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Diff angle dilemma.


Been doing a lot of googling and havent found a definitive answer for my application. So, looking for some thoughts / input on this:

Had diff rebuilt again (3rd time) new joints and balanced driveshaft, no indication of phasing, also 3rd time. There is a persistent irritating vibration, sort of rumble effect, that starts around 60-63 mph and up and most prominent when between power and coast that is, improves slightly when powered or coasting. Trans mount was worn out and replaced which alleviated some of the issue.

 

The diff can be adjusted and was told incorrect drive angles so adjusted to: Trans tail app. 4 degrees down with pinion 4 up, parallel. Didn't improve the issue much.

AS is.JPG

The diff used to point down and actually seemed to work better, referred to as broken back angles. Driveshaft nearly level.

WAS.JPG

          The old angles are actually unknown but likely closer to 3 degrees as the driveshaft had more angle.

So question is, which is correct and or, which is best?



-- Edited by 1965CS on Tuesday 13th of June 2017 02:22:42 PM

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65 Custom Sport Convertible

Southern Alberta



Canadian Poncho Superstar!

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I would feel the exact same thing in my 67, but it was very slight. Most noticeable when easing off after giving it a good run up. It was a minor enough harmonic that I never tried to chase it. I assumed it was either a worn UJ, tailshaft bush or the angle setting.

You could buy a set of adjustable upper control arms, and start playing with incremental angle adjustments.

 



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67' Grande Parisienne. Ex Ottawa USSR Embassy car, 67- 68.
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Don't know if this any help as this is for chevelle and beaumont.
Where it refers to steps 3 & 4 I think they mean steps 4 & 5

proshaft1 001.jpg

proshaft 001.jpg



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Surrey, BC



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For fun, can you try two things?

Pull it down the highway, no driveshaft?

Try a completely different set of wheels and tires (that are known to be perfectly balanced)?

By doing that, you eliminate the driveshaft itself, and the wheels/tires.

I know some of you think I'm nuts but to me, eliminate the easy stuff first.

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Carl Stevenson wrote:

For fun, can you try two things?

Pull it down the highway, no driveshaft?

Try a completely different set of wheels and tires (that are known to be perfectly balanced)?

By doing that, you eliminate the driveshaft itself, and the wheels/tires.

I know some of you think I'm nuts but to me, eliminate the easy stuff first.


 GOOD IDEA CARL, ALSO CAN YOU REV THE ENGINE IN PARK TO 25 OR 3000 RPM AND FEEL THE VIBRATION?



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Fortunately I do have adjustable upper arms on the rear and can alter the angles, but so far unable to omit the problem. Basically, the methods indicated in that chart are what I have done so far using a digital gauge.  I suspect, and hope, it may be a lot of "trial and error" to find that perfect angle combo.  Read a lot about 3 degrees being the limit and between 1 and 2 is best .... currently having around 4, is that too much?

I haven't tried towing it at speed, but have had different wheels / tires with no change.  Interesting point about the RPMs as maybe it's actually the engine.



-- Edited by 1965CS on Wednesday 14th of June 2017 07:35:59 AM

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65 Custom Sport Convertible

Southern Alberta



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I had the same problem with my Nova. Remedied by installing wedges in the rear end mount to achieve correct angles front and back. You've done that by adjusting trailing arms, your driveshaft is balanced so it would appear your problem is ahead or in the rear. The way you describe it seems as though it should be a pinion angle problem though.

You mention this is your third rear end rebuild. The vibration and repeated failure may be caused by something back there.



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72 Nova SS,   66 Beaumont Sport Deluxe,   09 Pontiac Solstice GXP Coupe

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