Need help with vibration.......Q45Tech are you out there?

[pdqwrx]

Hello- I am fighting a wicked vibration that seems to be coming from the entire car. It seems to be VERY low frequency (Maybe 20-30 Htz) and falls between 28 and 38 MPH. Now I have searched and found a old thread that talks about replacing the center bearing support on newer Q drive shafts and I am wondering if that is true?I have a 1994 non active Q45 with 110000 miles. This vibration has been there since I bought the car at 920000 miles or so. I have had 3 different sets of wheels on the car as well as new rotors front and back. Now, about 2 weeks ago I bought new motor and transmission mounts and installed the transmission mount first because it was easy. I then drove on a trip and put about 900 miles on the car with 4 adults and a trunk full of gear. On the way home for about the last 300 miles or so the vibration became much worse. Once home I installed the motor mounts, turned the front and rear rotors and had Americas Tire rotate and reballance the new tires (Less the 1100 miles) and saw no change. While it was on the rack we visually checked the drive line and everything else that spins under the car and saw no real source for the vibration.So I am hoping that I can replace the bearing support and perhaps with some help from the car Gods, fix this dang vibration..... with out buying a new shaft because the u-joints all seem fine and ther is no play ANYWHERE in the shaft. Thanks inadvance for any and all help....

Scott

[pdqwrx]

I forgot to post the link to the original thread that talked about the bearing support.

zerothread?id=19744

ThanksScott

[maxnix]

I would suspect the drive shaft. Loading the car as you did may have prematurely worn the 3rd motor mount as teh primary ones were probably shot and out of alignment.

It is possible you have damaged the pinion shaft on your differential. Read Q45techs vibration posts. Very difficult to describe, let alone to daignose, via text. Probably best to get it on a dynamometer set up and view the drive line in motion from underneath.
Modified by maxnix at 10:02 AM 4/1/2006

[Q45tech]

Put it on a 4 point lift, have someone [you trust] drive it in gear up to 70 mph and get under it ....feel look.

[pdqwrx]

Thank You Q45tech, I will try that. Just currious, why 70 mph? Are we looking for a odd harmonic of the actual frequency? I ask because I have no vibration when driving from 40 to past 100 mph.

ThanksScott

[elwesso]

Scott

Heres what I would do... Get a new center bearing from PTI (power train industires, http://www.powertrainindustries.com).. They are cheaper than the factory ones and are going to be about as good

While you got the shaft out, beat the living hell out of the U joints to make them smooth... I bet when you remove the driveshaft youll find the Ujoints are very notchy.. Take your hammer and bang onto them until they are nice and smooth...

With that plus the center bearing should eliminate the driveshaft, as the 94 driveshaft doesnt need replaced like the 90-93 due to the redesign.

[Q45tech]

Tires have a 55-70 mph [~~13Hz, 26 Hz vibration] drive shaft starts around 20-25 mph].....might as well check all possible additive sources/rpms while you have it in air.

[Q45tech]

'They are cheaper than the factory ones and are going to be about as good"

Not as good as a brand new complete drive shaft assembly.

All depends on your standards.

[pdqwrx]

Well I ordered a PTI bearing support (My local parts guy got it to me for $65.00 shipped) and it will be here Monday. Hopefully it will do the trick.

I do however have a question about hammering on the U-Joints. Am i pounding the caps back on or just blindly beating the s_it out of them????

I also am waiting for a call back from my not-so-local Infiniti dealer on a price of a new drive shaft. I am a little concearned though because they didn't see a complete unit part # she said it looked like it came in pieces....Anybody have the part # handy? Or do you have to buy it in pieces?

I am pretty picky and generally not a cheap ***, but I figure I will gamble with $65.00 to atleast see if it changes thing enough so I knoe that the drive line is my problem.

ThanksScott

[elwesso]

'They are cheaper than the factory ones and are going to be about as good"

Not as good as a brand new complete drive shaft assembly.

All depends on your standards.

However IMO its worth it if you get 90% of the vibration with about 10% of the cost!!!!!!!!!!!!!

You can get a complete shaft from PTI for $455 thats BETTER than OEM because you can fully rebuild it later if you so choose... new OEM from Joe is over $150 MORE Basically it should last a lifetime as long as its not physically damaged!

Regarding the shaft U Joints.. heres what I did... ONce the shaft is out, take your hammer and hit the back part of the joint back/forth... Then i like to take the round of a ball peen hammer and hit the caps a little..

occasionally I would take a low temp torch ( a smallish propane torch, not a gas cutting torch) and just warm the joints a little.. The jidea is that you move the grease around ot make it smooth.....

Its less important,but you can disconnect the 2nd half of the driveshaft from the 1st half and hit the front U joint but they arent nearly as stiff! BE SURE TO MARK ITS ORIENTATION....

[pdqwrx]

Good Info....Thank You All.We will see if this takes care of it next week.

Scott

[texasoil]

When whacking on the universal joints, be carefull not to hit directly on the thin metal cans/caps that hold the needle bearings. The caps are very thin and easy to dent (which makes for a REALLY notchy joint)

What you are trying to do is shake the needles loose from the packed and hardened grease. The Q45 joint has very little angular motion and lack of movement tend to cause the rollers to stick and slide rather than roll--which leads to the 'notcheyness' described.