Corsa C 1.7dti - Brakes suddently went hard, until restart

Honest John Back Room » Technical matters
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Sat 25 Jan 2014 18:18
Corsa C 1.7dti - Brakes suddently went hard, until restart - mfarrow

Hi

I had a bit of a scare earlier in wife's Corsa, downhill of course!

After a lot of rain I took it out, and 1/2 mile down the road the brakes suddenly went hard, no servo assistance what so ever, so aborted my mission to Sainsbury's and drove back home - carefully.

Upon arrival I popped the bonnet and could see no obvious split hoses etc. Went to the garage for vacuum gauge, couldn't find it so thought I'd restart and do some more playing. When I did, vacuum was back and all was well-ish again.

I say well-ish as when I pumped the brakes there on the drive I could consume the vacuum after about 4-5 pumps, although it replenished very quickly. When I tried again after a run, I was unable to consume the vacuum, constant pumping made no different.

What the devil's going on? Is it a pump problem? servo? non-return valve?

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Sat 25 Jan 2014 19:36
Corsa C 1.7dti - Brakes suddently went hard, until restart - bathtub tom

Could the first instance of a hard pedal have been the ABS (if it's fitted) activating? It can produce a hard pedal feel.

When you say you were unable to consume the vacuum, did you have the engine running?

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Sat 25 Jan 2014 20:13
Corsa C 1.7dti - Brakes suddently went hard, until restart - mfarrow

Tom

Thanks for the reply. No ABS (unfortunately). Yes all testing was done with engine running. With engine not running vacuum's depleted in a few presses, as usual.

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Sat 25 Jan 2014 21:21
Corsa C 1.7dti - Brakes suddently went hard, until restart - gordonbennet

Have had vacuum flexible pipes partically collapse inside before, might be worth checking that first.

Could be the first sign of the vacuum diaphragm deteriorating.

Edited by gordonbennet on 25/01/2014 at 21:22

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Sat 25 Jan 2014 21:29
Corsa C 1.7dti - Brakes suddently went hard, until restart - elekie&a/c doctor
"After a lot of rain" ,could be a clue.check the air intake/ plenum chamber area below the brake servo.If the drains are blocked,rain water can get sucked into the servo.
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Sun 26 Jan 2014 11:39
Corsa C 1.7dti - Brakes suddently went hard, until restart - mfarrow

Thanks for the replies.

The vacuum hoses themselves look OK externally. The main one up to the servo is hard-ish plastic, with a short section from the non-return valve to the pump made out of rubber. I might start on that and the non-return valve first, once the factors and dealers are back open.

The area around the servo is well drained. There is some water moving over it from the wipers today which appears to be by design, but other than that it looks fine. There is no water present inside on the bulkhead or gaitor.

The presence of vacuum was evident today from startup for about 3 miles, then suddenly depleted. It kept coming back momentarily, and if hard, when I held my foot on the brake with engine running it went down slowly. Note this doesn't happen with engine off.

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Sun 26 Jan 2014 22:52
Corsa C 1.7dti - Brakes suddently went hard, until restart - Cyd

sounds like you've an intermittant problem with the vacuum pump to me. It's where I'd look first anyway

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Mon 27 Jan 2014 19:46
Corsa C 1.7dti - Brakes suddently went hard, until restart - mfarrow

solved! vacuum pumping problem it was, but not the reason i was looking for.

where the vacuum pump joins the servo adaptor, the pipe had split, allowing air in. this was accompanied by water as the rain washed over it from the wipers/scuttle (the by-design system of drainage!). all compounded by lack of visibility of said pipe attaching until you pull the trim apart.

water was being sucked down into pipe, creating whatever blockage it needed to in order to stop the vacuum. old pipe end snapped off and fresh end heated and re-applied to servo - good as new.

whether the pipe was creating a 'u' of water or just creating an obstruction in the valve, i cannot say. i just dread to think what it's done to the oil!

thanks for the replies and apologies for the lack of capitals, the forum software and my smartphone don't mix

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