Mystery vibration? maybe drive line,--- help.

FIREBALL

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Sometime after doing IRS all poly upgrade and torsen diff. and new tires and sub frame connectors I started feeling a vibration that for me as an experienced car guy has me stumped. Its kind of like a tire flat spot vibrations but it seems like i only notice it after driven a few miles and the engine has warmed up. It is mostly at 50 mph and over but some times slower. Ive had the wheels/ tires re-balanced but the balance looked good to begin with and after it didnt change. The vibration seems to come from the whole car not just the steering wheel. It is not a bad vibration but its always noticeable. It seems to be more when accelerating but not always. I can be going down hill or uphill and doesnt change. If I slip it into neutral and coast there is not much change??????. Ive had the drive line disconnected a couple times without marking the position, could it be the drive line not put back in the same factory position on the diff.?? This car has 11k original miles and the U joints feel and look good.------any experienced ideas?
 

geoffmt

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When you replace all the stock rubber bushings with firmer or solid bushings you will get more noise and vibrations. Usually I would have went with bad u joints but if there is no movement(slop) I would see if it gets worse before being worried. But if either end of the driveshaft is loose, has 0 resistance in moving when out of the car, shows lack of lube under the caps then it could be out of balance. But typically it’s just the firmer bushings


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cidsamuth

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If the problem persists after the car is popped into neutral, would that not point to a suspension versus drivetrain issue?
 

FIREBALL

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Thanks for replies, Well if it is the driveshaft, that will be taken care of next month as I will be installing my new Magnum trans, with the kit I got the new aluminum drive shaft also has new joints. I remember from some post i read a couple years ago that an aluminum drive shaft makes a big improvement over the factory steel ones.
One thing Ive mentioned in prior thread is that I thought the sub-frame connectors caused more vibration but most have said that they dont.

forgot to mention, I did notice a little bit of a harsher ride after installing the bushings but the vibration came a little later.
 
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Mojo88

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Please be sure and update this post with your progress. NVH is something I hate, haha, so I'm always eager to learn any new methods to cure it... and what causes it.

Best of luck in your hunt for the cause/cure. :)

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FIREBALL

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Dont put many miles on car, but I took it out to see if i could narrow this down, here is what i got , first, there is a little vibration comming from chassis mostly on rougher roads. It does increase when accelerating on the flat and going uphill---a little better down hill and even better when in neutral going down hill. There is also a small rough vibration from engine around 2500 rpm and can feel it when sitting in driveway and hold it at 2500, its not a miss just feels a little rough. So right now I think its a combo from chassis, drive line and engine. Also Im thinking the possibility of tires being out of round, Its not bad but driving me crazy. Going to install that trans and aluminum drive shaft next month and then go from there. I will update then.
 

Mojo88

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Looking at your first post again got me thinking... always dangerous, haha..... but when installing replacement OEM suspension bushings, it's imperative that the chassis be at ride height prior to final tightening of the bolts that hold the bushings in place, otherwise the bushings would be stressed. Maybe your new poly bushings are binding a bit??

I'm sure you're aware of this already, but just thought it was worth mentioning. Perhaps the poly bushings you installed did not have that requirement.

Anyway, good luck, I TOTALLY get it when you say it's driving you crazy. One of my cars was '68 Camaro with big-block. I spent a ton of money on motor work, only to feel engine vibration at ~2k rpm, even after being balanced by local race shop. I had to take it out and they re-balanced the rotating assembly... it STILL shook... they thought I was crazy, but I took it all apart again, and they re-balanced it for a third time (this time I was at the shop watching and helping) and this time the balance tech saw for himself that it was WAY out of whack. He had to add over 100g of Mallory metal to the crank, but then it was finally smooth.

So you just gotta keep after it and you should be able to solve it.
 
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Hi bud just trying to help. It sounds like you have a bad u-joint, I have come across this same issue time and time again. I would recommend jacking up the car, putting it on jack-stands, grabbing the driveshaft and wiggling it back and forth to see if there is any play( in every direction as I have seen u-joints that looked good and felt good but if they were moved in a certain way you could tell they were worn)

If it isn't a u-joint start checking other areas of the car you have worked on recently and check to see if there is any play. Let me know if this helps!

