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#1009072 - 08/04/14 01:31 AM Pulsing Vibration 84 SS  
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TriumphoverU Offline
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TriumphoverU  Offline
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St. Johns, MI
I did a search, but came up empty handed, so here it goes!

All input is appreciated!

1984 SS with 350/th350. I have a vibration that comes in pulses about 55 mph and up. The faster the speed the faster the pulsing. It vibrates, stops for a split second, then vibrates again, and continues this cycle until I slow down below 55 mph. This is a speed related vibration and definitely not rpm related. The vibrations almost feel like I am going over small sets of rumble strips. I only feel the vibration in the body/rear of the car, not the steering wheel or the pedals.

I suspected the driveshaft, so I took it to the local drive train shop and had it balanced and had them install new u-joints while they had it. There was no change in the vibrations after the balance and new joints. I then spun the driveshaft 180 degrees and bolted it back down, this also had no effect on the vibrations.

This is also my second set of tires, so that should also rule that out.

I should also mention that this is a newly developed problem. The car has always ran smooth even after the engine swap.

#1009078 - 08/04/14 02:14 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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83StreetMachine Offline
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Central NJ
Since you checked the obvious already. I would now look at the flexplate and torque converter. See if there are any cracks in the flexplate. Maybe you lost a bolt or one is loose. Check to see if any of the bolts for the toque converter are loose or missing.

If all that checks out check your front wheel bearings and rear axle bearings. Have they ever been replaced? If so how long ago?

Next I would dive into the rear itself. It might be getting ready to grenade. How many miles are on it? Has it ever been rebuilt?

Good luck and keep us updated.

#1009079 - 08/04/14 02:17 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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BadSS Offline
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Is the pulsing there at speed with the car in neutral? Did it start after replacing the first set of tires?


Original owner of 1985 SS black hardtop w/gray interior. Frame-on restoration in progress. 406 sleeper w/ heavily ported FIRST TPI. 1.875" headers and dual 3.5" Borla exhaust. TH400, Ford 9", anti-roll bar, and notched frame. Dropped 2", 18" wheels, and F/R disk brakes. 10-point cage w/swing-out bars, custom gauges, and audiophile stereo system.
#1009082 - 08/04/14 02:30 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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TriumphoverU Offline
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St. Johns, MI
I'll dive into the questions you guys have asked one at a time.

The flexplate was new with the motor install, sfi, but I will still check it for cracks.

The torque converter is original to the car which has 130,000 miles on it.

The front wheel bearings were replaced about 2,000 miles ago since the originals were still in there when I did the brakes. No difference before/after the R&R.

The rear end is original with posi, with no abnormal whining or grinding noises. The wheel bearings in it are all original as well.

Not sure about if the vibration is there in neutral or not, never occurred to me to try that, but I will tomorrow if I get it out of the garage.

The tires have no effect on the vibration. It started after the first set had been on there about 20,000 miles. They began to weather check so I replaced them for safety reasons not for the vibration. (But I was hoping new tires might take care of the vibs, but it didn't)

Now, here is what I'm thinking, I don't think its a bearing because it pulses. If it were a bearing I would think it would be a constant vibration possibly accompanied with a growling or other noise.

I was starting to lean toward pinion angle, but on our cars, that is not adjustable, so unless the control arm bushings are completely toast, I don't see how that could have changed. Those bushings are probably next on my list to check.

Any other ideas?

Last edited by TriumphoverU; 08/04/14 02:35 AM.
#1009083 - 08/04/14 02:32 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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MecGen Offline
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Hello

What you are describing definitely sounds like a drive shaft related problem...

I have had bad luck with shops that balance driveshaft, is there anyway you could borrow a friends driveshaft? You also need to check your driveshaft angle in relation to the pinion and transmission angles, offset as well (side to side). Don't forget to check your trans mount for collapsing ~ changing tranny angle and rear diff control arms bushings ~ doing the same to the pinion angle. Have you had work on the diff, how's the pinion flange rounout?.

Sounds like a lot, sucks I know, been there done that. Good luck


Space may be the final frontier
but its made in a Hollywood basement.
RedHotChilliPeppers.

1987 MCSS.- Sold
1984 MCSS.- Sold
1984 MCSS - came back smile
1995 Mustang 5.0
1965 Pontiac GTO
1969 Pontiac Firebird
#1009084 - 08/04/14 02:33 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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MecGen Offline
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We posted at almost the same time...


Space may be the final frontier
but its made in a Hollywood basement.
RedHotChilliPeppers.

1987 MCSS.- Sold
1984 MCSS.- Sold
1984 MCSS - came back smile
1995 Mustang 5.0
1965 Pontiac GTO
1969 Pontiac Firebird
#1009092 - 08/04/14 03:06 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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83StreetMachine Offline
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Central NJ
I definitely agree with above. Check the trans mount. And see if you can't swap out the driveshaft for a whole different one.

