Adjustment of Magura hydraulic brakes on Kalkhoff Agattu

[danfoto]

I may well be having a brainfart here, but when all adjustment is taken up at the lever but there's still plenty of meat on the pad, is it actually possible to move the cylinders closer to the rim - and if so, how?

I know you can move the pads up and down (i.e. radially), you can twist them and you can tilt them, but it's the moving closer to take up play that's puzzling me ...

 

[Deleted member 4366]

They should be always close to the disc because there's nothing to pull them back out. You only have to adjust the pad position on cable brakes. If your lever comes too far back, it could be because you have air in the system or, if the lever starts too close to the handlebar, you can adjust its start position with the adjuster screw in the end of the piston rod, that you'll see if you look in the direction along the handlebars from outside. The screw is in the scissors of the lever.

 

[Blew it]

...but it's the moving closer to take up play that's puzzling me ...

The lateral position of the slave cylinders can be adjusted in relation to the rim by slackening the top allen screw of the EVO2 adaptor. Remove the quick-release first.

This is explained fully in the service PDF download.

CLICK HERE

 

[danfoto]

Cheers Blew it. I thought I'd tried that and they wouldn't go any nearer, but I'll try again later if it ever stops raining ...

(d8veh, thanks but it's rim brakes on the Agattu)

 

[danfoto]

Now sorted

I knew I'd tried pushing them in and I hadn't been able to, but I now know the reason why. In case it helps anybody else to know, the problem is a bit missing from page 8 of the service PDF.

After it says "Push the slave cylinders towards the rim while adjusting them properly", they missed out "and if that doesn't work, a sharp whack with a rawhide mallet will do the trick".

BTW, I can't see any reason to remove the QR

 

[tillson]

The lateral position of the slave cylinders can be adjusted in relation to the rim by slackening the top allen screw of the EVO2 adaptor. Remove the quick-release first.

This is explained fully in the service PDF download.

CLICK HERE

Is, "the top allen screw of the EVO2 adaptor" the one(s) shown on Page 7 Paragraph 11, of the PDF which you linked to? The ones with 6Nm arrows pointing at them?

If they are, I believe they act like a clamp and fix the slave cylinders in position once that you have positioned them. I have spent hours meticulously setting these up, using strips of 2mm ground silver steel to slip between the rim and brake pad in order to achieve the correct gap and observing all torque figures. The brakes work fantastically well right up to the point that pad wear need to be taken up. As the pads wear and I turn the red TPA adjuster on the lever, only one pad moves closer to the rim, so I end up with one pad with the correct 2 mm gap and the other pad is (2 mm + wear) away from the rim. So when I have say, 4 mm of pad wear, the best that I can achieve is a 2 mm gap on one side and a 6 mm gap on the other.

Magura have admitted to me that this can be the case and for that reason, I would advise people thinking of upgrading to these brake to bear this in mind. Its very poor situation to have on an expensive brake.

 

[danfoto]

The brakes work fantastically well right up to the point that pad wear need to be taken up. As the pads wear and I turn the red TPA adjuster on the lever, only one pad moves closer to the rim, so I end up with one pad with the correct 2 mm gap and the other pad is (2 mm + wear) away from the rim. So when I have say, 4 mm of pad wear, the best that I can achieve is a 2 mm gap on one side and a 6 mm gap on the other.

1. Slacken off the "TPA" all the way.

2. Slacken off the top Allen screw on each side i.e. those which clamp the slave cylinders

3. Push the slave cylinders in towards the rim as far as they will go. If your blocks are not then hard up against the rim on each side, whack the outer end of the slave cylinders with a soft mallet or whatever to overcome stiction and try again

4. Carefully squeeze the brake lever so as to push both cylinders away from the rim slightly.

5. Release brake lever, and check gap between block and rim. If not to your liking, either try another careful squeeze, or close the cylinders up again and repeat the process.

6. Repeat until you've got both sides how you want them.

7. Tighten both the Allen screws

At one time I'd have agreed with everything you said about these brakes, but having now seen the error of my ways, I've reverted to my original opinion, which is that they're the doggie's danglers.

 

[tillson]

1. Slacken off the "TPA" all the way.

2. Slacken off the top Allen screw on each side i.e. those which clamp the slave cylinders

3. Push the slave cylinders in towards the rim as far as they will go. If your blocks are not then hard up against the rim on each side, whack the outer end of the slave cylinders with a soft mallet or whatever to overcome stiction and try again

4. Carefully squeeze the brake lever so as to push both cylinders away from the rim slightly.

5. Release brake lever, and check gap between block and rim. If not to your liking, either try another careful squeeze, or close the cylinders up again and repeat the process.

6. Repeat until you've got both sides how you want them.

7. Tighten both the Allen screws

At one time I'd have agreed with everything you said about these brakes, but having now seen the error of my ways, I've reverted to my original opinion, which is that they're the doggie's danglers.

Thanks for taking the time to write a list of instructions danfoto, I appreciate it.

