Brake Master Cylinder Refurbishment

[iammooks]

This might become a how-to at some point, but after my brake bleed problems I'm still having problems with my brake pedal sinking, and rather than buy and fit a new master cylinder, I'm thinking about buying new seals and refurbishing it instead. I hate the idea of buying new and sending things to landfill when they can be easily repaired.

I don't have ESP on my Leon, so no fancy electronics to deal with, so was just hoping for some advice on what the correct refurbishment kit would be and if there are any issues I need to be aware of. It seems mad to spend a fortune on new when kits are available, but if a £5 eBay special won't cut it, what do I need to be looking for?

In time, hopefully this will turn into a how-to of getting the cylinder out, replacing the seals, bench bleeding and then putting it back in the car, so any help would be much appreciated.


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[iammooks]

Thanks to a master cylinder from @Manic172 I'm going to be working through this slowly with the master cylinder off the car, which will cause less stress (the reasons will become clear soon), so here goes...

First step is to find out what master cylinder you have. Is it ATE or is it Bosch? What size is it? Well, you'll be relieved to hear you more than likely have to take the bloody thing out of the car before you can do this, because it's stamped on the underside.

Excellent. So you'll need use a turkey baster or vacuum thing to extract as much brake fluid as you can out of the reservoir. Depending on your car, you'll need access, so when I get round to doing this on the car, I'm going to have to remove my boost pipe and probably my EGR valve too. Then you'll need to get your 11mm flare spanner out to undo the brake lines from the underside, as well as a 13mm socket to get the master cylinder off the brake servo. Save some of the brake fluid as it'll help with bleeding later.

So then, what you can ascertain from this photo is that it's a Bosch master cylinder (on the left and above the VW badge), and it's the 23.8mm bore size. Apparently "they" only list the first two numbers for the bore size and round down, so that big '23' you can see there means it's a 23.8mm.

So I visited the Bigg Red shop on eBay and picked up a Bosch/Bendix refurb kit for a 23.8mm bore size for £13.99.

And as I haven't got circlip pliers, I thought it was high time I got some. £4.99 from Screwfix - and now I can finally fix the door handle at my girlfriend's place too. Oh - and I got a Rolson pick and hook set from Halfords for £3. They sell a Draper one that's almost exactly the same for more than twice as much, because of course they do.

The reservoir won't come off unless you use an 8mm socket to undo the bolt on the underside. Take it out and then gently pull the reservoir out from the rubber seals.

Make sure you do most of this stuff either over newspaper or paper towels or something, because there will always be brake fluid to leak out - either from the bottom of the reservoir or just from releasing pressure as you go.

I also took out the bleed nipples with an 8mm socket just to give them a clean with a wire brush so the threads went in more cleanly. I also put the reservoir retaining bolt back in the hole because you know it's going to go missing.

I gave the whole lot a bit of a scrub with a scourer just to get rid of most of the dirt.

So now it's clean-ish, we can move on to getting the thing apart... That'll be in the next post.


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[iammooks]

Part two is devoted entirely to this thing. There's a circlip around the bore that should be easy to get out, but there are no holes in it for removal, so somebody out there doesn't want you to refurbish your master cylinder. These are single use and there's a replacement in the refurb kit - and that one has holes in it.

I did loads of searches to see if there was any advice on getting these out and pretty much everything was just people asking how to get them out and nothing helpful on how to do it. Some people say there are grooves you can get a screwdriver into etc. buy they're clearly liars.

There are a couple of ways, and mine is probably the hardest, because it always is.

You will need:

If you have any alcohol, prescription drugs, non-prescription drugs, hard drugs, tranquillisers... They'll help too. As will a clamp or bench vise.

And wear safety glasses. I'm serious.

A word of warning - the master cylinder is made of pretty soft metal and more or less anything you do here will leave marks and possibly some swarf, depending on how frustrated you get.

I got very frustrated.

I used the straight point pick and I pushed it along the circlip groove behind the end of the circlip, so I could lever out the end of it.

When I could see that the circlip had been pushed away from the edge, I quickly put a small but strong flathead screwdriver into that gap and gently levered it away from the edge, so it bent in slightly.

Then I took another flathead screwdriver and put it further round and again levered out, working my way around. It will ping back into place several times and you will get frustrated, but every time you try, the circlip is bent slightly, which means it's coming out.

After several attempts and wondering if there's a better way, I gave it one last go and it pinged out. This is why you need safety glasses - it can hit you as it pops out. Mine went all the way across the room and I've still not been able to find it. It comes out with enough force to blind you. Be careful.

So you're left with a slightly scratched master cylinder. This shouldn't cause any problems as a new circlip will go on fine, and all the bits and pieces that hold pressure and fluid are on the other side of this assembly. It's ugly, but it'll work. I'll be sanding the rough spots with fine wet and dry just to be sure.


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[iammooks]

So you've got the circlip out - congratulations. I've still not found mine.

Next step is to replace the different seals. It's good to have a system for doing this, as at least once I put the old seal back on. Take them off and put them in a box or the bin or something.

