For my twin-turbo crewcab project, I've been working out the concept of an additional overdrive... mostly because the engine is based on a 460, thus forcing me to a ZF manual transmission. Because the engine is being configured to produce lots of boost down low, much like a diesel, I'd want to compensate for this with gearing in the axle. I could just replace the ring/pinion gears and call it a day in the existing sterling, but I've run across an opportunity to purchase fairly inexpensively, a 1-ton, two speed dually rear.

I've done some googling, but haven't been successful in finding enough information to determine if this is a good choice. I imagine it will slide right under, but one never really knows

Might anyone know if it would fit? Maybe dimensions between the insides of the wheels? Gearing? Can it be shifted "on the fly" at speed?

If I do go this route, I'd have to find dually-compatible SRW wheels, as I'm not going to be running the truck as a dually. Wider tires will be necessary anyway, but I'm not going not going to be adding the dually fenders to the rear however.

What do you guys think?

Unfortunately, all I know is that its a 1-ton 2-sp ford rear, the person who has it acquired it on a pallet, and wasn't able to determine exactly what it came from, though I'd wage 1-ton means F450.

 

I have an Eaton two speed rear in old Dodge dump truck. It is electrically shifted using a motor-driven lead screw at the rear, with a control **** on the shifter. The selected range can be changed while moving. You do not need to depress the clutch, though you do need to "blip" the throttle when shifting from high range to low range.

It would be pretty cool to have something like it in a pickup. I suspect the main impediment for your application is likely to be the gear ratios. The one in my(gas powered) dump truck has low range in the "granny gear" 5.0:1 range, with high range being about 30% lower. Max speed on this 1964 truck was not very high. If the "donor" truck for the rear you propose to use was a diesel, the ratios may be useable.

 

if it is an eight lug bolt rear end the srw wheels should fit. but if it is a true super duty rear like my super duty is it is a dana and is use 10 lug bolts. Also cab and chassi rears are narrower than the trucks that came with a pickup bed on them.

 

Fredrick,
A two speed rear axle would just about be the icing on the cake on your truck. I have a goodly amount in everything up to out L-9000's with split axles. I'm sure if dimensionally a fit it will work. Is it electrically shifted? If so to up shift you run it up to a shift point, flip the button up and ease off throttle and it will shift up. To down shift at the correct RPM shift point you flip the button down and blip the throttle and it should down shift. Driving an F800 up through an L-9000 requires knowledge and ability to synchronize shift at load/rpm points in the power band. We only use the clutch to start rolling and unload when stopped. Hope it works out.

 

Thank you guys for the info...

What I'm building is a little "odd" in the sense that I'll need numerically lower gears in the rear for mileage as well as to compensate for the lower RPMs.

The 500cid has a virtual redline of 3500, even though I'm sure it could easily spin above 5K, we've done an odd cam profile and a variety of other things (including turbo sizing) to try and stick the peak torque at about 3500 or thereabouts.

The ZF 5sp that is going in there has the following ratios:

1st: 5.72
2nd: 2.94
3rd: 1.61
4th: 1.00
5th: 0.76

The rear currently is 3.55, and the tire size I believe is the factory LT235/85R16 tires, which have a 31.5" diameter?

If my assumptions are correct, I have the following results @ 3500 rpm

1st: 16.2 mph
2nd: 31.5 mph
3rd: 57.4 mph
4th: 92.5 mph
5th: 121.6 mph

I think my math is way off... something isn't right. Let me see what tires I actually have on the truck...

 

I checked your calculation for 4th gear, and it is correct.

(3500 / 3.55) * (31.5 * 3.14/12) * (60/5280) is about 92.5 MPH

So your guess on tire diameter might be off, but given that assumption your math is fine.

 

Fredrick,
I thought at one time you were running 285/70's? Actual yeild in mph will be affected by other factors as I know you are well aware, but the calcs are all correct given a 31.5" tire.

 

Yeah, I might be, I'll have to go outside and look for sure. Since I'm on baby watch, I'm sitting here listening to the little one snore, and guessed because I didn't feel like getting up

With 285's I'd have these speeds at 3500RPM:

1st: 16mph
2nd: 21mph
3rd: 58mph
4th: 92mph
5th:122mph

That's odd, the same results +/- a hair. Interesting... Still don't need a higher redline as say, 4500 RPM would give me a top speed of 163 in 5th... and that's completely unnecessary. I'm working this out to behave similar to a diesel - boost early, low rpms, break less parts.

 

No, and as you say similar to a diesel. Power band from 1500 to 2500, generally with 10 forward speeds to select. In at 1500 out at 2250 to 2500, back in at 1500 next gear. Boosted gasoline engine can approach the compresion numbers on a diesel, which is the wall off which the tremendous torque is developed. You should have seen some of those 16 cyl. loco engines on the test stands, they are incredible.

 

I find it interesting the gear ratios listed in #5 for the ZF 5 speed transmission. I was always wondering what the 5th gear ratio was in my '88 F150 with the Mazda 5 speed transmission. I would guess slower than the 0.76 for the ZF. Does anyone know the 5th gear ratio for the Mazda 5 speed? Thanks in advance.

 

Depending which mazda tranny it is:

R1: 3.40 2.05 1.31 1.00 0.79
R2: 3.91 2.24 1.49 1.00 0.80
R4: 3.38 2.06 1.30 1.00 0.79

 

Yeah, well, the ZF as you know has 5 forward speeds. I spent a lot of time trying to figure out how to get a "corporate" pattern adaptor for the 460, but to no avail, so I then started exploring ovedrive/underdrive units, and finally, this 2-speed rear.

I'm definately after silly torque at low RPMs. If I gear the truck right, I'm picturing cruising at 65mph at 1700 RPM with 6lbs of boost

(or something equally ridiculous).

I've done a lot of real experiements with this concept - and have proven repeatedly that lower compression, and higher boost at X RPM with Y displacement, consistantly yields more power than higher compression, lower boost at the same RPM and Displacement.

This is why this engine is being built to a very low c/r - 6(ish):1. The side effect of this is lower comrpession engines generally pass emissions very nicely at idle, something I have to comply with in NJ (idle test), so this really is a good combination for me to build against.

Just still working out the gearing... worse case - I'll see if I can find lower numerical gears for the rear, though I haven't seen anything aftermarket lower than 3.55 for the 10.25" sterling. As long as I don't change the rear tire diameter, I don't have to futz with PSOM module programming.