Buick brake fluid leak

'95 LeSabre Custom. Leak is easily visible at junction of master cylinder and power assist drum. Slow leak requires topping off reservoir every four days, otherwise, brakes feel and work normally. Is there a gasket, etc., sealing the cylinder/power assist that needs replacing, or is the problem buried deeper?

"Dr. Rev. Chuck, M.D. P.A." wrote

You need a new master cylinder. It's as simple as that.

Ian

"Dr. Rev. Chuck, M.D. P.A." wrote

There is an o-ring seal right at the rear of the master cylinder....on the rear piston assembly.

It is an easy job. If you are careful and pre-bleed the master cylinder (bench bleed it with some plastic hoses and adapters that screw into the ports, often aftermarket master cylinders will include this in the box) and then bleed right at the two lines that hook up to the master cylinder, you can avoid having to bleed the entire system. But in your case, because you have a leak from the master cylinder, I'd recommend that you change all the brake fluid anyway, just bench bleed the master, bleed at the lines attached to it, then either gravity bleed at the wheels or get someone to help you by pushing the pedal down.

I think you get better results if you "don't" pump the brake pedal, but simply open your bleeder screw, and then have the assistant push the pedal slowly to the floor, keep the pedal down while you close the bleeder screw, and then let the pedal up. Repeat that until you have clear fluid at the particular wheel.

Ian

Nothing. There's a seal in the master cylinder that shouldn't be leaking. It's a quick R&R with one BIG gotcha. Bleeding the system afterwards. You'll allow air into the system by disconnecting the brake lines. Do you have ABS? I've never worked on a 95 Buick, but some cars have specific procedures for MC changes with ABS.

Two bolts, looks like an easy DIY job.

What seals the master cylinder to the power assist?