Brake caliper rebuild - rear TRWs


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Jan 15, 2022
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In the process of rebuilding my rear brake calipers for an Audi A3 8p 2 2011, they are TRWs and I've come across a problem.
The internal circlip within the caliper that retains the handbrake mechanism. To start, couldn't get it out, then it pinged out and now I can't get it back in. Every time I'm close it will eventually pop back out. Looks like it will not locate properly, and I think that the handbrake mechanism spring must be compressed in order to place the circlip.
Anyone come across the problem before?

Well, after a couple of hours trying to fiddle it in, the circlip broke and I decided to just get calipers from eBay fully refurbed already.
In retrospect, should of just done the main piston seal and boot, all the other seals were perfect.
Be careful as there's a seller on ebay that sells refurbed genuine units that leak from day 1.

Whose the seller?

He's a **** also, doesn't honour the warranty & multiple units with the same issue.
Cancel it, that's the seller bud, I know first hand they leak, not once, twice, multiple times.
Can't cancel them now, no option to anymore. We'll have to wait and see. Either way I need to get something on my car, if it leaks I can probably sort it.

Had any issues with that circlip though? Really doing my head in
I’ve used Bigg Red Ltd on eBay for caliper spares etc. very good.

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I managed to get the circlip back in by bodging a couple of sockets and using a vice to compress the shaft that holds the piston, then managaged with a pair of 90 degree circlip pliers.
Right, so here's the update boys and girls. (This is long, but it's something that if I were doing the job for the first time, I'd want to read.)

The job is finished and tested, so I'll give a little bit of info for those with a similar issue.

- Firstly, if you have got a seized rear brake caliper and I don't have a workshop to work in its probably best to just replace the piston and the piston square section o-ring and rubber boot. Makes sure it's all clean and well greased, maybe change the handbrake return spring for a new one while you're there. Other than that, don't touch anything else, unless there is evidence of damage to seals, leaking from the rear where the mechanism protrudes or particularly bad quality hydraulic fluid that may have damaged the internal seal on the handbrake mechanism. Because taking the mechanism out is easy enough, but putting it back in requires a vice and a G clamp. I tried it with a just G clamp and it did not go very well. If the mechanism isn't kept straight up and you release the spring tension there are little ball bearings that slip out of position and getting them back in is right task. You are better off just replacing what's needed and flushing the caliper with new fluid and giving it a good clean. Also, the circlip I did in the end get from BiggRed, who were very helpful.

However, to put it into context, I'm yet to fix my mistake and ended up using the refurbished calipers I bought from eBay. I needed the car and couldn't wait to sort it the long way. If anyone has any secrets with the mechanism then please let me know.

- Reference the leaking calipers mentioned earlier from a specific eBay seller - mine are fine so far, I have tested them, inspected them and monitored fluid levels. I will recommend taking a fair amount of time to clean the threads and run a spare fitting/tap down each in order to clear out the threads. I will also say slap a bit of heavy copper grease onto the male threads to reduce any friction. I did this for both the bleed nipple and the hard pipe off the caliper. Once I'd done this, the threads were smooth and I was able to get a good tight fit without worrying about seizing. The calipers came with a note about cross threading the bleed nipple if you over tighten it. This shouldn't happen if you have started the thread correctly, don't use power tools, or use anything over than a normal 11mm spanner to tighten (or 1/4" ratchet). You shouldn't be going crazy on the torque on these, but they need to be tight.

- I would recommend using a flare (or line) wrench, preferably one that is of the single hex variety as opposed to the bi-hex. Some bleeders are fairly soft and have seen a bit of wear and tear. I had one on my fronts that wouldn't loosen with a normal open spanner or the ring, so I had to use a deep socket to break it loose. I also used a bit of heat and penetrating fluid and a good amount of wire brushing to get it as free as possible. I then replaced the bleeder.

- The hard brake lines are coated in PVC or something like it, and after snapping the line that goes from caliper to Flexi, I did a little research and the best way to prevent jamming up the fitting and twisting the line is a torch and screwdriver. Heat up the PVC until it bubbles and melts, then scrape it off. I took the opportunity to also spread a little heat over the whole union, along with some penetrant and the use of a small wire brush to clear the loose rust and try to reduce the risk of clogging up the threads and my tools from slipping off and rounding anything. I was replacing the flexible regardless, so I didn't care about damaging it with heat, however the flare fitting for hard-line brakes is pretty much permanent so you need to treat that with kindness.

- I live in a place where the roads are salted every winter, it rains all the time and the ocean is not too far away. So I came across a lot of rust and have had to handle it quite a lot. I recommend painting the fittings once all fitted and tight. Try not to get it on the flexible, however a little isn't anything to cry about.

- I then bled the hell out of both calipers, gave them a tap with a rubber mallet to jostle any trapped air, then did a full set of bleeding again and flushed the fluid with 1litre of Dot 4. During the process I managed to lose my lug bolt key on a test drive, having left it on the locking bolt by accident. Had to use a removal socket to get them off, luckily I always use anti seize so once they were broken off they were nice and easy to remove. New ones were pretty easy to get ahold off.

- I was also very concerned that I had gotten air in the clutch as I had left the brake system open. The Flexi clamped and the reservoir capped, but you can never be too careful. Luckily the clutch is fine. Just ensure your reservoir is topped up and never empties, other wise you'll get air in the master cylinder for the brakes and potentially into the clutch slave.

- I also took the opportunity to change the flexible hoses because they are a tenner each and I'd rather save myself the worry.

If anyone has any other tips and tricks, or any thing I missed, please let everyone know.
Tools I used:
- 11mm spanner/flare wrench for flare fittings and bleeder.
- 17mm open ended spanner for the flexibles.
- Laser flexible hose clamps (used an adjustable spanner and grips to tighten the wing nut to ensure no leakage).
- 13mm ratcheting ring and a 15mm open ended spanner that was thinner in width than the open side of a Halfords advanced 15mm ratchet spanner. This is for the sliding pins.
- Deep 11mm single hex socket and a 3/8th ratchet to loosen a slightly rounded bleeder.
- Wire brush.
- Butane torch.
- Flat head screwdriver for prying and scraping.
- Copper grease and red rubber grease.
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