Brake Failure

[owent2005]

Good morning all, Ive just returned from a trip and have a few queries. The first being quite an alarming brake failure! I had been driving for about half an hour. I stopped for ten minutes, when I started up and pulled off I had no brakes, pedal straight to the floor. I pumped the pedal and got some braking back all be it right at the bottom of the pedals movement. I elected to drive carefully home, after about three miles i got the full range of the pedal back with everything working fine.

Ive checked the forum and read similar stories with the master cylinder being mentioned (as i don't think anything over heating was an issue) but thought id re post to get any new thoughts.

Any guidance would be appreciated.

 

[speedwell68]

What braking system do you have? Disk/Drum? When did you last change the fluid?

 

[owent2005]

Ive discs at the front and drums at the back, I've only owned the van a few months so not sure on how old the fluid is

 

[Webbaldo]

Flexi house collapsed or leaking?

 

[Moseley]

If the pedal went to the floor but you could get braking by pumping, then this will be the master cylinder in my opinion. The only other cause for the pedal to drop to the floor suddenly would be a leak, but then you wouldn't have regained your braking afterwards as per your description.


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[owent2005]

The previous topic about brake failure on the forum mentioned the master cylinder, I'm not a mechanic and can't get my head round how it would stop working then work again, could someone explain how it works in simple terms please

 

[Zcat7]

This could happen with a calliper/shoe being seized on. It boils the fluid, which in turn forms gas bubbles in the brake lines, which then cause what you describe. The fact that it recovered suggests to me that the calliper may have released and after cooling down your fluid recovers its normal viscosity and your brake function returns. What I would say is that you would normally feel the vehicle pulling to one side if I were a calliper (as they are on the front wheels) though not always depending on how hard you are braking but if it was on the back you may notice it less. Didn't happen to leave the handbrake partially on did you?

If it were a master cylinder I don't see how it could have recovered its function back to normal. When a master cylinder fails the actual problem is that either the seals on the piston have eroded/split, allowing fluid to pass instead of being forced out to the wheels, or the bore has worn giving the same result. Yes pumping can help under these circumstances but I don't see how that situation can "get better" and allow normal function to return?

 

[Tofufi]

This could happen with a calliper/shoe being seized on. It boils the fluid, which in turn forms gas bubbles in the brake lines, which then cause what you describe. The fact that it recovered suggests to me that the calliper may have released and after cooling down your fluid recovers its normal viscosity and your brake function returns. What I would say is that you would normally feel the vehicle pulling to one side if I were a calliper (as they are on the front wheels) though not always depending on how hard you are braking but if it was on the back you may notice it less. Didn't happen to leave the handbrake partially on did you?

I would tend to agree with Zcat7 - I managed to boil my brake fluid on my '71 once (disc brakes) after a long descent down a mountain pass in the Pyrenees. I had brakes at the bottom of the hill, but 5 mins later the pedal just went to the floor. The brakes recovered once they had cooled.

Might be worth jacking the van up and making sure the wheels spin fairly freely (with handbrake off) to ensure the brakes aren't binding or dragging.

 

[Moseley]

Maybe a bit more info on the scenario when they failed? I read it as they had been in use but after sitting to cool they then showed signs of not working.


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[owent2005]

Thanks guys for the tips, I will jack it up and check the free movement in all the wheels.

I had been driving for about 30 minutes, nothing arduous, I parked up with the engine off for about 10 minutes. When I started up and reversed out of the parking spot I had no brakes at all. I pulled back into the spot, still no brakes. I pumped them and got a bit back at the bottom of the pedal. I drove home with them like this, then after 3 miles I got full function back.

 

[Moseley]

I'm still banking on the master cylinder. If they had gotten hot and the fluid had boiled on the first leg of your journey, your drive home would have only made it worse. It's definitely worthwhile jacking the van up and checking whether any of the corners are binding.


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[Robcod]

I know when I got my van the garage were going through the brakes and had the same problem and couldn't work it out. In the end a new master cylinder solved it. Might be worth doing anyway for peace of mind?

 

[owent2005]

£55 for a new master cylinder might be worth it for the peace of mind,

When operating the pedal does that activate the drums on the back as well as the discs on the front?

 

[Robcod]

I have drums all round and it operates both as it would do for disc and drum.

 

[Jejochem]

I think it sounds like master cylinder or old brake fluid which has drawn moisture in. Try doing a COMPLETE fluid change first to see it's condition then change the master cylinder. This way you you won't contaminate the new cylinder with old fluid. My van had been standing in a workshop for about 3 years and when I bled the brakes through initially the fluid was ok then just had loads of what was best described as brown watery sh**e!! Soon after the master cylinder then started leaking so I think the old fluid had just wrecked the cylinder seals.
Good luck.

 

[owent2005]

Just a quick update, after jacking the vehicle up I found that both rear drums were sticking a little so have backed them off slightly to allow the wheels to turn freely. The brake fluid is fine and there is no air leek in the lines. I'll update further if it happens again!

 

[StuF]

Replace your master cylinder or the next time the brakes fail it might be a little more dramatic - like if you were exiting a motorway at 55mph or going down a steep incline!

Don't want to chance it for £55 - or there is no way I would!