July 19, 2019, 04:07:46 AM

Author Topic: vibration help needed  (Read 2437 times)

Offline AZieger

Re: vibration help needed
« Reply #15 on: April 24, 2019, 11:39:57 PM »
I'm running a DSS with the CV upfront and UJ on the rear. I agree it makes little sense, but seems to work OK. I seem to hit a resonance at around 150mph, but for only a very narrow speed range. If I cruise through it in 6th it's obvious, but full throttle in 5th and I don't tend to notice it. None of the drivetrain is mounted with NVH in mind, so it's hard to tell where some of the vibrations are coming from. I think I noticed a change depending on how tight I torqued the engine mounts in the early days.

I have the exact same setup, and I am having vibrations around 80-100+ mph with the Ronin 8.8 rear.  When viewed from the side, my U-joint angle at the diff is as close to zero as I could get it.  However, when viewed from below it is not.  Nor can it ever be, because the pinon center line is offset significantly toward the right side of the car due to the design of the differential case and the need for equal length axles.  So no matter what there will still be an angle at the differential U-joint.

I may be able to rotate the entire motor/trans to shift the tail housing to the right, but it's going to affect the shifter, the exhaust, and the trans mount at a minimum.  Even then the U-joint still won't be at a 0 angle.  I doubt I will be able to move the tail housing much more than 3/8" anyway.  I am starting to think the TR6060 is just not a good idea because it lacks a slip yolk.  If it had one you could use U-joints on both ends of the driveshaft and actually do proper complementary angles to cancel out the sinusoidal effects.

Offline Cobranut

Re: vibration help needed
« Reply #16 on: April 25, 2019, 03:46:30 AM »
I'm running a DSS with the CV upfront and UJ on the rear. I agree it makes little sense, but seems to work OK. I seem to hit a resonance at around 150mph, but for only a very narrow speed range. If I cruise through it in 6th it's obvious, but full throttle in 5th and I don't tend to notice it. None of the drivetrain is mounted with NVH in mind, so it's hard to tell where some of the vibrations are coming from. I think I noticed a change depending on how tight I torqued the engine mounts in the early days.

I have the exact same setup, and I am having vibrations around 80-100+ mph with the Ronin 8.8 rear.  When viewed from the side, my U-joint angle at the diff is as close to zero as I could get it.  However, when viewed from below it is not.  Nor can it ever be, because the pinon center line is offset significantly toward the right side of the car due to the design of the differential case and the need for equal length axles.  So no matter what there will still be an angle at the differential U-joint.

I may be able to rotate the entire motor/trans to shift the tail housing to the right, but it's going to affect the shifter, the exhaust, and the trans mount at a minimum.  Even then the U-joint still won't be at a 0 angle.  I doubt I will be able to move the tail housing much more than 3/8" anyway.  I am starting to think the TR6060 is just not a good idea because it lacks a slip yolk.  If it had one you could use U-joints on both ends of the driveshaft and actually do proper complementary angles to cancel out the sinusoidal effects.

You could have a DS built with CV joints on both ends, or alternately, use U-Joints on both ends with a slip joint in the center.
1995 FD, 7.0 Liter stroked LS3, T56, 8.8, Samberg kit.

Offline Supe

Re: vibration help needed
« Reply #17 on: April 25, 2019, 06:16:34 AM »
I'm running a DSS with the CV upfront and UJ on the rear. I agree it makes little sense, but seems to work OK. I seem to hit a resonance at around 150mph, but for only a very narrow speed range. If I cruise through it in 6th it's obvious, but full throttle in 5th and I don't tend to notice it. None of the drivetrain is mounted with NVH in mind, so it's hard to tell where some of the vibrations are coming from. I think I noticed a change depending on how tight I torqued the engine mounts in the early days.

I have the exact same setup, and I am having vibrations around 80-100+ mph with the Ronin 8.8 rear.  When viewed from the side, my U-joint angle at the diff is as close to zero as I could get it.  However, when viewed from below it is not.  Nor can it ever be, because the pinon center line is offset significantly toward the right side of the car due to the design of the differential case and the need for equal length axles.  So no matter what there will still be an angle at the differential U-joint.

