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Pinion Angle 6.5%

4K views 23 replies 5 participants last post by  JohnTN 
#1 ·
I seem to have a little vibration at 25-35 mph and again at 55-60 mph on my street rod that was built by someone else.

I checked the driveline angles last night and got the following:
engine/trans down angle 2%
driveshaft up angle to rear 1%
rear end up angle to front of 6.5%

From what I have read engine and rear should have about the same angles and in the range of 1-3%.

Is this rear angle out enough to cause vibration?

John
 
#2 ·
That much difference in angles would cause vibrations.
You wrote % as your unit of measurement. Are you using one of those digital levels? If so, you should set it to degrees. It will be alot easier to visualize what's going on. The angles of operation of a u joint should not exceed a certain amount at a given shaft rpm. As long as you keep the operating angle under about 4 degrees (3* is better), and the trans shaft and pinion shaft are parallel after you compensate for suspension wrap you should be ok.

Here is a good website that explains some of it, although it is written more for trucks, and doesn't really take into account suspension wrap.
http://www.drivetrain.com/driveline_angle_problem.html

Here is an old thread from here with some more good info.
http://hotrodders.com/forum/trouble...n-18566.html?highlight=ujoint+operating+angle

Do a search, there are a bunch more just like that one. :thumbup:

Hope this helps, mikey
 
#3 ·
I think he is using the percent symbol, because there is no degrees symbol on a keyboard...at least not on my laptop....unless I am blind. Really, I am only half blind. I use the * as the degree symbol.

I have to agree................6* is too much.
 
#4 ·
poncho62 said:
I think he is using the percent symbol, because there is no degrees symbol on a keyboard...at least not on my laptop....unless I am blind. Really, I am only half blind. I use the * as the degree symbol.

I have to agree................6* is too much.
I would have assumed that too, But you never know. I have one of those digital levels that will read in percent, degrees or for plumbing...inches per foot.
(I have started to use my old Starrett bubble inclinometer for precise stuff. that "Smartlevel" is a POS.)

Later, mikey
 
#5 ·
Yes, I meant degrees, not percent.

Thanks for the links, I had seen some of them in a search.

The rear suspension is real unique. The 1939 Olds had trailing arms with coil springs originally. The springs were removed and coil over mounts were welded to the axles. Floating axle mounts were welded to the trailing arms and then new control arms with threaded ends were added on each side that connect forward to the frame and rearward to welded brackets on the axle. So, the axle location is fixed by the floating mounts welded to the original trailing arms, but it can be rotated by adjusting the length of the new control arms. Needless to say there are more squeaks and rattles than you can shake a stick at.

But, it appears I can change the pinion angle by shortening the new control arms that have threaded ends.

John
 
#6 ·
So the axle/suspension motion is similar to a four bar?

If there is alot of rubber in your mounts I'd set it up to compensate for axle wrap about 1/2* to 1* . Do it when the weight of the car is on the suspension.

Later, mikey
 
#7 ·
It is similar to a 4-bar suspension, but none of the bars are parallel to each other.

To compensate for axle wrap, would I put the rear end up angle at slightly less than the engine down angle, i.e., engine down at 2* and rear end up at 1-1.5*?

John
 
#9 ·
JohnTN said:
It is similar to a 4-bar suspension, but none of the bars are parallel to each other.

To compensate for axle wrap, would I put the rear end up angle at slightly less than the engine down angle, i.e., engine down at 2* and rear end up at 1-1.5*?

John
Yes that is correct.
If the engine hangs down in back at a 2* angle then the rear end should angle up at the front at a 1-to 1.5* angle . The pinion wants to climb the ring gear. The axle housing will roll, (wrap), up that .5* or 1* under power and bring the shafts nearly parallel.
Use your own judgement about how much axle movement due to rubber mounts you have.

later, mikey
 
#11 ·
Further adjustment needed. Smooth up to 60 mph but then start getting some vibes at 62-63 mph. I'll jack the car up today and take another 1 degree out of the rear angle. So, shooting for 2* down at engine and 1.5* up at rear end. Working angle at each end should be within 1*.

John
 
#12 ·
Made the 1 degree further adjustment and helped only a little. Still have slight vibes beginning around 65-66 mph. The driveshaft was a new custom length with new U-joints when insalled 2400 miles ago, but it was never balanced. Would balance be a culprit at this relatively low speed?

Also, have a new problem. Under hard acceleration in 1st or 2nd gear there is a very loud metalic screeching sound from under the car like metal rubbing metal. I sure don't see any signs of external contact of the drive shaft or U-joints with the frame. Also, the rear U-joint had slung some grease out onto the underside of the floor pan before I started messing with the pinion angle. But, I had never heard this screeching noise until after I adjusted the pinion angle.

