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Driveshaft recommendation

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Old 01-22-2017, 06:39 PM   #21
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I am getting ready to order my new driveshaft, but just trying to make sure my current shaft is whats giving me the vibration. I plan on getting a new shaft either way at this point.

With the car on jack stands, you can start to feel the vibration at 65-70 mph. It progressively gets worse until 100-110 mph then feels like it just stops and smooths out. Does this sound like an improperly balanced shaft? The car does have 4.30 gears so the shaft is spinning faster then a stock gear ratio.

In the video I took you can see the mirror shake at the worse point, then it gets instantly better?

I double checked the pinion angle , and they are good. the engines pointing down at 4* and the pinions pointing up at 3.5*.
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Old 02-03-2017, 10:46 PM   #22
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Well,
I just got done installing the new 3.5" aluminum pst driveshaft with sonnax c/m yoke and it still vibrates. It might be a little better then the 3" steel shaft I had but still there at the same speeds. I think I will be tearing the transmission out next.
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Old 02-04-2017, 02:55 AM   #23
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I could be wrong, but from the pic on the previous page, you have way too much downward angle on the transmission, versus the angle going back up to the driveshaft. If viewing on a laptop just run your mouse down the sidebar and put the straight line of the bottom or top of the laptop screen across the uni joint and you will see what I mean.

It looks way out to me. Your engine is too high and/or trans too low. If you have enough driveshaft and tunnel clearance, jack your transmission up 0.5" with spacers on the mount and see if you notice any difference.

I've has two PST steel shafts, one mild and now my full chrome moly and both shafts have been spot on.
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Old 02-04-2017, 03:39 PM   #24
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I have adjusted the pinion angle again since that pic. With the car sitting on jack stands so the axles at ride height. The engines pointing down 4.5 and pinion pointing up 4, driveshaft is damn near level.

I'm open for suggestions and adjusting things. I can try lifting trans up. I also might try putting a plug in the tail shaft and running it through the gears.
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Old 02-04-2017, 04:15 PM   #25
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Your rear axle pinion is pointing up 4 degrees?
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Old 02-04-2017, 04:20 PM   #26
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Yes, engines pointing down 4.5 pinion pointing up 4. My car is a g body so has 4 link with solid/adjustable arms and poly bushings.
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Old 02-04-2017, 04:27 PM   #27
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I'd point the rear axle pinion down to 1 or 2 degrees, lift the trans up at least 0.5", and see how that works.

Ignore how the driveshaft looks in relation to the car chassis. From what your saying, your u-joint angles are backwards to how they should be.
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Old 02-04-2017, 04:31 PM   #28
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Quote:
Originally Posted by onebadbowtie86 View Post
Yes, engines pointing down 4.5 pinion pointing up 4. My car is a g body so has 4 link with solid/adjustable arms and poly bushings.
Who told you to point the pinion up 4 degrees? Ive always run them pointing down a degree, if not 2.

Try what I said, better than buying more new parts for nothing.
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Old 02-04-2017, 05:27 PM   #29
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I thought the angles needed to match/cancel each other out?
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Old 02-04-2017, 06:52 PM   #30
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Quote:
Originally Posted by Launch View Post
Who told you to point the pinion up 4 degrees? Ive always run them pointing down a degree, if not 2.

Try what I said, better than buying more new parts for nothing.

1-2 degrees down from 0 on the gauge or 1-2 degrees less then the engines pointing down?

Right now the tailshaft of the trans is pointing down the same as the pinions pointing up, so they are parallel. I dont believe the pinion climbs much under load on this chassis with the solid arms and poly bushings.

I for sure am going to try shimming the trans up and adjusting the pinion down. just trying to get a grasp on the subject.
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Old 02-04-2017, 07:25 PM   #31
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Without finding diagrams and spending hours trying to explain it, you want each u-joint to not be on too much working angle when the car is under power.

Yours is backwards to how it should be.

I measure my rear pinion angle from the axle housing center section itself , as the car sits on all 4 wheels, as it drives. Get it 1 - 2 degree down.

