It sucks, but how much is enough?

There is clearly something up with the brakes in my 110. Driving along, brakes felt 'nominal', then the next time I went to use them the pedal was very hard to depress. I've started running the usual checks on the vacuum system, but my question is this, how much suck should I be getting from my vacuum pump?

I've take the hose off the servo end to run this check. I've not run any other cheks yet. So there may be leaks in the hose (hose looks OK from a cursory check) or pump end seal. I have no frame of reference for how hard the suction should be. It feels pretty weak. It can't hold the pipe to my thumb, but I can definitely feel the suction. It's certainly not going to give me a hickey Not sure how else to describe it. Does that sound too weak? Or if anyone in north Bristol has a vacuum gauge I can borrow?

Hi,

If you put your foot on the pedal and then start the engine , what happens with the pedal?

It should move down slightly when the engine starts if you are pushing on it.

CHeers

Nothing happens. There is no drop in the pedal after ignition.

The pedal is hard to push down before and after engine start. Hence I'm looking into the vacuum system.

Edit: I'm confident the pump and hose are OK now. I rev'ed the engine (which I wasn't doing before) and I can feel a very positive suction from the hose. It sucks my skin into the pipe end. Tested my non return valve. Think that needs replacing. Can suck a tiny amount of air the wrong wau through it. Certainly enough to loose vacuum after 20ish seconds I'd recon. I don't think its enough to mitigate the strength of the pump though at above idle revs.

So could be the servo or pedal linkage...

You need to empty servo first. Then foot on pedal and start engine, if servo is working it will go down.

As I said, I've tested this and it doesn't work as it should. To be clear. engine off, pump pedal till hard, depress pedal, start engine, no drop in pedal. Thus vacuum or servo problem. Vacuum is working, but feels weak. What should it feel like? Should it be able to suck onto my thumb? This is the first stage of diagnostics.

Sounds like your servo is on the way out. They are easy to fit, worth changing if it's over 20 years old anyway.

What engine are you running? The 300Tdi is notorious for eating its vac pumps.

Sucking your thumb like that sounds okay. Sounds servo related to me, I had similar symptoms

+1 on the above.

300TDI engine.
I've ordered a new servo, NRV and hose. I'll report back when fitted...
Thanks chaps!