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bigmal

Drive Line angle question

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Hi all, Still chasing annoying vibrations. The reconditioned tailshaft I fitted four years ago I always considered not part of the vibration. Running out of options I took it to another shop and had them check the balance. Turns out the shaft was bent 0.030", ends welded on crooked and not in balance. Really pissed off at the guy who sold it to me. And he now knows how pissed off I am. But didn't offer a refund.

So was very excited to fit my new shaft thinking all my problems would be solved. They're not. Definitely an improvement but still some vibration.

My question relates to drive line angles. The diff yoke is pitched down around 5 degrees compared to the transmission. The difficulty I have is that I know the diff pitches up when under load. Most of my vibration is around 55 mph (90 kmph over here). Would anyone know roughly how much the diff pitches up at around this speed or is it negligible?

I have seen some angle spacers to change the angle in 2, 3, 4 and 5 degrees. What are your thoughts?

Thanks,

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I have read about 1-2 degrees of pitch during acceleration, but it's pretty impossible to know the exact amount.

Since I put lowering reverse eye leaf springs and new motor mounts I've had a vibration as well. So far I think I have a 3 degree wedge installed, but I stopped there for now bc I'm planning on swapping a toploader in. My angle measurements will change after that.

 

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need to find the degree of transmission tail shaft (should be pointed down about 4 degrees or so. Then the yoke on rear end should be pointed up minus 1 degree.  Example  trans down 5 degree the rear end yoke should be pointed up 4 degrees.

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det0326 is right.  You want the two angles (diff and trans) to be roughly the same.  They will off set the U Joint velocity changes as it rotates.  Also check the plan view of the Trans.  They can be slightly off creating the same issue in that plane.  

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I've seen some good simple information on Spicer's website regarding this topic.  It's more a matter of the operating angles of the U-joints.  This is just their online calculator https://spicerparts.com/calculators/driveline-operating-angle-calculator  They have much more information on this topic as well.

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Mal,

You could take a measurement across the steel outer lip of your gearbox oil seal, just eyeball it to see if your degree measuring tool is straight up and down and not crooked.

If not enough room, take your tailshaft out, then do your measurement.

With the shaft out its also easier to measure your diff pinion angle, just rotate the yoke until its straight up and down then take your measurement.

If your jacking your car up to get under it make sure it is level, you could put a level on your rocker sill to check. 

Support your diff on ramps or jack stands, don't take a reading with it hanging down unsupported.

If as you say you have -5 degrees on your gearbox ideally you'd want a wedge to give you on your diff to give you +5, so that face of the yoke and pinion are parallel to each other.

I'd be chucking a +3 wedge in the diff and giving it a test run.

If you have room I've also seen where Ford used shims between the gearbox mount and gearbox to level things up a bit. Just be sure to double check the clearance between your fan and radiator if you try this.

Good luck.

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11 hours ago, bigmal said:

Trying to get an exact difference between the front and the rear. The front is giving me some grief measuring it. Any tips?

unnamed.jpg

u can get trans tailshaft angle also from crank pulley if u can get to it.

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Its easiest and more accurate if you remove the driveshaft.  Stick the magnetic angle gauge on the vertical face of the transmission output shaft, and then put the gauge across the flats of the rearend's yoke.  Make sure the widest part of the yoke is vertical.   I went through this when doing my T56 trans conversion.  As noted above, jack or jackstand can skew your measurements so you must make sure the suspension in the front and rear is loaded evenly and its raised in even amounts (use ramps preferably)

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While waiting on the shims I was running it on the stands again. As you do. And I noticed the right rear wheel appears to wobble slightly more than the left. Tires and wheels are new and I am wondering if my vibration issue may be a bent axle. I don't know what's normal and what's excessive. Could I get your thoughts on this.

Also, I bought a digital protractor yesterday and the drive line angles difference is 3 degrees. So the 4 degree shims I have ordered are too big. I will order some 3 degree shims shortly

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4 hours ago, bigmal said:

While waiting on the shims I was running it on the stands again. As you do. And I noticed the right rear wheel appears to wobble slightly more than the left. Tires and wheels are new and I am wondering if my vibration issue may be a bent axle. I don't know what's normal and what's excessive. Could I get your thoughts on this.

Also, I bought a digital protractor yesterday and the drive line angles difference is 3 degrees. So the 4 degree shims I have ordered are too big. I will order some 3 degree shims shortly

 

IMG-6781.MOV 8.62 MB · 1 download IMG-6782.MOV 5.22 MB · 0 downloads

Swop the rear wheels over and see if its the wheel or not.

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15 hours ago, bigmal said:

Also, I bought a digital protractor yesterday and the drive line angles difference is 3 degrees. So the 4 degree shims I have ordered are too big. I will order some 3 degree shims shortly

In general up to 3 degrees mismatch between driveline angles is tolerable.

Try your wedges to see if its an improvement, but I think it's possible your vibration issue may lay elsewhere.

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15 hours ago, unilec said:

Swop the rear wheels over and see if its the wheel or not.

Thanks for that. I swapped the wheels and the wobble changed sides. I will take it to the tire shop during the week and see what they say.

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4 hours ago, DocWok said:

In general up to 3 degrees mismatch between driveline angles is tolerable.

Try your wedges to see if its an improvement, but I think it's possible your vibration issue may lay elsewhere.

Its a really difficult one as I have identified so many sources and each time I think that's it, it's only a slight improvement. Has been both engine and driveline.

So far the trouble shooting has been

  • Run engine with belts removed - no change
  • Replace harmonic balancer - not change.
  • New rear wheels and tires - Unknown if changed as done early on.
  • Replaced tailshaft - no change
  • Rebuilt engine and balance - unfortunately when installing I damaged the flex plate and replace it with a new one without re-balance (and I've kicked myself ever since)
  • New Torque converter - unknown
  • New Coil, leads and plugs - Removed slight miss
  • Another new tailshaft - significant improvement but still a vibration

Currently the vibration in neutral is only slight and at around 2500rpm. In drive the vibration is greater and at similar RPM. 

The only options I can think of at the moment are - 1. Check rear wheel balance/buckle, 2. add pinion shim to reduce from 3 degrees, and 3. rebalance crank/flex plate.

While the vibration is only slight, and significantly better than before it still bugs me. I'm starting t wonder if I'm asking too much from an old car.

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18 minutes ago, unilec said:

Mal, do you have any wiggle room to place a shim at the transmission cross member?

Not sure. I know it's tight though. Could be cheaper than the $80 shims

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8 minutes ago, 1969_Mach1 said:

If the vibration is there in neutral, why are you looking at the driveline, etc.  Is it a vibration, or is it random misfires?

Hi Mate, it does have a slight vibration in neutral, but greater when in drive. One of the difficulties is that it's not a big vibration. But still annoying.

I did have misfire issues but they are sorted. 

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