Brake fluid appears low

When I put either of my brakes on the fluid in my master cylinder goes down and when I don’t use my brakes it goes back up, I have taken the top off the cylinder and the brake fluid is to the top but its quite nerving to see when you brake there is no fluid in the master cylinder. I have put a braided hose on the front but left the original hose on the back (cant see much point putting braided on the rear). There isn’t an airlock as if there was the brakes wouldn’t work the hoses aren’t bulging when the brakes are being used. If anyone has any ideas why this might be happening please let me know. Bit worried about using the bike now in case I do use the brakes and nothing happens… Thank you

It’s possible that there could be an air bubble up in the master cylinder - does the lever feel spongy at all?

No I think its ok, I pull it and it stops I pull it too hard and I stop quickly… So no I wouldnt have said there was an air lock…

Hi Lady P

You could have warped or dished discs. As you ride the bike without using the brakes, the disks will tend to push the pistons back in the caliper and consequently raise the level of fluid in the master cylinder. If this is the case then you would have to pull the lever a long way in order to brake hard, probably back to the bar.

The solution is to replace the discs.


Easy way to check that is to lift the front and spin the wheel - if they are that warped you’ll be able to hear it.

BTW - had a new front tyre fitted recently?

I am having specially made disc’s as I have some ohlins shocks to put on the bike but its not the disc’s and also I have a new tyre to put on so I know its not that, I am really baffled as to why this would happen, the brakes do seem ok but its really worrying as to why the fluid disappears and then reappears when you don’t use the brakes…

In that case I think it’s probably best to try another XT, the same as yours, and see if you can feel a difference between the two. There seem to be a fair number of XTs in LB, so it must be possible to find a match. Then we might be able to work out what is wrong with yours.


First port of call - change fluid / bleed brakes.

Don’t cost much.

Do you have a standard brake lever and master cylinder fitted?

Also is there any drag in the brakes - if you push the bike, then apply then front brake, release and push the bike forward again - can you feel any drag then?
If brake fluid isn’t returning to the reservoir you might expect the brakes to drag after you have applied them.


yes apart from the braided hose then every thing is standard, I will do what ducati pete says and bleed them. I am trying to get different levers and a new master cylinder but I have to see my mechanic (paulie) who will recommend the best to use while the new forks are on… Its just a weird thing to happen…Thanks Duncan for your suggestion of riding another XTR which I have done and the fluid doesnt disappear in that cylinder.

Dude just add some cooking oil…