So, push down on the central bore and this should release the end cap. Give it a pull using some needle nosed pliers and it'll come out.

It'll come out looking something like this:

You can do this in pretty much any order you like, but I took out the bungs where the reservoir fits in.

You can use your fingers or pliers. I found fingers easier. When you get the one furthest from the bulkhead side out, there's a round piece of metal with three holes in you'll need to take out.

Take it out and keep it in a safe place.

If you look inside, you'll see this part. It won't come out on its own - there's a retaining pin where you just took out the metal disc. Get your needle nosed pliers and give it a pull. It'll slide out easily.

The internal part will either spring to the end, or you can tap it on a table to get it out. There's also a spring behind it that needs taking out.

Have a look down the barrel. The inner surface should be clean and smooth, without any pitting or signs of rust, deep grooves or scratches.

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[iammooks]

So you've got everything out. Now it's just a matter of changing the seals. You can use fingers, pliers, hook tools - whatever you fancy to get them off. Just do them one at a time so you know you're replacing like with like and they're the correct size. Don't forget to replace the big o-ring that seals the master cylinder to the servo. I gave the whole surface here a good clean so it mated well.

Some are a little more complex than others. You'll need a torx bit (either T15 or T10) to release the spring.

That'll give you easy access to the seal in the middle of the assembly. Putting it back together is a bit of a pain - you'll have to compress the spring while also trying to screw the torx bolt back in, without cross threading it.

At this point, everything was out, so I gave it all a good old spray with brake cleaner.

Once you've done the other part, you'll need to put it back in the cylinder. Put the spring in first. The next step is to align it properly. There's a long slot down the middle, which is where the pin you took out goes. If you put the part in like this, it'll slide in nicely and you'll be able to put the pin through.

Use the small hole as a reference point for the slot in the top. You can use a screwdriver to push it down.

Put a little tension on the spring and you'll see the slot appear and the pin will push straight in. You won't need to use much pressure.

Then put the disc with three holes back where it came from. As far as I can tell this just goes in loose. When the disc and pin were out, I tried pushing the pin through the holes in the disc, but it doesn't fit, so don't worry if it's not straight. You can then put the replacement bungs in to stop the disc falling out.

Then I replaced the o-ring on the end cap and realised I had one seal left...

Easy to miss - there's a seal inside the top cap. Give it a tug with the needle nosed pliers to get it out.

I found it easier to put the replacement seal on the bore first and then slide the plastic end cap on. When I fitted it to the end cap first, it twisted and warped as I installed the end cap back on the bore.

Put it back in the cylinder and then push down on the end cap. You'll see the circlip grooves. In the kit there's a circlip with holes in it. All you need to do is put the circlip in and make sure it's all flush and the job's done.

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[iammooks]

If you've got the time and the patience, it's a lot cheaper to refurbish than buy new. You get to know another part of your car too and how it all works.

Hardest part by far is getting the original circlip out, but just take your time and don't lose your rag.


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[Thai-wronghorse]

I know it's an old post but hats off to you in the write up mate as I'm just about to rebuild a spare master cylinder as I can't bring myself to spending £244 on an almost impossible to source new replacement.

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[Nam-uk]

Missed this , good info that every credit

 

[iammooks]

No problem! It's why I did the guide after all! I've still not used my refurbished MC as my brakes have been fine and have passed the MoT without any issues, but it's always nice to have a spare. I have noticed that I haven't been able to get the reservoir properly seated with the new seals, so maybe some silicone spray or brake fluid might help ease that in there.

The hardest part of the whole job was the circlip. If I had a Dremel or something, I'd probably drill a hole in the original one if you can get the angle right and use that to take it out, because it really was a pig to get out.

 

[Nam-uk]

No problem! It's why I did the guide after all! I've still not used my refurbished MC as my brakes have been fine and have passed the MoT without any issues, but it's always nice to have a spare. I have noticed that I haven't been able to get the reservoir properly seated with the new seals, so maybe some silicone spray or brake fluid might help ease that in there.

The hardest part of the whole job was the circlip. If I had a Dremel or something, I'd probably drill a hole in the original one if you can get the angle right and use that to take it out, because it really was a pig to get out.

circlips can be a pain but theses make it allot easier , you wont use them much but handy to have around

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[Thai-wronghorse]

Finally had a pop at overhauling a spare master cylinder...f#ck me, you weren't kidding about that circlip been a pig to remove!
I ended pretty much trashing the first one removing it but it gave me a chance to look it inside anyway even if I wasn't going to use it again.
On my second attempt I tried drilling the circlip but it's so flipping hard it wasn't pretty much impossible so I abandoned that idea.
I finally cut it out by drilling a tiny hole in the wall around the circlip and pushing it forward whilst a colleague stuck a thin screwdriver in the slot.
All I can say is well done on doing by yourself and not destroying it

After all that faffing around I came across another issue, not all of seals supplied in my Bigg Red kit are correct.
None are suitable for the large main seal that sit directly behind the circlip.
I've spoken to Bigg Red quite extensively and that's the only kit that have listed so I have no idea how the hell I'm supposed to rebuild it now FFS

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