SlickTrackGod

I came across a fantastic video that is a very informative working model on how bad harmonics of improperly matched driveshaft angles will prematurely wear out u-joints. Enjoy.

Dean

92RS_Ttop

iTrader: (3)

Link just takes me to a Facebook login page?

SlickTrackGod

Sorry, somehow I copied the wrong link. It's fixed.

AlkyIROC

Really good video explaining driveline and pinion angles. Our one piece driveshafts don't need to worry about phasing. When you change your suspension height with lowering springs etc, you're also changing the driveline angles and they need to be checked.

The example show in the video is an over emphasized example of my driveline. My engine/tranny is pointing downward. I can't drop the front of the engine any more or move the tranny up any higher because of header clearance under the floor. The driveshaft goes upward towards the diff and the diff pinion is pointed upward on the same angle as the engine/tranny. An optimal setup would be to have the tranny yoke pointing straight at the diff yoke. This isn't always possible.

Everyone seems to think pinion angle needs to be pointed downward. It does in a way except pinion angle has no relation to the driveshaft or to the ground. Pinion angle is best adjusted with the driveshaft removed or completely ignored.

To properly adjust your diff's pinion angle, you need an angle finder. I use a digital one myself. Use whatever means possible to determine the angle the diff/tranny (crankshaft centerline) is sitting in the car. You can have the car sitting high up on 4 jackstands. It doesn't matter as long as the rear suspension is still loaded. You can take a measurement off the oil pan rail of the engine. Take it off the balancer and add/subtract 90* etc to get a horizontal angle.

Now get an angle off the diff. Getting the pinion angle can be a little tricky. You can't always get it off the diff housing because you don't know it that's on the same angle as the pinion. With the driveshaft off, you can get a vertical angle off the yoke and like getting it off the balancer, add or subtract 90* to get a horizontal angle.

Like in the video, you want the angle to be exactly the same however because a car's diff has suspension which moves, you'll never keep it perfectly the same. If the suspension is working properly, the pinion angle should remain the same through the suspensions arc of travel. As you accelerate, the pinion is trying to walk up the ring gear. The front of the diff wants to move upward. To compensate for this, you set the pinion angle down anywhere from 2-5 degrees from what the engine/tranny angle is. This downward angle can still have the diff pinion pointed upward so don't assume pinion angle will always have the diff pointed downward. When the diff rotates upward under hard acceleration, the pinion angle will be the same as the engine/tranny and the u-joints will stay happy.

Different types of suspension need different amounts of angle. Leaf spring suspension will allow the diff to rotate the most while 4-link suspension allows little to no rotation. A third gen's flimsy, squishy, torque arm system can easily move 3-5 degrees. Using an aftermarket tubular and adjustable torque arm with a poly or rod end front mount reduces the amount of rotation even more.

Bad u-joint angles will wear out u-joints but will also cause a vibration that can be felt while driving down the highway.

TallTim

iTrader: (2)

Slick thanks for that vid post very interesting.

Alky I'm trying to get my head around how a lowering spring changes the yoke to yoke angle. If I put shorter springs in the rear for example, that changes the yoke-yoke angle? Thx.

AlkyIROC

The trans yoke moves with the body so lowering the body will change the angle of both yokes. Lowering springs, air bags etc will move the trans yoke lower while the diff yoke will move higher up into the body as the body is dropped lower in relation to the diff..

I deal with driveline angles every week on medium and heavy duty trucks. The ones that use air bag suspension have a specific ride height to keep proper driveline angles. When the rear suspension sits higher or lower than the specified height, it will change the driveline angle going into the diff.

I use an Allison transmission calculator program to tell me if the angles are within acceptable limits or not. I use a digital angle finder to get the angle of the transmission, diff and all the driveshafts. The lengths of all the driveshafts are also used. If the ride right is too high or low, the angles get excessive and will cause a noticeable driveline vibration. That speeding up and slowing down of a driveline with bad angles can also damage transmissions.

Depending on the type of suspension setup, lowering the body/frame can roll the diff which can increase the amount of angle the pinion yoke will be at.

SlickTrackGod

The simple answer you are looking for is yes it changes. The only thing you need to visualise is the nose of the pinion yoke angles downward as the axle travels upward. You lower the car 2" and the new static pinion angle looses about 2-3*. You need to adjust the static angle back up so its not pointing towards the road surface as much.

The static pinion angle should be 1* lower on the pinion compared to the trans output shaft. This 1* static will compensate for the angles evening out under dynamic pinion thrust.

red rock

iTrader: (2)

As long as this thread is about driveline phasing, I'll add this to the mix. http://jniolon.clubfte.com/driveline...nephasing.html

Lonnie P

Good post Dean... like the visual instead of just theory.

Ran into an interesting issue with my car as the rear is further off the ground than the trans is, but the tail shaft also points down hill. To get them in phase the pinion had to point upward even though it increased the u-joint angle. Angles are admittedly low but none the less seemed a little odd setting it this way.

IROCgiraffe

iTrader: (3)

Subbed

SlickTrackGod

Hey Lonnie.

Just as long as the angles are not zero. as I'm sure you know but will post for others the u-joints need some angle (at least 1*) in order for the needle bearings inside them to rtate. Otherwise you will also get premature wear if the shaft is too straight coming off the trans with less than 1* of angle between them/ same with the driveshaft and rear yoke.

Since we do not have driveshafts with lip splines in the center of the shaft that can be pulled apart, we do not have to worry about phasing on a 3rd gen drivesaft. It is already phased when build. All we need to do is match angles.

I just like the video not paticularly for yoke phasing, but for angle match showing how harmonics form due to driveshaft speed inconsistancy of the angles are different front and rear. They need to be the same to cancel and to maintain smooth driveshaft speed.

Alice89

iTrader: (6)

X2. Its way easier to learn when you have something to look at. Thanks for sharing this.

SlickTrackGod

You guys are welcome. What the video does NOT necessarily discuss is how even when the angles match the driveshaft still speeds up and slows down in pulses- you just dont get harmonics transfer of this because the angles cancel this in the final drive yoke speed. Its important to understand rotation weight and thus critical speed of a driveshaft. The more the angles? The more the hidden pulse, and thus the lower the critical speed of the driveshaft until vibration occurs regardless. This is why I run carbon fiber shafts in a car seeing frequents speeds above 100mph for prolonged durations. This also helps rpm climb if either low rotation weight, reduced matching angles, or both.

SlickTrackGod

To give an example lets take the first joint from tailshaft to driveshaft at A and the rear joint from shaft to diff yoke as B.

Now if the joints are matched at 1* then at a full rotation 360* the speed of a lets say is 3000 rpm tailshaft through A at 90* makes the shaft 2975 and 270* @ 3025---while the joint b does the exact opposite with 90*@ 3025 and 270* @ 2975- then of coursr a final drive product staying at a constant 3000 into the diff. But see the driveshaft change or pulse.


Here's the kicker-.now with a matched A&B of 5* instead of 1*, the pulse would increase more like this example:
3000 @ tailshaft through A 90* @2900 and 270* @ 3100...with B 90* @ 3100 and 270* @ 2900.
This is an exaggerated example but you can see how driveshaft pulse speed increasrse with higher cancelled angles and thus lowers critical speed the driveshaft can reach because of weight, flex, and vibration resistance.