#1009095 - 08/04/14 03:25 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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Ninja85SS Offline
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Are you running the stock rear drums? (Or possibly aluminum drums?)

Reason I ask, is that the aluminum drums have weights on them and I have heard they have come off of some.

Just a thought!


1985 Monte Carlo SS 383MT Forced Induction
http://www.cardomain.com/ride/2228046
2004 Dale Earnhardt Jr. Supercharged Monte Carlo SS
#1009122 - 08/04/14 12:18 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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Jay jay Offline
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IMO you can pretty much rule out wheel bearings. I think your issue is showing up as a pulse type vibration due to the rear differential ratio. Don't get me wrong, the ratio isn't the problem but the vibration pulse tells me when you have two parts turning two different speeds that can cause a pulsing effect. My guess (and only a guess) would be a pinion bearing in the rear differential.


85 SS work in progress. Humor is the only way.
#1009134 - 08/04/14 01:19 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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mainer Offline
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I would put my money on a bad trans mount .

#1009153 - 08/04/14 05:19 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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Ole Blue Offline
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Does this happen while using cruise control or not using cruise control at all?
You might consider this a strange question but there is a reason or thought process for the information.

#1009156 - 08/04/14 06:10 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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cj84ss Offline
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Also check the front engine accessorie pullys. Make sure they run true and are tight? Water pump, alternator, power steering, air pump, AC and crank?


[Linked Image]
1984 SS, w/87 Grand National 2004R, 355 vortec, CCC, Crane XE262.
1969 Road Runner
2003 GMC Serria
#1009168 - 08/04/14 08:55 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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TriumphoverU Offline
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St. Johns, MI
Well I went for a short test drive today before the storms hit, so I didn't get too much accomplished. I couldn't even get the thing to vibrate at all. Todays drive was only about 20 miles, but it went smooth as silk.

Here are a few more answers to the questions you guys have asked.

I do not have access to another driveshaft, but since todays drive was smooth, I'm doubting that anything is out of balance.

I am running the stock rear drums, and as found out in my test drive today I do not believe these could be out of balance since todays drive was vibration free.

The trans mount is definitely something I will check out once I get under the car. Darn thunder storms anyways!

When the vibration is present, it will do it with the cruise or without the cruise, doesn't matter.

The engine pulleys are all running true with no wobbles or belts bouncing.

I'm believing this to be more related to the trans mount or rear control arm bushings after todays test drive. If it was a balance issue it would be there all the time and not disappear like it did today. I'm guessing that something in the mounts must have "realigned" itself today.

Keep the ideas coming, I'll let you all know what I find out once I get it fixed.

#1009236 - 08/05/14 02:42 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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87ChooChoo Offline
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I chased one of these vibrations for over a year, so I feel your pain. I just happened to notice a small scratch on the right rear muffler hanger, and upon investigation I found that under certain loads ( like full gas tank), the bolt from the rear sway bar was contacting the muffler bracket and pushing the exhaust up against the frame. Not saying it's your issue, but something to consider.

If your vibration is sort of a Wah-Wah_Wah- type of pulsation, it could be a rear axle bearing.

BTW, I didn't know this until I dug into my factory service manuals, but the rear control arms on the G-bodies have about 1 degree of adjustability for the pinion angle, due to the "slop" of the bolt holes.


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home
#1009355 - 08/06/14 05:41 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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Ole Blue Offline
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Lugoff, SC
Is your speedometer working properly?
Correct speed, any bouncing of the needle?

#1009379 - 08/06/14 10:32 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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JMonte7892 Offline
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Baltimore, MD
When you go above 55 mph, gas it then let off quickly. If your car starts bucking/shaking, (might be what is happening?) it might have something to do with your torque converter lockup system. Basically what that is is the synchronization of the engine and the rotation of your wheels. If you let off the gas and your torque converter lockup is still on, your engine will try to bog down, but it cannot because the TC is still locked up and is going to keep the engine spinning at the same RPM as your wheels. If this is the case, try pressing and holding your brake slightly at 55mph, then gas it and let off quickly again. (there is a switch on the brake pedal mounting bracket that tells the computer when to shut off the TC lockup) If it does not buck/shake the car when you gas and let off, that's your problem. Just don't brake for longer than a few seconds smile

If some of the ecu's wires have been disconnected, it might not be shutting off though..

Last edited by JMonte7892; 08/06/14 10:43 PM.

