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Author Topic: 69 350SS VIBRATION  (Read 10942 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
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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
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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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dutch
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« Reply #15 on: October 16, 2008, 02:45:00 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 .

   Your situation all sounds so very familar to mine that I thought I would jump in here somewhat and I hope it isn't considered a thread hijack - but I have endured the same problem with my '68 Z for many years. I now have all of the bearings / crush sleeve / and parts accumulated now for a rear end rebuild which I hoped would finally cure my vibration after seemingly trying everything else.
    This threat has me worried now if it will in fact end my problems or leave me searching further for answers as you are here in this thread....
    The one thing I always wondered about (thinking if the rebuild didn't cure my vibration) was whether the yoke on the pinion shaft itself could in fact be bent or out of spec slightly and how easy it could be to determine that or if I should just try and get a new one regardless and replace it at the same time as all of the other parts. Does anyone who cares to comment believe that the actual yoke on the pinion could be tweaked by racing (my car was at one point as were many similar cars) and the traction related twisting that occurs with slicks etc.
    I know parts like axles, driveshafts and u joints take most of the beating but I always wondered it the yokes themselves could be damaged by the twisting and shock during racing. I guess because it sits fairly low to the ground there is also a possiblity that it could have been hit on or by something over the years also.
    Is it easy to check one of these yokes out and if so how? Are the 12 bolt versions hard to come by or are they fairly generic? Like most anything else 12 bolt-related, I'm guessing they are probably fairly high $$ items...
    Maybe this could be 'our' answer... - Randy   
 

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tom
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« Reply #16 on: October 16, 2008, 09:34:53 PM »

Does the vibration occur at the same rpm range regardless of gear? If so I would be inclined to think Transmission or forward. If it comes and goes at the same speed regardless of gear I would look from the trans back. If it occurs at the same speed regardless of gear, does it happen in neutral (do you have a big enough hill to find out)? I would think drums or rotors if out of balance could cause a vibration as easily as a tire out of balance. Could the output shaft or housing on you trans be tweaked? Is the rear axle correctly aligned relative to the front end?
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69 X11 Z21 L14 glide
looking for a 69 export model (KPH) speedo
dutch
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« Reply #17 on: October 17, 2008, 05:53:06 AM »

   My vibration is from the tranny back since if I get it up to speed and slip it into neutral or push in the clutch it is still there and diminishes as the car coasts down in speed. The vibration builds with speed and peaks around 3000 + rpm (approx 60 mph) and is there regardless if the car is accelerating or slowing (usually not a sign of u joint issues).
   I'm inclined to think a bend axle, since I have swapped tires front to back and it persists. Over the years it has ruined my pinion bearing and especially the seal and it now leaks at the pinion so I know I might as well go through the whole unit and change everything once it is opened up.
   That is where my question regarding the yoke came up - whether it could be the cause to shake the end of the driveshaft (which was replaced with new pipe and u joints and balanced) and therefore screw up the pinion seal / bearing because the vibration would be directly focused there...
   I would have tried to get it fixed long ago but for lack of someone I trust to do it that is qualified and that won't charge an arm and a leg to do it, I haven't to this point. Wish I knew enough about setting the lash and pinion depth to do it myself but it sounds like a lot of black magic using the crush sleeve parts and I don't feel confident enough to tackle it.. the yoke is a different story though  - Randy
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Farm Boy
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« Reply #18 on: October 19, 2008, 10:34:13 PM »

I had a cyclical vibration above 65 MPH in my 67 for years. I changed wheels and tires, had the driveshaft balanced, and even replaced the driveshaft but never managed to get rid of the vibration. Nothing I tried got rid of the annoying vibration until last week.

The other day I was at Harbor Freight and picked up a cheap angle finder. When I checked the pinion on the rear end I found it was pointing down 4. The transmission was also pointing down 3. From everything I have read about proper driveline setup these numbers were way off. The way I understand it the transmission and the rear end should be parallel to each other for the U-joints to operate smooth.
 
   

In other words with my transmission pointing down -3, the pinion on the rear end should have been pointing up +3 not down -4. My pinion angle was way off.

I ordered some 4 leaf spring shims to correct the pinion angle. I actually used two 4 shims on each side. I placed one shim on top of the spring and one facing the other way on the bottom so the shock plate would sit level. I also eliminated the rubber spring pads in the spring perches. I had to add a 3/8 inch thick spacer and a longer bolt to the spring pack so it would fit tight in the perch.

I also made a inch spacer for under the transmission mount to raise the rear of the transmission. My transmission is now 2 down and the pinion is level or 0. The leaf springs should wrap up a couple of degrees from the axle torque which will hopefully put the pinion 2 up while running down the road.

Its now smooth as glass.

I am convinced Chevrolet Engineering simply screwed up when they came up with the out-of-phase driveshaft and the incorrect pinion angles in first generation Camaros. I wonder how many first gen Camaros are out there with a high speed driveshaft vibration from an incorect pinion angle.







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Steve
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« Reply #19 on: October 20, 2008, 03:16:15 PM »

   I obviously never gave the driveline/pinion angle thing much thought for a street car as I had always heard of it in a drag racing, traction, blown u joints - driveshaft, context - but it may explain a lot. Took a quick gander under the car yesterday and noticed that the pinion has a definite downward angle (how much in degrees I'm not quite sure yet) but downward none the less. Also I changed to stock tranny mount, sub frame bushings, spring eye bushings, and rubber cushions under the spring packs a few years back all because the stock stuff was well worn and or deteriorated. After that I didn't notice that the vibration was much worse although it certainly didn't help to alleviate any of it and now that I think about it, it may have been a bit more pronounced in the higher rpm ranges at that point onward. If anything I just chalked it up to the newer and tighter rubber bits in place making whatever vibration there was, somewhat more more noticeable.
   Regardless, I went out and found a cheap angle finder / protractor unit yesterday, as per the descriptions on the Team camaro site (can I say that here?) and will try and crawl underneath and measure what I find. The shims may be a bit hard to come by around here but it appears that I may end up needing some if what I see is true. I am very anxious to try this out as a possible cure to my problem. My car has always sat up more than many I had seen so maybe that is also something that has also contributed to the problem as it would seem to me that if the angles are off parallel, the sheeper the drivehsaft angle between the output shaft and pinion because the body sits higher, the worse the u joints would bind.
   Thanks everyone for the whole other avenue of thought on this - sure hope it works out! - Randy 


 
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DANW
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« Reply #20 on: November 22, 2008, 12:11:44 AM »

incom5633, if you are still out there, you didn't say whether this happened while just in gear or also in neutral too.  If the vibration is only rpm dependent, or also is present at rest in neutral, then it isn't likely that it has anything to do with the drivetrain from the transmission back. 
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