I have been following your instructions to the letter, but at (3) instead of pushing the blocks hard up against the rim and then squeezing the lever to push them off slightly, I have inserted a 2 mm strip between rim and brake block and pushed them up to that. This effectively sandwiches the 2 mm strip between rim and brake block. I then tighten everything up to the correct torque, slip the 2 mm strips out and I have, what I think are, perfectly adjusted brakes. They remain like this until the pads begin to wear and it is then that the trouble starts. Only one slave cylinder moves when I turn the TPA on the brake lever and this gives me the uneven gap between the pads and the rim.

I am not going to write off your suggestion and I will indeed tw@t the slave cylinders home with a big rubber mallet and I will report back regarding success or failure.

Thank you again.

 

[danfoto]

... the pads begin to wear and it is then that the trouble starts. Only one slave cylinder moves when I turn the TPA on the brake lever and this gives me the uneven gap between the pads and the rim.

Forgive me if I'm missing something here, but what's the problem with just repeating the adjustment procedure on the side with the oversize gap?

I admit that I'm not entirely clear if the TPA is supposed to achieve anything other than close up one block, but wtf - AFAIC these brakes are a doddle to set up and keep set up compared to cantilevers, and they work a treat, so I'm quite happy re-setting one side every now and then.

PS Couldn't be doing with your 2mm inserts, but each to their own

 

[tillson]

Forgive me if I'm missing something here, but what's the problem with just repeating the adjustment procedure on the side with the oversize gap?

I admit that I'm not entirely clear if the TPA is supposed to achieve anything other than close up one block, but wtf - AFAIC these brakes are a doddle to set up and keep set up compared to cantilevers, and they work a treat, so I'm quite happy re-setting one side every now and then.

PS Couldn't be doing with your 2mm inserts, but each to their own

I think that both cylinders are supposed to move, otherwise there would be no point in fitting the TPA to the brake lever, you may as well adjust both sides at the same time if you have to always manually adjust one side.

I'll give your suggestion a go and see what happens.

 

[danfoto]

On thinking about this, if the brake pipe went from the lever cylinder to a splitter and thence to both slave cylinders, any adjustment of the TPA should have an equal effect on both sides.

As things are, the pipe goes to one side then via a jumper pipe to t'other, but presumably the end result should be the same.

If it isn't (and we seem agreed that it isn't), I wonder why ...

ETA - if one piston moves before/further than the other, and/or it doesn't retract as much, I reckon that's got to be down to friction, so my money's on tolerances, either in the fit of the pistons in the slave cylinders, or in the drag induced by the seals.

 

[tillson]

On thinking about this, if the brake pipe went from the lever cylinder to a splitter and thence to both slave cylinders, any adjustment of the TPA should have an equal effect on both sides.

As things are, the pipe goes to one side then via a jumper pipe to t'other, but presumably the end result should be the same.

Absolutely correct, there is a balance tube which connects one slave cylinder to the other, so the pressure in each one should be the same.

If it isn't (and we seem agreed that it isn't), I wonder why ...

The pressure is the same in each slave cylinder, it has to be because they are connected together by the balance tube.

if one piston moves before/further than the other, and/or it doesn't retract as much, I reckon that's got to be down to friction, so my money's on tolerances, either in the fit of the pistons in the slave cylinders, or in the drag induced by the seals.

This is exactly what I am thinking. If one of the slave cylinders has a piston which, for the want of a better phrase, is more sticky than the other, the less sticky piston will move first, and it does. This is why when I turn the TPA adjuster on the brake lever (this just forces a bit of oil down the tube in the same way that pulling on the lever does) only one piston moves and takes up the wear in the pad. The sticky piston just sits there building up a progressively larger gap between brake pad and rim.

When you pull on the lever to stop the bike, the free piston moves first until the pad comes into contact with the rim. When it can't move any further and the rider continues to pull, the pressure in the system builds until it moves the sticky piston. That then makes contact with the rim and the braking action begins. I am only talking about very small pressure differentials here and the braking action is not effected by this, but it renders the TPA adjuster almost useless. As you have already mentioned the only way to take up the pad wear in this situation is to slacken off the sticky slave cylinder clamp and physically move the cylinder and pad closer to the rim. This may not be a major drama for some people, but it irritates me because these are expensive brakes and I bought them because I do a lot of miles and I thought it would make regular brake adjustment easy.

I have had quite lengthy email exchanges with Magura over this issue and I have been relentless in getting them to acknowledge that it is a problem. Eventually, they admitted that the design is such that if one slave cylinder has slightly more friction than the other, exactly what I have described will happen. It's pi$$ poor, I'm very disappointed with these brakes and as I have said before, anyone thinking of buying a set should have this in mind.

I still intend to thrash them with a big mallet (well gently tap them up to the rim) as you suggest, but I can't see any reason why it should alter the situation. Unless the tapping action somehow frees the sticky piston and I achieve frictional balance on both sides. That would be good.

 

[danfoto]

I can understand your vexation, but as far as both the Lady Wife and I are concerned, our Kalkhoffs came with excellent brakes with which we're quite happy despite their one peculiarity.

Having said that, though, we're also happy with the conventional Shimano vee brakes on our Thorn Sherpas. I just wish they weren't such a PITA to change the blocks on ...