Why huge differentials on trucks?

[k0ua]

Exactly. Load the curb weight barley 1 ton car like this and let us know how it turns out. Considering that load ( just the load ) weighs 8.3 times more than the Miata I don’t think it’s going to turn out good. View attachment 638804

The REAL question is why are truck differentials SO SMALL. Think about it. They are very small compared to the weights and loads they are required to handle compared to cars. If you add up the weight of the car and its approved load and the weight of that dump truck and its approved load, you will be asking why is the differential in that dump truck so small.

 

[clemsonfor]

Why do pickup trucks have such huge differentials?

The ones on Subarus are small. The one on our Miata is small, and its final drive ratio is 4.1. Same for our 1983 240D Benz. It was basically the same drive with independent rear axles as the Miata and Subaru have.

Why are pickup trucks (and the big truck's) differentials so large?

Ralph

Cause that Subaru would explode if you hook it up to a 10,000 pound trailer! They have to be big to handle the torque and stress of towing and hauling. I don't think Subaru makes a vehicle capable of hauling any real quantity of stuff let alone a trailer more than 3500 pounds maybe?

 

[clemsonfor]

I dug around in my shop and could only come up with two ring/pinion sets. Sorry. This would have been a great thread to display 3 or 4 different sizes.

First is from a Dana 44 differential. It's a common size in 1/2T equipment and actually some autos. This set is 4.56 ratio. The larger the number, the slower the gear ratio. The larger the number, the smaller (less teeth) the pinion gear has and more teeth the ring gear has.

This set failed. They came out of one of my offroad buggies. I'll let you guys see if you can spot the failure.

I laid the T square in the pic to give an idea of size.


View attachment 638744


Second is a Dana 30 set. It's commonly found in the front axle of Jeeps and other compact trucks. This set is 3.55 ratio. Notice larger pinion count compared to ring count.

This set was replaced to get a lower ratio, slower vehicle speed, more pulling power.


View attachment 638746



Here's a comparable pic with both sets. Notice how much larger the 44 is over the 30.



View attachment 638747


My Son's run Dana 60 axles. Their ring/pinions sets are gigantic compared to these sets. Dana 60 size is what's common in 3/4T or 1T trucks.

Over the road trucks have ring/pinion sets that would make these look tiny.

Hope this helps explain the differences in strength that larger axles have. Wish I had gears from one of the vehicles you listed to show how tiny they are.

I see busted teeth all over that ring. Right above the pinion gear and then one directly across from it.

 

[bcp]

I grew up in an area where they used "third members" instead of differentials. Maybe I should have put that in the You Might be Old thread.

That used to be common, and I always wondered why no one ever talked about the first member or second member.

Bruce

 

[clemsonfor]

In my modified world here's an example of tire diameter differences. The more stress applied to the differential, the bigger and stronger the differential needs to be.

The larger buggy is on 48" tires and Dana 60 axles. The smaller is on 33" tires and Dana 30 front, Dana 44 rear.



View attachment 638759

And for those of us who know trucks that really shows perspective!! Esp since my k10 is sitting on 33s I know exactly how big those are!!

 

[Gale Hawkins]

Cause that Subaru would explode if you hook it up to a 10,000 pound trailer! They have to be big to handle the torque and stress of towing and hauling. I don't think Subaru makes a vehicle capable of hauling any real quantity of stuff let alone a trailer more than 3500 pounds maybe?

While their new 7 passenger SUV and be maxed out to tow 5,000 pounds 1500-2500 is more like it for a Subaru but they are 4WD all of the time or at least on our 2010 Forester.

https://www.brooklynparksubaru.com/custom/subaru-towing-capacities.htm

 

[Racenut]

My kid's Miata diff with a hundred enraged squirrels under the hood. :shocked:

I don't think it would last as long under the RAM with diesel power.

 

[clemsonfor]

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).

Differentials are one thing that I haven't worked on. Have rebuilt engines and fixed a shifter fork on an Alfa Duetto transmission once. Think I saw a differential once that my father tore into (he was a mechanic).

Ralph

High hP out of a car at high RPMs after it's already rolling does not explode a rear end. Again. Your diesel slow Mercedes (I had one at one point) or Miata or Subaru do not tow heavy loads or get the abuse of a truck. I promise you if I ran a Miada or Subaru diff in my old K10 which does not get near the stuff modern work trucks do thrown at it I would strip out and explode that tiny thing. I have 33" tires and will pull trailers way to heavy to admit too with it at times. So heavy that I have bowed some of the cross members on my 7000 pound tandem car hauler trailer. Those little diffs probably would explode the first time I went to hit the gas with those loads.

 

[clemsonfor]

Ah, didn't realize you were talking about your dump truck.

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

 

[MossRoad]

Cause that Subaru would explode if you hook it up to a 10,000 pound trailer! They have to be big to handle the torque and stress of towing and hauling. I don't think Subaru makes a vehicle capable of hauling any real quantity of stuff let alone a trailer more than 3500 pounds maybe?

No, but they could hunt it down and kill it....



Look up Subaru Aerospace, and Fuji Heavy Industries.

They make city buses, too. Those are pretty big.