Does it sound like a U-joint might be bad and the sound is bearings rubbing inside the U-joint?

John
 
#13 ·
Is your new noise steady, (squeeeeeeeeeeeeeeeeeeeee....),or does it have a rhythm? Usually a bad U joint will make a clicking or crunchy sound. Sometimes if they are just dry they make a oscillating squeak as they move through their range of motion.

They make a sound like this :rolleyes: SqueaksqueaksqueaksqueaksqueakSqueaksqueaksqueaksqueaksqueak.... :p

Screeeeeeeeeeeee..sounds like it may be non U-joint related.

Try putting some grease in them and see what happens. If you ran them for a while and they were angled outside their operating range they may have pushed out their grease. Check for play at the joint. You may just want to replace it to rule out a loose joint as your source of vibration.


Balancing the shaft may help with the vibrations. I'd check the tires for balance also.

Hope this helps,
Mikey
 
#15 ·
U-joints don't make constant noises.
It only makes the sound when you are accelerating in 1 and 2nd gear?
Is the car squatting when the noise appears? I had a truck that when I loaded it some and accelerated, the drive shaft would just barely touch the side of my turbo muffler and it would howl like a banshee. It was actually painful to hear. :pain: I didn't see the mark it was making for quite some time.

Mikey
 
#16 ·
I've only heard it in 1st and 2nd at only at WOT. The car doesn't squat much, but I will get under it and look more carefully for any possible contact points. Seems like on my first look there was a couple inches clearance all around the driveshaft.

Thanks,

John
 
#17 ·
I have heard two new sounds since adjusting the driveline close to parrallel. Under hard acceleration I first hear a ticking sound from the engine compartment and then a metalic screeching sound from under the car.

In the engine compartment I have always had very little clearance between the metal alternator fan and the motor case on the electric cooling fan (about 1/4 inch).

I noticed today that there is a noticeable mark on the fan motor where the alternator fan has been making contact (gap is still 1/4 inch at idle). This is almost certainly the ticking from the engine compartment under hard acceleration. And I am pretty sure this hadn't occurred before changing the driveline angle.

Since the driveshaft is a custom one cut to a specified length, I wonder if the clearance between the transmission and the end of the driveshaft yoke is too little. Making the driveline almost parrellel would tend to push the front yoke a little further into the transmission. From under the car I can see a bright ring on the front yoke that is about 1/8 inch wide, indicating the yoke slides into the transmission this far sometimes.

And maybe the driveline is pushing the transmission/engine slightly forward (or angling it up) and now causing the alternator to contact the fan motor casing.

Even more reason to pull the driveshaft and check/measure stuff.

To pull driveshaft do you just take the four nuts off the rear U-joint, drop the shaft down in the back, and pull the shaft out of the transmissioin?

John
 
#18 ·
JohnTN said:
To pull driveshaft do you just take the four nuts off the rear U-joint, drop the shaft down in the back, and pull the shaft out of the transmissioin?

John
That's it. have a pan under the trans for some oil to escape when you pull the yoke.
you shoud have about 3/4 " to an inch of slip into the trans when your car is at ride height. I never heard of a bottoming out drivshaft making a noise, other than a clunking. I agree with your assumption. Maybe if your driveshaft is now too short the rear end is moving forward and pushing the motor and it' s associated rotating parts into forward into the fan radiator etc.

With the rear end being rotated up you used up some driveshaft length and made a straighter, less compliant link between the rear end and trans.

Mikey
 
#22 ·
Tazz,

I made the adjustments noted in responses #10 and #12 above. Angles are now:
transmission down angle (toward rear) 2*
driveshaft down angle (toward rear) 2.5*
Rearend up angle (toward trans) 1.5*

Now trying to diagnose the screeching sounds.

John
 
#24 ·
Removed the driveshaft and checked yoke free play -- it is about 1/2 inch. I don't see any evidence the drive shaft has contacted the frame or any brackets, so I suspect under hard acceleration the shaft is bottoming and pushing/tilting the engine forward enough for he alternator fan to contact the electric fan motor (only 1/8 inch clearance there to start with).

However, while under the car I noticed the driveshaft wasn't centered in the frame cutout so decided to check the front clip for alignment and found it to be skewed. This is a much bigger problem thant the driiveshaft being slightly too long.

The front clip problem is discussed under the Suspension/Steering heading in a thread titled something like "subframe results in too much positive caster".

John
 
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