Low Freq Body Vibration...Ideas?

[Airratchet]

Hi all, Posting is new to me so please bear with me. I have a 70 Bronco with a 2-inch suspension lift from Wild Horses…springs, bushings etc. I have a low frequency body shake starting around 52mph, peaks at 58mph and starts to taper off around 62 mph (accelerating and decelerating). I have not been able to isolate it between the front or rear of the vehicle. There is a very noticeable movement between the dash and roll bar during the peak. I have done the following without a significant change (parts were swapped out one piece at a time): swapped front axle assembly, swapped rear axle assembly, replaced the track bar with a BC Bronco’s heim joint unit (it re-centered the front end very nicely), rear spring packs (with stock units), front coils (with stock units), C bushings (tried 2 & 4 degree), balanced the rear drive shaft, replaced all suspension bushings. I have owned this Bronco for six years. I did most of the work on it the first few months I owned it. Unfortunately I did not drive it long enough before modifying it to know if this was an existing problem but if it was there it must have been much milder. I do have one small note about the original setup. The original Dana 30 was extremely toe’ed in (but drove fine). We found this out when my friend used this axle, without adjusting the toe'in, and experienced the Bronco 'death wobble'. I am beginning to wonder if this was a clue pointing toward a warped frame? I am considering a new frame next if I don’t come up with a solution to the problem, though I would be very disappointed if the problem was still there after replacing the frame. Is there a legitimate way to have the frame checked? Are there any other parts options I have missed? Any suggestions are appreciated…thanks for the help!

 

[trailpsycho]

Not trying to be a smart-a$$ or anything, but you have had the tires rotated and balanced at a good shop??? Right? A good shop can also check if you have a problem rim as well. The most common cause for any vibration in the drivetrain at specific speeds (especially highway) is an un-balance tire/wheel or multiple tires/wheels, it comes in at a certain speed and goes away above a certain speed (usually with 3-7 mph window). The death wobble would occur at lower speeds 15-30 mph and is typically a result of worn C-bushings. If you can borrow a set of rims and tires, try it and see if the problem persists. A rotation and balance should only run you $20-30 if you dont have a lifetime deal from wherever you bought your tires...even so you may wan to go somewhere else (apparently). Your frame will not cause the vehicle to vibrate at a particular speed, it just may track crooked or cause things to wear prematurely. Best of luck; let us know what you find out. Oh yeah, Welcome to the forum. This is the best site on the web for EBs.

 

[broncnaz]

I vote on the tires also since you had toe set to much the tires could be worn and are causing your vibration. Just had a similar problem on my 03 ranger ran the tires to long before rotating them and now have a similar vibration the tire shop told be they were worn but the balance was fine crossed the tires to help the wear pattern now just waiting for the vibration to go away it has shortened up a bit.

 

[Airratchet]

Sorry left that part out...I swapped out a completely different set of wheels and tires...no change.

 

[RangerRob]

Have you checked your pinion angle? Take a look at this link:

http://classicbroncos.com/pinion_angle.shtml

Good Luck!!!

 

[jeffdukovac]

I had a similar vibration, it was the rear t-case output yolk nut that was loose.
Rebalanced the tires, rotated,..... tightened the nut and no more vibration.

Jeff

 

[Airratchet]

Thanks for the ideas everyone...I have adjusted the pinion angle from 0 deg to 7 deg...one degree at a time I had access to a mill and a lot of aluminum at work to make shims and decided that about 1.5 to 2 deg worked best for elimanating high freq vibration produced by the rear drive shaft. I have had the rear T-case yoke off a couple of times to change out the rear seal (can't seem to get that one to stop leaking) but even if it was a lose yoke I would think it would be more along the lines of a high freq drive line vibration if that was a problem....but I will check it again.

This is all good it let's me know I have been looking at the right things.

 

[DonsBolt]

Have you taken it to a allignment shop??

If not put it on a allignment machine and see if it is tracking straight and that both axles are in line with each other. A good body shop can put it on a frame machine and check the frame for you.

Also check out the exhaust, I know it sounds crazy but on my Lightning I had a very similar problem, and it turned out my vibrations were comming from the exhaust system. In that case the vibration would come in at around 60 mph and was gone when I got to 70 mph. What we had to do was bring the truck up to full temp, loosen the exhaust and then retighten everything, and then add some weights to stop the exhaust from shaking.

I have since totally replaced the exhaust and don't need the counter weights any more. If you look at this picture you can see one of the counter weights on the exhaust.

 

[Skiddy]

Have you taken it to a allignment shop??


Also check out the exhaust, I know it sounds crazy but on my Lightning I had a very similar problem, and it turned out my vibrations were comming from the exhaust system. In that case the vibration would come in at around 60 mph and was gone when I got to 70 mph. What we had to do was bring the truck up to full temp, loosen the exhaust and then retighten everything, and then add some weights to stop the exhaust from shaking.

That is the exact same thing that happend to 76 explorer's (a member here) bronco, a good thing to check out.

 

[Airratchet]

Hi all,

I did another tire/wheel swap this weekend and I did get some changes. The problem did not go completely away but it shifted up a few miles per hour now its 60 to 65 and MUCH milder. I swapped back my old wheels two at a time to the front end and there was an immediate return to the old level of vibration with each pair. Perhaps there is a tire/wheel correlation that I missed with the first round of tire/wheel swaps (or perhaps they had a similar issue but the Bronco they were on drove fine). As per your advice I am going to try a NEW alignment shop but it will be a week or so. I will update as I get information, again.... thanks all.

 

[Airratchet]

Hi All,
It's been a while but I did some experimenting with wheels and tires...here is my follow-up: with the input from several comments I went to another tire shop and had my wheels and tires balanced on a "road load' balancing machine. They said two of my wheels were out of tolerance and two of my tires. I sat down with this information and went thru the history of wheel tire interchanges and this is what I came up with...

