Why huge differentials on trucks?

[MossRoad]

Hence the model number he kept saying of "6500" quite a bit bigger than your 1 ton 3500 pickup.

In the post I was reading and replying to, he said "my ton truck", so I didn't think he was talking about his dumptruck in that post. He didn't mention 6500, and I don't own a 1 ton 3500 pickup.

 

[4570Man]

In the post I was reading and replying to, he said "my ton truck", so I didn't think he was talking about his dumptruck in that post. He didn't mention 6500, and I don't own a 1 ton 3500 pickup.

I’d already used the 4low gears in a previous calculation but my ton truck is 2wd. The 10mph in first gear is achieved in my ton truck using only the transmission gears and stock rear end gears. My 6500 is geared even deeper. Also note the 6500 has 40” tires so the driveline has to handle a lot more torque to move the same load a pickup would. Also note a manual trans has deeper gears than an automatic. The nv4500 in my truck runs a 5.6-1 gear ratio in first where it’s automatic cousin the 4l80 runs a 2.4-1 first gear ratio. I expect you’d see the same tread if you checked other vehicles.

 

[MossRoad]

I’d already used the 4low gears in a previous calculation but my ton truck is 2wd. The 10mph in first gear is achieved in my ton truck using only the transmission gears and stock rear end gears. My 6500 is geared even deeper. Also note the 6500 has 40” tires so the driveline has to handle a lot more torque to move the same load a pickup would.

We had an aircraft tug at my airport job that weighed 10,000. It was only about 8' long. Solid cast iron rear fenders. Under those fenders was a 27:1 differential. It was pretty darn big. When the original 4 speed manual and 4 cylinder died, I helped our mechanic install a Chevy 350 and th350 tranny with some sort of shift kit. In drive at 4000rpm it had a top speed of about 10mph. It had no problems moving a 727.

 

[MossRoad]

Oh yeah, we put in a tilt-wheel steering column from an Oldsmobile, too. :laughing:

 

[hosspuller]

Wanna see a big differential ? Google mine haul trucks. Caterpillar factory in NC assembles them. Rear axle and diff in one housing. Shipped one diff per container or about 70,000 pounds. For a Cat 793F truck the rear axle fill is 260 gallons.

Cat | 793F Mining Truck / Haul Truck | Caterpillar



Just a photo unknown truck

 

[LouNY]

Wanna see a big differential ? Google mine haul trucks. Caterpillar factory in NC assembles them. Rear axle and diff in one housing. Shipped one diff per container or about 70,000 pounds. For a Cat 793F truck the rear axle fill is 260 gallons.

Cat | 793F Mining Truck / Haul Truck | Caterpillar



Just a photo unknown truck View attachment 638864

And those appear to have planetary reduction boxes after the differential.

 

[ruffdog]

Hmm. Nothing makes a whole lot of sense. There are some cars out there with some diesel engines with high torque not having differentials the size of even the fairly large one on our Tacoma (compared to those Subarus, Miatas and Benzes that I've seen them on).

Ralph

Think of it this way: Why is a 1/2" ratchet bigger than a 3/8" ratchet? The body is bigger, the gears are bigger, and most times the handle is longer. Why....you need those things to achieve higher torque levels. When a truck has a two speed transfer case, it is essentially a torque amplifier and all of the driveline must be heavier because of it. :duh:

 

[RalphVa]

I can understand the torque bit, especially for large equipment. However, how do they keep the ratio down to around 4.0 in regular pickups with such huge ring gears? Ratio on the tiny Miata differential is 4.1. Think the ratio in my Tacoma is about 3.6. It revs MUCH lower at speed than the Miata.

Most trucks get those granny gears via the gearbox and/or transfer case, not in the differential.

Ralph

 

[MossRoad]

I can understand the torque bit, especially for large equipment. However, how do they keep the ratio down to around 4.0 in regular pickups with such huge ring gears? Ratio on the tiny Miata differential is 4.1. Think the ratio in my Tacoma is about 3.6. It revs MUCH lower at speed than the Miata.

Most trucks get those granny gears via the gearbox and/or transfer case, not in the differential.

Ralph

On the bigger ring gears, the teeth are just larger.

Think of it this way.

A 6 pack of 8oz beer bottles and a 6 pack of 16oz beer bottles both have 6 beers. One is just bigger.

 

[k0ua]

Wanna see a big differential ? Google mine haul trucks. Caterpillar factory in NC assembles them. Rear axle and diff in one housing. Shipped one diff per container or about 70,000 pounds. For a Cat 793F truck the rear axle fill is 260 gallons.

Cat | 793F Mining Truck / Haul Truck | Caterpillar



Just a photo unknown truck View attachment 638864

Now that is a big diffy!