Pinion angle - interesting theory - discuss

OK... finally found part of the video I was talking about. Watch it and be amazed at the dpeed change the shaft makes as the angles are changed....

Posted for the nay sayers.

http://www.youtube.com/watch?v=gmV4qwLfOMY

 

greybeard360...that video was awesome! Thanks very much!

I wouldn't have believed that the driveshaft would speed up and slow down in any configuration.

But...as they proved, if everything is set up correctly, the driveshaft stays at a constant speed. All the more reason to have the trans output and the pinion angles the same, and the u-joints in phase.

As far as the Rover goes, it seems they built in some wrong engineering.

 

I do not think so.. ... about T.Tube diameters, the mid 30s (35/36)Ford is pretty large and cannot twist.


The torque tube setups I have worked on, have the crankshaft in a dead straight line, right through the pinion shaft, at ride height. The joint cups are not needle bearing type like open drive, so they don't get the same wear as a straight line open U-joint gets from lack of grease movements.

 

Wow, that's pretty wild.

 

If you ever drove a older 4wd pickup? Lock the front hubs, and on bare tar road, crank the steering to full lock turn. The nose will rock back and forth like it will break an axle. It is due to having cross-type U-joints on the outer axles.

I was shocked when I worked on a guys mid 50s Jeep pickup front axle rebuild, that never had unlocking hubs, and saw that Jeep used genuine CV joints on the outer axles in those. Pretty impressive IMO

 

Here are the facts on a torque tube drive.Apparently the speed fluctuations do cause vibration when the shaft angle deviates from zero and was the reason why it was replaced by the Hotchkiss drive system........

In addition to transmitting the traction forces, the torque tube is hollow and contains the rotating driveshaft. Inside the hollow torque ball is the universal joint of the driveshaft that allows relative motion between the two ends of the driveshaft. In most applications the drive shaft uses a single universal joint which has the disadvantage that it causes speed fluctuations in the driveshaft when the shaft is not straight. The Hotchkiss drive uses two universal joints which has the effect of canceling the speed fluctuations and gives a constant speed even when the shaft is no longer straight

 

That graphic gets posted every time this topic comes up, and it is just plain wrong.

The only proviso I'd add is that condition number 4 is likely to be more sensitive to changes in pinion angle over the range of suspension travel than condition number 2. Specifically, it needs the pinion angle to reduce in compression and increase in extension by around double the change in drive shaft angle. Presumably the Land-Rover coil-spring set-up approximates this adequately; your parallel-leaf Hotchkiss drive won't do that.

Where pinion-angle change is not an issue, e.g. IRS and such, condition 4 is a useful option to keep in mind.

As regards the shaft angular acceleration/deceleration thing, the geometry is in fact exactly the same as a bicycle's steering through an angled headstock. Think of the front wheel's axle as one bar of a U-joint cross-yoke and the front wheel's degree of freedom to tilt to left and right as the other bar.

When you turn the handlebars, the contact patch at the front wheel initially turns slightly less than the amount you've turned the handlebars, but then turns at an increasing rate of angular change until the contact patch and handlebars are both at 90°. The difference between the two angles is greatest around 40-50°. The rate of angular change is least at straight-ahead, reaches 1:1 somewhere around 40-50°, and is greatest at 90°. All this increases with the headstock rake. I've actually done the math and plotted all this for a range of headstock rakes.

This explains one of the reasons why traditional longbikes with lots of front-end rake appear to have steering ratios of less than 1:1 over the range of most steering, i.e. just either side of straight ahead: what is in fact happening is that the rising-rate characteristic induced by the rake angle is more pronounced in a longbike than in for instance a sport bike. I've even thought how this could be counteracted by introducing a U-joint between the handlebars and the front end: if the headstock is raked, say, 45° but the handlebar rotational axis is a sport-bike-like 20° off vertical, the instant angular rate characteristics will be as for a sport bike with 20° of rake. In this the front wheel is ****ogous to one U-joint of a drive shaft situation, the U-joint we've introduced at the handlebars is ****ogous to the other U-joint, and the fork is ****ogous to the drive shaft.

