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  #1  
Old 07-20-2002, 10:38 PM
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Default Vibration at 65 mph

Does anyone remember what the rule is about a vibration that is speed related? I have a vibration that seems to follow through the car making the hood shake and seats shake but not seriously in the steering wheel. It is more pronounced through the body and the hood really shakes at 65 mph. I tried different rear wheels, giving the driveshaft a half a turn, (its been balanced already), different brake drums. I noticed the vibration was at about 3700 rpm in 3rd gear so then I slowed down and shifted into 2nd gear and brought the revs back up to 3700 again and there was no vibration. I left it in 2nd and ran it up to 65 mph and there it was again! When the car is jacked up on stands and run up to 65 mph, I noticed the pass. side tire had a little bounce to it but the hood was not shaking and the vibration wasn't unbearable. It couldn't be the front tires that are the problem,is it? The steering wheel doesn't seem to shake. The same vibration was there with 2 different sets of rear wheels and after trying the driveshaft in different degrees of rotation. Got any ideas, this is nuts!
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  #2  
Old 07-20-2002, 10:49 PM
mtrv8n mtrv8n is offline
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I've always had a vibe at 3200-3800-- rpm in my cuda, much more pronounced at 60-70mph than any other speed, with it's original 340 and now the 360, I've balanced everything in sight, and all I can figure is that it's some vehicle dynamic with the small block hitting it's powerband. The torque strap made it worse, so I put some poly bushings around it.

I'd like to know the answer to this too, if there is one.
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Old 07-20-2002, 11:08 PM
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Default bad vibes

I know you had the drive shaft balanced . Howerver if it had been droped or has any sign of a dent in it .Or perhaps one of the weights fell off. Either way , If you could get another or maybe borrow one from a friend it may be worth a shot. After all that you have tried that is where I would look. Remember the drive shaft isn`t much more then exhaust pipe. Its amazing they stay together as it is. I woud also look in to the wheel balance on the rear that has the wobel.
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Old 07-20-2002, 11:19 PM
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You could also be looking at a problem with the bearings on the axle shaft or the pinion. That's where I would start looking.
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Old 07-20-2002, 11:21 PM
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Default Vibration?

Assuming the driveshaft and tires are balanced properly, it sounds like you have a tire out of round.
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  #6  
Old 07-20-2002, 11:37 PM
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Since you've already tried different wheels and tires, you can probably rule those out.

Ed could be on the right track, something in the diff.

Sometimes a loose pinion brg will cause a shake, but usually it's more noticable under load, and appears at lower speed.

