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Topic: Highway speed vibration, worse on deceleration (Read 4931 times) previous topic - next topic

Highway speed vibration, worse on deceleration

Reply #15 –
You work in a Ford dealership.  Ford dealership service departments are required by warranty to have a tire balancer that measures roadforce.  Measure roadforce.

Highway speed vibration, worse on deceleration

Reply #16 –
If you have another set of wheels, ideally heavy ones. It should shift the vibration down in speed.

Highway speed vibration, worse on deceleration

Reply #17 –
If the vibration is due to a tire or wheel issue.

83 351W TKO'd T-Bird on the bottle


93 331 Mustang Coupe - 368 rwhp
 

Highway speed vibration, worse on deceleration

Reply #18 –
Quote from: Aerocoupe;463255
If the vibration is due to a tire or wheel issue.


No, if you change the total rotating inertia of the rotating system that he resonant frequency will shift accordingly.

I am not saying imbalance, I am saying the system. You treat it like a series of rotating masses on a shaft, and the system resonances respond accordingly to the excitation all other things being equal.

Highway speed vibration, worse on deceleration

Reply #19 –
I saw your reply in the email on my phone and was confused but when I logged in I saw my mistake. What I wrote was supposed to be a question not a statement (? not a .) so thanks for the clarification on that and I do agree with what you are saying.

I will say that the only things that affect the critical speed of a driveshaft are length, material(s) it is made of, and diameter.  To fix a critical speed issue with the DS the only way is to alter one or more of those three things.

I also found another pretty good read here:

http://www.machineservice.com/technical-101/vibrational-issues/

83 351W TKO'd T-Bird on the bottle


93 331 Mustang Coupe - 368 rwhp

Highway speed vibration, worse on deceleration

Reply #20 –
Quote from: Aerocoupe;463319
I saw your reply in the email on my phone and was confused but when I logged in I saw my mistake. What I wrote was supposed to be a question not a statement (? not a .) so thanks for the clarification on that and I do agree with what you are saying.

I will say that the only things that affect the critical speed of a driveshaft are length, material(s) it is made of, and diameter.  To fix a critical speed issue with the DS the only way is to alter one or more of those three things.

I also found another pretty good read here:

http://www.machineservice.com/technical-101/vibrational-issues/


In industry, we use a torsional damper that you place part way down the length of the shaft. It basically shifts the resonance out of the speed range at the cost of added rotating mass. You couldn’t do that in a garage obviously without a lucky guess or trial and error.

Years ago we explored whether material really matters (as much as people believe) as stiffness is easier to alter. A steel shaft at 3.5” and the wall thickness of the AL will have quite the resonant frequency for instance.

Highway speed vibration, worse on deceleration

Reply #21 –
shop manual troubleshooting step for either confirming, or determining if the DS is the culpurt.

mark the DS near where the weights are at the 12, 3, 6 & 9 o'clock positions.

install a hose clamp around the ds while positioning the buckle to the 12 o'clock location.

drive car and observe symtom got worse or better.

rotate the hose clamp to the remaining 3 locations.

rotate accordingly as desired the hose clamp to the location that now removes or reduces the vibration.


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Apparently, the shop manual implies that if a remedy is reached, the hose clamp is then tightened down and kept in place, customer work order is completed.

This is easy and you should be able to have this small test wrapped up in one round trip test hit
not all hose clamps are designed equally so you can manipulate the weight felt on the DS by selecting one with a different amount of steel or bolt size to retest just in case you think the first hose clamp may have been too heavyl

Highway speed vibration, worse on deceleration

Reply #22 –
Quote from: TheFoeYouKnow;463190
You work in a Ford dealership.  Ford dealership service departments are required by warranty to have a tire balancer that measures roadforce.  Measure roadforce.


Good suggestion as that can be overlooked, but we have road force balanced my tires and rims.  Roadforce is well below spec so no problem there.  Thanks!
88 XR7 5.0L low mileage Florida Cat.  AOD, 8.8, headers with x-pipe and flowmaster cat-back, 3.73's, lowered 1".  1 of 421 according to Marti Report.

[SIGPIC][/SIGPIC]

Highway speed vibration, worse on deceleration

Reply #23 –
Quote from: jcassity;463368
shop manual troubleshooting step for either confirming, or determining if the DS is the culpurt.

mark the DS near where the weights are at the 12, 3, 6 & 9 o'clock positions.

install a hose clamp around the ds while positioning the buckle to the 12 o'clock location.

drive car and observe symtom got worse or better.

rotate the hose clamp to the remaining 3 locations.

rotate accordingly as desired the hose clamp to the location that now removes or reduces the vibration.


---------------------
Apparently, the shop manual implies that if a remedy is reached, the hose clamp is then tightened down and kept in place, customer work order is completed.

