guitarman376

So I understand that driveline angle includes transmission ouput angle, DS angle, and pinion angle. My car has been lowered in the rear, which obviously affects DS angle and pinion angle. The car has stock motor and transmission mounts, but I understand this can be part of the problem potentially.

The pinion angle needs to be at least 2 degrees downward more than the DS, is that correct? What is the magic number here, 2 degrees downward relative to DS or 3? Downwards means pointing towards ground.

I measured the driveshaft down 2.5 degrees and the pinion was down only 1 degree. This leads me to believe I need 3.5- 4 degree wedges depending on what the optimum angle to have is.

Unless I am missing something, I believe the right wedges should solve my vibration (which is happening under high throttle acceleration). It causes the tires to feel like they're skipping, which isn't normal wheel hop as my car isn't that powerful and I have 4.5 leafs.

I understand that the transmission angle is important too, but I forgot to measure it. However the DS angle is def wrong compared to the pinion right? Just want to make sure I'm on the right track. In my mind I can't help thinking that since the rear of the car is what changed, that's where the problem is...but maybe now that the pinion sits up higher (closer to trans) I will have to change the trans angle too.

Starfury

From what I recall of my drivetrains course, all things being static, the transmission output angle and the pinion input angle should be the same. In other words, the trans output to driveshaft angle plus the pinion to driveshaft angle should equal zero. This keeps the transmission output and pinion input operating on parallel planes and reduces the chance for vibrations.

Unfortunately, all things are not static. Under load, the pinion shaft wants to rotate towards the body of the vehicle, changing your pinion angle. This is where an experienced drivetrain guy is going to be able to help you more than I am.

The physics behind u-joints:
U-joints are not constant-velocity. When they operate at an angle, they are constantly speeding up and slowing down. Their velocity looks like a sine-wave when graphed. The u-joints on a driveshaft are set up so that while the input u-joint is speeding up, the output u-joint is slowing down. When you add the velocities of the two joints together, they average out to a constant output speed.

This only works if the two u-joints are operating at angles that add up to zero. If you increase one u-joint angle, the amplitude of the velocity sine wave increases (the joint output velocity changes more dramatically), requiring the opposing u-joint angle to be adjusted to counter the amplitude change. If the two joints angles are not the same, the input and output velocity do not match, causing a repeated change in velocity at the pinion input. This results in a drivetrain vibration.

BlindGUYnAR

Not a classic mustang, but instead a s197 it still good info in this video.


The question I have is should you also try to simulate the weight of the driver when setting the angle? Or since you aren't cancelling out the angles completely is that taking the avg weight of driver into account?

guitarman376

That is great information Starfury, and that backs up what I have been reading about the trans output angle and the pinion angle zero-ing out (relative to driveshaft).

However with the pinion angle and a leafspring car don't you need the pinion downward 2 degrees from the driveshaft angle? To account for the leafs wrapping from accelerating is what I understand.

For ex: My reading off DS was downwards 2.5 deg, and my pinion was downward about one degree. This would mean I need 3.5 degree pinion angle wedges right?

I acknowledge this isn't taking into account the trans to DS angles, but you have to get one in the correct range first right? With the car lowered, the TRANS - DS angle should change much less than the DS - PINION angle, which is why I am starting here.

Driveline angles are a new thing for me, but I have watched most of the common youtube videos and tried understanding many articles/threads but as always there's conflicting information.

Starfury

Pinion angle relative to the driveshaft angle doesn't really matter in and of itself, unless you're running such severe angles that it's burning out the u-joints (this isn't a problem unless you have a truck or jeep that sits really high). It's the pinion angle relative to the transmission output angle that matters.

The pinion angle needs to be slightly lower (more horizontal) than the transmission output angle to account for axle wrap. ~1.5* sounds right for a street car, but I'm pretty sure there are members here that can help you with a specific angle with much more certainty than I can.

guitarman376

I now see the fault in my logic. My only question then is what is the desirable range in general for standard u joints?

Today I detached the rear u joint to make the pinion measurements. Can the transmission yolk give an accurate reading for the trans angle measurement? I'm hoping I don't have to remove the yolk because I imagine fluid would come pouring out if I had to do that.

However I'm still betting I need to angle the pinion downwards more to correct everything. I will verify this before purchasing anything.

Starfury

The flat portion of the yoke should be perfectly perpendicular to the pinion axis and should make a decent surface to measure the pinion angle from. Alternatively, you could do what the video above recommends and measure the angle at the harmonic balancer.

barnett468

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you want the pinion and trans at the same angle when they are under load so estimate that the pinion will be elevated around 1 degree at highway speed meaning that the pinion can be out of line by 1 degree lower than the trans when the car is not moving

MonsterBilly

this video would have been a great help to me a few years ago. I struggled with this same thing a while back. the video explains it fantastically

guitarman376

I only need to account for 1 degree of pinion change during throttle? The rest all makes sense thanks so much. Everywhere I read says 2-3 degrees for leafsprung cars.