master brake cylinder problem

[Bill Conquest]

The cap on my m.brake cylider is stuck - one of the 3 screws won't come out, it just spins. Seems like the insert in the cylinder body is turning with the screw. Anyone have this happen before? Any idaes?
Thanks, Bill

[Bob_Roller]

Bill,

I've got a rectangular reservoir master cylinder, so I'm not real familiar with the round reservoir type, but the three screws that secure the cap to the reservoir, are threaded directly into the master cylinder body, no inserts.

The round reservoir master cylinder, has the reservoir bonded to the metal cylinder.

So there's the possibility that the screws are just threaded into the plastic reservoir, not into the metal.

Only suggestion I can make,is to try and get a thin screwdriver blade under the offending screw-head, and gently pry up on the screw while turning it out with a screwdriver.

Only other option I can think of is to drill off the screw head, which would be difficult, if you can't keep the screw from turning.

[Rob Valdez 79 R65]

Here is a picture of the offending inserts.  It is possible that the insert or the screw threads are stripped.  


click for larger


I can't think of any easy fix, in any case.

[Bob_Roller]

After seeing the picture from Rob, drilling off the screw-head seems to be the only option that I can see.

And that's not a particularly good option.

After thinking about this for a few minutes, ( and a few beers !!).

Another alternative possibility, use a small drill-bit, and drill into the plastic reservoir and the offending metal insert a small amount, and hopefully it will hold the insert while you can turn the screw out.

Again not a great option.

[Ed Miller]

Will some epoxy hold up against brake fluid if he repairs it afterward?

[Bengt_Phorqs]

The same thing happened to an '81 R65 I owned in a previous life.  Had to replace the resevoir in order to service the master cylinder.  I would probably try the side entry drill to stabilize the insert as a last resort.  Again not a good option but if you have to replace it anyhow, then why not try it?  

[vestandpants]

It happened to me with my '79 when I re-commissioned it 3 years back.

I tried to carefully drill the head of the screw off and the heat generated melted the rubber boot/float thing under the lid!

I replaced the clear plastic tub, rubber top and lid with a second hand one and bought s/s screws from my local (ish) BMW motor parts centre for the not-so financially well off.

[Bill Conquest]

Thanks everyone for the thoughts & ideas..& the great photo, Rob. I think the insert is just spinning in the cylinder body. Maybe i'll try drilling out the screw head, carefully -then buy a new cover if I mess it up or get a whole new assembly.
Bill

[Darwin_R65]

If the insert is spinning just remember the drill may only cut a small amount, then grip and the whole lot may spin when the drill bit cuts in.

I would be trying high speed light pressure. Patience.

John