750/101 Master Cylinder rebuild

[GTD]

This post is for the benefit of anyone who is rebuilding a master cylinder for a Giulietta/Giulia.
This pre-supposes that the MC body has been cleaned, honed and is ready for re-assembly with a fresh rebuild kit. It also assumes the MC will be put into service immediately; if an extended amount of time is expected before use, one should use brake assembly lube rather than brake fluid.

CLEANLINESS PRECEEDS GODLINESS when working on brake assemblies.

Rinse everything with Brake Cleaner (available in aerosol cans).
Have a shallow pan with fresh brake fluid at hand.
Layout your parts in order on a lint free surface.
Clamping MC body in a vise (on mounting bosses) facilitates assembly.
Cap the inlet and outlet ports with temporary plugs previously purchased at auto supply.
Have all necessary tools at hand.

Fit #22 onto 19, lubricate with brake fluid and install in MC body.
Assemble #12,10,11,15,13,14 and attach to MC body.
A small dab of grease on the ball end of #12 is recommended.
Re-position MC so that forward end is now vertical.
Dip #18 in brake fluid and insert into MC body.
Dip #21 in brake fluid and insert - I.D. should fit around #19.
Dip #16 in brake fluid and insert into #9; fit #17 onto #9.
Dip #20 in brake fluid and insert into #19.
Fill MC with brake fluid and thread #9 onto MC body, compressing #20.
Tighten #9 with a proper (1 1/2";38mm) wrench -DAMM TIGHT- Your LIFE depends on it.
Air should bleed via hole in #9; fill MC completely thru this hole and insert and tighten #48/8 - Good and SNUG.

MC can now be fitted to vehicle, inlet and outlet lines attached, brake fluid reservoir filled and lines bled.

This MC is exceedingly simple in operation. The point of sealing and compression is deceiving. #22 is simply a dust seal or wiper; #21 is the item that does all the fluid sealing.
When we remove these gems, brake fluid and slime have accumulated at the rear end of the MC and it appears that #22 has failed. What actually happens with time is the lowest of the six small holes behind #18 become plugged with slime/crud from moisture attracted to the brake fluid; seal #21 fails ... and so do your brakes!

FLUSH COMPLETE BRAKE SYSTEM ANNUALLY

[papajam]

GREAT write up!!

[GTD]

Thanks PPJ; I sent it to an Alfista and he suggested I post it, so...

[pathung]

Thanks for posting, GTD. Lots of folks will benefit.

[1166]

Another point of interest is that the PISTON needs to be perfect on the rear part where it contacts the main seal. Many pistons have rust damage (they look 'etched') there and should be replaced. The bore of the master cylinder can have minor pitting as it will affect the front seal only. It would be ideal to have good surfaces on both but it is more important on the piston.

[A V]

GTD

Great posting, very useful.

You say that

Quote:

if an extended amount of time is expected before use, one should use brake assembly lube rather than brake fluid.

[GTD]

Antonio
ATE lists several products in their European Catalog:
http://webshop.tecdoc.net/ows6/en/6A0B3E4709280D7C67075975EEAE0CB4.srv;jsessionid=6A 0B3E4709280D7C67075975EEAE0CB4?view=VIndexFrameset Jsp

[A V]

GTD

Thanks for the information.

Regards

Antonio

[gigem75]

Don't forget to put the heat shield back on. The brakes will lock up. Don't ask me how I know

[Gordon Raymond]

Thanks GTD. I was asked this the other day. I've printed out your instructions, simpler to follow than mine, and will hand it out now. Excellent technical write up. Four star!