New brake booster - pedal remains soft

[Josh0224]

Hey guys and gals, I was driving to the store yesterday when my brakes started hissing at me. (I'd press the pedal and hear a hiss inside the cab). A quick google search told me that my brake booster was bad. I replaced it this morning, and no more hiss, but my pedal is still soft. As in, I can get the pedal to the floor with minimal difficulty. I took it for a test drive around the block and it still stops, but I'm wondering if I need to bleed the system for some reason. I didn't open the system up (although i did knock the reservoir around a bit), so i don't think I got air into the system. Any other ideas?

 

[Josh0224]

For reference, the booster I installed: https://m.autozone.com/brakes-and-traction-control/brake-power-booster/duralast-remanufactured-brake-power-booster-54-73189/102614_0

I had to twist the pedal connection 90 degrees. Hopefully that didnt mess anything up.

 

[Eddo Rogue]

Did you replace the master cylinder too?

Try stabbing the brake firmly instead of applying slow pressure, if this firms things up, then you probably have fluid slipping by when under pressure inside master cylinder seals. it holds fluid when stabbed, but slips by when applied pressure slowly forces it past the seals.

You may still have air in the lines as well...get a mighty vac bleeder and hook it to the bleeder furthest from master cylinder (so passenger side rear brake bleeder)...That will suck everything through...keep going until the fluid being pulled into the vac bleeder lacks bubbles.

 

[Dirtman]

Also you bought a remanufactured booster. So there's a 50/50 chance its bad out of the box.

 

[Eddo Rogue]

Also you bought a remanufactured booster. So there's a 50/50 chance its bad out of the box.

+1....You might have a bunk one out of the box... Always go motorcraft or at least a brand name like bendix.

 

[Dirtman]

Back in the days of ole "remanufactured" ment the part in question was disasembled to its core components, those parts were checked to be within OEM specs and if they were then the part was entirely rebuilt with all new wear parts (seals, gaskets, bearings etc), then fully tested before being packaged. If anything was out of spec or failed testing it went in the trash.

Today however (and I mean this quite literally) remanufactured means the part gets sent to china, they clean it and throw some paint on it and will replace anything they can visually see is wrong if they feel like it. The part is never tested, just boxed up and shipped back to the parts store. Then you get to play the lottery of whether or not it will work.

 

[Josh0224]

Jamming the brake vs a slow depression has the same amount of resistance. And stops at the same place. When the car is off, the brakes do tighten really good, but never gets super solid. With repetitive punching of the brake, it the pedal still moves 2-3 inches before stopping.

How could I tell if the booster is bad out of the box? Theres no noise as there was with my last one.

I'll pick up a vac bleeder and bleed the brakes to see if that helps.

Also, the small reservoir next to the fender om the driver said says it's also for brake fluid, but is empty. What is that one for?

 

[Josh0224]

Back in the days of ole "remanufactured" ment the part in question was disasembled to its core components, those parts were checked to be within OEM specs and if they were then the part was entirely rebuilt with all new wear parts (seals, gaskets, bearings etc), then fully tested before being packaged. If anything was out of spec or failed testing it went in the trash.

Today however (and I mean this quite literally) remanufactured means the part gets sent to china, they clean it and throw some paint on it and will replace anything they can visually see is wrong if they feel like it. The part is never tested, just boxed up and shipped back to the parts store. Then you get to play the lottery of whether or not it will work.

Yeah, I noticed that with the big ol' made in china sticker on it. I didn't realize remans have went so far down hill.

 

[Uncle Gump]

Have you looked at the rear brakes? Clean lubed and properly adjusted?

Poor rear brake adjustment will create a low pedal.

If you didn't open a line to replace the booster.... you shouldn't have got air in the lines. It's impossible....

The other master.... is the clutch master.

 

[Uncle Gump]

So... the pedal was low before you started?

Do you have any visible leaks?

 

[Josh0224]

Have you looked at the rear brakes? Clean lubed and properly adjusted?

Poor rear brake adjustment will create a low pedal.

If you didn't open a line to replace the booster.... you shouldn't have got air in the lines. It's impossible....

The other master.... is the clutch master.

Well, don't I feel dumb. I'm used to seeing clutch masters on the firewall next to the brake master. /facepalm

I dont think they were low before I started, but I really didnt pay attention to it until the booster started hissing. They definitely weren't on par with my newer vehicles, but I dont recall them being overly spongy or soft.

It's been a while since I've done drum brakes so bear with me - you can only check the brake health with the drum off. Likewise for testing their adjustment - correct?

The fluid level hasnt changed since I got the truck, so I'm fairly certain that I dont have a leak. It could be that I'm being hyper sensitive due to the recent issue.

 

[Uncle Gump]

It would be best to pop the drums off and have a look. There should be a hole in the backing plate to adjust the shoes... but again... I would have a look. Chances are the adjuster is frozen and won't turn.

 

[Josh0224]

I'll try that tomorrow morning.

Thanks y'all!! I appreciate all the feedback!

 

[Dirtman]

Just throwing this out there. Master cylinders can fail without leaking and loosing fluid. Not saying your master is dead, just saying visible leaks are not the definitive test. They can leak internally where the fluid simply remains in the reservoir instead of being forced down the lines.

 

[Eddo Rogue]

Jamming the brake vs a slow depression has the same amount of resistance. And stops at the same place. When the car is off, the brakes do tighten really good, but never gets super solid. With repetitive punching of the brake, it the pedal still moves 2-3 inches before stopping.

How could I tell if the booster is bad out of the box? Theres no noise as there was with my last one.

Also, the small reservoir next to the fender om the driver said says it's also for brake fluid, but is empty. What is that one for?

Hmm yea try bleeding it might help....I actually run RBF600 motorcycle brake fluid same as in my R1, it has a 600 degree boiling point, awesome fluid but spendy ($20 a small jug). The small reservoir is your clutch master, it shouldn't be empty, and if your clutch works, then there's probably just barely enough in there (it doesn't use much)....maybe fill that to line w/ brake fluid too...