DRC Warranty

[rs4v8]

Changing only 1 shock is a seriously bad idea, they should always be changed in at least pairs (whole axle).

Totally agree PetrolDave. My car had only one of the rears changed last time. I asked the Master Tech about this and mentioned the reason why. He said that he'd been on the phone to Audi to check the vailidity of the extended warranty and that's what they said to do if the other one on that axle passed an overnight pressure test. I complained that it was very likely that the car would be back in again soon but to no avail

[PetrolDave]

Changing only 1 shock is a seriously bad idea, they should always be changed in at least pairs (whole axle).

Totally agree PetrolDave. My car had only one of the rears changed last time. I asked the Master Tech about this and mentioned the reason why. He said that he'd been on the phone to Audi to check the vailidity of the extended warranty and that's what they said to do if the other one on that axle passed an overnight pressure test. I complained that it was very likely that the car would be back in again soon but to no avail

My concern is also the effect on handling, especially under braking, if you have 1 "good" shock absorber and 1 "suspect" shock absorber on the same axle it is quite possible that you may have difficulty braking in a straight line under heavy braking on a bumpy surface (i.e. any British road). I think there's a serious safety issue here...

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Curious though - why would the other damper be suspect when they are diagonally linked? So if the offside front went bad why would the nearside be affected? If it's holding pressure and no signs of leaking I don't see the problem.

[PetrolDave]

Curious though - why would the other damper be suspect when they are diagonally linked? So if the offside front went bad why would the nearside be affected? If it's holding pressure and no signs of leaking I don't see the problem.

Because they are on the same axle, have covered the same distance on the same roads and been subject to similar loads and impacts.

Whenever shock absorbers need to be changed it is always advised that they are changed as an axle pair - to ensure that there is no yaw effect due to one shock absorber working better than the other. The fact that DRC is diagonally linked is irrelevant to this effect.

[ArthurPE]

if on a given axle (or diaganol circuit) one shock is bad, e, not carrying it's proportion of the load/forces, the other will carry a disproportionate amount, weaing it at a higher rate...

imo, in the case of DRC, if any one shock goes bad, they should all be replaced...
that is why we see so many repeat failures..
in fact the argument could be made the pressure resevoirs should be replaced also...at least for the failed circuit

the reason we see so many duplicate names on the drc list:
replacing only 1 shock
not replacing the failed circuits resevoir
improper repair, recharging, it's a fairly complicated procedure...

[rs4v8]

My concern is also the effect on handling, especially under braking, if you have 1 "good" shock absorber and 1 "suspect" shock absorber on the same axle it is quite possible that you may have difficulty braking in a straight line under heavy braking on a bumpy surface (i.e. any British road). I think there's a serious safety issue here...

Your right what you day PetrolDave about it being a wee bit dodgy but I'd only be worried if it discharges completely and you will notice that if it happens!!

From my recent experience a shock is only suspect in Audi's eyes if it fails the pressure test. In that case they will change it under the warranty no probs.

How long the other shock on the axle (which isn't changed out at the same time) lasts for is another issue. That is what pissed me off more, very likely another failure and another period of days without my car

[rs4v8]

in the case of DRC, if any one shock goes bad, they should all be replaced...

100% agree.

that is why we see so many repeat failures..

Quite possibly.

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But in itself damper doesn't carry any load? You could run completely undamped and load supported by the wheels under different conditions would be the same. Just the dynamics of the transient movement between two states would be completely different.
You could run one wheel without a damper and it' wouldn't affect the operation of the others. Yes, traction from the undamped wheel would be awful and the ride a bit... bouncy.. but I'm not sure it would cause the others to wear/fail that much quicker. I know this could be a little simplistic esp with the DRC the way it is and not trolling or trying to start an argument - genuinely interested.

Also, as an aside, as RS4's start to move to the end of the extended Audi DRC warranty I think I would look at conventional coilovers should they go wrong past the date. Has anybody done this before and does it ruin or impriove the car?

[ArthurPE]

say the front of the car is set into oscillation...speed bump at high speed...
so you have a given mass moving...

if you have 2 shocks they will disappate the energy equally...
with only 1 damper it will do twice the work...
chances are it will do some amount 'more' because it won't be exactly proportional and the car will take longer to stop oscillating...

now consider side to side load transfer...one side dampened, the other not, the dampened side will do all the work to stop the car from moving...
less what is absorbed by the springs...where as if both sides had good dampers, each would contribute to stopping the motion

same thing applies to yaw movement in this case because of DRC

But in itself damper doesn't carry any load? You could run completely undamped and load supported by the wheels under different conditions would be the same. Just the dynamics of the transient movement between two states would be completely different.
You could run one wheel without a damper and it' wouldn't affect the operation of the others. Yes, traction from the undamped wheel would be awful and the ride a bit... bouncy.. but I'm not sure it would cause the others to wear/fail that much quicker. I know this could be a little simplistic esp with the DRC the way it is and not trolling or trying to start an argument - genuinely interested.