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FIREBALL

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Hi bud just trying to help. It sounds like you have a bad u-joint, I have come across this same issue time and time again. I would recommend jacking up the car, putting it on jack-stands, grabbing the driveshaft and wiggling it back and forth to see if there is any play( in every direction as I have seen u-joints that looked good and felt good but if they were moved in a certain way you could tell they were worn) [/URL]


Thank You, It is a 19 year old car with 11K original miles, I havent checked the U joints that closely but you got me thinking they could be dried out and I drive the car spirited and have made just a few hard launches and a few 120mph runs so it could be drive line and joints, but as I said in my post# 5-- I am shortly going with a new aluminum shaft which has new joints and I will be changing the transmission mount along with the new transmission. Im hoping that takes care of most of it. Now that I think about it there did seem to be more vibration after some spirited driving but I didnt think of it at the time.
 
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Thank You, It is a 19 year old car with 11K original miles, I havent checked the U joints that closely but you got me thinking they could be dried out and I drive the car spirited and have made just a few hard launches and a few 120mph runs so it could be drive line and joints, but as I said in my post# 5-- I am shortly going with a new aluminum shaft which has new joints and I will be changing the transmission mount along with the new transmission. Im hoping that takes care of most of it. Now that I think about it there did seem to be more vibration after some spirited driving but I didnt think of it at the time.
Sounds good Bud, keep me posted as I would like to help you diagnose your issue!

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FIREBALL

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With all this virus thing going on I dont know when Im going to get to transmission and drive line but I took it out today for further evaluation and now Im 90% sure most of the vibration is coming from the engine, It starts around 2400rpm and stops about 3400,(it never did this in the past) thats in the cruising range and probably why originally I thought it could be in the chassis/suspension All I can think of is maybe an injector problem but its not missing and no codes. I bought 2 bottles of SeaFoam and put it in with about a 1/3 tank gas but havent ran it enough for it to take effect. Im going to put some miles on it tomorrow and see if the SeaFoam clears anything up. Plugs are new and like I was saying there is no miss. The vibration is in that rpm range going down the road or in neutral, gets a little worse under load like when going up hill.
 
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01yellercobra

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Make sure the dampner isn't coming apart. It probably isn't, but worth checking. Might be worth scanning for codes. There might be something pending. Had an issue with a Lincoln LS where it gave every indication it had a miss, but wouldn't throw a code. He finally got it to throw a code going up a hill and then we were able to fix it. But this was a couple month ordeal.
 

Mojo88

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Maybe a piece of your clutch disc fell off. That would throw the engine out of balance. Good suggestion too, about the damper, check that carefully.

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FIREBALL

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Thanks for the replies, yep I will be replacing clutch disk with new trans, and I have the Steeda pulley kit that is going to go on at the same time.
 

FIREBALL

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Got the trans out and new clutch disk and bell housing are in and ready to mount new trans.

Transmission mount problem solved (I think)---I received my ebay 03/04 cobra crossmember and mount and it was in excellent condition so its going to be just a bolt in for the magnum. I still think most of my vibration is coming from the engine but we will see after getting new trans in and the new aluminum drive line.
 
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Bdubbs

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I had a bad vibration in my 90 coupe. It has a irs. The whole car would shake violently. Generally, only at speeds less than 50 mph and in high gear. Some said I was lugging the motor. Even a mechanic friend drove it and said I lugging the motor. I could drive around it as long as I kept the rpms up.

But just a couple days ago I replaced motor mounts and transmission mount. The motor mounts definitely looked bad. It fixed my problem!

Last year I also replaced u joints hoping that was the problem.

Good chance your mounts aren't bad, but you never know!

Mine was driving me crazy.

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01yellercobra

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I had a bad vibration in my 90 coupe. It has a irs. The whole car would shake violently. Generally, only at speeds less than 50 mph and in high gear. Some said I was lugging the motor. Even a mechanic friend drove it and said I lugging the motor. I could drive around it as long as I kept the rpms up.

But just a couple days ago I replaced motor mounts and transmission mount. The motor mounts definitely looked bad. It fixed my problem!

Last year I also replaced u joints hoping that was the problem.

Good chance your mounts aren't bad, but you never know!

Mine was driving me crazy.

Sent from my Moto E (4) Plus using Tapatalk
I wonder if something was touching randomly at the lower speeds? My son had something similar in his 98. I kept telling him something on the exhaust was touching the body, but when the car was on stands everything seemed fine. When we pulled the engine we found rub marks between the K member and mid pipe. And the motor mounts fell apart once they were clear.
 

1CobraSVT

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Not positive this is your issue but it helped mine and I had a very similar issue with a slight vibration. Did you set the pinion angle after replacing the front differential bushings? It needs to be set at -3 degrees.
 

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