These things affect throttle response, on and off throttle transitions, shifting, and shifter movement getting on and off of the throttle. At higher hp levels these things can make a huge difference getting power down from the engine to the tires. There will also be less wear to engine wire harnesses, hoses and vacuum lines, and exhaust joints(the A4 exhaust flex pipe is a common failure point with bad engine and transmission mounts). Most importantly it makes any car much nicer to drive. It will feel like one piece instead of 3 or 4, sharp, predictable, and responsive.

 Bushings

There are a lot of bushings on a multi link suspension and that's a lot of room for miss-alignment of the arms/wheels/tires. A solid suspension creates confidence and makes driving faster easier (and more fun) and so these worn out luxury marshmallow bushings have to go. Come to the rescue - Powerflex out of the UK. The only set of bushings that I could find for the B5 chassis Audi A4/S4. There are also replacement suspension links with solid spherical bearings instead of bushings for about half of the factory links. The life on solid bearings in a suspension are usually short so be prepared to have them rebuilt when they start to clunk.

 

 

B5 Anti-roll bar reference:
16mm stock S4/A4 sport rear
12-15mm stock non-sport rear A4
22mm  Neuspeed race rear (w/ reinforcement brackets)
22mm  Hotchkis rear (tubular, adjustable, w/reinforcement brackets)
19mm Neuspeed rear
21mm H&R rear

32mm H&R front
35mm Hotchkis front (tubular)
29mm stock S4/A4 sport front
2?mm stock A4 non-sport front

Drivetrain mounts

On a luxury AWD vehicle there are a lot of big squishy mounts between the drivetrain and the body to keep vibration and noise to a minimum. Even new these mounts are barely adequate and after many years they become too soft letting the engine, transmission, and the rear differential move far more than they should. This problem would manifest the most at acceleration, elevated speeds, shifting, and throttle adjustment. The A4 has 8 drivetrain mounts in all along with 8 subframe mounts.

Parts for total replacement:

• Engine mounts (034 Shore 50 or 80 mounts or solid Stasis mounts- don't bother with the BS "RS4" mounts, they're not worth it)
  
• Engine mount, front (called a snub mount) (mount bracket and polyurethane mount from 034 or just the bushing part from other tuners)
  
• Transmission mount (034 mounts (in solid delrin or shore 80)
  
• Transmission mount (drivers side - Stern solid mount, 034 Solid shore 80, filled stock, or convert to V6 style drivers side mount)
  
• Differential mount (rear bushings)(Stern polyurethane, filled new stock, fabricated/spherical bearings)
• Differential mount (front mount)(034 solid mount, New stock, filled stock, or use the Stern "power ring" (a spacer))
• Subframe mounts (new filled stock or used to fabricate solid units.)
• Transmission mount (third)/chassis brace (Drivetrain stabilizer from AWE or AutoSpeed).
  

The drivers side A4 transmission mount. I filled those holes with window weld as per usual. Stern makes a solid version which looks like it would work a lot better.

This detail shot shows the cracks in the old passenger side A4 mount.

Here is the RS4 transmission mount filled with window weld loosely mounted. This was before 034 had the solid shore 80 mounts available.

The stock snub mount that is supposed to eliminate fore/aft and side to side movement at the front of the engine. Ha! I can totally squish that rubber thing with my hand, let alone a 400+ lb engine under power. Getting on and off the throttle with this on the car was like trying to drive a slinky.

Look at that, why did they even bother?!

The 034 Snub mount pictured at the top is gorgeous in a way that OEM parts can never be.
It's almost too beautiful to put on the car. It was a serious pita to put on, i had to heat up the urethane part (you have to do that to all of them) and trim that lip off the edge with a knife. Then the bracket was oriented wrong and I had to push and tug like crazy to get one side on.  I had to widen the mounting hole with a drill on the other side for the bolts to be able to thread in - all that while it was on the car. 034 has since fixed the problem and there are multiple brackets for the B5's that should line up perfectly.

The rear differential is held up by a large mount at the front that looks like a transverse engine mount (11) and two small bushings at the rear(6), fixed to an aluminum truss. All three of them are a joke for eliminating movement especially after 100k miles.

