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Air getting in brakes?

I drive a 98 dodge dakota and my brakes are rock solid when i first tap them, then they sink to the floor. We bled the master cylinder and calipers and it fixed it for a little while and then it went back to the way it was. The rubber insert on the cap is loose and probably not air tight. Could this be the problem or do i need a new master cylinder?

A brake master may be leaking internally.

This means that brake fluid doesn’t leak out of the master cylinder. But the seals inside the master cylinder leak and don’t produce enough hydraulic pressure.

Tester

3 Likes

So the best bet would be to replace the whole cylinder?

It’s a brake master cylinder.

That’s the only way it can be replaced.

https://www.rockauto.com/en/catalog/dodge,1998,dakota,3.9l+v6,1314423,brake+&+wheel+hub,master+cylinder,1836

Tester

If so, chances are you have air in your brake lines. A hydraulic braking system, like the one found in most cars and trucks, relies on brake fluid for pressure. … The hydraulic pistons within the brake calipers slowly extend to keep the brake pads at a uniform distance from the brake rotors as the pads wear.