Run it on stands, and see what wobbles. Maybe you've got a bent axle flange. Not rare at all.
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  #7  
Old 07-20-2002, 11:37 PM
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O.K., now to get to work on these ideas. I have a tow bar that I use to tow my car to the racetrack with. I always have to remove the driveshaft to do this because of the 727. Did I not get it phased in again? I am going to get someone to tow me and I will sit in the car without the driveshaft in it and see if it still vibrates at 65. If it does, then its a tire or wheel rotating problem, not driveshaft. Maybe I'll get the answer I'm after. This is a good way to check out the speedo while I'm at it. Stay tuned.
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  #8  
Old 07-21-2002, 04:24 PM
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Could possibly be a bent axle shaft, or a bad tranny mount.
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  #9  
Old 07-21-2002, 04:58 PM
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Took the car down the road without the driveshaft on being pulled by my Dakota and low and behold the vibration was there at 65 mph! Seems to be though the body but some through the steering wheel. Makes the hood shake. Guess this rules out any drivetrain problems. Came back to the garage and put the driveshaft back on and run her up to 65 mph. Hardly felt a thing on the rear quarter panels or in the seat and the hood didn't move. Could it be an out of round tire on the back that is thumping the pavement but is o.k. when on the jack stands? Driveshaft runs straight and true and brake drums and axles run out o.k. I am taking all four tires in tommorrow to see what they look like on the balancer. I think I am getting closer!! And the speedo was out 5 mph. I know I couldn't check it without a driveshaft but I knew the speed before, and being pulled my buddy had to go 70 mph to make it vibrate. I will continue with this after I get back from the tire shop. Thanks for all the suggestions.
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  #10  
Old 07-21-2002, 06:00 PM
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An out of round rear tire would still vibrate up on stands. Seems more like it's got to be in the front.
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  #11  
Old 07-21-2002, 09:47 PM
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I would suspect bearings. Either on one of the axle shafts or on the front spindles.
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  #12  
Old 07-21-2002, 10:28 PM
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Well... you sure have plenty to check out. Start with the easiest.
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  #13  
Old 07-21-2002, 10:58 PM
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make sure your wheel bearings in the front are o.k. and greased. also look at the front sway bar bushings and the linking bolts and bushings. hope you figure it out
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  #14  
Old 07-24-2002, 12:35 AM
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I have the Exact same problem with my 340 Challenger. I also have the same cam as you. Could it b....no .
I also notice it more when decelerating on a down hill and less during acceleration at 60mph+
I had the drive shaft balanced but no fix to the vibration. I did have the diff rebuilt when I restored the car. Maybe it's a bearing? Tires are new...bad balance job? One thing I left off the car when I put it together was that 15 pound chunk of steel that attaches to the tailshaft of the tranny. I was told that it is suppose to reduce harmonics. Maybe I'll put it on and see if it helps.
Let us know if you find the cure.
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  #15  
Old 07-24-2002, 12:44 AM
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Just a thought, but it kinda fits the same description as a pinion angle problem. I had a vibe threw my whole car at 60 mph. Came in like clock work. Had the pinion shimed down 2 degrees and it disapeared. Just my 2 bits.
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  #16  
Old 07-24-2002, 09:19 AM
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HUmmm..I would be checking the front end parts...sounds like a bad tie rod end.

It's not the drive shaft, and on stands it didn't vibrate so you've eliminated evrything from the front pulley to the rear tires. Seems to me that it's got to be in the front end.
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  #17  
Old 07-25-2002, 02:30 AM
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Default Pinion Angle? Lets think about this!

One thing the jack stand test does not simulate is a load on the powertrain.

Lets say your pinion angle seems Ok, but at 65-70 MPH, the power train is under a lot of stress pushing all that wind out of the way. Wouldn't it make sense that the pinion angle would actually change under these conditions?

I've had several MOPAR's over the years that had these types of vibration problems. One was actually related to solid core spark-plug wires interfearing with an ECM! (Screwing up the park enough to cause vibrations most noticably at higher RPM.)

But this pinion angle topic has me thinking. It would be interesting to add a snubber (sp?) and adj. it real tight (No Bumps though!) to limit the deflection/angle during a test run. Could this condition be a result of old shackle bushings or weak leaf springs, or a combination of both? What about a gear change? This would change the dynamics of the chasis as well! I know these cars didn't come from the factory that way! This is something that gets worse as our cars get older, and this idea seems to fit!

Hey 68charger6: how did you go about changing the angle 2 degrees? Did you do it yourself? If you payed to have it done, how much? I would like to do this myself, as it may be a trial and error type of deal I would hate to pay for more than once!

Anyone else think this idea makes sense? Even a little?
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  #18  
Old 07-25-2002, 09:12 AM
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Timty2: It's very easy to adjust your pinion angle, go to NAPA or any other good parts store and purchase "Rear axle caster wedges" for a mini van, they come in various sizes from 1-5 degrees and run about $5 a pair.

