master cylinder beast
 

My rear brakes have gone to mush. No stopping power at all. I have bled the the brake and although the bleed nipple sounds like its trying to pump air and fluid...its does not develop pressure.
I wonder if when I replaced my swing arm bushings I distorted a compression fitting on the brake line or if I just need a new master cylinder.
Gio does not have one listed as a replacement part....anyone know a source?.........thx....waynec

Have you tried raising the rear end while bleeding them?, i know on our microsprints it was tough to get all the air out, it's probably worse on our beast because the master is higher than the caliper and air always rises to the top. Fill your master with fluid, raise the rearend, bleed the brakes and then top off the master with brake fluid.

Also is there any fluid leaking from the piston?, maybe one of the o-rings on the pistons is bad too.

No sign of any leaks. The resevoir had not lost its level. l was bleeding with the rear end way high....although quite by accident. On my machine the bleed valve is blocked by the the bottom plate so I had to remove the caliper to access it. I had the butt strung from a rafter to ease the removal. I also removed the master to investigate possible o ring replacement.....but it did not look terribly serviceable (quick and dirty, I mean) so I held off ..........waynec

The good news is that a similar caliper was used on several Honda products. Make sure to include dirt bikes, quads and trikes in your search.

Thx w&g I expanded my search parameter on the Gio site and they do sell the mst cylinder. It'll be $90 with shipping and tax.......but that will give me a spare caliper complete.....have to think on that......waynec

BLEEDING BRAKES..
 

You have to shorted the stroke and bleed it slowly.. put a wedge in the brake calipher to hold the pistons in as far as you can so they really do not move much at all... short strokes and hope it works for you... they are very hard to bleed.. on the atvs I have noticed that if there is air in the system from the factory.. little strokes will bleed the air out.. you will see small bubbles in the reservoir as you move the plunger... time and patience ... or money and no time.. take your choice..

thanks for the advice. I will try that. I have seen a few cylinders on ebay that appear the same. migh get in under $50. delivered....but..I have decided I will not spend $90 from Gio. If your tip does not work I will pull the o rings and see what I can find.........thx...waynec

I got around to pulling my master cylinder and have a pic of whats there. Its not much. I was hoping there might be a generic o ring with a bit of damage but everyting seems in order. The black seals are 'bell or umbrella" style seals. I have only had one other mst cylinder apart and it had similar type plungers. All I could think to do was run a little silicone under the seals to provide a little more pressure to the cylinder body. I hope there is no conflict with silicone and brake fluid. As I wrote previously this thing squirted a little like it was trying hard to develop pressure so i'm hopeful its just a minor problem.....waynec

http://s628.photobucket.com/albums/u...ast%20caliper/

Any roughness in the bore that would create a pressure loss?

Perhaps my final update on my brake struggle. I got a master cylinder off Ebay for a very good price. I think its from a Honda. Spent another couple of hours trying to bleed the brakes with no sucess. Maybe I just suck at this...but I have kept my sons Fourtrax going including brake work. I'm done. Tired of messing with stuff. The Beast is for sale.
http://ottawa.kijiji.ca/c-cars-vehic...AdIdZ226879202
waynec

Bummer. I hate when machines win.

DO NOT PAY GIO PRICES

i had this same problem for a good year and a half, had no rear brakes.
when i would press the pedal and crack the bleeder valve open it would squirt the fluid out like there was pressure.. but the master was failing under pressure..

this is the person i ordered my brakes from on ebay.. 40 bucks for a whole new rear brake system.. this is exactly what i ordered and use..now i have rear brakes and no brake issues

http://cgi.ebay.com/ebaymotors/Rear-...Q5fAccessories

That's crappy. Sorry to hear you're coming to this step.

Can't think of why this would be giving you all the trouble, especially with new parts.

my bad didnt read the comment saying it was for sale, read down to where it was said 90 bucks from gio.. bleeding should be the same as on the fourtrax.. if you have replaced everything it should all be working.. did you get rid of the craptastic brake fluid it comes with ?

Thx for the tip. yes i used new brake fluid. The cylinder for the Fourtax is on the handlebars. Bit of a different style and more meat inside the chamber but the concept is the same. At least with the Honda branded cylinder I now have I can probably order up a mst cylinder kit. If I calm down a little i may do this and keep the machine.

Hey Turbo....no it was a used cylinder off Ebay...not new..and I only paid 12 bucks incl delivery..so it may not have been working when it was last in service.

I have been fighting with the engine in a stern drive ski boat for 3 years now....the story I could tell about that adventure and I finally have it beat. I am still just a little tired of massaging all this stuff i have to keep it running. More time fiddling than having fun with some of it.....waynec