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Author Topic: 69 350SS VIBRATION  (Read 11268 times)
incom5633
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« on: October 14, 2008, 04:16:10 PM »

good afternoon,
i have a 1969ss 350coupe turbo 350 3:31posi gear. i have had an oscillating vibration since restoration at different rpms for about 10 years. it vibrates in console area , steering wheel , rear view mirror. engine was ballanced, plus i removed it and sent it back to be checked for
accuracy. non was found. i have changed all pulleys, fans etc. i have had  transmission rebuilt- tried 3 different torque converters, new mounts, 2 drive shafts , 2 different rear ends,(both rebuit professionally) , checked to make sure exhaust is not touching frame . the vibration is very evident at 1500- 1900 rpms- then smooths out . it re appears at about 3300 rpm on.  i guess i'm obsessed with finding a cure. my question : is there any place i can take the car to be checked for hard to find vibrations or does anyone have any suggestions? i live in georgia.
         
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tom
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« Reply #1 on: October 14, 2008, 04:45:31 PM »

Is the vibration limited to any specific gear?
Do the virbations happen at certain speeds?
Are all the wheels corectly balanced and in good condition? Many years ago I managed a volume tire shop, and a couple of hard to trace vibrations were because of belt problems in the tires. Tire vibrations tend to be speed related. They can become very bad at one speed, and go away completely at higher or lower speeds.
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69 X11 Z21 L14 glide
looking for a 69 export model (KPH) speedo
camaronut
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« Reply #2 on: October 15, 2008, 08:34:33 AM »

Sounds like rotational mass inbalance.......most likely the tires / rotors / drums....

All of your tires could be balanced, but if one or two of them are out of round, that could cause the problems your talking about.....

It's really noticeable, when tires are spun on a tire balancing machine.... all the balancing in the world won't cure this....

Back in the day, I bought a set of Goodyear Eagle GT's....mounted them, and had two tires that were out of round.....it was a real mess

I had my lawyer buddy call the store owner and convince him to do the right thing......... Grin

Check the rotors and drums, thay have to be balanced also.....

Also...how good are your shocks?

Wheel locks also add to the problem.......

Good luck....
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3Zs
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« Reply #3 on: October 15, 2008, 09:00:45 AM »

Is there any play between the universal joint and the companion flange on the differential?  If it is not a snug fit, the u-joint will move around in the companion flange at certain rpms and cause a driveshaft vibration.
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tom
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« Reply #4 on: October 15, 2008, 09:56:33 AM »

One way I used to find out of round and belt shift on tires was to run a tire crayon across the tread slowly while the tire was on the high speed balancer. When there was a problem it showed up very clearly. Probably not a safe or recommended way of doing things, but it was effective. High speed balancing will balance an out of round or belt shifted tire, but only for the speed the tire was balanced at. Faster or slower speeds will still have the vibration.
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69 X11 Z21 L14 glide
looking for a 69 export model (KPH) speedo
incom5633
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« Reply #5 on: October 15, 2008, 11:14:57 AM »

as far as the tires and rims- the rims have been checked for run out and the tires have been changed.
u- joints - drive shaft and flanges have been replaced.
this vibration appears to be harmonic coming from center line of the car. it occurs at different rpms - it is a come and go vibration getting faster as the rpms increase. 

i have often wondered if it is an alignment issue .
ie pinion angle or centerline position.
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rich69rs
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« Reply #6 on: October 15, 2008, 12:10:07 PM »

After eliminating all that you have already checked;

First thing I would also verify is that at idle the harmonic balancer is not oscillating excessively; i.e. verify that it is still good.  If you had a weak balancer allowing for excessive torsional oscillations, I doubt that the engine would have survived for 10 years - but still worth checking.

Secondly, If the angle between the transmission and the driveshaft and the drive shaft and the rear end; i.e. the driveline angles are not the same or nearly the same, one of the possible outcomes is a cyclical (or beat frequency) type of vibration.  This means that the vibration varies in pitch or intensity, not only at different speeds, but also can be "felt" at times even when traveling at a steady speed.  The vibration often "feels" or is "heard" as a "whir, whir, whir" type of noise. 

A peculiarity of the standard 69 drive shaft (Discussed previously 2 years ago.  Refer to the following link:  http://www.camaros.org/forum/index.php?topic=914.0) is that the standard drive shaft for '69 (not including BB with TH400) utilized an arrangement where the yokes from one end of the drive shaft to the opposite end are not "in phase" but offset by approximately 20 degrees.  This sort of non-standard phasing makes proper drive line agles even that much more important. 

You state that you've changed the driveshafts out twice.  What did you install and how did you phase the yokes?  Have you checked the angles between the tranny and the driveshaft and the driveshaft and the rear end?  Are you using "taller" tires?  Has the rear end been lifted at all?  Taller tires, lifting the rear end, etc. can affect the pinion angle.