I may be able to rotate the entire motor/trans to shift the tail housing to the right, but it's going to affect the shifter, the exhaust, and the trans mount at a minimum.  Even then the U-joint still won't be at a 0 angle.  I doubt I will be able to move the tail housing much more than 3/8" anyway.  I am starting to think the TR6060 is just not a good idea because it lacks a slip yolk.  If it had one you could use U-joints on both ends of the driveshaft and actually do proper complementary angles to cancel out the sinusoidal effects.

What is your trans tailshaft angle (up/down, not side to side)?  You may want to try shimming the pinion up.

Offline AZieger

Re: vibration help needed
« Reply #18 on: May 06, 2019, 11:57:39 PM »
I'm running a DSS with the CV upfront and UJ on the rear. I agree it makes little sense, but seems to work OK. I seem to hit a resonance at around 150mph, but for only a very narrow speed range. If I cruise through it in 6th it's obvious, but full throttle in 5th and I don't tend to notice it. None of the drivetrain is mounted with NVH in mind, so it's hard to tell where some of the vibrations are coming from. I think I noticed a change depending on how tight I torqued the engine mounts in the early days.

I have the exact same setup, and I am having vibrations around 80-100+ mph with the Ronin 8.8 rear.  When viewed from the side, my U-joint angle at the diff is as close to zero as I could get it.  However, when viewed from below it is not.  Nor can it ever be, because the pinon center line is offset significantly toward the right side of the car due to the design of the differential case and the need for equal length axles.  So no matter what there will still be an angle at the differential U-joint.

I may be able to rotate the entire motor/trans to shift the tail housing to the right, but it's going to affect the shifter, the exhaust, and the trans mount at a minimum.  Even then the U-joint still won't be at a 0 angle.  I doubt I will be able to move the tail housing much more than 3/8" anyway.  I am starting to think the TR6060 is just not a good idea because it lacks a slip yolk.  If it had one you could use U-joints on both ends of the driveshaft and actually do proper complementary angles to cancel out the sinusoidal effects.

You could have a DS built with CV joints on both ends, or alternately, use U-Joints on both ends with a slip joint in the center.

Is that possible?  I emailed DSS asking that very question, and they never responded.  Guess I need to call them.

From what I am able to measure, the side-view pinion to driveshaft angle is about 0.7 degrees, and probably increases a little with throttle as the front of the diff will tend to rise up (rubber mounts).  I added some 3/16Ē thick washers between the bushings and Ronin subframe mounts to lower the front of the diff, and now the angle is about -0.5 degrees and will get closer to 0 under load.  I will test and report back.

Offline Supe

Re: vibration help needed
« Reply #19 on: May 07, 2019, 08:35:38 AM »
But what is your tailshaft angle?  If your trans tailshaft is pointing down, you can get vibrations unless your pinion is pointing UP.  Shimming the nose of the pinion down is only going to put the u-joints further out of phase.  The tailshaft and pinion do not need to be in perfect alignment laterally provided they're both parallel to the centerline of the driveline (i.e. neither is pointing left or right).

Offline AZieger

Re: vibration help needed
« Reply #20 on: May 07, 2019, 11:44:34 AM »
But what is your tailshaft angle?  If your trans tailshaft is pointing down, you can get vibrations unless your pinion is pointing UP.  Shimming the nose of the pinion down is only going to put the u-joints further out of phase.  The tailshaft and pinion do not need to be in perfect alignment laterally provided they're both parallel to the centerline of the driveline (i.e. neither is pointing left or right).

I have a CV joint in front and a U Joint in rear.  So the equal and opposite angle idea goes out the window.  The best I can do is try to get the UJ angle to zero in both planes.  Yes I know people say this is ďbadĒ for the U joint (I disagree) but itís better than vibration!!