Loosen your u-bolts and slid them in, retighten and your done....about 30 minutes including jack time...degree of difficulty about a 2.
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  #19  
Old 07-25-2002, 07:46 PM
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Thanks cuda... Nice tip!
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  #20  
Old 07-26-2002, 12:36 AM
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Had the wheels balanced and it helped a little but its still there. Put in all new front bearings and set them up right. Checked all front end parts, I've got mostly all new stuff under there. Pinion angle sounds like a good guess. What should it actually be set at? As I go faster to about 4200 rpm I get a cyclic vibration and I can watch the tach move up and down 100 rpm each way in tune with the vibration. I think its at around 70 or 75 mph but if I slow down and put it in 2nd gear and rev her up to 4200 rpm there is no vibration so it is speed sensitive, not rpm sensitive. What the sam hell is it !!!!!!!! This is driving me nuts. Please somebody out there HELP!
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  #21  
Old 07-26-2002, 01:14 AM
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Default Driveshaft angle?

Mother Mopar says the ideal driveshaft angle is 5-7 degrees down.
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  #22  
Old 07-26-2002, 02:44 AM
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Just for grins...
Measure from the center of the front spindle to any specific point on the rear wheel and the same on the other side...just to make sure your not tweaked and the rear end is running sideways.
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  #23  
Old 07-26-2002, 02:20 PM
Tarrbabe Tarrbabe is offline
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Question cuda66273!

Cuda66273, not sure what you are refering to, but wheel-base is not the same on both sides of a car, or at least they weren't years ago.
Okay, someone jump on me!!!!!
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  #24  
Old 07-26-2002, 06:47 PM
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Consider yourself jumped on.
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  #25  
Old 07-26-2002, 07:35 PM
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O.K., you think it is what we call "dog tracking"?. Could be, I am willing to try everything. 5 to 7 degrees nosed down, alright I will try that also. Sooner or later I will get it and when I do there will be some celebration! Why wouldn't the wheelbase be the same on bothsides? Just asking.
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  #26  
Old 07-26-2002, 09:01 PM
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It is, within normal engineering and production tolerances.
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  #27  
Old 07-27-2002, 12:06 AM
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Here's one that probably won't help but I'll throw it in anyway.

On my 85 lebaron gts, it had a vibration, through the whole car at about 110 kph(65mph for those of you south of the 49th).

Generally a vibation has to be caused by something that rotates, so first I checked the tires. Checked them on the balancer at the shop.

One of the rears was a slight bit out of round. It was visable on the balancer. What annoyed me was that I have quite a bit of experience with tires and this variance was far too little to cause such a horrific shake.

Then I noticed the right rear shock had lost all of it's oil. I figured the vibration had caused the seals in the shock to fail. I decided to change thet shocks, even though I didn't think it would help the vibration.

Sure as hell, the vibration was gone. I'm still running the same tires two years later. All I can theorize, is that the shock was so bad, that the slight runout in the tire caused a resonance in the solid rear axle, that shook the whole car.

Does it apply to you? I don't know. Hope it helps anyway.
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  #28  
Old 07-27-2002, 03:03 PM
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I didn't see in your replies that you verified that the tires are round. It is possible that the wheels could be properly balanced but not round.
You may have another rotating part like a brake drum that is out of balance.
The reason wheel balance/roundness problems show up at 60-70 MPH is that the frequency of the wheel rotation matches the resonant frequency of the wheel/suspension system.
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  #29  
Old 07-31-2002, 07:31 PM
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I have a similar vibration at 70 and up in my bee. From reading my 71 shop manual it says that a vibration caused at high speeds (70+) is best tested by observing the RPM at the vibration speed and then driving the car in a lower gear at the same RPM. If the vibration persists then it is a driveshaft problem.

I took my shaft in which was already balanced. The guy called me today and said that the shaft was not balanced properly and he re did it. This guy was cool too cause he said if that doesn't do it he'll build me a new shaft minus the rebuild cost!

I'll try it out this weekend if it worked or not.
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  #30  
Old 07-31-2002, 08:10 PM
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Default bad vibes

if you can try a different set of front tires and rims do it,alot of muscle cars sit for long periods which creates a minor flat spot that may not be visible,be sure your not toed out too much either.Dave 571,if you have a 2 piece rh axle shaft on your 85 gts be sure the inner axle shaft has 0 movement front to back or it will vibrate enough to wipe out your cv's and motor mounts,hope you solve it......PRO...
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