Driveshaft Angle Question

While troubleshooting a vibration problem in my 54 Chevy, I discovered that I had virtually no angle between my tailshaft and driveshaft. I.e. they were in a virtually straight line. This was created when I put 3" lowering blocks on it.

Since I couldn't change the engine ****** centerline very much, I ended up raising the rear of the car. Now I don't like the stance.

What kind of u-joint and other problems will I encounter if I lower the rear back to where I had it?

 

Did the vibration problem go away? You might be able to shim up the trans a little on the crossmember.

 

Shim the trans or engine mounts depending on which way you need to change the angle?

 

A static setting of 1 to 3 degrees is recommended to try make the needles roll all the time, which is good for bearing life.
Phased front and rear yokes plus Equal angles in 3D front and rear (or a fancy "equivalent" angle) is to make the non-constant velocity action stay in the driveshaft and not be fed into the rear axle, which could make some annoying vibration.
Angles much more than 3 degrees result in "secondary couple" which under load tries to make the diff nose bob up and down twice each driveshaft revolution. Depending on how the axle is mounted it is easy for the axle to "bob", and there may even be a nice resonant frequency or 2 lurking in there to amplify the bobbing 10X. That usually is REAL noticeable

 

Have you tried angle cut lowering blocks? I had my dad machine me a set for my 52 ford and they work great. 2 inches at the center of the block, billet steel (aluminum mushrooms and doesn't hold torque very well) with a 5 degree angle down with a press in dowell pin on the top. Pm me if you have any questions...hope this helps

 

stock motor/trans? what is angle of engine/trans? running stock leaf springs? there are aftermarket angle wedges to change pinion angle at Jeg's, etc

 

As pointed out, there should be some angle in order to maximize U-joint life. As for your vibration problem, if the trans/driveshaft/pinion shaft are in a straight line, there shouldn't be any u-joint induced vibration. Of course that doesn't mean it couldn't be an out of balance or bent driveshaft.

 

I thought the same thing.

It could be that when he lowered it, the slip yoke bottomed out in the trans and now the driveshaft is in a bind...causing the vibration.

 

Shim wedges that are very thin can adjust the angle of your third member by slipping them between the springs and the axle perches. Summit, Jegs, etc. all sell them in everything from 1 to 6 degrees.

 

You need some offset to stop brinnelling of the roller bearings. There needs to be some movement off centre.

 

The vibration was caused by brake drums out of balance. I know the angles are right, measured with a digital inclinometer. There is no way to get the stance I want and not have the driveshaft virtually in line. I can't raise the ****** any more without taking the car apart.

If I do put it back that way, how long will the u-joints last? I understand that it is not going to be circulating the rollers very much. If they will last 10-20k miles, I don't really care as long as I don't creat another problem.

Thanks.

 

Re-grease the joints whenever you think of it. Remember, it is only in that position when you are not moving. The angle will change as you drive. You will be fine.

 

This might ***ist.

 

If the driveshaft angle is 0, which is basically what the OP said, there will be no yoke rotation, so the needle bearings will remain in virtually the same position in relation to the cups and yoke. The angle will change slightly as the suspension works, but probably not enough to result in extended u-joint life.

 

1º is enough for u-joint survival. He will see at-least 1.

 

what part of shimming the rear axle dont you understand?

 

You can't really set 0 angle, nobody is that accurate. The needles are going to roll a little no matter where you set the angle. Never measure the driveshaft angle. Just the trans output shaft and the rear end pinion angle. Make them the same and you will be good enough. Racing leaf springs can go down on the pinion angle couple of degrees.

example: trans angle down 2, the pinion should be set at 2 up. All while sitting on the suspension.

 

I sure have learned a lot from your '54 woes!

 

Good! I would hate for all this "experience" to be wasted. You should just buy mine.

 

I hope this will be of help to you. I keep it in my files for use. Every time I do any drive line work I run a copy of it.
Normbc9

 

Position #4 in that diagram is NOT an incorrect setup. The "broken back" arrangement has been used successfully in Land Rovers.

 

I agree with the posts that have commented on having a slight angle at both ends, and that it should be equal both ends. But I don't think anyone has mentioned this: the angles do not have to be vertical. They can be horizontal. If your ****** tailshaft is on centerline with the frame, but your rearend yoke is a little off center (which it will be if you centered the pumpkin from rear view), then you inherently have a small angle front and rear, and they will be equal. If that's the case, you can have 0º vertical angle both ends, but the u-joints will still have the horizontal angle to move their bearings.

 

This is correct but not the case with my car. Thanks.

 

Well, I hunkered it back down in the rear. If I develop any problems, I'll let you know. Thanks for the inputs.

 

I think this is a good option especially for the 1930's style hot rod builds, it helps to accommodate low builds and also gives you the option when building a rear end to have the visual diff center in the center from a rear view of the car which provides for that drive shaft offset mentioned above...