What should 4x4 with axle shafts that have U Joints rather than CV behave?

[AuroraGirl]

When I used my truck to plow snow, I always noticed how 4wd seemed to really bind up turning. I am guessing its from the joints being u joints rather than CV.

But i also remembered its open diffs. I guess it seemed fine in a straight line, but thats to be expected.

However, I learned that the rear end was REPLACED at one point(14 bolt) and i am not sure if thats the pinion gears or if it was the whole thing.

Either way, theres a chance I dont have 4.10 in the rear differential like the front. Im guessing 4x4 that came with 4.10 had them match so the transfer case didnt have extra stress on it. Im guessing.

Is there a tag on both differentials to confirm? Or a simple visual way to know. I can do that math homework @HotRodPC posted but i will actively make life harder for myself to avoid math. I dont know what front dif i have. I can count bolts of find numbers if needed.

 

[MrMarty51]

Relax, if they was odd gear ratios the truck would not move more than a few feet and it would be bound so bad it`d either come to an abrupt halt or else bust a whole bunch of real expensive items.
Bumping and jumping in 4X4 when turning is normal.

 

[75gmck25]

My ‘75 with NP203 has a cv joint in the front driveshaft, and when one u-joint in that cv joint went bad it made quite a bit of noise under load. I don’t know if your ‘80 (with NP205?) has a cv joint in the driveshaft.

Bruce

 

[Vbb199]

Jack up the ass of the truck, put blocks in front and behind the front tires, put the transmission in neutral, place a mark on the tire at the 12 o clock position, spin the pinion... If the drivehaft spins 4 times for every 1 revolution of the mark on the wheel, its likely you have 4.10 ratio.

Optionally you can just pop the diff cover and look for the stamped numbers on the ring gear.

Or count the number of teeth on the pinion gear and ring gear, do the math.


To the best of my knowledge, Ford is the only mfg that makes slightly different front and rear gear ratios for the same tire size front to back.

The front axle will be like, 4.12, and the rear will be 4.10 for example. This is because in a part time 4x4, there's a certain power application to each axle. Usually the front axle has less power applied than the rear, like 40%/60% or 30/70.
So a slightly lower ratio in the front offsets that a tad.
You can safely have a different ratio front to back, by no more than x.x1-x.x3, otherwise, as @MrMarty51 said, the truck will come to a hault completely, or blow up the t case, or twist t off a driveshaft.

Now when you get into full time t cases like what I have in my big k5, it's a straight thru chain driven case... 50/50 power is applied, or at least very close to 50/50

 

[AuroraGirl]

My ‘75 with NP203 has a cv joint in the front driveshaft, and when one u-joint in that cv joint went bad it made quite a bit of noise under load. I don’t know if your ‘80 (with NP205?) has a cv joint in the driveshaft.

Bruce

I have a NP205 yes. Im saying the axle shafts themselves are U joints, so they cant spin at different rates. but that shouldnt matter i dont think since dif is open. It kinda binds and hates turning in 4wd. I have nothing to compare the experience to, i dont have another 4wd, so this could be normal. I just know newer trucks have CVs so they can have auto 4wd and all that jazz

 

[Vbb199]

While I'm thinking about it.
The first is actually a CV or rzeppa joint

Second is a double cardon joint

Third is a standard universal joint.

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[Blue Ox]

It's normal for them to kind of hop in a tight turn. The newer trucks have CV joints because they have independent front suspension. It's not because of auto 4WD. My truck has auto hubs and the same beam axle with U-joints as yours.

 

[AuroraGirl]

It's normal for them to kind of hop in a tight turn. The newer trucks have CV joints because they have independent front suspension. It's not because of auto 4WD. My truck has auto hubs and the same beam axle with U-joints as yours.

I meant like, doesnt CV joints allow them to spin different speeds so that way they dont bind?

 

[Blue Ox]

I meant like, doesnt CV joints allow them to spin different speeds so that way they dont bind?

Theoretically I guess it would. I think it's more the space and cost constraints, they're pretty limited on what they can do in that axle tube and knuckle. So the hop is normal for this application.

 

[Bextreme04]

I meant like, doesnt CV joints allow them to spin different speeds so that way they dont bind?

No, a CV joint allows the shaft to spin at a constant velocity regardless of the angle of the joint, hence the name. It has nothing to do with allowing the right and left shafts to spin at different speeds, that is handled by the differential.

A u-joint will cause the shaft to have variable velocity depending on the angle of the shaft. The greater the angle of the wheel, the greater the change in velocity. This causes the lurching or jumping feel in the cab of the truck as you turn. You can google it and see a pretty neat CAD model of a U-joint versus CV joint with comparable velocity of the input shaft to demonstrate.

 

[77 K20]

If the 4 wheel drive has a locked center differential then when turning there is binding/wheel slippage/and steering wheel jerking.
On the full time 203 case you could turn sharply and there was no binding (*when the shifter was in HI or LOW). But moving the shifter into the LOC position (*HI LOC or LO LOC) would lock the differential in the transfer case. This was for low traction surfaces only. NOT for pavement. The 205 would be like the 203 in the LOC position.

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They do in fact make CV axle shafts for the front axle of squares for off roading. Roughly $1,400 for them... the nice thing about CV joints is they retain 100% strength at any angle the front wheels are at. With the axle U-joints they only have 100% strength when pointed straight. The more you turn the weaker they get. Seen several blow apart when I was younger and someone gets stuck, cranks the wheel all the way to one side then floors it. BANG! No more axleshaft/joint.

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