Q45 Vibration Problem

[rover3l]

I need some fault finding help on this one

Since I have owned the Q few months, I have noticed a mild but irritating vibration felt through the body structure. I thought it might be the active suspension but since replacing the strut accumulators on Wednesday the vibration is still present.

I can feel the vibration to the greatest extent at about 40-45 mph but it is there as I accelerate to this point.

Idle quality is very smooth, I changed the plugs recently

Could it be tires, wheels, engine / transmission mounts, anything else

[911/Q45]

Try the trans mount first.

[Chally]

If it's in 3rd gear, you may never remove it. I've done my rear mounts & removed the Exhaust ones, & it seems to be a Harmonic balance from the Engine/gearbox. Knock it into 4th & see if all is OK.

[Q45tech]

Normally 40-45 mph is where the drive shaft imbalance shows up.That is easily checked on a lift with a helper holding/accelerating various speed while you are under the car feeling/ looking /measuring the vibration of components.

Some problems/sounds require the car to be the coorect distance of the road [sound cavity created between floor pan and road.......these require a dyno to simulate the road and a brave tech to crawl under............why I like elevated dyno with working space under.

http://www.acsoft.co.uk/page6.htm

[rover3l]

If this is the problem what is the solution?

1. New drive shaft $$$$$$$2. Hopefully rebalance existing drive shaft $

[maxnix]

If it's in 3rd gear, you may never remove it. I've done my rear mounts & removed the Exhaust ones, & it seems to be a Harmonic balance from the Engine/gearbox. Knock it into 4th & see if all is OK.

There is a TSB on this for 1995, but I think it applies to 1994 G50 also.

[Q45denver]

There is a good article in the November Popular Mechanics magazine on balancing a driveshaft while it is on the car. Basically use two hose clamps and rotate until balanced. Didn't the 1994 have the updated driveshaft?

[Chally]

I've had mine out & checked & balanced & still have the same problem.If the shaft was unbalanced, the vibration should be there in any gear. That's why I consider it a Harmonic Vibration & not the usual Static one.It's more of a pain than a problem.

Let me know if & how you stop yours, especially in 3rd gear.

[zfixxer]

check the center suport bearing on the driveline. if it is sagging this will cause a vibration at lower road speed. and can be very noticable on med to heavy accl. look at the bearing and its mounting. you can see if it is sagging downward.

[Q45tech]

Another source of vibration changes are the rubber exhaust hangers and isolator supports near the rear of transmission.

Again if it's rubber it must be changed frequently

[rover3l]

ok I will check all these items. I have just been on a fairly long trip today 120 miles so was able to evaluate this further from inside the car. It is at a maximum at 45mph and revs at about 1600/1700. I can feel it as a high frequency vibration through the car. It is quite low in amplitude but still annoying. The rear view mirror vibrates as a consequence. I have tried putting the car into neutral and trying to hold the revs constant and it under this condition the vibration is still there.

Note I have not ever had the wheels balance in my 2 months of ownership. The balance weights are 35g on both of the passenger side wheels and 10g on the drivers side rear and 20g on the drivers side front. At least I think g are the units. Putting it another way the weights are 1.5inch long, 0.5 inch and 1 inch respectively.