1983 Monte Carlo Sport Coupe [sold]
1984 Monte Carlo Super Sport [deathmatch with a Santa Fe]
1985 Monte Carlo Sport Coupe [frame-off in progress]
#1009441 - 08/07/14 04:37 PM Re: Pulsing Vibration 84 SS [Re: Ole Blue]  
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Ole Blue Offline
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Lugoff, SC
Originally Posted By: Ole Blue
Is your speedometer working properly?
Correct speed, any bouncing of the needle?
Originally Posted By: JMonte7892
When you go above 55 mph, gas it then let off quickly. If your car starts bucking/shaking, (might be what is happening?) it might have something to do with your torque converter lockup system. Basically what that is is the synchronization of the engine and the rotation of your wheels. If you let off the gas and your torque converter lockup is still on, your engine will try to bog down, but it cannot because the TC is still locked up and is going to keep the engine spinning at the same RPM as your wheels. If this is the case, try pressing and holding your brake slightly at 55mph, then gas it and let off quickly again. (there is a switch on the brake pedal mounting bracket that tells the computer when to shut off the TC lockup) If it does not buck/shake the car when you gas and let off, that's your problem. Just don't brake for longer than a few seconds smile

If some of the ecu's wires have been disconnected, it might not be shutting off though..
Your point is where I was getting to as well as the VSS also sends signals to the trans.
If there is a problem with the brake switch, VSS or even the ECM, there could be problems with the TCC or trans in general communicating.

#1009454 - 08/07/14 06:10 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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TriumphoverU Offline
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St. Johns, MI
Guess I should have also said right off the bat, that there is no ECM any more nor is there a TCC lockup. I'm going to take a look at the car today to see if I notice anything out of the ordinary. Paying special attention to the trans mount and control arm bushings. I'll let you know what I find out if anything.

#1009477 - 08/07/14 10:02 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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Abington,ma
look at the motor mounts... also check the driveline angles as you put a th350 in it..

put the rear up on jack stands.. and see if running up to 55 with no load, does it still do it? yes or no..
if yes, remove wheels and with lug nuts on (to keep drum from fly'n, do it again.. same yes or no...
remove drums, try again.. just remember to not hit the brakes..
still does it yes or no?

put it back together.. put jack stands under frame, and with jack bring rear end up to ride height..
still does it.. now test with using the jack to push the rear end up but not off the stands, still there, now try 1" lower than ride height(e.i. rear end hanging down 1 inch.. still there, try another inch, then it just hanging..
if the stands under frame and putting the rear in a different spot than where it be normally makes it go away, the angles are furbard..

#1009607 - 08/10/14 12:13 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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TriumphoverU Offline
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St. Johns, MI
Eric, the th350 is what came in it from GM, the 200-4r was not available until the 85 model year.

So anyways, I did a little investigating, and I may have found an issue. The tailshaft bushing seems to have some play. I don't know what is excessive or the tolerance is though. But I can definitely feel it when I checked the front u-joint.

#1009855 - 08/13/14 02:15 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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Dand Offline
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I think you found your problem!! there should be no play. So if engine and tranny mounts are good, take a look at your rearend bushings for excessive cracking or play, jack up the car. I have poly bushings al around. Try lubing the bushings if they are the style with grease fittings. Last but not least check your rear schocks.
Dan

#1009867 - 08/13/14 03:16 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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SSLance Online content
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SSLance  Online Content
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The weak driveshaft these cars came with is most likely the cause of that tailshaft bushing failure. Not sure what is involved in fixing it on the T350, but I'd put a larger diameter driveshaft in at the same time you replace the bushing and you'll love the feel from the car afterward. Been there, done that...


Lance
1985 Monte Carlo SS Street Car
#1009906 - 08/13/14 05:03 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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TriumphoverU Offline
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St. Johns, MI
Thanks for all the input guys, I am going to change out that bushing in the tail shaft to start with. If the vibration is gone I am definitely going to look into changing out the driveshaft with a larger diameter (probably aluminum) version!

I'll keep you guys posted on the outcome!

#1009944 - 08/14/14 03:26 AM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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Andy85SS Offline
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Your problem sounds identical to a vibration I chased a few years ago. After checking all the same things you have, my problem turned out to be a worn carrier bearing in the rear end. Even with the d/shaft and axles out, the ring and pinion setup still felt fine. But upon further disassembly, when I removed the carrier one of the carrier bearings had 2 consecutive rollers badly worn down.

My friend that does rear-end setups also said at that time that the pulsating nature of the vibration would lead him to believe the ring and pinion and/or their associated bearings were at fault.

The bad bearing was real fun to get off the carrier. We had to cut it apart into pieces and then polish the carrier journal that the bearing presses onto using a lathe. In the end though, with a pair of new carrier bearings, the vibration was gone. Yay.

So if that tail shaft bushing doesn't fix your problem, and since you've already ruled out everything else that's easier to check, I'd consider checking those carrier bearings next.

#1011255 - 08/29/14 03:56 PM Re: Pulsing Vibration 84 SS [Re: TriumphoverU]  
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TriumphoverU Offline
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St. Johns, MI
Just wanted to follow up. I changed out the bushing today and while it did not fix the problem, it changed it. The vibration does not start now until about 65-70 mph.

With the bushing changing the vibration, I would say that would rule out the bearings and everything with the rear end. I'm going to check out the engine mounts and maybe even change the trans mount again. It has got to be something with the drive line angles. Again, I'll keep you all posted as I dig further into the issue.

Thanks again for all the suggestions!


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