Why huge differentials on trucks?

[ovrszd]

I bet he said a word or two that you can't print!..

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

 

[ruffdog]

Anyone running a Miata axle in those buggies or rock climbers? I wonder why not.:confused3:

 

[k0ua]

By the way, I repaired that lawn mower diffy. I followed the trail of oil back to where the piece popped out of the diffy case, and found the piece. Thoroughly cleaned the case and use "liquid steel" epoxy with metal particles in it to glue the piece back in the case, and replaced the gear and refilled the case. Good to go. Of course that mower was why I bought a welder and learned to weld too. We beat the "he77" out of the little old mower. I finally bought a tractor and finish mower. It was just too much to expect a little cheap lawn mower from K mart to keep up with . It had a lot of ugly welds on it's various pieces including sheet metal with 6013 when I got rid of it. I actually traded it in on the tractor, believe it or not. Got $300 off of the tractor!.

 

[k0ua]

Anyone running a Miata axle in those buggies or rock climbers? I wonder why not.:confused3:

Because you don't want to hear a big loud sound when you climb up on a rock of the diffy letting go.

 

[ovrszd]

Because you don't want to hear a big loud sound when you climb up on a rock of the diffy letting go.

It'd probably more like a little "tink".

 

[LouNY]

As others have said it is a case of how much torque is going to be applied and also how much gear reduction is planned.
If the reduction is going to be after the differential it can be much smaller(the differential).
Most heavy equipment gets a lot of its reduction after the differentials.
Most all tractors front axles get the major part of there gear reduction after the differential.
Most larger units use planetary reductions at the wheels,
lighter duty units will often use a spur and bevel gear reduction at the wheel.
When a differential is the last gear reduction in a drive train it has to handle the complete
amount of torque the engine can put out multiplied by the transmission and any reduction box gear ratios.

 

[kcflhrc]

Do you tow horse trailers and such with your Miata?

 

[oldballs]

:laughing:..................

 

[k0ua]

It'd probably more like a little "tink".

I will bet you have heard similar things. I was at a truck/tractor pull once and an old Ford 4wd pulling for all it was worth, let go in its transfer case. And a gear or case fragment whizzed past my head. Needless to say, I was concerned. I never went back.. That "brush with death" was enough for me. I was a spectator on the sidelines and a pretty fair distance from it also.

 

[4570Man]

I will bet you have heard similar things. I was at a truck/tractor pull once and an old Ford 4wd pulling for all it was worth, let go in its transfer case. And a gear or case fragment whizzed past my head. Needless to say, I was concerned. I never went back.. That "brush with death" was enough for me. I was a spectator on the sidelines and a pretty fair distance from it also.

One of my buddies had his truck hit by a flying driveshaft. But that’s a prime case of why pickup diffs are bigger than a car. At 450 ft pound for from the engine which is way less than modern pickup diesels, big truck diesels, and built pull trucks are putting out you’re getting a 7-1 reduction in rpm from a granny gear trans and a 2-1 reduction in the transfer case for 6300 FP hitting the drive shaft. I’d be surprised if the car is hitting 500 FP on the driveshaft to a 4:11 rear end. The engine toque is lower, the trans gears are higher and there’s no transfer case to further drop the ratio. Most medium duty trucks don’t have super deep trans gears and get most of the gear reduction from the ring & pinion itself. I think my 6500 has 6.50 gears on the high range side of the rear end. A semi truck has way deeper transmission gears. Look how much bigger a semi drive shaft is vs a medium duty.

 

[Jstpssng]

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


View attachment 638763

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.