Got new tires, vibration still there!

[mersidoe]

Well, I finally got the other two Yokahama Avid H4's, so I have matching tires all around. They aligned the car again, so that's covered. I was really hoping that would do it! The good news, I guess, is that the "little shake" around 35 is gone, but the other vibration, that was around 50 mph, has now moved to 60 mph! It seems to be speed specific, not RPM specific. (Does that make sense?)

It's most noticable in the steering wheel. My son, as a passenger, didn't feel it, but whoever's driving certainly does! Cruises nicely at 80, tho!

I plan on "ignoring" it for a while, while I pay off the other repairs, and the repairs on my son's Toyota, but I know it will get to me eventually. My question is this: Since the speed at which it vibrates changed with the new tires, does that mean it's somehow related to the tires, or could it still be elsewhere in the system?

I had the carrier bearings replaced a few months ago, and the dealer says the next thing to do would be to have the driveshaft rebalanced or replaced, but I'm hoping not to have to go there. Is there more I should check into with the new tires?

[maxnix]

If it changed with speed and and the new tires, it probably is tire (or perhaps, wheel) related, expecially if the suspension rubber is up to new specifications. How thorough was the the tire mount and balance? Did they check the whels first for in specification performance?

Do read Q45tech posts on tire balancing, and you can grasp how difficult and time consuming it can be to do properly.

Looks like you are making progress!

[rsiwicki]

I don't think it is the driveshaft. For driveshaft problems, you should feel that throughout the body of the car, kinda like from the rear of the car versus just the steering wheel. When my Q driveshaft went, my steering wheel was perfect, but you could feel a vibration coming from the floor board of the car and toward the rear....especially in the back seats. I would suggest going to a different place and have them first take off all the existing balancing weights before balancing and then have them rebalance them. I bet that some of the weights will not be in the same place as before as this is what happend with my car one time.....the existing weights made the wheel balance, but when you took off the weights and then balanced it we consistently got a different spot and weight amount....after that, all good.

[Q45tech]

Wheels, brake rotors, tires.What is radial force imbalance of each tire wheel combo? Without an accurate number everything is speculization!

[carlos_knology]

... everything is speculization!

You should never speculize.

Dennis, I missed ya last friday. I was at T3 (South Cobb) for most of the day. Byron did a great job on the J30. Sorry I missed you.

Carlos

[HeavyDuty]

Discount Tire stores seem to have the newer equipment for force balancing.

My vibration was at 40mph, but my driveshaft was kaput. The driveshaft took out the pinion bearing, so after a brief fix with the new ds, it's back, but diff related.

[Q45tech]

By now hopefully members know 30-40 mph vibration = driveshaftand 55-65 mph = tires wheel balance [and warped rotors] and a steady increasing vibration with peaks at 55-65 and 110-130 = tires that have too much radial force variations.

Vibrations that change with temperature, get better as tires warm up at same speed is a radial force problem.

[shadedoc]

Q45Tech is right on the money(as usual). I'll try not to get too technical here, but if I digress, just ignore. If the vibration is between 12-17Hz (12-17 shakes per second) at a speed of 50~60mph, it is not caused by your drive shaft. The drive shaft turns at a much higer rate, hence the vibration will be at a higher frequency. Long story short, try swapping wheel/tire assemblies front to rear first. If it doen't improve, find a shop that will "finish balance" ("on the car balance") your front wheels. THIS WILL IMPROVE YOUR VIBRATION if it is a singular or combined weight induced vibration. Down side is that it will have to be performed each time you rotate your tires. Even if you don't rotate your tires, the force variation will change over time/driving and you will have to get it rebalanced.