This is easy and you should be able to have this small test wrapped up in one round trip test hit
not all hose clamps are designed equally so you can manipulate the weight felt on the DS by selecting one with a different amount of steel or bolt size to retest just in case you think the first hose clamp may have been too heavyl

I guess I should try this method with a hose clamp before spending a lot of money on a custom made DS as it won't cost a lot other than my time spent.  It's just I've seen so many on this forum say they've done the same 3.73 mod that I have done and they've sent their DS out for balancing and this doesn't fix their vibration problem.  I've probably seen at least a half dozen on this forum who have had no luck balancing the original steel shaft so I guess this put me off spending time and effort and money into trying to fix something that probably isn't fixable.  Doesn't hurt to try though, so I think I'll go through the motions.  :D
88 XR7 5.0L low mileage Florida Cat.  AOD, 8.8, headers with x-pipe and flowmaster cat-back, 3.73's, lowered 1".  1 of 421 according to Marti Report.

[SIGPIC][/SIGPIC]

Highway speed vibration, worse on deceleration

Reply #24 –
Had car up on hoist after work today and noticed a small dent in my DS, about the size of a dime and about 1/8" deep.  Would this affect the balance of said DS?
88 XR7 5.0L low mileage Florida Cat.  AOD, 8.8, headers with x-pipe and flowmaster cat-back, 3.73's, lowered 1".  1 of 421 according to Marti Report.

[SIGPIC][/SIGPIC]

Highway speed vibration, worse on deceleration

Reply #25 –
if you have a magnetic base dial indicator .............
-locate dent
-position magnetic base dial indicator to the floor pan of the car
-clean off until smooth with emory cloth the drive shaft all the way around "next to the dent.
-position / set up dial indicator to where its touching the ds.
-zero out the dial indicator guage.
-i think you can turn one of your wheels to get the ds to rotate
-dospoogeent the amount of thousands of an inch out of round.
-wash/rense/repeat in the dead center of the ds.
-with the two values you can on grid paper dospoogeent the arch of bend "if" the ds is bent and where the arch is.
-obviously a bend in the middle would be absolute worse case vibration symtom but... the closer to the rear diff the worse as well from what i am told.


If you dont have a magnetic dial indicator.......
-locate dent
-tie thread to one ujoint retainer clip to one end of the DS.
-scotch brite the length of the ds  you plan to pull the string across.. any debris will screw up your measurement
-pull string to an 'equal plane" location on the other end of the ds then wrap string and sinch tight.
-using a machinist ruler, measure the ds depth from the ds surface to the string.

Highway speed vibration, worse on deceleration

Reply #26 –
maybe we should do a CSI investigation into if the DS for a 3.73 is a different weight set / design than those cars with other rear ratios?

Highway speed vibration, worse on deceleration

Reply #27 –
Quote from: AT8 Cat;463390
Had car up on hoist after work today and noticed a small dent in my DS, about the size of a dime and about 1/8" deep.  Would this affect the balance of said DS?

considering it would take a really good hard hit to make that dent,.........
you may have the ds slightly bent.
if the ds is not bent but the metal is bent inwards,, it represents a value of ounces.
its relocating these ounces closer to the center line of the ds which is centrifically tied to the exterior oem tac welded counter weights.
I would speculate that if simply dented but your ds is not bent, the problem would be more on the minor side, hard to see on a balancer and somewhat moot.

if the dent has bent the ds.... welp,, you just found your problem.

go find yourself a chunk of 1/8'' thick steel.

lay it down on a rubber mud flap or something that gives,, maybe cork board (simulating the air gap inside your ds.
hit it the 1/8'' s steel with a ball pin hammer as hard as you can swing.
you would be hard pressed to with one swing move that amount of metal 1/8'' deep!!!!!!  Im being serious

thats what  happened to your ds at some point


within the location of this dent, can you detect any of your floor pan areas showing damage ?

Highway speed vibration, worse on deceleration

Reply #28 –
someone mentioned clocking the ds by re-connecting it to the rear diff 90deg or 180deg from where it is now.
clocking ds's that telescope and have a knuckle and more than two ujoints like in my bronco or those with a carrier bearing , this is improtant.  Normally no clocking needed on a two ujoint single pipe DS like on our cars.

our ds's are three piece.  Ive worked on equipment with 8 pieces to make up the DS assembly and usually there are arrows welded or stamped or some sort of indicator to assist the tech in getting the telescoping spline setup to the orientation of the remaining two ends for ujoint and yokes at either end.  Still yet the final front and rear connections better have been marked before the DS assembly came down or its going to be trial and error getting rid of the vibration.

Highway speed vibration, worse on deceleration

Reply #29 –
by the way everyone................

inside the tail shaft housing,, inside the transmission of an AOD.. isnt that big hunk of metal clamped on the output shaft a counter weight?