(Then I started dreaming of modified Hossack front ends, and that obviated the need for silly U-joints in the steering )

 

When the hubs are locked, the two drive axles are going a different speed as you turn a corner (remember the outside wheel is moving faster) the rocking you feel is the front drive axles twisting, then usually the inner wheel will slip on the road surface to catch up to the other wheel. This is why it is a bad idea to drive a 4X4 on pavement when the hubs are locked. From what I understand, the axles can twist almost a full turn before the tire looses grip and lets it slip and play catchup to the other one.... that means BOTH axles are twisted pretty close to that (shorter axle probably not as much)

 

The rpm ( rotations per minuet) of the shaft can remain the same.
The FPS feet per second speed of the shaft for each rotation increases and decreases in each revolution.

 

Thanks for posting that video greybeard - that should be mandatory viewing....

 

Great video! I'm a believer now! This brings up another question for me. Over the years I've noticed several Chevy driveshafts that were factory built with the yokes out of phase front to rear. Seeing the Youtube video, it would seem this would make them vibrate, as they wouldn't cancel each other? I just put a '68 Camaro driveshaft in my Falcon build, as it was a prefect fit (with adapter joints) for my build. It has the same issue of not being indexed to cancel vibration, but works great. Wonder how this works for Chevy?

 

Some of the shafts that take a CV at one end I noticed are 90 out of phase. Not Camaro though, no CV there.

 

I respectfully disagree with this premise. It is true that the front wheels travel greater and lesser distances in a turn.......but that is accommodated in the front axle's differential, just like it is in the rear axle differential. I think the 'rocking' or 'hopping' is caused more by the more extreme angle of the front axle u-joints. Those fitted with front axle CV joints seem less susceptible to this problem.

Further, the reason it is not recommended to engage 4 wheel drive on a dry pavement has nothing (or at most, very little) to do with the front axle u-joints or CV joints.

It depends on the transfer case design. Older designs, and less expensive models, typically have geared and/or chain driven transfer cases with no differential action between the front and rear drive shafts. In that instance, the varying tire diameters, due to loading, tire pressure and tread wear cause a small difference in driveshaft rpm between front and rear. Unless the tires are on a slippery surface, tire friction causes a 'loading' on the gears in the transfer case.

Newer/more expensive transfer cases designed for full time 4 wheel drive (aka all wheel drive) have either a viscous or mechanical limited slip differential action to prevent the internal 'loading' described in the above paragraph.

 

If you want to see it in action, drive a 4X4 in a bit of a turn, stop and jack up one of the front wheels and see how far the wheel rotates as it "unwinds"..... even a car with a spool... make a turn and jack up a wheel and you can get a good idea how much axles twist.

 

The original post is pretty correct, although a little difficult to read. Havn't read all replies.
It is sometimes worth considering the view from above when looking at UJ angles. If the pinion is offset the angle viewed from above may be enough to prevent brinelling, and if so, the angles from the side could be set at zero. But a small angle in both planes is probably the most visually acceptable.

Mart.

 

I have a lot of first hand 4x4 experience and am familiar with the wheel hopping you are referencing. The axle shafts in these vehicles do not twist any appreciable amount. Maybe a few thousands at best. They are far too stout for that to be feasible.

It is more likely what you are observing when it 'unwinds' is a combination of stored energy in tire deflection and all the slack in the gear train, i.e., axle splines, differential gears, ring and pinion, etc,. that was taken up during the turn. Just as in the main driveshaft u-joint discussion here, the drive axles are just as affected, and they have only one joint which increases the strain in a high angle turn, but again, I submit the shafts themselves do not twist enough to account for what you are observing. The tires will slip before that occurs and, in fact do, as that is the 'hopping' that is felt.

EDIT: Another thought occurred to me. That gear train slack mentioned above is magnified when you see it at the outside diameter of the wheel. A couple/few degrees at the hub is exaggerated by the "arm" (radius of the tire) which is in the 14" to 16" range for most street vehicles and even longer for bigger tires favored by off roaders.

