I would say, time to bite the bullet and get another brake handle assembly.

No not from just pouring it in.. Pressure sends it out of the reservoir.

OK but if I pump the handle fluid still doesnt come out. I guess of course there is no pressure built up if the line is disconnected. But with the line hooked up nothing comes out either. Is there a quick way to definitely confirm the master cylinders bad before I spend 45.00 for nothing? Also does anyone know what size the threads are on the automatic shift lever on the MPX 150? The black knob on mine came off and I need to replace it with something.

With the pipe disconnected and the reservoir full, pull the lever down. Stick your finger over the outlet and let the lever return, press again and the pressure should blow your finger off the outlet. If it does, refit the pipe but leave slightly loose, press on the lever, fluid should squirt out of the union. Tighten the pipe before letting the lever return.

If the machine is Chinese the gearchange thread will be metric. 6,8,10 are common diameters, measure it. Thread forms are more tricky as various pitches are used on quads. Best to find a metric bolt of the same dia and pitch, take it to a local engineers suppliers and say I want a knob to fit that. Use threadlocker to ensure you don't loose another.

If it doesnt pump brake fluid its junk.. No way to remove the piston?

Once you determine the thread size..Id think its a 10 X 1.5 mm (match it up with a metric nut/) Then go to mcmaster.com ... put "metric knobs" in the search..

Yes I was able to tear the mast cylinder all the way apart. Everything looked alright but I don't really know what to look for. There was 2 rubber pieces. One was like a cup on the end of the piston where the spring is and one was like a rubber sleeve up at the other end of the piston.

Either one of the rubber seals is worn or there is a plugged hole at the end of the piston chamber/bore.

10-4. Im going to take my chances and just order a new assembly. So does anyone know where I can get a new left rear brake lever master cylinder assembly from a trust worthy site online that is for a 2003 Redcat MPX 150?? Not sure if it matters or means anything but the one on there now had a aluminum finish brake lever.

I did some more looking today for a new brake lever assembly and the 1st link below the guy said he's not sure if it will work on my atv or not. The 2nd link below the guy told me that it will work only on a Redcat VX-110. Please help anyone. I need to find a new reliable rear brake lever master cylinder aaembly for a 2003 Redcat MPX 150 ATV.


This guy said no guarentee and wasnt sure.
Brake Master Cylinder Left Hand Lever 50 70 90 110 125 150 CC ATV UAD Tao Tao | eBay

This guy said only work on Redcat VX-110
Hydraulic Brake Master Cylinder Left Lever ATV Super Dirt Bike Scooter Bonus | eBay

They both look like they would work to me. both have the same fitting/thread in the end.