Offline MPbdy

Re: vibration help needed
« Reply #21 on: May 07, 2019, 03:17:51 PM »
I spent the time to plumb bob my driveline at the trans, diff, and the axles. With T squares I found the diff and trans werenít quite pointing at each other. It was a bit of a bitch and a half, but worth the time to do it. Things are smoother since I went through the exercise. I had to slot my trans mount about 3/8Ē to get them aligned.

Iíve had 6 or more different iterations of driveshafts through my car and each one of them has a vibration. I want to stab someone. Every time Iím told the shaft has been balanced I have a vibe, take it out (which is a shitty job dropping my exhaust) and have it rebalanced and it improves. Absolute jackassery from every driveshaft shop Iíve been to.

Iím trying to take my car to 200mph and I canít get the most simplistic thing worked out. Itís agonizing. Iíd pay stupid money for a driveshaft if I were guaranteed it wonít shake the car. I may make a move to a carbon shaft, but Iím not excited about forking out the dough without confidence itíll be fixed.

Thereís something about a v8 in an FD with the Samberg mounts that transmits a metric crapton of driveline vibration if things arenít perfect. Itís like the chassis is a tuning fork.

Offline Supe

Re: vibration help needed
« Reply #22 on: May 07, 2019, 03:23:45 PM »
As short as the driveshafts are in these cars, I wouldn't place an ounce of faith in a carbon shaft fixing the issue.

Offline AZieger

Re: vibration help needed
« Reply #23 on: May 11, 2019, 10:45:13 PM »
I was able to shim the front mounts of the diff to move it downward just the right amount to get the pinion to driveshaft angle exactly zero when viewed from the side. Previously it was close to 1 degree.  After a test drive I can confirm that it didnít help at all.

So I spent some time with lasers and strings to find the location of the crank pulley, tail housing, and pinion relative to the centerline of the chassis.  I found that the crank pulley (and therefore the engine as a whole) is offset toward the right side of the car by about 1/4Ē.  The tail housing is dead center.  The pinion is offset toward the right side by 9/16Ē as expected, since that is the known pinion offset of a Ford 8.8.

The driveshaft is roughly 34Ē long, so the 9/16Ē offset equates to 0.95 degrees at the u-joint.  This doesnít seem like it would be enough to cause the vibration I am feeling.  Even if I go through the effort of shifting the tail housing to the right, I donít think I would be able to move it more than 1/4Ē, which would align the engine with the chassis but would only decrease the angle to 0.53 degrees.

I am going to have the wheels and tires checked for balance.  One of them has an awful lot of weights on it, and I wouldnít put it past the tire shop to have screwed them up.

If that doesnít do it then I will try clocking the driveshaft 180 degrees (Iím using a pinion yoke).  If that fails then I guess I will try to have the driveshaft rebalanced.

Offline MPbdy

Re: vibration help needed
« Reply #24 on: May 12, 2019, 12:20:48 AM »
Have your tires road force balanced

Offline AZieger

Re: vibration help needed
« Reply #25 on: June 03, 2019, 02:31:28 PM »
Small update.

I had the tires road force balanced.  They were out, but not by much.  The tire techs thought it would solve my problem.  However I still have the vibration.  It seems better, but maybe I am just getting used to it. It definitely didn't go away.  Seems worse when everything is cold, on the first drive of the day.

As I drive the car more I have started to notice speeds at which the vibration peaks.  It seems most prevalent at ~55mph and 80+.  At 60-70 it is actually really smooth.  So there are harmonics at play here.  Curious if it is possible to use rubber bushings at the rear of the diff.

I can't see much out of my side view mirrors while cruising at 55 mph - the vibration is shaking the lenses and making everything blurry.  Annoying.

Offline AZieger

Re: vibration help needed
« Reply #26 on: July 17, 2019, 04:33:06 PM »
Good news!  Mine is FIXED.  All it took was indexing the driveshaft.  I have a pinion yoke so I had to index it 180 degrees, but I'll be damned it worked like a charm.  I can now look into my side view mirrors at 55mph and actually see something.  Cabin "boom" is 90% gone now too.  I was skeptical that indexing would help, but it took all of 15 minutes and problem solved.  Stoked!