Brake servo - faulty?

Icy road.

Good point - it has ABS though so would have thought that operating would have been noticed, will ask in the morning - and take it for a

-very- slow run myself.

Found this

That page spouts a load of s*it, ignore it.

If the vacuum is derived from the engine, any split in a hose would make it run oddly. Most likely raise the idle speed.

Not on a diesel, as diesels have open intakes they have insignificant intake vacuum and cannot generate enough significant suck for a servo, the diesel way to get brake vacuum is to run a vacuum pump off the camshaft, or alternator (or any turning source on the engine). Those pumps can and do fail, but usually it is a terminal failure rather than intermittent. I have occasionally repaired the diaphragm in awkward to get or expensive ones. Cracked vacuum hoses do happen, failed vacuum check valves could happen, the seal at the servo would be the most likely leak point. Finding the leak is usually just to have a good listen after running the engine. Checking that the pump works is to disconnect the hose and make sure it generates plenty of suck. Servo failure is extremely unlikely, but a leak at the check valve area or on some types where the master cylinder connects would be the most likely. IF an brake problem exists.

tvm

Yup. Which is why I said derived from the engine, rather than a pump.

How would it alter/raise the idle?

A leak into the plenum of an injection car has this effect. Of course the idle valve may attempt to compensate.

yes, but this is a diesel.

or so I thought, in which case ignore everything I said, sorry.

Ah. Didn't say that in the post I replied to. ;-)

The instaneous loss of braing and then recovery to normal performance at this time of the year and with prevaling weather conditons mean it might be nothing to do with the servo but just salt on the pads.

I've driven disc-braked vehicles since the 1960's, in all sorts of weather conditions, and never, ever experienced a loss of 'braing' due to salt on the pads.

Can you explain by what mechanism that might happen?

Chris

See post in this group this month for Corsa B steering. John Weale found ice had caused loss of function in early morning but OK by lunch.

Ice in the vac system could cause problems. Ice in a brake cylinder if fluid has not be changed for years. Or just some sound insulation wadding fallen and froze to jam pedal.

Salt will promote a thin layer of rust, rather like you get with brakes unused for a significant period (weeks, months). But it doesn't normally take very long to recover the grip. How long is the street?

I reiterate that I've never experienced anything like that, in over half a century of driving, including a short period of winter driving in Sweden.

Chris

Tend not to use salt on roads in Scandinavia as it attracts reindeer and elks to the roads.

That said, never heard of "salt on discs" being a cause of brake problems.

Tim