Noonievut

My wife has a GT mountain bike with these hydros. It’s about three years old and she only rides a couple hundred km a year. Was bringing it outside after being in the basement in the winter and the back wheel barely rolled. The pistons wont retract and when I removed the wheel with the plan to take the pads out, push the pistons in, etc., I discovered that you can’t pull out the pads without dismantling the caliper. Not sure if they simply need the pistons pushed back in, bleeding (I’ve never done and don’t own the kit) or something else. LBS in my area are 4+ weeks until they will look at the bike.

Anyone know this brake and can offer some tips? I can’t find relevant info online.

thanks!

travbikeman

When the wheel was on, were you able to use the brake? Meaning, does it actually move the pads to and from rotor and offer an actual brake? It's very possible since the bike has been sitting in basement, they just need a light pumping action to get the fluid moving through it again.

If not, it's very possible you need to bleed the brake. Or if there is a very loose feeling brake lever action, you may need to just burp the brakes.


Am a bit confused as to why you have to dismantle the caliper, pads should have a pin to pull out and you "should" be able to just pull or push the pads out.

Noonievut

Thanks for the links. I did watch the first one but the brakes on my wife’s bike are different. Second video I believe is the same so I’ll watch it tomorrow.

I did kind of sort it out though. Found a comment online about the dot fluid expanding, and how you open the port at the lever slightly and then push the pistons in. These brakes don’t have the pin I’m used to, but I did the above and it worked. A bit too much though as more fluid came out then I planned. Wheels spins freely now but brakes are weak, but for now manageable for the short and flat rides my wife does. I may bite the bullet and buy a bleed kit and bottle of fluid and try this myself. Will give me some confidence should I want to try and bleed my GRX brakes on my gravel bike

jimc101

If looking to service, would also look at the cost of replacement with lower end Shimano, say MT200, to see if there is any price difference,

In general hydro brakes at the caliper have little in the way of serviceability, with the exception of high end low volume brands like Hope, it fit and replace rather than repair, which for a critical safety item is probably for the best for most users

travbikeman

OH, it has DOT fluid! OK, just remember, the GRX brakes may not use DOT fluid, I think it uses mineral oil. You don't want to mix the two otherwise that will mess up the brakes.

I agree with jimc101 though, Shimano MT200's are so very affordable and good brakes, it maybe cheaper to replace the set than have a shop look and "maybe" fix.

Noonievut

Thanks for the tip on the MT200's. Called my LBS and they have them (selling like hot cakes apparently). And they are very affordable. I'll be picking those up today. Good thing is I can get a bleed kit and use it on both sets of shimano hydro brakes.