Hello everyone,
braking problem: Regularly the pedal gradually sinks under braking; the brake light comes on intermittently. I'm thinking of the faulty master cylinder. (No drop in brake fluid level) What do you think ? Thank you for your opinions.

(NINETY EIGHT 403 CI 1978)

 

Correct, fluid is getting past the piston seals internally. Time for a rebuild.

 

Agree...

 

Thank you. And what is your opinion on brands? Is Raybestos as good as Ac Delco?

 

If there is any wetness behind the master cylinder, rebuild your power brake booster too.

 

All of the "brand names", including Raybestos and Delco and Wagner, are imported today. If your M/C is original, you can also rebuild it.

 

I had White Post restoration rebuild mine. Shipping back and forth from France may be a non starter for you. Unless you can find a reputable shop locally, I would buy a AC Delco unit. Not likely any better than any of the others, but just my preference.

Good Luck with the solution,
tc

 

You also may have air in the brake lines.

 

Thank you all for your advices. I will buy a new MC; it's not so expensive. After a general control of the lines, distributor, hoses, wheel cylinders of course.

Have a nice day.

 

Hello everyone,

To replace the master cylinder, is it necessary to disconnect the pushrod from the brake pedal? (I have a brake booster). And once reassembled, should you bleed the master cylinder?

Thanks for the answers.

 

No, simply remove the two nuts holding the M/C to the booster and it pulls right off. Verify that the rubber seal stays in the booster and isn't stuck to the old M/C.





Not only "should", it is mandatory to bleed the M/C and the entire brake system at each of the wheels.

 

No need to disconnect the push rod at the pedal. This rod goes through the booster only and pushes into the piston of the master cylinder. It isn't physically connected to the master cylinder.

Before installing the new master cylinder, you should "bench bleed" it to remove any air inside the cylinder. This process involves clamping the master cylinder in a vice, filling with fluid and slowly pushing the piston several times to fill the cylinder with fluid. You will want to run some tygon tubing from the outlet ports back into the reservoir. You can buy a bench bleed kit at most any auto parts store that has everything you will need. Youtube has several videos to help you as well.

Once installed, you need to bleed the entire system. You can find this procedure in your chassis service manual.

good luck.
tc

 

So, bleed in first the MC and after the 4 wheels. Right ?

 

Bench bleed the M/C, install it, & then bleed the system at each wheel per the chassis service manual.

 

Yes, sure do it in first.

Thanks to all of you.

 

Some of the master cylinders come with plastic fittings and hoses to bench bleed them.

 

.I also ordered a set...

(You have a nice car).!