Brake fading

[alpac]

When I drove my truck 1990 Ranger 4.4 today I felt immediately that the brake power was very low. Very unusual as it normally brakes pretty hard. Then I noticed that if I kept pushing on the brake pedal the pedal just kept going down all the way slowly but surely until it touched the floor. The master cylinder was changed 3 years ago, I do not see any leak anywhere and the brake fluid is still at the top mark. No work done on brakes recently. Last work I did on the brakes was to change rear drums and shoes but that was back 5 months ago. Any idea what's going on?
Thanks
Al

 

[alpac]

Something interesting I just found out tonight. When the engine is not running I can only push the brake pedal half the way down which sounds like normal to me. It is only when the engine is running, therefore with powered brakes, that I can go all the way down easily with very low brake power.

 

[MAKG]

Sounds like a bad master to me, especially if pumping the brakes helps.

They can be bad on the shelf.

 

[alpac]

Sounds like a bad master to me, especially if pumping the brakes helps.

They can be bad on the shelf.

Yeah! I think this is what it is but it is a pain to have to replace it again after less than 3 years.

 

[metalmacguyver]

Did it come with a warranty?

 

[BOSS302Man]

If you bench bleed them, they aren't that hard to replace. Are you using DOT 3 fluid or silicone?

 

[alpac]

If you bench bleed them, they aren't that hard to replace. Are you using DOT 3 fluid or silicone?

I have been using Dot 3 but I may start using silicone after I replace it. I have heard it is less aggressive on the brake line. I am planning to replace it myself. Not a big deal. Will ask my 11 years old daughter to be my assistant for bleeding the brakes I did replace master cylinders on other cars. Anything I need to pay particular attention in the process of replacing the master cylinder? What do you mean by bench bleeding?
Thanks
Alain

 

[alpac]

Autozone has a master cylinder for my truck for $50. Do I need to change some gaskets where the master cylinder connects to the brake line?

 

[alpac]

Although the power booster works ok it does look old (it is a 1990 truck) and I noticed tonight that it makes a pssshhh sound when I turned the truck off. I may need to change it by the same token while I am working on the master cylinder. What do you guys think? Replacing the power booster should not be that hard is it?

 

[MAKG]

Replacing a power brake booster is very easy. But make sure yours is bad first. A booster costs quite a bit more than the check valve.

Or replace it out of hand if you really want to. Some master cylinders come with boosters attached (though they do cost quite a bit more).

No, there are no gaskets on the brake lines. If they leak, you have to reflare or replace them.

 

[rickcdewitt]

A booster costs quite a bit more than the check valve.

call me an idiot but where is the check valve on an rbv booster?

 

[MAKG]

It's where the vacuum line connects to the booster. Help! sells a replacement.

 

[rickcdewitt]

i never looked inside of that black elbow,assumed it was just a fitting.mine works but its good to know,thanks.

 

[MAKG]

Pulling that out of the booster is a good and very fast way to check if it's good. Shut the engine off, pull it out. You should hear a distinct "pop" as you release the vacuum. If you don't, the check valve might be dead, or the booster itself might be leaking.

 

[alpac]

When I drove my truck 1990 Ranger 4.4 today I felt immediately that the brake power was very low. Very unusual as it normally brakes pretty hard. Then I noticed that if I kept pushing on the brake pedal the pedal just kept going down all the way slowly but surely until it touched the floor. The master cylinder was changed 3 years ago, I do not see any leak anywhere and the brake fluid is still at the top mark. No work done on brakes recently. Last work I did on the brakes was to change rear drums and shoes but that was back 5 months ago. Any idea what's going on?
Thanks
Al

Master cylinder it was! Spent $70 at autozone between master cylinder and brake fluid and about 1h of work including bleeding the master cylinder and the 4 wheels. Had my 11 years old daughter assisting me for the bleeding.
Thanks to you all