I don't have advice for how to troubleshoot, but the not-always-there intermittency makes me think of exhaust hangers and flexible sections in the exhaust system. When failing, they can transmit vibration (and often noise) to the car body in various configurations of gear and load and speed.

 

I?ll give it a look when I can get the Passat into my garage. The odd thing about these vibrations is that there is really no noise associated with them. No clicking during wide turns at slower speeds to indicate cv joints, no thumps or pops to hint at a blown ball joint.

When I purchased the vehicle I mentioned the vibrations and thought they were maybe unbalanced tires. So to make the deal they claimed they would have them balanced before I bought it. I test drove it and the vibrations seemed less apparent, so I made the deal. However, being a used car dealership, I wouldn?t be the least bit surprised to learn they never balanced the tires. I?ve experienced unbalanced tires and there?s usually a small speed rage that you can feel it, not 30+ mph. So I?m hesitant to believe that is it.

Truethfully, I know I need to just get it up on jack stands and take the wheels off and start testing bushings, ball joints and tie rods and maybe ensuring that they?re all snug, but it?s hard to find the time. Money is somewhat tight so I?d like to pin point the issue before I start replacing everything.

 

Check the motor and trans mounts along with the snub. Are they original axles?

 

An out-of-round tire could behave as you describe, vibing above a certain speed.

 

Tires..

 

Today I listened while driving on the interstate and there was a harmonic hum that I would think has to be a tire. Bearings make noise at slower speeds as do other typically worn parts but I am thinking that maybe a tire is out of round. There is probably just enough tread on them to pass inspection so I will be due for some new ones come snow season. Also, I am much preferable to road force balancing than the speed balancing that the dealer claimed they had done.

I do no know if they are the original axles. I did get under and try and give the cv shafts a wiggle and they didn't seem to have slop. But again I'd like to get it in the garage and get it on jack stands before I assume they are fine.

 

when i got my car used (05 4motion 1.8 ) it had 3 out of shape rims . changed all 4 for like 100 bucks a rim .. 194,000 late the car still rides excellent . good tires help a lot too .

 

Another detail, this morning was colder than it has been and the vibrations were much more present at first. I am guessing until the tires warmed up. I've been setting the cruise control on my way to work and I tend to not feel much of the vibrations while under load going uphill, but once I level out or go downhill they come back. I wouldn't think tire vibrations would change under those conditions. I'm hoping to find some time tomorrow to crawl under this thing and take a look.

 

that seems to point towards your drive axles/cv's which can be exacerbated by a number of things, tire/rim(wheel balance) , brake rotor warped or not balanced, and crap built up on inside and outside of brake rotor where it mates against drive axle hub (crap on it too) and wheel ,just a tad at those mating surfaces/points ,lets say 1/2 mm translates to 4mm at the tires circumference,especially in Northern climates, snow ,hot and cold......

 

I disagree: I think tire vibration would indeed increase when cold, and persist until the tire was warmed. If cold, the tires will be far less flexible until they warm up.

 

Sorry, I did say ?under those conditions? but did not specify. I agree cold would make a change in their performance, I meant not felt under an acceleration to keep speed up hill and then present when flat or down hill when the throttle would be steady or coasting. Tires should vibrate both up and downhill, acceleration wouldn?t make that better. Maybe the CV joint(s) have slop but not enough to be audible...

 

Took the wheels off yesterday and took a glance at the suspension components. Everything looked surprisingly good for 86K miles, but it was apparent that at least one axle has been replaced because the passenger side had the recessed hex button head bolt and the drivers side had a hex head bolt. The passenger side looked newer than the drivers side and had no noticeable slop. The driver side had some rotational slop and in and out play and had a good coating of surface rust on the axle. I also found that there are two pairs of tires on my Passat. Both have decent tread, but the newer pair was in the rear so I did a rotation to get them to wear evenly. The front driver side had more wear on the inside edge so I'm thinking I'm going to be due for new struts and/or alignment in the near future. I will know more once i drive on the rotated tires, and I still need to check on all the mounts.

 

An after market axle can cause unusual vibrations. Aftermarkets have solid shafts while originals have hollow shafts. Do the bounce test on all four corners to check the bounce (there shouldn't be any) It's should be fairly stiff.

Other than that see what happens after the rotation.

 

Well rotating the tires made it terrible. Apparently the rears may have had more tread, but are less balanced. Tons of shake in the steering wheel now, to the point it worries me enough that I will swap on the spare or rotate them back when I get the chance. I need to have an inspection done probably this weekend and I am going to have the tires road force balanced. I also noticed a popping noise when I was checking for play of my tie rod. I didn't see it on the outer rod and thought maybe I was pushing too hard, but when I did a search it seemed to be a common symptom of inner tie rod failure. Today when I parked at work I moved the steering wheel back and forth and could hear a distinctive click. I did some quick research and found many others mentioning the loose steering rack bolt(s). I ordered some new complete tie rods from ECS because the outer seems loose on its side to side play. Looks like I will have a few things to tear apart and inspect further.

Also, the brakes are all brand new, very little surface rust and a ton of pads left. Oddly though, the brakes seem too spongy. They stop well enough, but with brand new rotors and pads all around I would think they would be a lot more touchy than there are. Looks like I may need to bleed them.

 

Worn tie rods can cause vibration, get the tires balanced and bleed the brakes.

 

So I've made some progress. I went to get my Passat inspected and have the tires balanced. I got a call saying they didn't balance two of the tires because they had excessive inner tire wear and they wouldn't pass inspection. The two tires they did balance (and didn't charge me to balance) now feel much better. I am hoping that when I order a pair for the rear and they get mounted and balanced that almost all my vibrations go away. I did tightened both of the upper steering rack bolts and they maybe moved a quarter turn, but there's still some vibration present in the steering wheel. I will keep you guys up to date, but for now I am just trying to slowly fix a few problems at a time before I start throwing money.