Which of these paths should I try first?

[firstq]

My Q is starts to vibrate right around 30MPH (vibration in the seat, hand rest, and steering is observed with a growling noise as well).

- I have 4 new Yokahama Yk420 ride matched/balanced (2 times) tires (hunter 9700 machine @ discount tires)- The car does not pull in any direction - very straight- Reving up the engine does not bring the vibration before hitting the 30MPH threshold- Manual shifting of gears does not make any difference (happens in 2nd as well as 3rd)- With more speed > 40 MPH - either the vibration lessens or other noises subdues this vibration

Some options I am considering:

1. Do a pan drop and ATF flush with Mobil 1. I had done a flush recently (2k miles ago) but the fluid is not Mobil 1 yet. I removed some of the ATF and the vibration has lessened a bit (but not gone completely). The car just got a new transmission mount, but the vibration is still there.

Cost around $130.

2. Have the car alligned. The car is not pulling in any direction, very straight. But I am not sure when last alignment was done by the previous owner.

Cost = $50 for cheapo place or $120 for the dealership

3. Go for the Drive Shaft.

Cost = roughly $1k

I would really appreciate if you gurus can help me prioritize the next steps. I know number 1 & 2 are not that expensive and should be done alnyways - but if my priority #1 is to fix the vibration, what makes most sense here?

Anything that I may have missed (wheel bearing out, etc)

Thanks.

[maxnix]

Sounds suspiciously like driveshaft and/or bearing from other previous posts. I am sure some members who have experienced this failure mode personally will reply soon.

[Q45tech]

Put the car on a lift have someone slow accelerate in drive while you watch from the underside.

What is the total gram weights added to both the inside and outside of each tire?What is a Yk420 ?.....the tread wear........ is this a v rated tire per manufacturers specification? What was the radial force imbalance in pounds from the Hunter 9700..............less than 5% of the techs that have access to one know really how to use it!

[Mayhem_J30]

Sounds suspiciously like drivehsaft and/or bearing from other previous posts. I am sure some members who have experienced this failure mode personally will reply soon.

my thoughts exactly. i didn't know it costed so much to repair the Q's driveshaft.

[Q45tech]

The drive shaft is the least expensive subassembly in the powertrain! $6k engine,$3k transmission, $1k driveshaft, $2.8k diff..

[Mayhem_J30]

The drive shaft is the least expensive subassembly in the powertrain! $6k engine,$3k transmission, $1k driveshaft, $2.8k diff..

cheap in perspective to the rest of the powertrain, BUT when put next to what it costs me to fix my beater's driveshaft($15 for new bearings at NAPA) it's astonomical.

[firstq]

YK420 = Yokahma tire line (Discount tires are selling them for some time)

These are H rated tires. But let me say this, I had the worst four tires on the car (previous owner) before I got Yokahamas. The discount tires would not even touch those for balancing (fearing liability). Now even with the new set of 4 tires, the vibration start exactly at the same speed 30MPH.

The true match was 3% for the fronts and perhaps 7% for the rear (if I remember correctly). The tech told me that anything under 15% is acceptable - so for him , the fronts were excellent and rear well within the specs (per his numbers).

The heaviest wt was perhaps 1.5 grams the rest were less than that.

The behavior is exactly the same - 4 rotten out of balanced bald tires as opposed to brand new ride matched yokahama's Yk420. Upto the speed of 30MPH, the car glides on the new tires - does even feel if it is on the road, as soon as I hit 30MPH it just starts vibrating - everytime.

[Q451990]

What's the mileage on your Q, what year is it, etc? This will help a lot in telling you what's common and what to try first.

Heath

[Q45tech]

The smallest commercial weight is 5 grams clip on, 7 grams adhesive stick on. Hopefully [not] you are reading the 1.5 on the weight as grams when it is ounces........anything more than 1/2 [0.5] ounce [14 grams is a lot] .

So you decided to purchase a tire with a compound more than twice [?] as hard as the factory recommendation [tires that left the factory on the Q were 200 tread wear] and one that was less robust [weaker] than the factory requirement .....V rated required per manual! It is not a mandantory requirement to meet the factory specifications only a legal proof of negligence in an accident if you don't, same as using after market brake pads.

9 out of 10 times a vibration that starts at 30 mph is caused by the drive shaft the other 10% are caused by out of balance torque convertors. Tire vibrations start around 55-60 mph.

Assuming that the tires are not flat spotted [fairly rare on new H rated]. And this would go away [diminish] after 10-15 miles of highway driving as the tires warm and get rounder!

Anyway you said the old tires did the same thing so its not the tires.

[firstq]

Heath - it is 92Q with 100K miles on it.

Seems like it is the deadsful Drive shaft -

Have members been dropping drive shafts themselves or is it a tough one due to weight, effort, complexity, tools, etc ?

[Q451990]

That's my guess. I was lucky keeping the OEM unit until 160K or so, but the center bearing was shot. Dennis (Q45Tech) said the carrier play was the worst (or nearly the worst) they'd seen, but the shaft was remarkably still balanced.

I'd say it's not a bad job if you're somewhat mechanically inclined. I replaced mine with the help of my dad in about two hours. You don't have to drop the exhaust. Remove center carrier, unbolt tail flange, then drop the back and slide the front out. Reverse for installation. I avoided it for a long time, but it's really pretty easy if you're comfortable with some large wrenches and a big torque wrench.

If you do the drive shaft DIY it should cost about $450 plus about $37 for updated center carrier brackets if your car came with the old-style carrier bearing. I believe Scottsdale and Lisle are both offering free shipping on $100+ orders...

Good luck!

Heath

[Professor_Mike]

You could raise the rear of the car up and put the frame on jackstands, remove the rear wheels and reinstall the lug nuts. Usually if the vibration is still present the driveshaft is the culprit. Also you can check underneath while someone runs the car up to 30. Be careful the driveshaft will be spinning and the exhaust very hot.