1) Original purchase of truck...stock wheels, stock tires...didn't notice any out of the ordinary vibration (did notice excessive tow in adjustment).
2) Did all kinds of work on the truck...changes out to a set of stock late model Bronco wheels used two 31x10.5's that I had from another truck and purchased 2 new 31x10.5's...started driving truck noted vibration.
3) Changed to a set of used aluminum wheels with same tires...vibration might have increased but not much.
4) Had wheels/tires balanced with road force machine...showed problems with wheels and tires and made vibration worse.
5) Swapped out with a set of badly worn stock wheels and tires from another truck. All vibration gone....
6) Put a brand new set of 32x11.5 tires on the stock wheels from step 5) and vibration was back but very mild and narrower speed range.
7) Went back to the shop and watched them rebalance the new tires using the road force machine (all the wheels were out according to the machine and once they were done the machine said everything was beautiful).

Results: Truck still vibrates between 58 and 62mph...only time it doesn't seems to be with stock size tires installed. Is there a chance that this is a frame issue that is only evident with the stresses of a larger tire?

Any more thoughts?

Thanks

 

[Pa PITT]

tire problem

i work for chrysler ...and at work we have a problem with some 4x4 started in 2004 ...viberation at 55 to 60 mph ..i'll tell the things we've done .....
pinion angle a couple of times but we never got to 7 degree we stayed under 5degree....
we have a shop foreman that puts the truck... only 4x4 trucks ...on our rack that will pick both ends up at once at road highth.... he run the truck at all spped feeling of viberation ...then he starts to "clock the driveshaft ""
turing the u joint frist ...to all positions ...1st the front drive shaft then the rear shaft ...if this doesnt do anything then ...he starts over he pulls each shaft and trys to move it one "spline at a time and drives it on the rack thru the viberation area.... this is very time consuming ...but he trys hard to fix their shake ..people who have never pulled a drive shaft just "bitch" about how long it taking we spend sometimes 3 days driving and turning the shafts ..
....after no sweet spot is found we order a new drive shaft for either the front of rear .and start over turning and checking ...we have ordered 3 front shafts for one truck ....american axle sucks...they no longer have dana axle ...
you might send your shafts out and have them balanced it sound like you'll spend the dollar to try anything....
i sure dont think it's the frame but if i wasn't sure ..i'd take it to a good body shop ...the guys in our body shop have told me that they can get a frame straighter than it was when new ...so it can be checked but it aint the frame ...dont throw that money away....
we also have that road force balance machine ...for those of you who dont know what we're talking about it a balance machine that ..spins the tire with a force pushing against the tire to simulate the road force it can tell if it's the wheel or the tire that is the problem.....other dodge shops replaced the transfer cases and axle ass.front and rear but we've not seem any of these that this helped
past this.. keep us informed... this could be helpful if and when you figure it out ....dont give up i've got a 200 6cyl overheating i've been asking questions about for 2 years now still overheating but lot of good help form several sights ...
hope that helped any .....PaPitt.............

 

[bronco977]

I had the same problem with my '70. I tried everything, including new wheels. After installing a Duff's Ultimate suspension it still vibrated. I finally rebuilt the rear driveshaft, including the carden joint. THAT finally fixed it!

 

[Flash69]

It sounds like you have checked about everything. Have you checked your axles? Spindles? If they was warped a little you would get a viberation. That is about the only thing i see that you havnt mentioned or i didnt see it mentioned.

 

[Tapp Daddy]

What kind of wheels are you running? There are some special lugs you can use to help center aftermarket wheels. Stock wheels are the only ones that are hub centric. Also, drums can be un=balanced. Just a couple of thoughts.

 

[Airratchet]

Just to kinda review earlier stuff...I have done the following:

I have two Broncos so with that said....

1) I have swapped out the front and rear end assemblies one at a time.
2) I have swapped out suspension with stock componanets first the rear then the front.
3) I have recentered the front end after the 2 inch lift with a hiem joint track bar from BCbroncos.
4) I have not swapped out the rear drive shaft but it was balanced with all new u-joints (plus it doesn't feel like a drive shaft vibration much lower frequency...its more like a harmonic set up wobble all over).
5) This truck was originally a manual trans...I swapped in all 75 Bronco original auto-trans stuff.
6) I have re-shimmed the rear end with pinion angles from 0 to 6 deg only noticed changes in drive shaft vibration not this speed induced vibration.

Current config: 1.5 deg pinion angle, 2 inch WH lift with 10 leaf rears, big bearing rear with stock drums, f150 disks and knuckles with tie rod over conversion, Heim Joint track bar, stock late model bronco 15" wheels with new 32x11.5 BFG AT KO...

Only things that seem to change the vibration intensity or frequency...changing tires/wheels and when I went from a four point role bar to a six point...thats why I start thinking its a harmonic thing with the frame/forces on the front end issue? Why would a roll bar change anything...could body mounts do something like this...they look alright? Right now its very mild perhaps some people wouldn't notice it. I am very anal to say the least and something like this just bugs me to death :'( I don't much care how it looks but mechanically it has to be right...this vibration/wobble says something aint right!

I will keep at it....I appreciate the inputs....

 

[eds66bronco]

changing the stiffness of the body by adding a stiffer cage makes sense from an overall harmonic vibration sense. a few things i've noticed over the years that have given me greif were worn shocks (intermittent vibes between 55-65) loose output yolk on transfer case, thrown balance weight on rear brake drum. they all felt about the same as you have described. it makes it worse when everything on the truck is tight and running well.. all you can focus on is the one little thing that bugs you. thats why i let a couple of things go bad at once and play the radio real loud ;D