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Discussion Starter · #1,721 · (Edited)
One-Piece Driveshaft:
The slope of the transmission output shaft and pinion shaft should be in the same direction. They should also be within ½° of each other to avoid driveline vibration.

Most driveline companies recommend operating angles of 3° or less for maximum u-joint life. There should be a minimum of ½° to allow the needles to rotate. The higher the operating angle, the more likely your vehicle will develop a vibration at high driveshaft speeds. The lower the angle, the lower the chance of vibration at high driveshaft speeds.

Might need to shim the rear transmission support mount?
The driveline (trans and diff) is mounted in factory mounts in factory locations and factory orientation and the driveshaft is now a one-piece. I doubt that the factory layout requires special mount modifications….. that aren’t already known about when swapping these shafts.
Maybe explain the thinking further?

i had a tyre not seated properly and i couldnt tell at all when driving (was rear rhs ) but soon as i went on dyno (rolling dyno) it shook the whole car so bad it couldnt do a proper run
I found that my local HF has their bubble balancer on a big sale so I picked one up.
I dismounted the tire and first, cleaned off all the Sticky Tack. I then rotated it 180*, very carefully mounted the bead-lock ring. I then lubed the rear bead seat (Simple Green was handy) and set the wheel over a bucket which allowed the back of the tire to hang freely, I made certain that the tire was in no bind at all and was situated as neutrally as possible. Then I aired it up to seat it.
On the bubble balancer it now takes FIVE ounces to center the bubble, not ten. The weight is needed at the same location relative to the tire
In the morning I’ll see how round it is, now.

There are two distinct vibrations in the in car: one is the diff, which i have been calling out ever since I installed it, but I didn’t want to believe it. I have now proven that it is the cause of a prop-shaft speed buzz that shows up at eighty and increases to a loud HUMMMMM at a hundred.
Tomorrow I may reinstall my old diff which put new bearings in last year.
The second vibe (really bad above 100) is clearly this wheel/tire.
I’ll know more tomorrow.
BtW: that Sticky Tack is damned sticky… and I don’t have a tire machine.
Gas Font Machine Handwriting Publication

Blue Automotive tire Tread Tire Musical instrument

Tire Wheel Automotive tire Locking hubs Tread

Tire Wheel Automotive tire Locking hubs Synthetic rubber
 

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Fun pedal, Few doors
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Discussion Starter · #1,722 ·
Well, color me surprised! After the meticulous remount (and I think not using Sticky Tack) the wheel assembly needs FIVE ounces to bubble balance (not 10.25) AND using my most sophisticated runout gauge, the tire shows Zero out-of-round.
Tire Wheel Automotive tire Motor vehicle Light

Tire Wheel Automotive tire Locking hubs Tread

Tire Wheel Automotive tire Locking hubs Synthetic rubber

Hot DAMN, Sam!
Real progress.
It is POURing rain today so there will be no DRs tested today but I’m very convinced that this will be much much better.
Now to address the other vibe…
I need to complete reassembly of my old diff and reinstall it.
I had replaced it due to whining; new diff was a trade off of vibration instead of whine.
Orig diff had toasted lube, roasted bearings and damaged gear teeth. I replaced the bearings for a future re-use just to see how whiney it would be.
Now I will find out if refreshing one of these has any value.
 

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2011 CTSV Coupe M BLK LSX376-B15
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The driveline (trans and diff) is mounted in factory mounts in factory locations and factory orientation and the driveshaft is now a one-piece. I doubt that the factory layout requires special mount modifications….. that aren’t already known about when swapping these shafts.
Maybe explain the thinking further?



I found that my local HF has their bubble balancer on a big sale so I picked one up.
I dismounted the tire and first, cleaned off all the Sticky Tack. I then rotated it 180*, very carefully mounted the bead-lock ring. I then lubed the rear bead seat (Simple Green was handy) and set the wheel over a bucket which allowed the back of the tire to hang freely, I made certain that the tire was in no bind at all and was situated as neutrally as possible. Then I aired it up to seat it.
On the bubble balancer it now takes FIVE ounces to center the bubble, not ten. The weight is needed at the same location relative to the tire
In the morning I’ll see how round it is, now.

There are two distinct vibrations in the in car: one is the diff, which i have been calling out ever since I installed it, but I didn’t want to believe it. I have now proven that it is the cause of a prop-shaft speed buzz that shows up at eighty and increases to a loud HUMMMMM at a hundred.
Tomorrow I may reinstall my old diff which put new bearings in last year.
The second vibe (really bad above 100) is clearly this wheel/tire.
I’ll know more tomorrow.
BtW: that Sticky Tack is damned sticky… and I don’t have a tire machine.
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The factory does shim when needed. I'm sure you already understand. If you don't think it's important enough, and a waste of time to take some very easy measurements, then don't.
 

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Discussion Starter · #1,724 · (Edited)
A significant update, I think.
I’ve not driven on the Drag Radials due to wet roads but the measurable changes to the tire/wheel assembly in balance and runout have me feeling that the tire shake issue is likely solved.
After refreshing my old diff and swapping out the ‘new’ replacement diff, I have 1.cured the 80mph buzz, and proven that it WAS the differential that was causing it.
2. The biggest win today is discovering that after new bearings and seals, my original rear end which I replaced because it whined (howled actually) is now (drum roll) quiet as a church mouse.
Yes, it still has its original gear set which had been run many miles with bad bearings and misalignment and had gear face damage… And now… no noise. In fact, it is actually QUIETER than the new replacement diff.
The replacement is still in warranty, but not available, so they’re going to refund me!
Something is going my way!

Also, my daughter surprised me with a custom addition under hood. I love it!
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Excellent Mr. S! Now hammer down to Cadillac Town!
 
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Discussion Starter · #1,727 · (Edited)
The factory does shim when needed. I'm sure you already understand. If you don't think it's important enough, and a waste of time to take some very easy measurements, then don't.
When the drive shaft was out, I threw an angle finder at it and while the car is on my two-post lift, it (edit) does not sit "level" (unless I go to lengths to arrange it) but the diff and trans flanges showed to be parallel or within a tiny variance of it.
 

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Safe travels! Does anybody know if there is a live feed of the event?
 

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Good luck and safe travels surly
 

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Discussion Starter · #1,739 ·
got to the track too late for track rental but got parked. Talked to Cal Hartline and a few others.
It’s gonna be great!
Got to the Rock and Brew..
shared a table with Chris and Ryan from Lingenfelter. Great guys, great times were had!
 
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