[T3] Master Brake Cylinder

Jim Adney jadney at vwtype3.org
Fri Dec 22 07:59:56 PST 2017

On 22 Dec 2017 at 2:05, J. Jonik wrote:

> Re:  '71 Sqbk Std   With loaner car to use for now, decided to remove
> the obviously bad master brake cylinder..to be replaced by a rebuild
> (Jim A. likely) or a shot in the dark with the best looking of my
> good-when-salvaged cylinders.

Your old MCs are almost certain in worse shape that the one you've got in 
there now. If you decide to send me one (or 2) please hold off until Jan 1 or 
later, as I'm going to be out of town for a few days over Christmas.

> I've dunked the replacement in brake fluid for going on 3 days...in
> case that helps anything. 

It won't help. It will just make the outside rust worse.

Did not try to open it and do anything.  Can't be worse than the one that's in 
the car...which, bad as it is, does stop the car.

Yes, it CAN be worse.  ;-)

So...got all but one fluid line disconnected, with some effort and even small 
breaker pipes on that 11 mm wrench.   But the final one, for the 
through-the-car tube...the nut turns a tiny fraction...so it's not frozen to the 
cylinder, BUT it's frozen to the fluid tube.   If it's turned any more, the tube 
will break. 

Good for you for stopping. That's an unfortunate, but common problem, and 
yes, you DO NOT want to break that long line. You could probably replace it 
even if you can't get the driver's seat out, but it's a real pain in the a$$ to do.

That's now soaking, for 3 days, with a tight strip of cloth around it to keep it 
wet with Liquid Wrench. 

That might help, but I doubt it. A lot of gentle wiggling of the line nut might 
eventually free it from the line, but the only thing that really works is heat.

If you decide to use a torch, do it with the line nut backed out as much as 
you can without twisting the line. Drain out all the brake fluid you can, and 
remove the brake light switch that's opposite the reluctant line nut. Then 
direct the torch to the line nut only. Try not to heat the MC or the line itself. 
You could even put a rag soaked in water around the line itself while you do 

You should not have to get the line nut all that hot. Just stop and try the 
wrench on the nut occasionally to see if it will wiggle free. Once it turns 
freely, apply some oil where the line disappears into the line nut and let it all 
cool with oil in there.

Finally a bit of warning: The long line to the rear is often quite rusty by now. 
Even minor stress on it may cause it to spring a leak under the pedal cluster, 
no matter how careful you are. I can make you a correct long line from 
non-rusting CuNi tubing if that happens, but let's hope it doesn't.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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