New Levers Monster 620, Uneven Braking!

I might be misunderstanding you but the brake cylinder is the thing on top of the right hand handlebar which the brake lever squeezes when you pull the lever. Above the cylinder is a reservoir that holds the brake fluid (it is not oil). You only have one of these. There is a tube (or pipe, whatever you want to call it) that goes from the brake cylinder to the brakes. At some point that tube will split into two, one to feed the right hand disk and one to feed the left hand disk.

The brakes themselves are callipers on each disk, the calliper holds the brake pads.

If you’re bike has a hydraulic clutch then there is a second cylinder and reservoir on the left hand handlebar, this is to operate the clutch.

If by ‘cylinder’ you mean this (see photo) that’s a caliper and yes there are 2 of them if you have dual disks

What year is your bike?



EDIT : that was in response to the post you deleted so ignore it as well.

 

That piston can come out but it looks like it’s missing the rubber o-ring seal. Do you have a better photo? If the seal is missing it won’t work, it will leak brake fluid.

 

Give me some time and I’ll see what I can find for a parts diagram.

 

You’ll find a parts diagram for the front brake system here

https://www.bike-parts-ducati.com/d..._620_IE/Monster-620-IE/FRONT-BRAKE/94/31/0/94

However, the internals of the brake cylinder itself are not shown.

That piston should have an o-ring on the end of it which seals the brake fluid inside the cylinder and stops it leaking past when you squeeze the lever. It looks like you need to strip down the brake cylinder and rebuild it. Hopefully the o-ring isn’t damaged and you can reuse it. There are videos on YouTube about overhauling motorcycle brake cylinders, or you just take it apart and put it back together, there aren’t many parts to it. The main thing is to make sure you do it in a clean environment, and when it’s stripped down make sure the 2 little holes inside the cylinder aren’t blocked with gunk.

 

It will be something like this inside

https://images.app.goo.gl/z5x4QQxQ1PvAPpvw9

 

First of all you need to put a tray down to capture all of the leaking fluid. Then clean it off the bike as brake fluid is corrosive and will harm any coated surface, Push that piston back in to stop any more fluid from leaking out. Check that no pistons are seized by seeing if you can push the piston into the caliper with reasonable ease.


If it was my bike, I would uncouple each brake line from the caliper whilst the caliper is still bolted to the fork. Have a receptacle ready for the brake fluid to drain into. Then remove the caliper and make sure that all the pistons are not seized by pushing them into the caliper. This will cause more brake fluid to come out of the hole and thread where the brake line is normally bolted to,

So with everything drained of old brake fluid and happy that no piston is seized put everything back together. The copper washers that seal the brake line to the caliper can be reused rather than replaced. Normally I heat them up until cherry red with a blowtorch and then put them somewhere safe to air-cool - thus annealing them. When it is all back together, you can them refill with brake fluid and bleed the brakes (after putting back the front wheel to ensure that the brake pads (which you have refitted) stop any pistons from popping out as you bleed the brakes.

 

No, I would take off the brake lines if I wanted to get the calipers on a workbench in order to strip then. If you are confident that all of the pistons are free, then you could just bleed the system as it is - with everything in place. Put back the disc pads and have the brake calipers back on the forks with the front wheel in. This will ensure that no piston can get blown out of the caliper. So, with calipers and wheel in place you can bleed the system. The result of that should be that the front wheel spins freely until you put on the brake. Then the front wheel should not turn until the brake is released.

 

My first thought was the piston and seals damaged through impact....I had the same on my Pantah 500 when dropped on the M1 Southbound in the 80's.....lever wrecked and had imparted a rapid force onto the piston /cylinder assembly. I needed to buy the Brembo repair pack that contained all seals, circles, piston and special grease etc......worked well....

 

This link should take you to a download for the full parts diagram for a 2003 M620, you may have it already in which case just ignore this.

https://www.carlsalter.com/download.asp?p=1458

Manoit above has a point, assuming the damage was to that side, hence the lever change, you may have damaged the internals of the cylinder.

Yes, there should be an o-ring in the groove on the end of the piston, the groove is to hold the o-ring in place.

The narrow, internal, end of the piston is what pushes against the plunger inside the cylinder which compresses the fluid when the brake lever is pulled back.

You should be able to extract all the internal parts ie the piston (already out), o-ring, plunger, return spring, through the hole at the end of the cylinder.

Your brake cylinder reservoir is now empty so it’s an opportunity when all the parts are out to make sure it’s clean inside and there are no gummy or congealed bits of brake fluid (Fluido dal freno) which may block the tiny holes in the bottom of the reservoir and through which the fluid fills the cylinder.

Don’t worry about the callipers for now fix the master cylinder first then return to the callipers.

NB I’m not 100% familiar with the type of brake cylinder on that model, it may very well be, to save costs, the o- ring which should be in the groove on the piston is the only seal between the brake fluid and the outside world. In some there are 2 seals in others there are only the one. It will all become apparent when you get all the parts out.

 

From all the above information it appears your master cylinder is not functioning correctly and that the brake fluid is, at times, leaking past the seal(s). It appears the leak is not consistent and thus at times the pressure in the brake lines builds and the brakes work well but at other times the master cylinder leaks and pressure in the brake lines does not build as it should and thus the brakes are not as effective.

 

BTW, you do know you can upload photos (but not videos) directly into here, use the upload file button, no need to use Imgur