Short

2003 w/105k miles.

What happens: Pulsing vibration felt in the seat only. It is very subtle and sometimes hard to tell on different pavement. It has a very steady cadence and gets more noticeable when you accelerate. The pulsing continues when you let off the gas and brake, but doesn't get worse like it does when you accelerate. I cannot feel anything in the steering wheel or visually see any kind of shaking.

What has been changed before the vibrations in the last month:
- Over a month ago I had Jason at CNC adjust my valves and look over my car (for the 105k service), he suggested I change my rear differential mounts and repack the driveshaft with grease ( grease had flung in the transmission tunnel).
- I had two new rear tires mounted, balanced, and the car aligned about 3 weeks ago.
- 4 weeks ago I installed new rear brake pads and rotors. OEM pads and Centric Rotors.
- Four days ago I installed the Megan Racing Differential Mounting Kit with Redcelica. On the 3rd day after the diff mount installation was when the pulsing vibration was noticed. Everything was fine until then.

What I have done so far:
- Wheels were checked by Discount Tire and rebalanced. They said all wheels looked good and were all true, only a little out of balance.
- I jacked the car up and noticed the Differential mount bolts were all very loose. Bam I thought that was the cause. I took them to my mechanic and had them torque everything down to spec.

Notes:

UPDATE: As soon as I disengage the clutch, the vibration goes away immediately. Re engage and the vibration comes right back..

The pulsing vibration is still there...not as bad as it was before re-torqueing the differential mount bolts but still noticeable.

Redcelica recommended I drive the car for a few days and see if anything gets worse. I will also keep an eye out for the diff mount bolts and make sure the vibration is causing them to back out.

The only other thing I can think of is the CV boot, but I get the vibration off throttle too.

Jason @ CNC did mention if I didn't get the driveshaft re-packed with grease I would eventually get vibration but I feel like it would happen all the time, or atleast under load and not just at highway speeds (60 mph+).

I've read every thread on this possible, not sure what else to check.

Sticking Rear Brake caliper?

Slowcrash_101

Maybe whoever balanced your tires did a poop job. Happens more often than you think, maybe take it some place else.

Short

Yeah, maybe...I probably shouldn't have taken it to Discount Tire.

I'm going to check my rear brake calipers tonight and make sure they are not sticking...after that idk what to do.

I did notice an excessive (what I think is excessive) amount of weights on one of the rear wheels. I think I counted 4-5 and usually I see no more than 2-3..

Slowcrash_101

Yeah probably badly balanced tire, if the tire is properly lined up to the wheel you shouldn't have much weight on it at all. Some new tires come with markings, sometimes red sometimes yellow, sometimes both. The red mark is supposed to be aligned with a mark on the rim, the red dot is the area of max run-out and there's usually a mark on the wheel that corresponds to this. The yellow marking is supposed to be aligned to the air valve, this is the high spot on the tire, which goes with the low spot on the wheel(valve stem, as that area has less wheel material). If there are no marks, then the tire should be de-flated and moved on the rim, re-inflated and re-balanced. I barely have to use any weights on my wheels, and you'd be surprised how many techs don't know this.

If the tire only has a red mark, and your wheel has no mark, then align it to the valve stem, it usually lowers the amount of weights needed to balance the tire.

Short

I didnt see any red or yellow dots on the tires. I did notice these markings on the tire which seem odd? Maybe it just happened during shipping?

I do indeed have 5 weights on my rear drivers tire. I also remember being able to feel the vibration a tad bit more in the driver seat verse the passenger side.

Slowcrash_101

That is odd because I have those same tires, and I'm expecting a new set today, and I clearly remembered a red dot on them. Those markings are just the soap based lubricant being flung out.

Slowcrash_101

Maybe worn shocks? Are they the original ones on your car? Maybe the vibration is the lack of damping letting the wheel assembly jump up and down at highway speeds.

Slowcrash_101

These are the markings I'm talking about.

Short

Yeah my front tires have red dots but they don't seem to be aligned with the valve stem or any special marking. There is no markings on the rear, unless they are on the inside of the tire..

I checked my psi and had 35 psi in the rear and 30 in the front, I put 32 all the way around and that didn't help one bit.

I may take it for another balance in the next few days..

Short

I don't think its my shocks, Jason at CNC who specializes in S2000's told me my shocks and springs look fine.