Any chance you found a way to fix the leak?

Just FYI in case someone has the same problem. I have searched all over the country for spare parts and finally got pissed and solved it myself.

Here is a link with picture and more detail. https://imgur.com/gallery/QVcXYH0

You can fix the lever by ...

1. Remove the lever from the bike and drain oil.
2. Remove the small pin on the side of the lever that holds the lever's pivot point. Use a small punch or screwdriver
   
3. Pull out the white cap. It is attached to a spring and seal.
4. Replace that crappy o-ring with a #83 O-Ring (1/2" OD x 5/16" ID). Found at most hardware stores and sold to replace American Standard and Gerber appliances.
5. Lube it up with your brake fluid (mineral oil or royal blood) and replace the white cap, spring and o-ring
6. Re-assemble the lever.

Tips for lever assembly:

• Make sure the silver plunger thing is backed all the way out first so you aren't working against the springs resistance. Do this from the front of the lever using the sizing set screw.
• I used a small punch and hammer to get the pin out.
• When you insert the pin watch the hole as a small wire from the lever spring will get in the way. You don't want to break that! I used a small flat head screwdriver to move it aside while I pushed in the pin. Then once past that wire/spring use a small hammer to push the pin flush

Happy to help anyone willing to try this. I have pictures of everything and I can make a longer post.

Would be awesome if you could posts some pics and details on how to!!!

This is awesome. I was just taking my lever apart and trying to fix it. I will try with your method. Thanks!

Thanks for posting! I had two levers in my parts bin that were leaking but I had no idea the fix was so simple. I have previously disassembled the lever when I screwed the adjustment screw in too far - so that part was familiar. Your photos and write-up in the link are great, let me just add a few here that may help. FWIW, I used a piece of fishing line to pull the 'lever spring' out of the way - as indicated in the first photo.



All taken apart


New and old O-ring


Another shot of how the spring blocks the pin, until you maneuver it


I guess this goes to show just how much we love our Maguras ....just can't let them die!

I follow all threads regarding Magura hydraulic rim brakes as I've fitted a set to a Orbea Ordu frame that I picked up second hand. I love the power and feel, they were a 100% improvement over the awful TRP behind B/B brakes that came as standard with the frame. I bought the brakes second hand and didn't realise until fitting that the weld on the back of one of the levers where the brake line attaches had cracked. I wrote to Magura who put me in touch with the UK Magura service guys. I sent the lever assembly off and was very pleased to receive a replacement lever assembly FOC. I intend to use these brakes for some time, I'm building up another bike and have sourced another set ( and some spares ) to keep me going. Thanks for the advice mentioned in this thread, very useful !

Thank you for making this post!!

I also have what appears to be the same issue with my Magura RT8tt rear brake lever. The brake levers came on my 2018 Cervelo P5. I only use that bike for racing and I’m ashamed to say that it has been used only 4-5 times and for less than 200 miles.
I’m puzzled because I don’t see any apparent leaks anywhere. I noticed the right level seemed a bit greasy but it’s almost not noticeable. I checked all the connections and they are dry.
Now that you have replaced the seal has this solved the problem?

Thank you again!!

This is a downright dangerous repair.
The O-ring is quite capable of letting go quite abruptly under pressure and leaving you with no brakes.
The original seal is made so that increasing pressure will make it seal better and will not catastrophically fail.
Go to a seal shop and get the right sort of seal and do not encourage anybody else to do this modification as you do not understand what you are doing.

Thanks for the reply.

I was about to do this repair and noticed that the shape of seal is different. From reading the post I was assuming the O-rings/seals are the same.
Any idea where I could get this type of seal? Store name?
Also, how did you come to the conclusion that the existing seal design will seal better when the pressure is increased.

Thanks for posting this, a couple of days ago I saved all of the pictures for a possible future-repair myself (although my Maguras still function perfect until now), but now that I read your post I would not be so sure anymore to use a simple o-ring.

But I have a question: how do you know that the o-ring can malfunction abruptly?

I have the same question. Looking at the design of the original seal I can see that its shape is totally different. I called Magura and asked where I could find a replacement seal and they told me they don't carry it. They told me that those brakes aren't serviceable. They basically told me to replace the brakes with something else. My brake levers are basically new. I'd say they have been pressed less than 100 times and one of them is leaking.

I have a set of Magura rt6 that i pulled off a 2016 Cervelo P3 if anybody wants them for cheap.

