brake pedal going to the floor

[ticaf]

I did a brake flush a while ago.

The brakes perform fine. However, I noticed if I keep a good pressure on the brake pedal, with the engine idling, the pedal would eventually reach the floor!

Is this normal ?

 

[Mike_04GolfTDI]

That doesn’t sound normal to me. How long does it take for the pedal to sink to the floor?

Would it happen sitting at a red light with your foot on the brake, for example?

 

[ticaf]

That doesn’t sound normal to me. How long does it take for the pedal to sink to the floor?

Would it happen sitting at a red light with your foot on the brake, for example?

No it does not happen at all during "normal" operation. what I mean, is that if I "keep" my foot on the pedal during a red light, with 'normal' pressure, it feels fine.

It's just that if I push hard, and maintain hard pressure, then slowly but surely it will go to the floor. it takes a while, maybe 30 secs or more.

The reason I was pressing hard was to check after brake flush, so I have no idea if it was like that before.

 

[Mike_04GolfTDI]

I wouldn’t worry about it then. If it feels normal during normal driving, then it’s probably safe. Maybe keep an eye on the fluid level.

 

[ssalaun]

i think this is normal response from the brake system. If you gently push on the pedal, the travel will reach the floor. However, if you were to do a fast acceleration to brake ( like an emergency braking), the pedal should be hard. I noticed same "issue" on my VW a few years back and had the dealer bleed and rebleed the brakes , they could not find anything wrong, I came to the conclusion, the brakes are designed to harden if the ECU is sensing an emergency braking situation. Under normal circumstances, the brake pedal slowly travel down.

 

[thundershorts]

My 15 passat had a pedal bleed down that with engine running pedal would hit floor in about 30 seconds. While it was still under warranty, made dealer replace m/c. No further problem. While they were at it they replaced vac check valve as it wouldn't hold vac overnight making high foot pressure necessary for starting.

 

[ticaf]

Interesting. Would be interesting if someone could do the test. Press 'Hard' on the brake pedal while idling, and see if it goes to the floor.

 

[thundershorts]

If m/c is bad, a 5lb steady press on pedal will make it bleed down to floor.

 

[rocky raccoon]

'shorts is correct The effect described is caused by the master cylinder piston seal leaking. Steady pressure allows brake fluid to leak into the space behind the piston. Braking depends on differential pressure between the front and rear of the master cylinder piston.

 

[ticaf]

I think we all agree that a bad m/c will do that.
But like ssalaun, if I press hard while driving, it is fine, and the pedal is noticably harder. Any explanation?

 

[thundershorts]

Even with a failing m/c quick pedal press while driving will feel firm unless internal rubber cups have totally disintergrated. M/C failing is usually in most cases progressive, getting gradually worse, never better. Most of these sat dormant for a couple years so its not surprising.

 

[mkane]

Brake pedal should never hit the floor.

 

[ticaf]

Could it also be a bad ABS unit?
How to tell?

 

[thundershorts]

I don't think abs has any effect on an internal m/c leak. especially if car is not moving. abs doesn't interfere with brake fluid pressures unless it detects uneven braking, unless of course the abs block itself is leaking which is highly unlikely. M/c failures are not that rare. Eventually they wear out or the cups deteriorate.

 

[AGOODHI]

Interesting. Would be interesting if someone could do the test. Press 'Hard' on the brake pedal while idling, and see if it goes to the floor.

I tried it at a light. I could feel the pedal move down very, very slowly. It didn't hit the floor though, or I didn't try long enough since the light turned green.

 

[ticaf]

I tried it at a light. I could feel the pedal move down very, very slowly. It didn't hit the floor though, or I didn't try long enough since the light turned green.

Thanks for trying. I want to rule out 'normal' behavior, before trying to fix something that's not broken.?

 

[thundershorts]

Warranty billing was close to 600 for m/c so if you have any warranty left I'd get it replaced. It will only get worse, nt better.

 

[ticaf]

Unfortunately, I have no warranty. I still have a hard time to believe my m/c would go bad after 4 years. I've owned the car since new.
I'll wait to see if it gets worse. I noticed that a year ago, after doing a brake flush, which is the reason why I was pushing hard on the pedal to test. It was flushed at the two year mark by the dealer (did they really do it?), and then at the 4 year mark by me. Fluid was nice and clear, could not see any difference with new fluid, except for what came out of the clutch slave bleeding, which was cloudish.

 

[thundershorts]

M/c can go bad any old time, ask any mechanic/tech.

 

[rocky raccoon]

When bleeding brakes, it is bad practice to allow the bake pedal to go to the floor as many amateurs do. That practice pushes the piston seals into an area never used in normal braking. That area often has a ring of corrosion with a roughened surface that tears up the seal resultIng in a leak.

 

[ticaf]

When bleeding brakes, it is bad practice to allow the bake pedal to go to the floor as many amateurs do. That practice pushes the piston seals into an area never used in normal braking. That area often has a ring of corrosion with a roughened surface that tears up the seal resultIng in a leak.

a few things here, I followed the service manual, and I did not touch the brake pedal at all. All was done under pressure, at around 10-15PSI ( I don't remember). Manual calls for 30PSI, I was a little scared to put that much pressure in the system, so the ABS module probably kept old fluid.
That being said, the manual also calls for a "POST-BLEEDING" procedure, if pedal is soft, and it DOES require the brake pedal to go to the floor, about 5 times per caliper. I did not do the "POST-BLEEDING" procedure.

Also, the manual calls to engage the ABS at least once. I also did not do that, since I was too lazy to find a gravel/dirt road to slam on the brakes, and I did not feel like doing it on a paved road ( I may be wrong about that).

At my next flush in a year or so, I'll try replacing the M/C if not too expensive. I had many used car, and never had a bad M/C. Bought a brand new car, and now maybe a M/C failure, go figure.

 

[thundershorts]

My golf gravity bleeds easily, no pressure required, no muss no fuss.

 

[wonneber]

I'll wait to see if it gets worse.

Do you want to wait until you are going down the highway at high speed and need to do a panic stop?
You never know.

 

[ticaf]

Do you want to wait until you are going down the highway at high speed and need to do a panic stop?
You never know.

That's the thing, the brakes are working fine. If a buyer would test drive the car right now, they wouldn't notice any issues at all.

If somebody can guarantee me that if they press the brake pedal as hard as they can, while idling, and it does not go to the floor 'eventually' then I would accept that I have a failure. Until then, I'm not too keen on fixing something that is not broken.

 

[rocky raccoon]

I think there is concurrence that you have a leaking master cylinder, minor though it may presently be. A sudden blow-out of that seal at high speed and pedal pressure could be catastrophic. It happened to me years ago with an old '62 Jaguar and I ended up rear-ending some poor lady.

Master cylinder replacement is not that hard or expensive. I recommend you Get 'er Done and sleep better.

 

[thundershorts]

I wholeheartedly concur. Be safe and forget trying to justify not replacing m/c.