« Last Edit: October 15, 2008, 12:18:46 PM by rich69rs » Logged

Richard Thomas
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incom5633
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« Reply #7 on: October 15, 2008, 02:16:18 PM »

rich,
engine has a fluid damper. the engine was gone through again in feb. this year. car has original 14" rally wheels and bf goodrich tires.
the  original drive shaft had the above mentioned yokes aprox. 20 degrees out of phase. the drive shaft manufacterer told me this was incorrect and buit me a shaft in phase. later i  sent this shaft off to balance shop and had it re-balanced. rearend is stock 12-bolt and 5-leaf springs.
i have not checked driveline  angles because i could not see any way to change them.
you mentioned a beat frequency in the vibration . when i put the car into 1st or second gear and bring rpms up to 4200 plus , i get a thumping sound and feel with the vibration.
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rich69rs
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« Reply #8 on: October 15, 2008, 04:25:25 PM »

Outside of using a protractor to verify the driveline angles, I can't think of anything you haven't already checked.

By the way, I also had the yokes on my driveshaft changed to "in phase" about 15 yrs ago. 

There is no sound engineering principle for off setting the yokes.   Unless the driveshaft from end to end is exactly colinear and coplanar, there will be a differential angular velocity from end to end, which is accomodated by a double u-joint drive shaft if and only if the yokes are in phase, the drive line angles are equal from end to end, and the extreme ends of the driveshaft are parallel.  Offsetting the yokes by 20 degrees obviously negates the ability for the driveshaft to compensate for the angular velocity differences from end to end.

My personal speculation as to why Chevy did this gets back to the homologation rules that were in effect for Trans Am racing back in the day.  Two things that offsetting the yokes would do are: 1) to add stiffness to the drive shaft and rear end (due to binding) at the expense of proper dirveshaft operation, 2) shift up the critical speed of the drive shaft due to the stiffening effect.  By comparison, take a look at a BB drive shaft from a '69 Camaro with a TH400.  The yokes are in line - no need for these cars to use homologated parts.

From a race perspective, the driveline only had to last for the length of the race and if an advantage could be gained......

The though at Chevy may have simply been that the Camaro would long be out of warranty before any drive shaft issues would manifest themselves.  The drive to be successful in Trans Am racing in '69 was a very big deal.
« Last Edit: October 15, 2008, 04:45:47 PM by rich69rs » Logged

Richard Thomas
1969 RS
william
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« Reply #9 on: October 15, 2008, 09:31:29 PM »

Even though you replaced the motor mounts they may be incorrect.

For 69 Chevy used two styles of motor mount and frame bracket on small-blocks: 307/327 continued to use the 67-68 stuff but 302/350 received a different mount that used different frame brackets. The 67-68 motor mount will fit on 69 302/350 brackets but it is a loose, sloppy fit. The engine will sit too low and because the 67-68 mount is 1/2" or so wider than the 69 brackets the engine can move around. The correct mount is a tight fit on the frame brackets.
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incom5633
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« Reply #10 on: October 16, 2008, 09:09:53 AM »

rich
is there specific degree of angle to look for? also if this angle is found to be incorrect , how do you correct it. i have not seen any thing offered relating to this subject. 
 william,
i have checked the no,s stamped on the frame brackets and they are the ones for a 350, also i purchased the usa motor mounts from heartbeat city, they fit tight on the brackets.
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rich69rs
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« Reply #11 on: October 16, 2008, 11:44:07 AM »

Pic in the attached PDF file shows what you want in the ideal case - equal angles both ends.  However, remember that the actual angle varies as the rear end moves up and down within the limits of its normal travel. 

A totally stock engine, tranny, rear end setup using stock locations with stock hardware has (or should have) taken this into consideration already.  It's when people start changing from stock that checking the driveline angle becomes more of a potential issue.  One way of adjusting the driveline angle is by shimming under the rear tranny mount - however, for totally stock setup, this shouldn't be necessary.

If you do a "Google search" on driveline basics, several good sites will pop up which offer good illustrations, animations, etc.
« Last Edit: October 16, 2008, 11:52:59 AM by rich69rs » Logged

Richard Thomas
1969 RS
william
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« Reply #12 on: October 16, 2008, 12:03:45 PM »

The wrong motor mounts will also alter the driveline angle. First things first.
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tom
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« Reply #13 on: October 16, 2008, 01:17:54 PM »

When you had the rears rebuilt, did that include inspect the axle shafts? A bent or out of balance shaft could aslo cause a vibration.
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69 X11 Z21 L14 glide
looking for a 69 export model (KPH) speedo
incom5633
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« Reply #14 on: October 16, 2008, 02:04:56 PM »

rear end rebuild included all bearings and axles from randy's rig gear and pinion.
motor mounts replaced 3 -times the last with usa made from heartbeat city. all with same results. heartbeat city verified that my frame bracket no's were correct.

i will explore trying to verify my pinion angles .
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