Brakes won't build pressure. Booster?

Hey y'all. My brake pedal is going ask the way to the floor now, very poor braking. I tried bleeding the lines, which helped a little but the pedal doesn't seem to be building pressure. I think it's a problem with the booster. When i push the pedal, I can hear and feel air coming out of the rubber part (pictured). I tried bleeding more, but it seemed difficult, as if there was very little pressure building up in the system.


What do you guys think? I'm thinking replace the booster. $211 AutoZone. They have two different parts with two different diameters (8.5" and 9" iirc?) The guy said he would check based on my vin.

Thanks!




2000 trd 4x4 6cyl 3.4l

 

A failed/failing booster would result in a hard pedal and rpm variation as you brake.
A soft pedal would be due to air in the system, failing soft lines that swell when you press the brakes, failing/failed master cylinder. Also, check the adjustment of your rear brakes.

 

Using the Parking brake if it works correct keeps the rear shoes adjusted.

The shoes get out of Adjustment it takes pedal travel to meet the drum.

Has the fluid level in the Master Cylinder dropped??

 

That's not how a booster works, it only amplifies the effort you apply to the brake pedal into the input of the master cylinder. It doesn't have a thing to do with the hydraulics. You probably have a failing master cylinder.

 

The fluid level in the master did not drop. I ordered a new master, we will see how that works. I'll do some diagnostics today since it doesn't arrive till afternoon.

I talked to my neighbor, who is very savvy, he said it might be a check valve in the brake lines, and it is essential to bleed the brakes evenly, the same amount on all 4 valves. I've definitely never worried much about that, bleeding the passenger rear side most since it's furthest from the master.

(Unrelated, but he has Toyota truck pre 1st gen with over a million miles!) He thinks it's a booster problem, likely the diaphragm burst and won't hold pressure. He said I could check it with a host to see if it holds pressure. I'll be trying to find a YouTube video on that this morning...

Thanks guys!