Then, get your driveshaft from the transmission to get to it as straight as possible from the output shaft of your transmission.

If your transmission is pointing too far downwards, you will see your driveshaft needing to point back upwards to go to the rear axle. That is wrong. Manufacturers sit the engine/transmission on a slight downwards angle so that it becomes a straight line by the time the driveshaft gets to the rear axle. You want your u-joints to run as straight as possible.

You can't have the driveshaft on angles the way you have it. You want it as straight as possible, and the reason to point the rear pinion down 1 or 2 degrees on solid axle cars is that almost always the pinion will lift under power and straighten the angle to near 0
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Old 02-04-2017, 07:41 PM   #32
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So even if I can get my tail shaft so it's only pointing down 3-3.5 degrees I should still shoot for 0 degrees at the pinion instead of having the pinion pointing up to be parallel with the tail shaft?
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Old 02-04-2017, 07:48 PM   #33
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Quote:
Originally Posted by onebadbowtie86 View Post
So even if I can get my tail shaft so it's only pointing down 3-3.5 degrees I should still shoot for 0 degrees at the pinion instead of having the pinion pointing up to be parallel with the tail shaft?
Yes..
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Old 02-04-2017, 07:50 PM   #34
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Ok thanks for the help! Working on it now.
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Old 02-04-2017, 07:59 PM   #35
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It's easy to get confused with everyone talking about angles. What you want is the centerline from your crankshaft to your rear pinion, to be as straight line as possible, to itself. Doesn't matter if the line doesn't follow a straight line with the vehicle chassis.. you only need consider the engine/transmission/axle to be in a straight line

Just imagine drawing a straight line from the centerline of your crankshaft to your rear pinion.

You don't want u-joints running on more than 2 degree angles, either up or down, left or right, doesn't matter. They simply need to run as straight as possible.

Last edited by Launch; 02-04-2017 at 08:18 PM.
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Old 02-04-2017, 08:12 PM   #36
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From your pics I think your engine is too high, trans too low, and they're way out of being in a straight line to the axle pinion

Put a wedge on your front wheel, lift the rear end with a jack under the axle housing, so the rear suspension is loaded, as it is when it drives, and look underneath from the side of the car and look visually at how the transmission pan follows a straight line with the driveshaft all the way to the rear axle pinion, that's when you will see if it's way off

This one explains it better...


Last edited by Launch; 02-04-2017 at 08:17 PM.
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Old 02-04-2017, 08:23 PM   #37
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I have the car on my 2 post lift right now. I raised the transmission as high as I could with out being in contact with the floor. Engine/trans is still sloped down 3*. I can't get the engine and trans sitting at 0* in this car.

So the transmission slip yoke is pointing down 3*, or -3* the driveshaft runs at 0* to my pinion that's pointing up +3 right now.

Your saying I should have the slip yoke/driveshaft running at the same -3* as the engine/trans to the pinion at 0*?
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Old 02-04-2017, 08:24 PM   #38
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I also removed the rear springs and put a jack under axle so it's mocking ride heaight while on the lift.
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Old 02-04-2017, 08:35 PM   #39
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Quote:
Originally Posted by onebadbowtie86 View Post
I have the car on my 2 post lift right now. I raised the transmission as high as I could with out being in contact with the floor. Engine/trans is still sloped down 3*. I can't get the engine and trans sitting at 0* in this car.

So the transmission slip yoke is pointing down 3*, or -3* the driveshaft runs at 0* to my pinion that's pointing up +3 right now.

Your saying I should have the slip yoke/driveshaft running at the same -3* as the engine/trans to the pinion at 0*?

See this, and then I might try explain further..


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Old 02-04-2017, 08:39 PM   #40
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Leave your transmission on a 3 degree downwards angle. Now your rear pinion pointing upwards is backwards to how you need it to be.

The last diagram on that pic above is how you want to be, because it will straighten out your u-joints

It is very difficult to try explain driveshaft angles in words.

I think simply pointing your rear axle (pinion) down, rather than up, is what you have to do.

Last edited by Launch; 02-04-2017 at 08:45 PM.
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