3 replies to this topic

[mini_man96]

So I am part way through rebuilding the master cylinder on my mini. It is a 1996 car so has the later type servo mounted to the master cylinder.

I have removed the circlip that holds the whole thing together and pulled the plunger out, however there seems to be two separate plungers! One to operate the rear brakes and one to operate the fronts with the rear brake plunger (the one located furthest down inside the master) actuated by the front plunger via some kind of spring arrangement.

My question is, how do I remove this second plunger as there doesn't seem to be any way of getting it out due to it being too far down inside the bore of the master to grab with any tools! It also seems to have a fairly powerful spring behind it as it is difficult to press in using a screwdriver and springs back very quickly. Not sure if any of that makes any sense! 

If it helps the rebuild kit is GRK1039 from minispares.

Any help would be appreciated!

[absx2]

You have to remove the plastic tank from the cylinder, then under the rubber seal you will find a small locating pin under a thin washer. Preload the plunger with a piece of wood or plastic so as not to scratch the bore and pull the pin out with a pair of long nose pliers. It`s a good idea to have a rag over the end as the spring is quite strong.

 

Now for the bit you won`t like or a least your pocket won`t.

Using an endoscope to check the bores for pitting and score marks I have yet to find a serviceable item. The second circuit seems to get the worst damage and its impossible to check  the bore without one as it will look fine. 

I did one last week where the car has been sat idle for a couple of years and although the brakes worked fine with no apparent leaks it required rear slave cylinders as they had seized, caliper rebuilds as the outer seals popped out with the pistons due to corrosion and the master was removed as the clutch bearing was noisy.

 

The master cylinder looked in great condition but on inspection with the endoscope heavy pitting on the second circuit rendered it useless.

 

Being one of the main components that can kill you and others if it fails I strongly recommend you buy a new one or a lease borrow an endoscope and have a proper look but it`s always corrosion due to old brake fluid that causes issues.

Edited by absx2, 23 December 2017 - 09:19 AM.

[slidehammer]

After years of rebuilding master and wheel cylinders, always with great success I do agree with the above and would not bother now just buy a complete replacement uni., Especially as they are such an awkward component to remove and refit. The last one I rebuilt lasted about 18 months and then the seals to the rear brakes failed and this resulted in no rear braking at all (the seal kit was the genuine one and the bores looked fine, so I replaced it with a genuine new one and has been fine ever since. 

[mini_man96]

Okay, thanks for the advice guys! I'll pull the master completely apart tomorrow and see whats what but like you both said I will likely end up buying a new replacement!