Vibration Chasing
#2815524
08/31/20 01:58 PM
08/31/20 01:58 PM
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Joined: Mar 2005
Posts: 403 Colorado front range
BcudaChris
OP
mopar
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OP
mopar
Joined: Mar 2005
Posts: 403
Colorado front range
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Hey guys, Working on my '73 Barracuda. It has been through a re-power (LA to stroker Magnum), front end resto-mod, subframe connector/torque boxes welded in and a custom drive shaft. Brakes have been completely rebuilt with modern friction materials and new rotors/drums/front bearings, wheel cylinders and rebuilt slider calipers and they perform flawlessly. 3.55 8.75" with old school XHD MP leaf springs (Made in USA) with good bushings. 3.55SG with cones machined and all new axle bearings (standard outers) done 5 yrs/12K miles ago, endplay corrected in other vibration chasing. I have got this thing as dialed in as I can, no binding in the suspension, solid alignment, nothing moving in any way that it shouldn't. Handles very well on the street. I had the chassis shop that did the SFC's and torque boxes check the body it for square and make sure everything was in spec dimensionally (with the improved K-frame installed) and was told it is good to go. I'm down to a vibration that the car has always had (I've owned it since 1988, bone stock when purchased) that comes in at around 65MPH, gets worse until around 75 and remains minimal but constant as fast as I go, and goes away completely when I decel below 65. These speeds are on smooth highway. If I'm on bumpier roads the onset speed is lower, but everything else is the same. The vibration I believe to be drive-train independent as it is present regardless of gear. I've had 3.23, 3.55 and 3.91's over the years with the same vibration pattern at the same speed. One other observation that is hard to explain, but I'll try is that the vibration escalates in intensity and settles down, then de-escalates and mirrors the behavior on decel through the speed range. Always. It doesn't just start and stop. Any ideas on the brain trust on this one? Monday car Thanks Chris
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Re: Vibration Chasing
[Re: BcudaChris]
#2815565
08/31/20 03:30 PM
08/31/20 03:30 PM
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Joined: Dec 2003
Posts: 22,728 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,728
Bitopia
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"I've had 3.23, 3.55 and 3.91's over the years with the same vibration pattern at the same speed"
Engine or Vehicle speed?
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Vibration Chasing
[Re: BcudaChris]
#2815587
08/31/20 04:15 PM
08/31/20 04:15 PM
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Joined: Dec 2003
Posts: 22,728 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,728
Bitopia
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Well that should eliminate a lot of possibilities. Ever check for a bent rear axle/flange/wheel?
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Vibration Chasing
[Re: jcc]
#2815604
08/31/20 05:16 PM
08/31/20 05:16 PM
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Joined: Mar 2005
Posts: 403 Colorado front range
BcudaChris
OP
mopar
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OP
mopar
Joined: Mar 2005
Posts: 403
Colorado front range
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Not specifically, but I have been in there on both sides chasing an oil leak, doing brakes, etc. and didn't notice anything. Wheels all bolt up nicely and everything spins nicely with no inappropriate drag or anything.
That reminds me though, when I put the 3.55 R&P in (dropping from a 3.91 may have been the event that made me realize I had grown older), I had a shop machine the SG cones, replace the bearings in the chunk and outer axles. One of my axles suffered a shop accident and the guy got me a proper length/spline, etc. axle of unknown provenance.
The way it worked out, the other axle was installed and I just took the guy's word that the provided one would work, I just picked it up after work one evening, slammed it home, set the endplay and went driving. I've never looked at the axles side by side thinking about it. I suppose some are heavier than others too. How much bend would an axle need to cause a problem? I did sight it and eyeball the splines before I had him put the bearing on. Also, would excessively worn axle or carrier splines cause such a vibration?
A further detail I neglected to provide, the vibration seems to be in the front end. The front clip does a dance in the worst of the vibration.
Last edited by BcudaChris; 08/31/20 05:25 PM. Reason: add detail
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Re: Vibration Chasing
[Re: BcudaChris]
#2815704
08/31/20 10:40 PM
08/31/20 10:40 PM
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Joined: Aug 2003
Posts: 43,303 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,303
Bend,OR USA
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Last edited by Cab_Burge; 08/31/20 10:41 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Vibration Chasing
[Re: BcudaChris]
#2823473
09/21/20 10:31 PM
09/21/20 10:31 PM
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65hemis/s
Unregistered
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65hemis/s
Unregistered
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You changed gears, but have always had the same axles? Maybe try a dial indicator on the rear axle flanges.
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Re: Vibration Chasing
[Re: ek3]
#2851603
11/25/20 09:57 PM
11/25/20 09:57 PM
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Joined: Dec 2014
Posts: 5,947 ohio
ruderunner
master
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master
Joined: Dec 2014
Posts: 5,947
ohio
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What wheels are you running?
Angry white pureblood male
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Re: Vibration Chasing
[Re: BDW]
#2852680
11/28/20 07:35 PM
11/28/20 07:35 PM
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Joined: Mar 2005
Posts: 403 Colorado front range
BcudaChris
OP
mopar
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OP
mopar
Joined: Mar 2005
Posts: 403
Colorado front range
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Hey guys, thanks for keeping this up on the list. Sorry for the delay in updates. I've been giving little attention to the interwebs of late.
I put it on stands and ran it through the vibration speed range, no vibe. To me, that isolated things to the front. I checked every pivot, attachment point, mount point and all tight.
Wheel and tire package is 235/65-15s (Firestone Firehawk Indy 500 (their take on BFG T/A) on 15x7 cop wheels. The tires are from like 2009, but in great condition with low miles. Few places around here will touch them except to remove them.
Anyhow, I called the shop that got my alignment dialed for me with the adj strut rods and other tweaks and was bending the guy's ear about it. He has the gear to balance the tires on the car, and invited me back to visit his establishment. Interesting process if you haven't seen it and actually took care of it, though I'm not convinced it didn't just cover something else up. When I commented as such, the guy who did the work said that it was covering up old tire carcasses.
I'll be committing on a brake/wheel combo before long and there is much more available in 17. I guess I shouldn't be surprised that it is from the only wear items on the car that aren't actually new at this point.
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Re: Vibration Chasing
[Re: BcudaChris]
#2867217
12/31/20 10:21 PM
12/31/20 10:21 PM
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Joined: Jan 2003
Posts: 5,791 Hamilton, Ontario Canada
Magnum
master
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master
Joined: Jan 2003
Posts: 5,791
Hamilton, Ontario Canada
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The test on stands does not rule out out of round wheels/tires or axle flange runout.
A balanced tire can still shake a car. It may be out of round or have a sidewall problem but still balances zero.
Cab mentioned checking for runout. Was that done?
69 Super Bee, 93 Mustang LX, 04 Allure Super
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