HELP - Front Caliper Pistons and seals

[ATinOf]

OK so I am in the swing of upgrading my standard discs for the AP Racing 390mm's with braided lines, ATE200 fluid and DS2500 pads; #excitedheadon, and just when I dont want it to (as it always happens) I find the inner pistons both sides are extremely stubborn in retracting. They were at their limit of travel, they do move under pressure of a 12" prybar but Im not too happy leaving them as they are, at least not long term

Anyone know if anyone stocks these so I can service the calipers while they are off - I really could do with Them tomorrow (saturday 06th) - Im supposed to be running up to Middlesborough Sunday ;(

Yes thats the long sigh of an exasperated part time spanner jockey (at least I have a cold beer in my hand)

[Jim Haseltine]

Might be that the pistons and seals are dry, perhaps a bit of RRG (red rubber grease) lubricating things could help. At a push a bit of brake fluid could be used.

[IanH755]

The pistons & seals are Item 3 on this diagram -



Link to website - http://www.oemepc.com/audi/part_single/ ... ng/e#sec_3

Pt No 4F0698471A - No idea on price or availability.

[ATinOf]

I cant source them anywhere so far. Brembo dont even list the caliper on line. I have sent them a tech request for info.
There is someone on ebay in Germany selling a kit but not a Brembo kit and its 150 quid per side.

I have had an absolute mare today changing the discs, not due to the discs thats an easy job (and now done), but I planned to do the wheel bearings while I was at it and the bloody pinch bolt was a right saga. Followed by the bearings not being the right size. Having to put the old bearing back on. Followed by finding out the discs I took off were both right hand discs!!!!

When Im in a better mood I will upload some pics of the pinch bolt saga.

Phase 2 will have to be pistons and seals on the calipers, fluid and hoses, and decide whether that noisy wheel bearing really is bothering me enough to have another bash.

[ATinOf]

I always tend to use 7zap rather than oempc but I guess they are all using the same source data

[Jim Haseltine]

Followed by finding out the discs I took off were both right hand discs!!!!

Unlike the C5, C6 discs aren't handed, there's only one part number listed. The drillings face in the same direction on each disc and that's despite there appearing to be a direction arrow on the bells.

[douglas96]

I cant source them anywhere so far. Brembo dont even list the caliper on line. I have sent them a tech request for info.
There is someone on ebay in Germany selling a kit but not a Brembo kit and its 150 quid per side.

I have had an absolute mare today changing the discs, not due to the discs thats an easy job (and now done), but I planned to do the wheel bearings while I was at it and the bloody pinch bolt was a right saga. Followed by the bearings not being the right size. Having to put the old bearing back on. Followed by finding out the discs I took off were both right hand discs!!!!

When Im in a better mood I will upload some pics of the pinch bolt saga.

Phase 2 will have to be pistons and seals on the calipers, fluid and hoses, and decide whether that noisy wheel bearing really is bothering me enough to have another bash.

I take it that the pinch bolt was seized solid? I had exactly the same bother a year and a half ago with my Skoda Superb when replacing the upper control arms - same suspension setup, only steel instead of alloy. When taking the nut off the bolt just snapped, which was actually quite lucky as it allowed me to sit the punch in the hole so that you didn't need to readjust the punch every time it was struck. Anyway, after hours of hitting it with a 3lb hammer (and believe me I was hitting it), it had moved say 15mm and stopped. I got my father to help and we were using a 14lb sledge hammer, and again believe me that neither of us are shy using it, it still wouldn't budge - not even 1mm. I didn't want to heat the housing, but I ended up having no choice. Anyway after heating the housing a bit the bolt started coming out no problem.

I would never have thought that a 10mm bolt could seize like that.

I have heard that the alloy housings have a tendency of breaking when trying to remove the pinch bolt. I don't know whether the pinch bolts on the alloy housings seize up any worse than on the steel housings due to bimetallic corrosion? Although, how it could seize up any worse than what i had I don't know! It may be worthwhile using some Duralac paste when refitting the new bolt to try and avoid the galvanic reaction between the metals. I haven't used it myself but I have heard good things about it.

I keep looking at the pinch bolts on my RS and keep telling myself not to touch them until I need to! I wouldn't mind just taking them out and replacing the bolts and coat them with some Duralac, but as the old saying goes; "If it ain't broke, don't fix it".

[Jim Haseltine]

Problem is that a lot of the impact is absorbed by movement in the arm bushes. What you need to do is damp it by having an assistant hold a heavy hammer tight against the opposite side of the arm - something I learned many, many years ago when I had to remove wedge cotter pins on a regular basis. Could hammer away for hours with no result but with a counter weight it'd usually take no more than a couple of strikes.

[douglas96]

Problem is that a lot of the impact is absorbed by movement in the arm bushes. What you need to do is damp it by having an assistant hold a heavy hammer tight against the opposite side of the arm - something I learned many, many years ago when I had to remove wedge cotter pins on a regular basis. Could hammer away for hours with no result but with a counter weight it'd usually take no more than a couple of strikes.

Ahh I see exactly what you mean now. That's a great tip Jim, thanks!

[ATinOf]

I had response from Brembo in Italy. I asked if they did front caliper pistons and seals separately or as a kit and where to source them. Their reply;

"please be informed that we do not list the items you are looking for. Shoulld you need any further information from our side, please feel free to contact us anytime."

Looks like I need to strip one to measure the pistons for aftermarket parts which means I need to get my backup vehicle running first.... unless anyone has a spare lying around ....

[welwynnick]

Does the RS6 share it's front brakes with any other car?

Nick

[IanH755]

One of the later year GTR's (think '17?) which uses the same caliper and same size brakes (tadge thinner - 390x34mm).

[welwynnick]

Thanks Ian

I had difficulty getting a caliper repair kit for 8 piston Brembo calipers a few years, and Rockauto came to the rescue:

https://www.rockauto.com/en/catalog/nis ... r+kit,1720

It sounds like that caliper is used on several high performance BMW, Lexus and Nissan models.

Nick

[Jim Haseltine]

Seals: https://www.design911.co.uk/fu/prod1114 ... -Calipers/
I think the pistons are 30mm but can't measure them until this evening.

[Jim Haseltine]

Assuming that I've measured them correctly as the pistons in my calipers are almost at base 'cos the pads are nearly new, (I've measured 3) I reckon that they're 32mm.