B6 A4 rear brakes on S4 rear spindles

[seanf86]

Has anyone swapped in S4 rear spindles and used the A4 rear brakes? Basically I have a few complete S4 rear subframes and am looking to reduce as much unsprung weight as I can for as little $$$ as possible.

It started life as a 3.0 car it now has a K04 2.7T in it. Up front it has 2.0T Q5 brembos with 320mm rotors and I'd like to keep the 255mm A4 rears with alum calipers and just use the S4 spindles.

[kwilson]

I had a parts S4 for a while while my son and I slowly moved parts to his A4. Since I wanted to keep the S4 mobile, I would swap the A4 parts (suspension, etc.) back to the S4. I couldn't get the 1.8t A4 rear calipers on the S4 uprights. I don't know if your 3.0 rears are different.

[seanf86]

The rotors are 10mm larger otherwise the same, was there a clearance issue that could be hit with a grinder and solved or something else?

I just thought of this as my spare subframe is buried under 3ft of snow in my storage area in the backyard otherwise I'd just go check for myself

Sent from my Pixel 6a using Tapatalk

[Kevin C]

The B6 A4 rear brakes wont clear, I ran into the same issue when I did this swap. I was using the 255 mm 3.0 rear brakes. If I remember right the hub is too small to clear the bolt in bearing that the S4 uses (its been about 6 years) . I used B7 A4 rear brakes, they worked out great. They even work with the stock B6 e-brake cable. The S4 rear brakes need either some cable work or longer cables.

[kwilson]

I think the issue was with the calipers not bolting on. I was surprised, as S4 rear brakes work great with the A4 uprights.

[Kevin C]

I think the issue was with the calipers not bolting on. I was surprised, as S4 rear brakes work great with the A4 uprights.

Either way, the B6 A4 brakes dont fit :) I do know the caliper mount pattern is the same but the S4 knuckles with the thicker aluminum and four bolt flange add a lot of bulk. I do remember that it was not even close, no simple mod to make the small brakes work. EDIT: Also the ID of where the rotor fits over the bearing on the S4 and the B7 A4 rotor is much larger than the B6 A4. Take a look at some of the part pictures on Rock Auto.

20190127_212619.jpg

[Gin+]

I've been mulling this over myself. Anyone happen to know the weight difference?

[Kevin C]

About 4 lbs per side.

[BumblebVR6]

Either way, the B6 A4 brakes dont fit :) I do know the caliper mount pattern is the same but the S4 knuckles with the thicker aluminum and four bolt flange add a lot of bulk. I do remember that it was not even close, no simple mod to make the small brakes work. EDIT: Also the ID of where the rotor fits over the bearing on the S4 and the B7 A4 rotor is much larger than the B6 A4. Take a look at some of the part pictures on Rock Auto.

20190127_212619.jpg

So what else besides the knuckles and bearings/hubs is needed for the swap? I already have the S4 calipers, rotors (300x22), and e-brake cables on my A4 and everything bolted up fine.

[Gin+]

About 4 lbs per side.

Thanks! For the record I believe I have a tweaked rear knuckle so I might as well attempt to replace with s4 parts.

[BumblebVR6]

So what else besides the knuckles and bearings/hubs is needed for the swap? I already have the S4 calipers, rotors (300x22), and e-brake cables on my A4 and everything bolted up fine.

Kevin, following up on this from a while back :-)

[Kevin C]

Kevin, following up on this from a while back :-)

From memory, that should be all you need.

[BumblebVR6]

From memory, that should be all you need.

Thank you sir.

[Kevin C]

Thank you sir.

And of course a new TTY bolt for the bearing. The rear bolt has a lower TQ spec. Also, the caliper bracket bolts to the spindle are longer. It was a few years ago, so my memory of the swap is a bit fuzzy. I just hit ten years of owning my A4.

[BumblebVR6]

And of course a new TTY bolt for the bearing. The rear bolt has a lower TQ spec. Also, the caliper bracket bolts to the spindle are longer. It was a few years ago, so my memory of the swap is a bit fuzzy. I just hit ten years of owning my A4.

Allright, ordered a set of spindles, fresh bearings, and hubs. Already running S4 300mm rotors and calipers so hopefully everything just swaps in.

[easyAudi]

for others stumbling onto this, i believe these are the lower S4 B6 rear caliper bracket bolts mentioned:
N91036902 [ m10 x 1.25m x 60mm long ], per ECS. But def double-check.

..and rear S4 knuckles need S4 specific dust shields / splash guards. These:
p/n: 4F0615612 and 4F0615611 ...also fit C6 A6, which are much easier junkyard finds.

or if you're super super lucky and pulled early model B6 S4 rear knuckles, (2004, before VIN: 8E-4-239326 ) likely need even different dust shields, to bolt right up:
p/n: 8E0615611N and 8E0615612N