How does a two speed rear axle operate? I know there is a switch in the cab, and a electric or vacuum motor as an actuatior on the diff. But what takes place inside in order to change the ratio? Pictures of a diff would be great.
thanks

 

Sound like a question for someone with [font size =4]REAL BIG [/font size] trucks...Uh, BigD et al?

 

All I know is I drove one once and the guy who instructed me kept saying: "Now DON'T blow the rear end out of it". He said this about 5 times . Well, I didn't blow it out, but I had sweaty palms

 

We have a 2-speed rearend in one of our old fire tankers. It's like a 2-speed transmission...a 1:1 gear and a lower gear. It is cable actuated. The shift lever is on the shifter. Up is 1:1, down is the reduction. I think other trucks also use air shifting, electric, etc.

 

>Sound like a question for someone with [font size =4]REAL
>BIG [/font size] trucks...Uh, BigD et al?

Oh sure, put me on the spot. First of all, [font size =4]REAL
BIG [/font size](Class 8) trucks don't have two-speed axles. We just have[font size =4]REAL BIG [/font size] transmissions!

Well,I don't know a whole lot about them, but since you asked. buffy pretty much nailed it on the head. There are two ratios in the carrier. 1:1(a.k.a. DIRECT) and a deep reduction ratio. Most common were the electric motor driven ones. They had that little red push/pull button on the gearshift. An electric motor on the carrier drives a worm gear that actuates the shift fork for the different power flow. You had to make sure the axle did indeed shift before you mashed the throttle, or you could drastically shorten it's life span.
They had to change the ratio in the speedometer cable too. That's how I made sure that the shift was completed, because the speedo would jump when it changed gears.

 

Give me the type of Truck an idea of what you are looking for etc. and I might be able to help you. we love details here.

 

As a young lad growing up on the farm I drove several 2-Ton trucks, all equipped with the mechanical (cable activated) 2-Speed rear axels.

The majority were Chevy C-60's, but I've also driven Dodge and Ford's as well.

They are all as others have said, a pinion/ring gear system providing two different rear gear options (Hi/Lo).

They were mainly used when loaded, as the three/four speed transmission’s gear ratio's were so large that you would have trouble going from one gear to the other if you didn't use the 2 speed axel.

When loaded you would go through the gears as follows:
1st-Low
1st-Hi
2nd-Low
2nd-Hi
3rd-Low
3rd-Hi
4th-Low
4th-Hi

When empty you would do one of two options:
1st-Hi
2nd-Hi
3rd-Hi
4th-HI

or

1st-Lo
2md-Low
3rd-Lo
3rd-Hi

You could go from Low to Hi with out clutching, just let off the gas and pull the ****, then once you heard the axel shift re-apply the gas.

Going from Hi to Low was another story, you generally only did this while setting still, but on action you would find your self in a loaded condition where you needed to down shift and with some practice you could make it work.

I don't have the exact mechanical details on the axel construction/design, but hope this helped.

 

Great reply guys. Too bad a scaled down version can't be made. Or something similar that would allow us to between 3.73's OR 4.30's with a flick of the switch/lever/cable/whatever...

 

>Great reply guys. Too bad a scaled down version can't be
>made.
Actually there is. A friend of mine had a 92 or 93 GMC 3500 dually with a two-speed rear. electric shift. They are out there. I just don't know where to find them off hand.


Or something similar that would allow us to between
>3.73's OR 4.30's with a flick of the
>switch/lever/cable/whatever...

Be kinda tough to run two sets of ring and pinion gears in one diff., but I'm sure it could be done.(is that what you mean? because if it is I think it would be cool too, but if this is not what you mean, then I am an idiot and I apologize)
2 speed axles were basically like having an auxilliary tranny........just on the diff. Visteon Corporation is "Cutting Edge" as far as torque management(pol. correct term), but I don't have a link for them. I know they had something to do with a lot of the all wheel drive stuff.

 

 

My opinion of a two speed axle is that I wouldn't wish one on my worst enemy! Most medium duty trucks up until the 90's had these abominations on them. Hard to shift (when they actually shifted) and don't work well even when shifted properly. And if not shifted properly, well, you better have a pile of spare rear diffs kicking around.