You probably should have quoted the original poster who 'invented' this repair.....but anyways, your genuine concern is appreciated. We (the "Magura-brakes-for-life" people) understand the lever was not made as a serviceable part and this is not a repair endorsed in any way by Magura. We accept the risk of working on our own brakes but suggesting that the replacement o-ring will just spontaneously and catastrophically fail seems a bit histrionic. I'll admit, I'm not an engineer in any capacity but I must have missed your area of expertise? (Seems that some other posters are also wondering how you can so confidently predict that this o-ring will just "let go"). You've disassembled the Magura lever and examined the OE o-ring vs. the replacement ? Or you're an o-ring engineer that can tell just by looking at a picture? Don't worry, I'm on my way now to my neighborhood seal shop to get this taken care of.

A527G,

Will you pick up a few of those seals for me too? I have two sets of RT8 brakes and want to have those seals in case another one starts leaking. :)

If you look at the shape of the seal, it's in the form of a "cup", so that as the plunger is depressed, the fluid pressure will tend to push the outer lip of the cup harder against the bore of the cylinder.

As far as failure goes, I think lyrrad may be referring to the fact that increasing pressure could "push" fluid past the O-ring seal surface easier than the original seal design. On that point, I don't know enough about these sorts of details of hydraulic system designs to offer an opinion. I do know that the increasing pressure on the o-ring will tend to push it against the bore at the outer, rearward corner of the "gland" (the circumferential groove the seal is located in) which will also decrease the likelihood of leakage past the seal, as long as there is sufficient compression on the outer diameter of the O-ring when installed. I suspect the cup type of seal was also done as a way to decrease the seal drag when released so that lever return is faster/easier...but, like I said, most of what I just wrote is informed speculation based on other O-ring seal design experience. I would guess that using an O-ring in this location (of proper radial compression) might make the lever travel a bit slow, in both directions, even if it ends up operating OK.

Of course, if you can source the same type of seal used by the factory, that will be the best, most prudent, choice, obviously...

Side note: Based on the above description of the O-ring, I take it the piston bore diameter is ~12mm? Does anyone know, or can you figure out the total travel of the piston? I'm always trying to figure out if various master cylinders can be used with the Magura rim brakes (both these RT style, and the HS ones as well). I guess I could just disassemble one of the RT levers I have in the garage if nobody knows ;-)

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Given these brakes leak so much with the 'proper' seals I'm not sure putting the bogus trade shop ones in could be any worse, may even be an improvement..

I know that these aren't your brakes, but I gotta say that these kind of headaches make me steer away from hydro braking for disc brakes, or for rim brakes.

To have a consumable part like a rubber o-ring be no longer available from any manufacturer, and therefore making an expensive hydro brake lever or brake caliper become useless paperweights would be pretty frustrating.

I like cable actuated rim brakes. And, even for disc brakes, I like cable actuated brakes. Simple, repairable, and rebuildable. And they work great.

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I'd be willing to bet that cup seal is a standard size. I doubt if Magura designed/sourced their own seal for that lever. It's really just matter of identifying what size it is and finding a source.

It's also possible the O-ring fix could be just fine in that application...they ARE low pressure systems, after all...

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But if it is/was a standard size of o-ring, you would think that Magura would then offer up to customers that are looking for these the manufacturer name and part number of these rings.

But that seems to be not happening, based on posts above. Instead Magura they just say that it is not serviceable.

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Like most things service related, "not serviceable" probably means "I can't get that part"...and I don't necessarily blame Magura for not stocking replacements of every seal in their brakes.

I'm sure if you could get a hold of one of the design engineers, and they were amenable, you could quickly find out a stock replacement source/number...the hard part is finding that one person. Reverse engineering is probably the easier task...

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"Not serviceable" means "we haven't verified a user-implemented repair process and therefore won't accept responsibility for modifications to a critical system that we haven't tested and can't control". Basically just covering their arses.

I'm not a seal expert (I am a mech engineer) but o-rings ARE designed to create a better seal the more pressure is applied. That's literally how they work, I'm sure a quick google will tell you that. The fancy profile that Magura uses I don't believe will have any better sealing performance, but it may have other beneficial properties (retraction, one-way flow to replenish fluid in the cylinder, better compliance to a poor surface, wear characteristics, etc).

If you want to get fancy you could try an X ring:
https://www.mcmaster.com/90025K368/
or a double-x ring:
https://www.mcmaster.com/1161N33/


*Insert all appropriate disclaimers here*

It's also possible the use of the single U-cup seal might be part of the cause of the problems reported. In my brief research into the U-cup seals, I saw mentioned that for piston applications they should be used in pairs, installed in opposite directions...so??

And yeah, I agree with you that an O-ring seal design with proper radial compression should seal better with increasing pressure.

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Thanks Tom A.

I just ordered a double-x ring and will give it a try.

Just came across this thread 'cause my Magura RT8 are leaking :(


How's this fix right now in the long term? Still sealed... or started leaking again?

Anyone else with some experience here? Would love to hear it :)