I am trying to help a friend rebuild his front master cylinder. It is a single rotor, 5/8 bore. I did not get to see the ordering of the parts upon dis assembly, so I am looking for how the parts go together.

Here is a picture of the rebuild kit, with numbers added by me:



1 = Rubber cup
2 = Plastic pin
3 = Bore end seal
4 = Spring
5 = Piston
6 = Piston O-ring

Here is an ordering that we tried, to no avail:

We cleaned the empty master cylinder completely. There was some gummy yuckyness in it, but I am fairly confident that it was cleaned thoroughly, including all passages.

We slid the spring in to the cavity, large end first. This entails that the large end of the spring encircles the hole that the banjo fitting screws in to - i.e. where the fluid goes.

We slid the plastic pin into the small end of the spring, so it sits almost entirely within the spring, and the top lip sits on the spring. On top of this, we put the rubber cup, with the open part of the cup first. By this, I mean that the cup sits on the plastic spring and the washer, with the edges of the cup pointing toward the banjo fitting end of the master cylinder.

The o-ring went on the piston, and the piston went in, with the hole end of the piston point out towards the lever. Then the bore end seal was fitted into the cavity of the cylinder, effectively sealing the unit. The plunger was fitted in to the bore end seal, and the lever was attached. We mounted the master cylinder, attached the brake line, added fluid, and commenced to bleeding. We did not get any fluid to the caliper - none was coming out of the brake line, which makes me believe that the ordering is wrong.

Help?

 

There will be a good diagram in the factory service manual that will give you the proper order for reassembly. Take it back apart and double check the assembly sequence and also the holes in the cylinder with a flashlight to make sure they are not blocked.

After you put it back together and fill it with fluid you should be able to pump the lever and squirt some fluid out. I would do this anyway to help purge any crap out of the line before you attach it to the caliper.

 

My 04 service manual looks different. However it has starting first. spring, primary cup with larger diameter end facing in, piston,o ring piston cap,wiper with flat side facing in. My piston has a smaller diameter pin facing toward outside were you load it from.

Sure am glad he did not take the rear one apart.