These were fine (well not really) on old underpowered grains trucks that you drove for maybe a month a year, but you wouldn't want one on your daily driver.

Now a scaled down version of a good heavy truck tranny like a 13spd or an 18 double over, THAT would be VERY INTERESTING. Chebby could have their Allison if I had an EATON

 

Actually, most 2-speed rear axles are geared pretty deep. I have a 2 speed on my 1954 F800. It has a 6 series high gear and an 8 series low gear. The low gear is for getting started with a near maximum weight load. On later model trucks, they still run 5 series and 7 series gears. These are primarily work truck rears, designed for dumps, towing construction equipment, etc. These rears just make up for a lack of power.

 

After reading this post I just had to respond. I couldn't disagree more. Two speed rear ends are one of the finest inventions ever made. I have driven one for many years and they are smooth and effective. Number one mistake most people make when driving a truck equipped with a two speed axle, is they hurry the shift. It's a truck!!!! It's meant to be driven carefully. By this I mean if you want to keep it together you must treat it like a lady. Be nice to it. Shift it softly and don't shake the driveline with the clutch. My 1959 F-700 still has the original 5 speed clark transmission in it. I very seldom even use the clutch to shift.

I have modified my F-700 from it's original form to a conversation starter every time I drive onto a construction site. It started life as truck powered by a 292 cu in in 1959 to a marine 460 cu in power plant, bored and stroked to 545 cu in at 700 horsepower on the dyno. It now has a full service bed equipped with portable welder and air compressor. It looks just like most of the Caterpillar repair trucks you would expect to see on any construction site. The difference it is a 1959 F-700 Ford with all original sheet metal, glass, chrome, even the stock mirrors with the FoMoCo symbol still proudly displayed. I always get a crowd of guys around it since I added five inch chrome exhaust stacks. The truck sports a beautiful black paint job with pin striping done by a local artist. But it still has it's 1959 Eaton rear end under it.

Making these rear ends work is all about understanding the beast. My youngest daughter when she was just a little girl used to love to go with me and shift the truck. By the time she was six or seven she would sit beside me and say, "now dad now". She had watched me shift the truck so she knew where the gears were located and she knew about the little red button. By the time she was ten years old she could shift all the way through all ten gears and never grind a gear without using the clutch. But it's all about being gentle and paying attention to your RPM. Now when I say gentle I don't want you to think I don't call on the old truck.

One of my workers blew a 3208 Cat in a fuel truck we had on a project. The truck was a three axle fuel truck with a 4000 gallon diesel tank on it. He was down to about 1000 gallons when the engine went out. He was about thirty miles out from yard and we had two sets of hills to pull to get to the yard. So I rigged an air line from my truck to his so he would have air for his brakes. He was broke down right at the bottom of a one mile hill at seven percent grade. I pulled him to the top of the first hill, and believe me I had to use that two speed eaton that day. Then he used his brakes to keep the chain tight and hold us back as we went down the other side. Then we had about ten miles of easy running until we got to the next BIG hill. On the second hill I was watching my temperature gauge climb and I could see the exhaust pipe glow bright orange down through the floor past the gear shift boot. The big ole' Marine 460 with the 750 Eldelbrock was screaming pulling the hill at a steady 4000 RPM. But she topped the hill with the wounded fuel truck in tow. And I had to drop two gears in the hard pull on that hill. Thank GOD for EATON two speeds. My F-700 weighs 18000 all by itself loaded with tools. She's one hell of a truck. Fords are tough. Just be kind to your two speeds, they will give you many years of service.

1959 Ford F-700
1977 Ford E-350 with Marine 460 (stroked to 545 cu in)(4X4 Van) 10 inch lift
1989 Ford Crown Vic
2000 Mercury Grand Marquis

 

Those use power dividers on the rear of the transmission, and are actually fairly simple. In short its two different gears on the output shaft that are engaged by a air-actuated piston on a shift fork. I see ALOT more of these than I do two speed rears, but like was mentioned earlier that's because of the times. And most of the two speed rears I've seen don't work, but they were on pretty clapped out trucks.

 

Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.
For our trucks you can always get one of these. If money wasn't an option for me I would have one. Seems like it would work really well for towing.