83 240d brake master cylinder

[Argospete33]

I have noticed that brake fluid is leaking from mc connection to the booster. Fluid level on reservoir is good and the brakes are working normal. I just changed front pads, rotors, and calipers 2 months ago. Do I replace the mc or change the o-ring between mc and booster?

[Sugar Bear]

Replace master, it is leaking. Replace the O-ring out of practice but it is not the cause of the leak.

[Argospete33]

Thanks ...will do asap as I don't want to damage the booster from leaking brake fluid

[Sugar Bear]

Yes, don't delay. Have you replaced a master cylinder?

[Argospete33]

No ...I have never had to change one. Anything I should look for?

[Diesel911]

Originally Posted by Argospete33

No ...I have never had to change one. Anything I should look for?

If brake fluid got down inside of the power brake booster you need to get something down in there that you can pull out to soak up the brake fluid.

[Sugar Bear]

Follow all factory recommended procedures.

In addition I'd start soaking every brake connection with penetrating oil several times in advance of doing the work. don't allow the penetrating oil to stay on rubber components. Soak the fittings at the master cylinder (MC), at the hose to steel line connection at the wheels and the bleeder screws at each wheel. Use line/tubing wrenches on the tubing nuts. IIRC, they are 11mm and the bleeder screws are 9mm. Use six point tools to prevent rounding the hex.

Use new unopened fluid, two quarts will be plenty.

Bench bleeding the MC before installation saves a ton of bleeding.

I use a Motive pressure bleeder and am satisfied with its performance.

If the brake hoses are old this is a good time to change them.

Before putting fluid in the MC look at the reservoir to see and understand the inner construction and the dam between the front and rear sections. It is common for bleeding problems especially on the rear brakes when insufficient fluid is in the reservoir, specifically not enough to go over the dam and fill both sections. Make sure both sections have fluid in them continually whilst bleeding the system.

[Sugar Bear]

Manual or auto transmission car?

[Argospete33]

Manual

[Argospete33]

Does a replacement mc come with the o ring and rubber grommets for the reservoir?

[Sugar Bear]

Usually comes with reservoir grommets but not the O ring.

Get some of the cloth braided hose that attaches to the reservoir to supply fluid to the clutch, it is usually in bad shape and can't be reused.

[Shern]

Definitely change the reservoir/clutch line. Mine was deteriorating internally which meant that bleeding the slave cylinder resulted in black fluid. If you’re using a motive power bleeder, which is the easiest, most foolproof method imaginable, you simply open the valve at the slave cylinder and let it bleed, same as the brakes.

[Argospete33]

When changing the braided line that feeds the slave cylinder do I have to bleed after as well?

[Shern]

No.

Here's a thread from when I replaced mine:

w123 clutch reservoir line

If you have a motive bleeder, you'll want to run fresh fluid through the clutch system anyway, which just involves opening the slave bleed nipple and letting it drain. If you were to replace the master cyclinder or the slave cylinder, the bleeding process is bottom to top. When there's no air in the system, you're simply pushing a column of fluid, doesn't matter which direction.

[tqwrench]

I just did the slave and master for the clutch on my 240D manual. Here's a link in case it helps: '83 240d clutch master and slave cylinders job