Hi all,

I bought a set of Tanke TB-800 4-piston brakes to upgrade an old bike on the 11/11 sale and they arrived this week. I've installed the front one (haven't got the back one on yet) and am having a problem that Google isn't helping me solve.

Basically, the pistons seem to be overextending and not backing out again. Within 1-2 pumps of the lever, the pistons extend so far that they permanently engage the disc and the wheel can barely move. If I take the wheel out and push the pistons back out, as soon as the wheel is back on and I pump the lever, the same thing happens again. With the wheel off and before pushing them back in, the pads rest probably about 2/3 of the thickness of the disc apart whereas brakes on my other bikes would be fractionally wider than the thickness of the disc.

They are easy to push all the way back out with the wheel off, so I don't think there is too much fluid in the system, but just in case I tried loosening the lever bleed screw and pushing out the pistons to the wide-open position with that opened, which ejected a small amount of fluid. This made little or no difference to the piston extension issue. Figuring that I may have now gotten air into the system I did a quick lever bleed, which got out a few bubbles of air but again made no other difference. I haven't bothered to fully bleed the system as yet as to my knowledge that is unlikely to do anything useful, as dirty fluid or air in the system shouldn't be causing this problem.

Interestingly, this brake arrived with the pistons so far out that the little spacer they had in transport needed a pair of pliers to pull out, whereas the back brake lets me easily pull out the spacer. I'll see if the other side has the same issue when I install it tomorrow, but in the interim was wondering if anyone here has any ideas about what would be causing this issue.

Have I just got a defective brake or is there some easy fix that I'm not thinking of?

Thanks in advance!

A standard hex wrench - I think it was 8mm, is what is needed to install the arms. If you want to remove the self-extracting caps a set of needle-nose pliers can remove them. Just put the tip of pliers and hold the handles open to wedge the tips in the caps. A slight turn will loosen the caps without a huge amount of pressure. The caps are left hand threaded - so Righty Loosey. I have removed and reinstalled the cap on one arm and had no issues with damaging the finish.

Yep, I know the cranks themselves attach using a hex wrench, it was the caps I was talking about. I don't think I have any needle-nose pliers fine enough to fit in there, hence the pin wrench. When I was fiddling around with loosely putting them together when they first arrived the drive side threads got damaged (I think there was some swarf in the threads of the spindle) and I had to remove the cap on that side to get the bolt out so that I could clean it up. I was worried that a few thousand km down the track I'll have a similar issue when I take them off to service my BB etc., the caps will have managed to clog themselves up with dirt or cold weld themselves to the spindle or similar, and I might need more force than pliers or my pin wrench can exert to get them out.

Thus if it was a standard fitting for some other more popular brand of crank I figured I'd just buy the right tool off AliExpress for a few dollars and be done with it. But if it is a proprietary thing obviously that won't be possible. Does anyone else recognise the spline pattern?