485 brakes

Hi all
I'm having some problems withthe brakes on our 485 and hope I can get some advice
We parked the tractor in the barn the next week we go out to get it and there is no brakes on the left side
We have never had any problems with the brakes before this and we have owned the tractor for 20 years
We tried bleeding the left side but all we got was bubbles
We had a guy replace the master cylinder for that side
agin bleeding bubbles and would not pump up
We thought it was a bad master cylinder so we got another one put it on tried to bleed the brakes
It feels like they pump up some but never to where they should be and the fluid never gets clear from that side just bubbles
We are now thinking that the o rings in the brake piston may be bad
Any advice would be greatly appreciated
Thanks

Good chance of that, remove brake line, put compressed air at about 30 p.s.i into the brake and listen at the trans oil filler cap, if it is
really bad you should get oil in your ear. Also check that the other side brake pedal is returning fully and not holding the balance valve,
and that the PTO valve is adjusted correctly to obtain the correct oil flow to the master cylinders.

When you bleed to brakes,with engine running,you are supposed to pinch the return line from the brake reservoir which goes to the top of the tranny.This makes sure the reservoir stays full.Then bleed the left brake.Then hold left pedal 1/2 way down,and pump up the right pedal,but bleed the left brake.Then hold right pedal 1/2 way down and pump left pedal and bleed right brake.This checks out the equalizers.All that said,I have been able to bleed one side and get away with it for a short time,like a day.You need to first make sure the line from the master cylinder to the brake piston is not leaking.Next pressurize the brake piston.Use a gauge in line.It should hold 60psi for a day.If it doesn't hold ,replace the piston o rings.They usually don't appear bad,but maybe a little worn.Since you have to pull the fuel tank and fenders,replace the other side as well,because the most labor is in pulling the tank and fenders.Pull the tank and fenders as a unit.You have to drain the tank also.Pulling the axle is the easier part of the job.The o rings are not that expensive.Use anaerobic sealant for axle gaskets.You will also want to change your hydraulic filter since you have drain the fluid.Takes 9+ gallons.Another reason to replace both sides at the same time.Be careful when assembling the pistons so that the o rings go in place properly.Good luck,Mark