 

Look under any rear wheel drive car from the factory and you will find there is no angle on the u joint.There is enough movement when hitting bumps in the road or going around corners with body sway that a u joint will than perform as required.With buildt in 1,2or 3 degrees the little rollers are going back and forth with each rotation and that is what causes the indentations and failure.I have set all my cars up at o degrees and have not one issue.My SS Monte Carlo has 121000 miles with the original u joints and the drive shaft is banjo string straight from the factory.Disagree if you want, if its ok from the factory,its ok with me.My .002.

 

Every single rear wheel drive I've ever been under has plenty of ujoint working angle. Damn near every ford has the drive shaft offset to the side, which also creates a u joint working angle.

I can't think of one rwd that the drive shaft runs straight and level on?
Including a OT Monte Carlo SS.

 

X2, also a G body and many other cars have some engine offset that puts a bit of angle in it as well.

Edit: just checked and the G body offset may also be in the rear axle too by 1/2". Still find it hard to believe they come from the factory with 0 U joint angle though.

 

I've read that as well. I used to have the link saved, but lost it in a crash. Basically, the slight angle was needed to take advantage of lubrication effects. I wish I could find that link. It gave a very detailed, how and why, when it comes to those angles.

I've seen photos of ch***is setups and they were not bad, but they were far from good.

 

It's there, just hard to spot with the naked eye. When I first built my T Bucket, my boss asked about the drive shaft and yoke angles. He wondered about the off set at the differential. That's when I went on Google and found a link that explained why that angle is important.

The video that was posted explains it as easy as it can be. I'll bet the guys trying to eyeball it straight have put in an angle and don't even realize it. 1 degree would not be noticeable to the naked eye.

 

My eyecrometer is often out of calibration.

 

As luck would have it, saw a friend today who was driving his Rover. So of course I crawled under it. The front shaft is indeed like the lower drawing in the Hotrodder.com picture. The u joints are out of phase, but not 90 degrees, more like 45. Figure that one out.

 

The first CJ Jeeps in 1946 has real CV joints...I believe the MB WW2 Jeeps had them also.

 

Being a 2 piece splined shaft, someone could have easily ***embled it wrong at some point and since it's on the front might not even see enough use to get noticed.

 

I suspect the cars you are seeing with straight drivelines have a offset left to right instead of up and down. Either way does the same thing. No driveline going down the road will stay at a constant angle, starting with a few degrees just gives the u-joints more time before they wear out.

A few post back, someone asked about setting up a rear axle. Before doing any welding, the truck should be on four wheels with the final weight on both axles.
The frame being level has nothing to do with driveline angle. All you need to know is the transmission to driveshaft angle and driveshaft to pinion angle. Both should be close to each other with no more then 5 degrees and no less then 1 degree. Frame level or ground level has nothing to do it. Left to right or up and down, angles are angles.


Joe

 

Great discussion. I built a roadster with a 39 Ford trans, an enclosed driveshaft, and a quick change rear end. With the quick change the driveshaft is not at rear axle height, it connects below the ring gear, this results in a considerable u joint angle I feel no driveshaft vibration. I believe this is due to the very unique design of the u joint. Normally there would be little u joint angle on a stock old Ford. A previous entry was correct stating that br*** bushings rather than needle bearings are used to prevent Brinnelling(pitting) of the cross of the joint. I believe the output splined yoke is designed so that it can move radially on the cross,(up & down movement). Then the front of the enclosed driveshaft is held centered in the front of the housing by a bushingin the housing. The result is the cross is moving off center constantly, causing the driveshaft to vibrate &speedup & slow down on every rev. This is prevented by the output yoke being allowed to move radially& the d shaft held centered by the housing, sort of a poor man's constant velocity joint. Asking fellow HAMBers for their input on this. Greg

 

Nope, that is bone-stock. I have worked on them, on 3 continents, every one that I have seen looked like that.

 

Seems your right.

Any chance they shun engaging 4WD on anything other than loose terrain?

 

I might be crazy, but this, in particular, is not an indicator.

Most of the ones I have seen are full-time four-wheel-drive.

I know, this should not work, but there it is.