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Is it time to replace my dual master cylinder?
Posted by: Andrew B ()
Date: September 17, 2022 09:13AM

Hey folks,

I have been replacing my brake lines and I could not bleed the front brakes. I bench tested the dual master cylinder and found the front brakes part was clogged. The fluid was very dirty. I spent time flushing it out with warm soapy water. It is now all clear. Do I dry and reinstall or is this a sign that a seal is broken in the master cylinder and the entire unit must be replaced?

Re: Is it time to replace my dual master cylinder?
Posted by: Marco_a_p ()
Date: September 17, 2022 10:23AM

flush with denatured alcohol and new fresh brake fluid. As long as it holds pressure and doesn't sink when you put a lot of pressure on it and hold it, should be fine. But since its already out of the car on the bench, a rebuild kit should be around $20 and take about 10 mins to install. Will give you a chance to inspect the bore and maybe run a brake hone though it to clean it up.

I'd take it apart, hone it, wash out with brake kleen and inspect, if not all pitted get a kit an rebuild. if pitted, get new M/C.

A 2nd Gen Monza Wagon, a 2nd Gen GB 8door, a 2nd Gen (61's were 1st Gen) R/s and a 62nd Gen Turbo coupe..

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Re: Is it time to replace my dual master cylinder?
Posted by: junkman ()
Date: September 17, 2022 12:00PM

Follow the above advice, and make sure to wash the bore with hot soapy water, and then blow it dry. Lubricate the new parts as you install them. No need to buy a new master unless the old one is badly pitted. I personally like silicone brake fluid, since it never goes bad in the system and doesn't absorb water as other brake fluids can. It will cost more initially but is well worth the additional cost.

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