Master Cylinder Seized

[fermin]

After receiving my new brake line and cleaning the master cylinder I tried to bleed the assembly before attaching the line but couldnt get fluid to come out after repeated pumpings.  I can feel pressure when I squeeze the brake lever and a vacuum when I release it but unable to get fluid out even after using a hand vacuum device.

So I am thinking master cylinder rebuild.  Problem is I am unable to separate the cylinder body from the throttle grip assembly (or the reservoir for that matter). I think due to age and inactivity they may have rusted.  Is there a trick to this?.  Theres a notch on the underside of the assembly and I've even hammered it a couple of times to try to separate the cylinder body .

Sprayed penetrating oil all over and left it for tomorrow......  

[nhmaf]

Did you remove the piston assembly and examine the bore when "cleaning" the master cylinder?    What year R65 do you have?  Does the assembly have a "round" plastic reservoir/cap or a rectangular reservoir/cap?    The round style aren't really rebuildable, but one can replace the piston assembly in them.  Some have successfully "rebuil"t the round units (involves epoxy-ing the reservoir back in place after delicately removing it) but most end up buying new ($)  The rectangular ones that come on the 81-later R65s are fully rebuildable.

[bruce_launceston]

I believe there is a screw up from underneath holding the reservoir to the m/c that you may have missed?

[Bob_Roller]

I'm assuming that you removed the two Allen head screws that hold the master cylinder to the 'perch' assembly .

If you have them removed, you need to a piece of hard wood, place it on the piston plunger side of the master cylinder, and give it a bit of 'persuasion' .

You've most likely have corrosion between the two parts .

Can't remember what year bike you have, it would be helpful, if you put it in your profile, as the '79-80 year bikes, came with a different reservoir than the '81 and later bikes .

There is a small hole visible from the inside of the reservoir drilled into the master cylinder body, if this becomes clogged, it will give you problems, use a soft material like a piece of copper wire to check to see if it is clear .

Like Bruce stated, there is a Phillips head screw on the bottom of the master cylinder, that holds the reservoir on, but even with the screw removed, there is an o-ring in there that can keep the reservoir from being removed .

You need to twist the reservoir back and forth to get it loose .

[Yikes]

Separating the MC from the throttle was certainly the most difficult part of the cylinder rebuild that I did.  I ended up using a thick paint scraper (not the flexible kind) as a wedge,  carefully set it in the seam and gave it a whack with a big hammer.  It is a bear getting those apart and it does give you one of those "This can''t be right" moments.  Just be sure all the fasteners are out and keep at it.  Funny thing is once it was apart,  there was not that much visible corrosion in there.

Good  luck with it!

[fermin]

Thanks for the tips.  Its a '83 with the rectangular reservoir and yes I did remove all fasteners holding the body and reservoir.  Like I said I even wacked it a couple of times on a nudge between the two parts located at the bottom side of the assembly, but no separation and like Yikes said, I kept thinking "this cant be right".
Will try after lunch after regaining strength

[fermin]

OK, finally able to separate cylinder & reservoir, they had been glued with some kind of grey silicone gasket material.  Now one of the holes in the cylinder assembly reservoir well is open and enters the piston shaft, but what about the other, the one on the right ?.  I appears clogged.  After battling this part for 1 hr I am ready to drill , but better wait....

[Bob_Roller]

That hole being clogged, will cause you problems with the brakes, you need to get it opened up .

[fermin]

Bob,
The hole which was clogged was opened, but it is such a small opening!. I mean I cannot get my smallest drill bit, nor a surgical needle in.  I am affraid that any debris could restrict flow. Are both openings supposed to be the same diameter?

[Bob_Roller]

No, the second hole is about one tenth the size of the other one .

[fermin]

Got it Thanks, then its ready to be tested.

[Bob_Roller]

I think members here have reported, that with the small hole plugged, the brake lever won't return all the way, and the front brakes may drag a bit on the rotors .

[fermin]

Thats a lot better than what I was expecting; locked up front disk. This clogging is probably what caused the demise of the previous rotor which was all grooved.  Luckily a new rotor was included in the purchase.  I am wondering if the old rotor can be brought back to life after resurfacing, its got enough width, but some of the rivets are loose.

[Bob_Roller]

The minimum rotor thickness is .180 inches, the stainless rotors are difficult to machine .

My '84 LS had the rotors machined to below minimum thickness, I found 13 cracks between both rotors after I removed the rotors, for refurbishment .

Spiegler Performance, can refurbish OEM BMW rotors, if the carrier, or hub is not damaged .

http://www.spieglerusa.com/BMWConversions/