Unanswered HELP! Major issues installing an M520 calliper on an M8000 lever...

[Nautonier]

I've got a Merida e160 900 and recently decided to up my braking power with 4 pots. I purchased a M8020 calliper + hose and successfully installed the front and was about to do the same with the rear when I read that the cheaper M520 (Deore) calliper worked just as well, so purchased one of those.

The first thing that was challenging was installing the hose, which needed the XT banjo snipped off and a barb, olive and screw installed. Basically the exact same set-up as on the lever. As the Merida is internally routed, I really didn't want to remove the hose to install the barb, which requires clamping the hose in a vice and tapping the barb in with a hammer, so had to very awkwardly get the hose on the bike to the vice...

Once the hose was installed in the calliper, I bled the system about 5 times, using every Shimano bleeding technique known to humankind and kept getting the same result:

The brakes work, but the lever pumps up massively, to the point where it's really sticky and won't back off. I really don't think it's my bleeding technique as the front brake has been perfect and just this morning I installed M8020s on another bike and the bleeding was super easy.

At the moment, the brake is unusable and annoyingly I can't go back to my XT calliper as I would need to buy another hose. This means that the bike is out of action until I can figure out what is going on.

I can only conclude that the M520 isn't as compatible with XT levers as people have said, with different flow rates or something.

Has anyone on here successfully mated an M520 calliper to an XT lever? Were there any tricks?

It's driving me nuts!!

 

[DrChris]

One thing I have learned from multiple Shimano brake bleeds on the rear brake is the the caliper needs to be significantly lower than the lever to get gravity to assist with the bleeding process. This means completely removing the caliper from the frame and letting it hang as low as possible as you bleed.

I've got a Merida e160 900 and recently decided to up my braking power with 4 pots. I purchased a M8020 calliper + hose and successfully installed the front and was about to do the same with the rear when I read that the cheaper M520 (Deore) calliper worked just as well, so purchased one of those.

The first thing that was challenging was installing the hose, which needed the XT banjo snipped off and a barb, olive and screw installed. Basically the exact same set-up as on the lever. As the Merida is internally routed, I really didn't want to remove the hose to install the barb, which requires clamping the hose in a vice and tapping the barb in with a hammer, so had to very awkwardly get the hose on the bike to the vice...

Once the hose was installed in the calliper, I bled the system about 5 times, using every Shimano bleeding technique known to humankind and kept getting the same result:

The brakes work, but the lever pumps up massively, to the point where it's really sticky and won't back off. I really don't think it's my bleeding technique as the front brake has been perfect and just this morning I installed M8020s on another bike and the bleeding was super easy.

At the moment, the brake is unusable and annoyingly I can't go back to my XT calliper as I would need to buy another hose. This means that the bike is out of action until I can figure out what is going on.

I can only conclude that the M520 isn't as compatible with XT levers as people have said, with different flow rates or something.

Has anyone on here successfully mated an M520 calliper to an XT lever? Were there any tricks?

It's driving me nuts!!

 

[Nautonier]

One thing I have learned from multiple Shimano brake bleeds on the rear brake is the the caliper needs to be significantly lower than the lever to get gravity to assist with the bleeding process. This means completely removing the caliper from the frame and letting it hang as low as possible as you bleed.

Yep, that was one of the things I tried. I really don't think there is air in the system, even on the first pump the lever is really solid - too solid in fact. I'd put it down to a bad bleed if I hadn't done it so many times with exactly the same result.

I'm just assuming that the calliper takes the same olive and barb as the lever end, it's not leaking and fluid seems to be passing through OK.

 

[ccrdave]

I just use a set of mole grips to hold the clamp blocks while I fit the olive and barb
I am sure I read something about noncompatibility between servowave systems and non servowave systems, the xt stuff being servowave but dont know if the m520 is
that could all be wrong though but it is strange, I find Shimano brakes very easy to bleed

 

[Nautonier]

Should I be using the gold or silver barbs at the calliper end? I've read that the gold barbs have a smaller flow, which might be causing my issue. The bike shop where I got the calliper gave me a gold barb, but I think I've seen silver ones on all my other Shimano brakes.

 

[khorn]

Usually when the brake lever is rock hard it is due to a piston diameter mismatch between the master(brake lever) and the calliper itself. Too big a piston in the brake lever will give a rock hard feeling and not enough force behind the pistons in the calliper. Air in the system will give a very spongy feeling and a good hint if it is air, is the fact that you can "pump"up the brake for a short while before it gets spongy again. If the piston in the master is too small it will also give a spongy feeling but you will not be able to "pump" it up. Another reason for the rock hard feeling at the brake lever could be that the internal bleed vale in the master is blocked somehow.

I have read that you can only match M8000 and 8020 between 2 and 4 pot callipers. I have XT 785 on Wifes Emtb and was wondering if I could upgrade to 4 pot callipers but did not do it based on the above information.

Karsten

 

[Nautonier]

Turns out the issue was solely with the barbs the bike shop gave me to fit the calliper end of the hose. The gold barbs do not work and cause the brakes to pump up and stick. The silver barbs work perfectly. I wish I had known this 5 bleeds and many hours ago!

I rode the bike this afternoon with the M520 calliper and it worked perfectly, just as good as the M8020 calliper on the front in fact.

 

[ccrdave]

Thats good news glad you got it sorted

 

[Re-Cycle]

I'm glad that your problem is solved, but I don't understand how the barb can cause such a problem.
There are two kinds of Shimano hoses, "old" and "new". The old ones use the gold colored barbs, the new ones use the silver ones. The difference is a slightly other internal diameter of the hoses.

You can combine any Shimano brake caliper and lever, as long as you use the right barb in the right hose. You can use an "old" type hose with a "new" type brake, because the outer diameter of the hoses is the same. It's also no problem to use servo wave levers on non servo wave calipers or the other way round. The feel of the brake will probably be different, but it will work.

What I do know is that there have been problems with the 8000 series levers with the bite point being inconsistent (some XTR brakes had the same problem). These problems are what you described: pulling the lever several times will move the bite point and can make the brake pump up to the point you can hardly pull the lever anymore.
If that is the case it should be a warranty issue.

From what I've read these problems should have been solved with the newer XT brakes.

But mixing different Shimano calipers and levers should not be a problem.
Using the wrong barb could cause leakage (and as a result air can enter the system) but it doesn't sound logical that it should cause the problem you described.

 

[Nautonier]

It was 100% the barb. I’ve mixed and matched shimano levers and callipers before, always successfully. Usually you have to buy a calliper specific hose, but not in the case of the m520s, where you can use an XT hose with a new olive and barb at the callous end. I think the flow rate of the different internal diameters of the barbs is enough to completely change the feel and performance of the brakes. The bleed I did with the silver barb was exactly the same as the 5 unsuccessful bleeds with the gold barb.