Why huge differentials on trucks?

[Jstpssng]

Definitely. This is the Blazer. My Son owns it now. It was freshly restored when Mike blew out the rear end.


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When you said "Blazer" I thought that you were talking about one of those little things the size of my Ranger. I didn't know that you meant a Blazer

 

[RalphVa]

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

 

[4570Man]

A car is very limited by traction. Regardless of whatever engine power the car has it can’t deliver the drive line twisting, diff busting torque a truck can. And load carrying ability isn’t a concern. The axels in ton trucks is already one of the weaker links. In a F450 truck the tires are the first upgrade you’ll find followed by bigger brakes, bigger axels, heavier springs and a beefed up frame. What gear ratio do the cars have? My ton truck will only go 10 mph in first gear at redline. I’m guessing most cars would run 40 or so in first.

 

[MossRoad]

A car is very limited by traction. Regardless of whatever engine power the car has it can’t deliver the drive line twisting, diff busting torque a truck can. And load carrying ability isn’t a concern. The axels in ton trucks is already one of the weaker links. In a F450 truck the tires are the first upgrade you’ll find followed by bigger brakes, bigger axels, heavier springs and a beefed up frame. What gear ratio do the cars have? My ton truck will only go 10 mph in first gear at redline. I’m guessing most cars would run 40 or so in first.

That's a creeper gear and kinda apples to oranges.

 

[4570Man]

A single axel housing plus tires from a semi will weigh more than most cars. A quick google search says about 2500 pounds and 22.5 tires are over 200 pounds each. Spring suspension which isn’t very common anymore would be another several hundred pounds. Nothing about heavy trucks is light. My single axel gas burner is 12,000 pounds empty. Most class 8 dumps are nearing 30,000 empty. The local cement trucks are 34,000 empty.

 

[MossRoad]

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

The simple answer is they're bigger to handle higher loads and stress. While the gear ratios may be exactly the same, they can't handle the same loads and stresses. They need more material in them to handle those loads and stresses. More material means larger size. Larger size means larger case to hold it all. Easy peasy.

 

[4570Man]

That's a creeper gear and kinda apples to oranges.

It’s not like 4low. It is a service gear. I hit it for pretty much every start loaded. My 6500 will only go about 5 mph in first/low. For on road use usually first/high or second/low is a better choice but when the truck is marred on soft ground or pulling the steep hill out of the quarry first/low isn’t overkill at all.

 

[4570Man]

The simple answer is they're bigger to handle higher loads and stress. While the gear ratios may be exactly the same, they can't handle the same loads and stresses. They need more material in them to handle those loads and stresses. More material means larger size. Larger size means larger case to hold it all. Easy peasy.

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.

 

[Gale Hawkins]

Good thread. I was reading about Mercedes Benz EV trucks with no transmission or differential because the motor output shaft is at the wheel. 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.

 

[MossRoad]

It’s not like 4low. It is a service gear. I hit it for pretty much every start loaded. My 6500 will only go about 5 mph in first/low. For on road use usually first/high or second/low is a better choice but when the truck is marred on soft ground or pulling the steep hill out of the quarry first/low isn’t overkill at all.

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