars. The previously-mentioned GearVendors unit will get you the same thing, and it is a proven system.

For example, put 4.11 gears in the rear, then multiply that by the .78 reduction of the GV unit, and you have 3.21 when the unit is activated. Or, let's say I like my 3.55 rear for the street, but want more on occasion - I could have 4.55 (or whatever ratio is close to that) in the rear, activate the unit, and have the 3.55 back for street use. Plus, you get the benefit of being able to use the same thing to split the gearing between the ratios, essentially doubling the number of gears your car has (6 instead of 3, for example).

I mean, with enough money and time, I'm sure you could find a way to put in a 2-speed rear end, but I just think it's re-inventing the wheel - a number of other companies already make auxilliary transmissions.

Joe

 

[Bob Chadwick]

I don't understand how this two-speed rear would work. How could you change gears in the differential? Wouldn't there have to be a clutch of some sort? :confused

As I recall from my government intern days at the Petaluma Publics Works Department, there was an electric switch on the shifter that changed the differential gears.

 

[yakatak76]

bobchad has it correct. there will be an electric switch on the shifter. back in the days of driving grain trucks with the two speed rear end, the best way of going to hi-speed was to pull the switch out, press the clutch, and wa-la you were in hi-gear. going back down into lo-gear required you to pretty much bog down the engine by going as far up the hill as you could, pushing in the switch, pressing the clutch, revving the engine a touch letting out the clutch, listen to the rear end trying to catch the lo-gear, cuss a little as it is not catching, press clutch again, rev engine again, cuss a little more, c'mon baby, bam, you're in low. and away you go....

 

[Stallion]

I was never sure of what "overdrive" was on a car. Is this what it is with a multiple speed rear? Or is OD something else?

 

[Bob Chadwick]

Overdrive is a gear on a car, generally a fourth gear or more, that drives the wheels at a lower engine speed at a stated mph. It works similiar to second producing lower rpm's than first, etc.

People talk in ratios to explain it. I think if you get below a 1 to 1 ratio then the rotating input into the transmission is lower than the output to the drive shaft. An example would be First 3.09:1; Second, 1.67:1; Third, 1.00:1; and OD, 0.73:1.

Bob

 

[Stallion]

But I was looking at a C4 add and for the tranny it said 4 + 3 which I believe they are referring to OD. With a 4th gear, how does OD work?

Thanks!

 

[fasterthanu]

The gear vendor OD would really be nice on my 700R4 trans. Would give me a .55 over drive.. Not bad with a 4.11 gear. Would be like 2.60's =)

 

[Stallion]

Is overdrive just another gear in the transmission to change the ratio maybe?

 

[MaineShark]

Yes.

The term "overdrive" just means that it is a lower than 1:1 ratio. (yes, "over" to describe lower - I believe it originates with people working backwards from the tires to the engine)

For example, my current THM350 transmission has a 2.52:1 first gear. This is an underdrive ratio, being higher than 1:1. The second gear is also an underdrive, at 1.52:1. The third gear is just "drive," being 1:1. If I had a fourth gear that was lower than that, it would be an overdrive.

Your transmission ratios really don't mean much, alone. Assuming you are keeping tire diameter the same, and just playing with gears, you have to multiply your rear-end gearing by the transmission ratio in each gear, to get your overall ratio.

More on that subject here.

Joe

 

[Stallion]

Hey thanks a lot, Joe!! I understand now. Overdrive seems to be a good thing to have for a daily drive so it's not too stressing on the engine. Thanks again!!

TR