Also, as an aside, as RS4's start to move to the end of the extended Audi DRC warranty I think I would look at conventional coilovers should they go wrong past the date. Has anybody done this before and does it ruin or impriove the car?

[PetrolDave]

say the front of the car is set into oscillation...speed bump at high speed...
so you have a given mass moving...

if you have 2 shocks they will disappate the energy equally...
with only 1 damper it will do twice the work...
chances are it will do some amount 'more' because it won't be exactly proportional and the car will take longer to stop oscillating...

now consider side to side load transfer...one side dampened, the other not, the dampened side will do all the work to stop the car from moving...
less what is absorbed by the springs...where as if both sides had good dampers, each would contribute to stopping the motion

same thing applies to yaw movement in this case because of DRC

But in itself damper doesn't carry any load? You could run completely undamped and load supported by the wheels under different conditions would be the same. Just the dynamics of the transient movement between two states would be completely different.
You could run one wheel without a damper and it' wouldn't affect the operation of the others. Yes, traction from the undamped wheel would be awful and the ride a bit... bouncy.. but I'm not sure it would cause the others to wear/fail that much quicker. I know this could be a little simplistic esp with the DRC the way it is and not trolling or trying to start an argument - genuinely interested.

Also, as an aside, as RS4's start to move to the end of the extended Audi DRC warranty I think I would look at conventional coilovers should they go wrong past the date. Has anybody done this before and does it ruin or impriove the car?

+1

The effect that shock absorbers have on ride & handling is underestimated by most people.

I've had the great pleasure to work with a couple of the "greats" of the late 20th Century regarding setting up vehicle ride & handling - and believe me, subtle changes to shock absorber spec make a huge difference to the feel (and safety) of an enthusiastically driven car - like all RS4's should be!

[sonny]

+2

I have not looked back since replacing mine with coilovers, they are set at a moderate (medium) setting for normal road use.

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Oh I know how much difference it makes - I've ran a Lotus 211 for a few years now and with 60 settings for bump and rebound I was always stunned how much difference a single click can make.

I get where you're coming from but the example of a speed bump at high speed isn't a good one - faster you hit the bump the more the movement becomes an impulse and has no affect on the attitude of the car. All the damper has to respond to is the weight of the wheel.

Whilst a failed damper is a safety concern I'm still a bit hesitant to say that because one damper has operated out of spec it automatically means that the other one on the same axle is assumed to have been damaged in this way.

[ArthurPE]

although it will model an impulse if both shocks are working, it won't be the case without shocks...or malfunctioning ones...
the car will oscillate wildly without them...the body will move...
and with only 1, one side will dampen, the other not, but some of that moment will be transferred to the other side, so the shock will do it's own load servce, plus some from the other side...

Audi in their service stuff say to do diagonal pairs...

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But if you hit a bump at high speed with no shocks then the force doesn't have time to affect the mass of the car? All the impact is taken with the spring movement so you have a nice smooth ride.

This is why with bumpy tracks I always had to soften the damping on my track car otherwise with it to highly damped the irregular road surface would bump the car badly and unsettle it to the point it was scary to drive.

Now if you go slowly over a bump then it'd be different - without damping you'd get the pimp-mobile bouncing car effect.

I can see why to do diagonal pairs as they are linked so any leak in one would affect the fluid in the system and such the other damper.

Sonny - thanks for the info. good to hear that there is a solution should the DRC system pack up. Any ball park cost?

[ArthurPE]

the spring is compressed
when it it rebounds it will propel the car upward
unless of course it can push the earth down out of orbit
physics 101

But if you hit a bump at high speed with no shocks then the force doesn't have time to affect the mass of the car? All the impact is taken with the spring movement so you have a nice smooth ride.

This is why with bumpy tracks I always had to soften the damping on my track car otherwise with it to highly damped the irregular road surface would bump the car badly and unsettle it to the point it was scary to drive.

Now if you go slowly over a bump then it'd be different - without damping you'd get the pimp-mobile bouncing car effect.

I can see why to do diagonal pairs as they are linked so any leak in one would affect the fluid in the system and such the other damper.

Sonny - thanks for the info. good to hear that there is a solution should the DRC system pack up. Any ball park cost?