The more detailed version:

If the shake in the steering wheel is oscillitory (rotational) rather than purley vertical or laterally, then this is usually caused by force imbalances at the wheel. The force excitation which causes the larger amplitude displacements which most customers complain about is a 1st order harmonic. This corresponds to once per revolution of the wheel. The force variations which cause the vibration can come from a varity of different sources. The tire, the wheel, the combination of tire and wheel, or any other rotating component at the wheel (hub, brake rotor, etc.) From a very refined perspective tires are never round, more egglike. This egglike shape can be the cause of your 1st harmonic. Tires are also considered springs, and just like the egg shape, their spring constant is not uniform all the way around, hence this can also be the source of the 1st harmonic. Wheel can have the same effect (egg shape) as the tire. Additionnaly, if the wheel does not attach exactly at the center of the wheel hub ( and it never is 100% true) this effectivly give youthe same excitation force as an egg shaped wheel. Usally peoplebalance wheel/tire assemblies on a traditional static/dynamicbalancer and then mount the wheel/tire assembly on the vehicle. But lets say the brake rotor also has an inbalance. If the wheel ismounted in such a way that the brake rotor imbalance adds to thewheel/tire assembly imbalance + wheel & tire R1H (spring etc.) you can have an ugly excitation force. Even a very good RFV wheel/tire assembly may not improve the vibration to a suitable level for you if you have other issues. Suspension geometry & bushings have a significant effect on this type of issue, but if you can remove the excitation force, vibration is gone. As far as temperature effects, tires will "flat spot" after sitting parked for as little as overnight. Usually the flat spots will disapear after driving about a few miles. However, if the weather is cold, flat spots may take longer to drive out. Different tires may have different construction that are more resistant to flat spotting. Worst tires for this are usually summer/performance oriented with Nylon cap construction (look at the type of belts in the tire, this is printed on the side along with tire size DOT code, etc.). I suggest increasing your tire pressure to the higherpressure specified on the vehicle tire placard to improveresistance to flat spotting.

[shadedoc]

Sorry missed some things.

To get a "good" dynamic balance and phase matching of the wheel/tire, you need to find a shop that has a Hunter DSP9700 which all-be-it crude, is the best Road Force Variation / match mounting available to the general public.

The finish balancer is a different machine that measures the imbalance of the spinning assembly on the vehicle. It looks like a little cart the tech sits on and presses a small driving wheel against the vehicle tire to spin it up. I've never used anything other than a Hoffman, but I know there are others out there. Last I recall, this was a standard piece of equipment at Lexus dealers.

[Alan]

This is very interesting. Shadedoc, sounds like you must have studied extensively in this field.

I have a 1972 Italia, with a vibration that I have been trying to diagnose. Just took a run with the things you and Dennis have said in mind. I know the car has worn upper A arm bushes, but new ones are currently unavailable. Altho the wheels were just balanced the tires are very old and the quality and tune of the wire wheels is dubious. I think I'll try a "finish balance"

Thanks, Alan

[shadedoc]

Can't imagine dealing with wire wheels. Talk about a uniformity nighmare. I imagine you wan't to keep the same rubber you have, so make sure you have them try to phase match the wheels & tires on a 9700 first. The upper bushings, will play a role in the vibration. But primary influence is going to come from the lower control arm. I'm not that familiar with low volume Italian, but I'm guessing it is built around A-arm configuration with a Rack & Pinion steering gear. Steering gear mounting can be a splayer in redcuing this vibration as well. If the gear is hard mounted (no bushing), check the alignment to the gear fore-aft. Do this by measuring from the center point of the knuckle (lower control arm attachment to the wheel side) to the end of the steering gear case. You want the same longitudinal distance side to side. If it is bushing mounted, check the condition of the bushings. You can also adjust the preload on the gear. This will increase the system friction, but may also help damp the vibration.

[natsoundup]

are lower control arm bushings replaceable in the front of a first gen Q?

[shadedoc]

In the Q45, the "ride" bushing is contained in the Tension Link. It is a hydrobush. If the bushing is torn/cracked, etc. it looses hadraulic flud and it's damping capability. Yes, I think there are replacement bushings out there, but I don't think the hydrobush in the Q45 can be purchased seperately. And before you ask, No I would not replace the bushing with solid bushing. I would imagine, Nissan engineers tuned this bushing to reduce the vehicle sensitivity to the vibrations we are talking about. A solid bushing will not provide nearly the same dynamic damping as the hydraulic bushing.