The Stovebolt Site Forums The Shop Area Driveline Master Cylinder Cap

I am starting the rebuild of my Master Cylinder. The Cap seemed to have a hole in it. But, after removal, I see a kind of soft piece under the Cap.

Master Cylinder

Wow, it was very dirty and gunky inside. I will follow the manual and clean it out with alcohol, and then try and rebuild.

Any other advice on cleaning, or the cap? Does it look right, or should I buy another?

I suppose that as filthy as the MC is, I should plan on replacing brake lines.?.

Thanks

My theory on brakes is do it once, do it right. For you to be asking on this forum means your brake system is at least 30 years old. Most vehicles have never had the brake fluid changed. Brake fluid absorbs moisture and lines rust from the inside out. If your master cylinder looks like that your wheel cylinders do too. The flex hoses are deteriorating. Replace everything. Do it once, do it right.

The "soft" part in the cap is an early method to keep from pressurizing the MC. Just like the rubber cup that will expand to compensate for lower fluid levels in the modern reservoir. Clean it as well as you can. And yes if there is rust you have had moisture in the system, the entire system. Take it all apart. Lines, hoses, wheel cylinders and the MC. Careful inspection now will save your life later. 60 year old rubber parts? Time for some new ones. Rust and pits on a brake line? Replace. Little pits in the wheel cylinder? Hone and fit new cups. If it don't leak OK. If it does? New part. You get the idea. Enjoy

thanks guys. I disassembled the MC as the photos show. I have a rebuild kit, and will apply that to the MC. I was unsure what to do with the lines. I also have rebuild parts for the wheel cylinders, and will take care of that in due course. I will now try to find the proper brake tubing and replace that. Being in Italy, ordering pre-bent stuff is very expensive due to abnormal sizes. If I can find the nuts, I should be able to find appropriate tubing here.....off I go.

Guys, here in Italy, I am finding DOT3 and DOT4. Does it really matter which I use? I have read on a search here that DOT 5 is better, but DOT 4 or 5.....what do I need to know.

DOT 3 is recommended for older brake systems. DOT 4 is for more modern systems and might cause the rubber parts to break down. DOT 5 is a silicone based fluid and I have no experience with it. If DOT 3 is available I would use it. Are there any other thoughts out there?

I use DOT 3, using DOT 5 could be acceptable but requires a complete new system as discussed in another thread here recently .... and make sure that hole in the MC cap is open, the cylinder needs to 'breathe' to work

Bill

Thanks guys. Sounds like it was wise to wait. I'll go back fo rthe DOT 3.

You don't want to mix different types of brake fluid.

Ok guys. I've disassembled the Master Cylinder and cleaned it up with alcohol as specified. It looks REALLY pitted. So, I suppose best to replace it.

I plan to order a new, original MC, and assemble with new lines

I have also been reading posts about upgrading to a dual reservoir non boosted system. Of course, this is a modification that I will be trying to do here in Italy with no assistance. Worth it or not?

Yeah I believe you can only hone .004 on a master cylinder bore. Sounds like it will need replaced.

John