So about a year ago I did a major overhaul and spent about 10K+ on getting all the little things taken care of on my 2002 a4 firehawk, and pretty much have not driven it much since, maybe 5K miles. Recently my Audi RS5 got it's 6th flat tire for this year, and it's sitting until I can afford a replacement rim since it took out the rim when the sidewall blew. Lately I have noticed a strange driveline vibration that has been getting worse at speed, and I can replicate the shutter in park or neutral. It did not happen when I first had all these mods put on the car by RPM motorsports:

ARH 1 7/8th Headers and Offroad Y
Circle D 3400RPM Stall
BMR Trans Cooler
Fixed Rear leaking Pinon Seal
Waterpump
Rear Main Seal
Dyno Tune
BMR Lower Control arm and poly mounts (Had this prior to last mod frenzy)
Most pullies replaced, except for tensioner, new belts
Trans flushed, fluid/filter replaced
Front Control arm bushings replaced
Poly Motor Mounts installed
My flex plate had grenaded and split in half, so a new SFI flex plate was installed with the converter along with a new starter
New cover installed over flex plate and converter (broken flex plate took out a cover housing bolt, so it was drilled out and replaced)
All hoses touching anything coolant related were replaced
Thermostat replaced with 160Tstat
New spark plugs and wires
New Diff Fluid with limited slip additive.
Alignment, Tires Balanced


I would say after about 3,500 miles and a year later, suddenly after about 3K RPM I get this pulsating vibration you can feel in the steering wheel, and it gets worse and seems to be a "circular" rotational vibration, especially at speeds of over 80. WAAAAAAaaaaa___aaaAAAAHHHhhhh____aaAAAAAhhhh___aaa aAAAAAAHH_____It feels the same in neutral when I get the RPMS up to 4/5k, but not quite as bad since it's not moving. I first noticed this problem about 3 months ago when a SES light was coming on, and I felt the car or converter was not locking up right keeping the RPM's up way high. It went away after a couple WOT bursts, but has intermittently popped back up since then, which worried me but it kept going away quickly and not coming back too often. Today it kicked on again and I managed to catch the codes at autozone before it cleared:

P0128 Coolant Thermostat
P0757 Shift Solenoid "B" Stuck On

What perplexes me is the fact that I have not felt this vibration before, and due to the fact that my flexplate had split in two before the converter/housing/rear main seal/starter/flexplate replacement, I am worried that I am doing damage to something. It's quite loud and makes the car feel like something is going to blow up, but it shifts smooth as always and the motor does not feel like it's missing. I am wondering if maybe I scraped the y pipe and its vibrating against the chassy, since RPM highly recommended the ARH headers and offroad Y for fitment. They tucked right up and had no prior rattle, but I can't see anything visibly wrong. When I shake the exhaust by kicking it, it is solid as a rock. Would it be the U-joints if this vibration that I can feel in the steering happens in neutral as well? Tensioner or harmonic balancer? It sucks to have dumped so much money in the car only to have it feel like it's about to vibrate apart on the freeway, something that never happened prior since I always take good care of it. This is the 3rd thermostat replacement I have put in the car, I went through a bad one, then a leaking one, and then finally replaced with the aftermarket 160.

On a side note my car EATS wheel bearings, I have probably replaced at least 8-10 in the 8 years I have had the car. I finally got fed up and bought a timken bearing for the one side at double cost, which has a lifetime warranty, but lately I am getting a lot of highway wander, where the car seems to have a mind of its own pulling all over the place. The only thing I can really think of at this point with 93k miles that I have not replaced is the shocks, they are dried out and starting to squeak, and power steering pump which leaks about a drop a year and fluid wetness can be seen around the cap (has had this since 20k miles, but steering works fine), and I have the most stubborn brakes in the world. Brembo blanks, drilled and slotted, OEM, powerstop, doesnt matter they warp eventually, and my caliper boots always seem to get a hole in them causing the piston to lock up, a big *** hammer and torch, and a rebuild kit. No matter how expensive the brakes/rotor combo I put on the car, they still always make a noise as if the clips are rubbing since maybe 40k miles. I think the best brakes I had were the 90 dollar ebay rotor/brake combo for all 4 recommended in the fourm worked the best, because when they eventually warped I was not upset since I did not pay 100 plus a rotor. What suspension related item am I missing to firm up the directional pointing of the car? Tierods? The wander combined with the vibration in the pedal, steering, and under my butt make the car feel like crap. I know my buddy and I were having problems getting the car aligned specifically with caster on the left wheel, the best it could be adjusted was 5.61 degrees, which the specifications are 4.30 to 5.30 max. We did find a bushing split in half for the control arm, and that was replaced, fixing the "popping" noise I would get backing out of my driveway at full turn, and RPM did not report any problems with aligning the car afterwards.

Any ideas? The few posts i have found that the vibration persists when the car is in neutral, have no answer, because most of the posts the vibration exists only when driving.

 

That was a very well detailed post describing a very difficult problem to diagnose.

I'm going to try to infer a few things:

1. The vibration follows vehicle sped not RPM. In other words it does the same at 80 MPH whether in 4th or 3rd gear? If so, you can mostly rule out the motor. Sometimes the trans mount can cause issues if it is poly. Lots of guys on here, myself included, find the best configuration is poly motor mounts but stock trans mount.

2. The individual pulses of the vibration can be felt, not an audible vibration? Or is it both, but the audible one comes and goes? The reason this makes a difference is at 80 MPH, the driveshaft spins at 70-something revs per second, which is audible. The wheels spin at 20 or so which is basically inaudible, but you can feel it in your gut or the steering wheel. Usually if it's the steering wheel, it's a front wheel causing it. In my case, an air bubble in the passenger front tire caused the steering wheel flutter I was feeling.

3. If you can feel and hear a vibration that comes and goes, the U joints are a good thing to check. Mine had a flat spot where it sort of clicked into place, but it felt fine otherwise. Two lakewoods later (front and back) and that quit happening. You would also want to check pinion angles. There are about a million threads on that, but the easy way to look at it is to make your trans tail shaft and rear axle pinion parallel. Ignore the driveshaft angle, if the other two are parallel, the angles will cancel out and you'll be ok.

4. Chewing through brakes and wheel bearings is something else though. And could be causing a tire to fail and make a bubble. Out of time for now, but at least there is a few things you can at least investigate without throwing parts at it.

 

Well if you are certain that it is the same vibration/sound that you replicate when reving in park/neutral, then it is not a rotational vibration (i.e. wheel bearings, driveshaft, diff, ect). This then, in my opinion, would narrow it down to something the engine is connected to, since the rpms are seemingly causing the problem. Definately check the exhaust components. Best way to do this is lift the car and have someone inside the car reving and replicating the vibration, as you are under it trying to find the source. Do a cold start and wear some heat resistand gloves and apply tension to various parts of the exhaust while you hear the vibration and see if it stops when applying pressure to the exhaust system, or changes tone. Be careful not to burn yourself! If not the exhaust, then look elsewhere like motor mounts, or tranny mounts; hell push up on the engine and tranny, put your hands in various places near the sound to try and feel the vibration and track it down. Either way, best way to find it is have a buddy rev it and replicate it as you do, as you look around under the hood, and under the car trying to find it.

 

Possibly the converter?

 

Thats why I was saying track down the source first. If he puts his hands on the tranny and determines it to be the source, then it is something inside it if not the mount, like the convertor as you said, or worse! Hopefull it is something simple and external, wherever it is comming from.

 

The converter not locking up properly would have me worried

 

agreed