Stumped on drive train issue

[richardodn]

I'm trying to diagnose a drive train issue and could use some input. The car is a 99.5 A4QA. The symptoms are similar to what you would feel if the drive train was binding due to different sized wheels/tires; the jerking as the car is rolling. The symptoms started when we put on a new set of wheels/tires. It had been running on a set of 15x7 205/60/15 snow tires. I now have it on 16x7 205/55/16. I verified all the tires are the same make/model/size. Unlike a typical binding issue, there is no problem driving straight. However when you execute a sharp turn you get the lurching behavior. Previously, it felt and sounded like it was coming from the front right axle. So I swapped that for a reman OE axle. Left side had been done previously. Anyway, now it feels like its coming from the rear. Could this actually be a transmission problem? Any other thoughts? Thanks!

[Corrado_Guy]

If you are feeling a lurch or odd movement then take a look at the control arms and make sure the bushings and ball joints are good. With the 15" tires you have more movement and it may be progressive enough that you didn't really feel it but with stiffer sidewalls it may be more noticeable. This is assuming the car will do it in and out of gear and the lurch is movement in the movement of the car which would typically indicate suspension and not driveline.

[richardodn]

I'll take it for another drive, but suspension bits are unlikely. They're all relatively new (front and rear) but there is always a possibility of premature failure. I'll also try and see what happens when I execute a turn in neutral.

[richardodn]

It's definitely the drive train. My guess is the center diff is binding up, but the question is why? My best theory right now is the auto tranny is low on fluid which is reducing lube to the gears. Anyone with any insight there?

[Audiwan Kenobi]

Same complications...after a snub mount, motor/tranny mounts, AWE DTS, ECS diff mount,window welded center driveshaft bearing and diff carrier bushings I'm still having this bouncy,lurching sensation...its gotta be the rear diff, cv axles, driveshaft end cv's or maybe something in the suspension bushings....I plan to get a diff from a 2001 A4 and rebuild it. The fluid are full.

[richardodn]

Here's an update on this issue. I found the cause and now I really feel like a dolt. It turned out the center diff (transfer case) had just about run out of oil. Why it only showed up with the tire change is a mystery. That's a reminder to always check the basics. As this car is really just a beater for my teen kids to drive, I'm not going to worry about changing the seals unless I'm in there for some other reason.