Brake pedal moves but it's not applying brakes

[tocruise]

This might be an incredibly stupid or noob question, so I apologize for always bothering ya'll with this stuff.

Essentially, I don't know how much play is supposed to be in the brake pedal, and because of that I'm struggling to diagnose why my brakes aren't working. I can compress the pedal about 1-2 inches with incredible ease, lke there's no resistance at all, and nothing comes out at the calipers (if I remove the nipple entirely literally nothing comes out even with the master cylinder full). Obviously something is wrong with my brake system somewhere.

This video is of a different car, but it shows the brake booster going in quite far from the pedal:

On my car it seems to lock way earlier, which I've got a video of here (please ignore the mountains of rust, I'm working on it ):

To my understanding, the pedal should be pretty hard to move but should still move further than this, and with some stiffness if it's all working correctly.

To proceed (and please let me know if this is a bad idea or if I'm misunderstanding how this works), I could take the master cylinder off, and then compress the pedal again. If the pedal is still sticking the same way it is now, then it's likely the booster is stuck and needs replacing. However, if the cylinder is broken but the booster is not, then after taking the master off, I should see the pedal start working, and from the engine bay, I would see the rod moving in and out where the master cylinder was. Am I right in thinking that?

Excuse my ignorance too, but the car has been sat for a long time, is there a chance the brake booster plate could be rusted to the walls of the booster?

 

[Zach]

Nothing is a stupid question when it comes to brakes, very important item. Nothing coming from the front calipers is definitely an issue. If it were me I’d trace back until you do find a hole, collapsed line, brake fluid, etc. if the reservoir is full there is an issue somewhere in between. Could be a clog or bad seal in the resivour. The booster just assists shouldn’t have an effect on the actual hydraulics of the system. Someone more knowledgeable can probably give a better diagnosis.

 

[tocruise]

Nothing is a stupid question when it comes to brakes, very important item. Nothing coming from the front calipers is definitely an issue. If it were me I’d trace back until you do find a hole, collapsed line, brake fluid, etc. if the reservoir is full there is an issue somewhere in between. Could be a clog or bad seal in the resivour. The booster just assists shouldn’t have an effect on the actual hydraulics of the system. Someone more knowledgeable can probably give a better diagnosis.

Thank you, I agree.

That's my understand too. I guess the reason I suggested the booster could be stuck is because the car has been sat for a long time. I was wondering if there's a chance the plate inside the booster could be rusted stuck to walls? A good kick at the brake pedal might break it free?

It feels like there's so many systems at work when it comes to brakes it's hard to actually put your finger on what could be going wrong.

 

[giantpune]

If you suspect the master cylinder is rusted stuck, just breaking it free is not the answer. Pull it off and either replace or rebuild it.

 

[tocruise]

If you suspect the master cylinder is rusted stuck, just breaking it free is not the answer. Pull it off and either replace or rebuild it.

Respectfully, I think that's obvious. If there's an issue with the booster, it'll be replaced, it's whether there is an issue with the booster that I'm trying to diagnose. I intend to fix it properly.

My thought process is a) am I even having symptoms of an issue (is the pedal supposed to do this, is my understanding the brake system correct etc.), b) if there is an issue with the brakes, based on my symptoms where would that issue most likely lie (in the master, the booster, or some other part of the brake system?), and c) if it can't be diagnosed, I'll take things apart and go through each part of the system to see what the issue is , but knowing where to look and what to look for is key. Any of these 3 steps is effectively what I'm trying to get guidance or affirmation on. I'm not look for a cheap hack to fix my brake system.

I suppose my point is, you have to fill a broken radiator with water to see if it works, it's not the correct "repair", but it does test your diagnosis. That's what I'm trying to do here.

 

[turtle5353]

Pull your vacuum line to booster and see if booster is holding vacuum. If it’s not then it definitely bad. Pretty simple check for booster.

 

[Steven Citrone]

I watched your video. It looks like the pedal movement is merely taking up the play, and it doesn't look like the brake pedal is actually moving the pushrod into the master cylinder. It sounds like you have not yet removed the master cylinder. My guess is that the brake pedal pushrod is not able to compress the master cylinder, as if the master cylinder might be frozen internally. You might try loosening the nuts holding the master cylinder to the booster, and see if the brake pedal can then move farther, indicating that it's the master cylinder that's not allowing the pedal to move further. If that's the case, R&R the master cylinder. I don't suspect the booster is the problem here.

It looks like you're in the Seattle area, as I am. If you're not terribly far away, I could help you figure this out.

 

[Hemikiller]

I've never seen a brake booster lock up from rust. You can remove the master and gently press on the pedal to see the pushrod moving. I'd say a more likely issue is the piston in the master is stuck and that's causing the play you are seeing. Sometimes a couple firm presses will loosen them up. If not, it's time to replace the master.

 

[ROCKET70]

If it's been sitting a long time I would replace everything, master, lines, flex hoses, calipers (if disc brakes) and wheel cylinders then you have no worries.

 

[Mac]

Thank you, I agree.

That's my understand too. I guess the reason I suggested the booster could be stuck is because the car has been sat for a long time. I was wondering if there's a chance the plate inside the booster could be rusted stuck to walls? A good kick at the brake pedal might break it free?

It feels like there's so many systems at work when it comes to brakes it's hard to actually put your finger on what could be going wrong.

The brake pedal moves a small shaft inside the master cylinder. If this shaft is stuck or not long enough it will not engage the spool in the master cylinder. The booster is not relevant at this point. Suggest removing the master cylinder, position it upright in a bench vise, remove the cap, top off the brake fluid level. Fabricate two brake lines and put them in the two ports on the side of the master cylinder body where the car's brake lines would normally be, and have these two fabricated lines empty into the two bowls. Now use a long bolt, screw driver or a long shaft into the port on the butt of the master cylinder where the small shaft would normally be. Then manually push the long bolt, screw driver or whatever in and out while watching the inside of the two bowls. You should see the fluid coming out of the two fabricated lines emptying into the bowls. If not then your master cylinder is plugged. A word of caution, never spill brake fluid on any painted surfaces as it will destroy the paint.