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Old 10-25-2006, 10:00 AM
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Pinion Angle 6.5%

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

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Old 10-25-2006, 10:25 AM
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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/troubles...perating+angle

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

Hope this helps, mikey
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Old 10-25-2006, 10:29 AM
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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.
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Old 10-25-2006, 10:35 AM
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Quote:
Originally Posted by poncho62
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
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Old 10-25-2006, 10:46 AM
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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
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Old 10-25-2006, 11:24 AM
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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
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Old 10-25-2006, 11:47 AM
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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
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Old 10-25-2006, 11:49 AM
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Oh, about the rubber. The only rubber is where the original trailing arms attach forward to the frame. Everything else is "bearing" joints (hotchiss?) I guess you would call them.

John
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Old 10-25-2006, 12:04 PM
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Quote:
Originally Posted by JohnTN
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
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Old 10-26-2006, 07:15 PM
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I was able to adjust the upper control rod arms today and bring the pinion angle to 2.5 degrees up. Vibration is gone and rear view mirror is rock steady now instead of giving me a fuzzy image.

John
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Old 10-31-2006, 10:28 AM
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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
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Old 11-06-2006, 07:19 PM
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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
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Old 11-06-2006, 08:03 PM
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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 SqueaksqueaksqueaksqueaksqueakSqueaksqueaksqueaksq ueaksqueak....

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
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Old 11-06-2006, 10:18 PM
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The screeching sound is not rythmetic, just a constant screech until I back off the throttle.
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Old 11-06-2006, 10:37 PM
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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. I didn't see the mark it was making for quite some time.

Mikey
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