master brake cylinder 83VR

[barend]

went for a ride today and discovered my foot brake bottoms out with no discernible braking action. I do not appear to have any leaks (no spots on the garage floor), so I am figuring the master cylinder is shot. If someone has a good used one they want to unload let me know, otherwise I'll be going the rebuild route.

Thanks!

[Snaggletooth]

Save your self the headache and a few bucks and just rebuld the one you got. If it isn't eaten up inside you'll be good to go.

 

If you bought a used one your best bet would be to rebuid it before you put it in anyway to be on the safe side.

 

But first things first I'd try to bleed the lines before I got started on the master. Who knows.......you may just have a bubble in there.

 

Mike

[skydoc_17]

Hey Barend,

You might want to take the cover off of the Rear Master Cylinder Reservoir and make sure the accordion style diaphragm is not swollen and sticking down in the reservoir. This would cause the fluid to be low and you might have sucked some air into the system. Just an FYI, the MKII rear master has a larger piston bore, with a rebuild you could increase your braking power with the addition of the MKII Master. Lastly, check the linkage and pivot at the foot pedal, rust and lack of lube will sometimes cause the rear foot pedal to compress the rear master and not let the piston to return. Plus, your rear caliper could need a rebuild and the pistons are Stuck. All good things to check out. Any one "weak link" in the braking system will effectively "take out" your brakes. After all, all of those parts are 27 years old.

Earl

[barend]

Would I not have at least some spongy braking with a bubble?? Probably need to rebuild the master cylinder anyway 'cause that's the only thing that was not cleaned, replaced or rebuild (supposedly) when I got the bike a year and a half ago.

[warthogcrewchief]

When I purchased my VR, it had NO brakes or clutch. All hydraulic systems were dry. After a good flush, fill, and bleed, all systems are operational again!

 

I'd start with the easiest first - Bleed, then look at eventually a rebuild or placement/rebuild.

[barend]

Hey Barend,

You might want to take the cover off of the Rear Master Cylinder Reservoir and make sure the accordion style diaphragm is not swollen and sticking down in the reservoir. This would cause the fluid to be low and you might have sucked some air into the system. Just an FYI, the MKII rear master has a larger piston bore, with a rebuild you could increase your braking power with the addition of the MKII Master. Lastly, check the linkage and pivot at the foot pedal, rust and lack of lube will sometimes cause the rear foot pedal to compress the rear master and not let the piston to return. Plus, your rear caliper could need a rebuild and the pistons are Stuck. All good things to check out. Any one "weak link" in the braking system will effectively "take out" your brakes. After all, all of those parts are 27 years old.

Earl

 

Earl,

Would I need a MkII master cylinder or a MkII rebuild kit? does the MkII cylinder work with a MkI reservoir or would that need to be exchanged as well? and lastly (for now), do you (anyone) have one? (does MiCarl sell these things??)

[skydoc_17]

Hey Barend,

Because of the difference in bore size between the MKI and MKII rear Master Cylinder, the MKI rebuild kit WILL NOT fit the MKII Master Cylinder. (and vise versa) When I got my 87'VR (5th one I had) I rebuilt the MKII master cylinder and replaced the Diaphragm in the rear master cylinder right off the bat and have not had a problem since. I have a MKII master cylinder and can get the diaphragm for you. If you are interested, PM me.

Earl

[Ben Rollins]

Any idea if there is a step by step to rebuild rear master in forums? I have looked and don't see one.

Thanks, Ben

[chocking]

I have been dealing with the same type of issue..no fluid leak on my 84 with an updated MKII rear master, but I'll slowly build up air in the lines and loose all rear brake.

Not sure if it is a rear caliper leak or master cylinder leak??? Have new braided line on from 1 year ago...

Better to rebuild rear caliper or simply buy a used one...And any good places to get a master rebuild kit

 

Thanks

 

Clay