The two rear bushings look like they go to a control arm except that they have very little supporting material. There are two huge holes that go straight through from one side to another. You can move the centers easily with your hands, imagine 200hp!. Or 400!?

The casings are 45mm at the widest point but they aren't true. They're more of an oval shape really and 44mm at the narrow point >_<'. The easy fix for these is the window weld I use on most mounts. Generally you buy the whole truss that these sit in and not just the bushings. If you do get the bushings, i recommend pressing them in and then filling them instead of vice versa. Stern now makes a polyurethane bushing to replace the stock pieces currently available through PureMS.

My crude photoshop work gives you a rough idea of how little rubber is actually supporting the rear of your differential. The gray represents through holes/air. Worse yet, the rubber that actually is there isn't flush with the casing either, it starts about 7 1/2 mm in from the edge. The case itself is only 30mm long so the rubber is only half of its length. They cost me 15$ each from the dealer. 30mm of combined rubber at $1/mm. Thanks a lot Audi. As this photo illustrates filling these would be very easy. The stern pieces are totally worth it, don't bother with getting stock ones.

This photo shows, like the one of my transmission mount, what 100k miles and more than 10 years of use does to rubber. The rubber is torn and cracked along the main support ribs which renders the mount more or less useless. This is a 250$ part from the dealer, and purems now sells them for 220$. Window weld is 11$/tube. 034 sells a solid urethane version for 250$ and that is the one to get absolutely.

I filled the entire thing with 3M Window Weld (polyurethane goo in a tube). It takes a while to fill that all of the way up. there's a lot of empty space on this mount. On the lower picture all of that goop was just air with the rubber mount going down the middle. Ideally you would cut out the rubber and fill the whole thing with polyurethane, sealing off the bottom with some tape. Another option would be to fill the holes in the mount with window weld, then fill that gap in the lower picture with some square tubing or any kind of solid material to keep it from compressing. Stern now makes a spacer they call a "power ring" that i imagine spaces that big gap in the bottom with metal. Not much better than what I've done, again the best bet is 034's solid mount.

Engine Mounts

I procrastinated and procrastinated on this one because I didn't want to use the stupid overpriced stock mounts (A4, S4, RS4whatever) and the stasis mounts are stupid expensive. Thankfully 034 motorsport came to my rescue and made shore 80 rubber units. I immediately installed a set and have been getting regular massages on my drives ever since. They were unbearably loud and vibratey. After a week or so they were tolerable but only just (for a daily driver). Shifting and throttle response were much much improved and they're inexpensive to boot! Plus no more torn exhaust flex joints.

Chassis bracing:

This I covered in theory on the chassis page so I'll only cover specifics here.

S4/A6 Shock tower bar:
The cheapest effective bolt on brace available is the factory S4 strut tower bar. Order the brackets for the A6 as the S4 brackets are welded to the chassis, then order the crossbar for the S4 and drill new holes so that it will fit in the a4's engine bay. There is a plug and play version made by PureMS but it's about twice the price with the only difference being the drilling. There is a full how to on audiworld.com. If you have a drill press and a metric ruler this is a half hour job.

A6 brackets:
  4B0 803 357A
  4B0 803 358A

S4 Cross bar: (you could really use any steel bar of the same width and length)
  8D0 805 645A

Screws:
  (4) m8 x 35

I got my parts from Shokan used Audi parts. I ordered the three pieces plus my headlight washer lid and with shipping it was less than the price of buying these three factory parts new. I got the bolts at my favorite hardware store sized: m8 x 1.25 x 30 hex key. 

If I were to do this again I would flip the bar over and drill the holes that way so that the middle nut on the bar is pointing up. I tried to put a hole in the firewall for that nut on the bar and there just isn't enough room for leverage or a drill. A Dremel or a right angle drill may work. Another option that those of you with the PureMS bar can do as well is to just drill through the firewall and the bar and put a bolt and a nut through there, I would actually do it in two or three spots if possible. The second firewall isn't very robust though so it may be a better idea to just leave it as is..

This modification was well worth the meager effort. Pulling into my parking garage I could immediately feel a markedly improved difference. Less creaks, more solid steering input, and a better ride. This car now feels like a tank, totally solid!

The rest of the chassis bracing I did involved this piece