Help! My brakes are have gone rock hard?

Hi all, firstly happy New Year to you all! Right then, yesterday I spent the whole day 1) changing the alternator on my (2002) TD5 auto and replacing the O rings in the fuel cooler. What a bloody job that was, nearly had to take out half the car to remove and fit the spare (and yes it has been tested) alternator, thing is today while driving to London on a couple of occasions when I put my foot on the brake it was rock hard? Don't get me wrong most of the time the brakes were fine, foot down and the car stops nice and smoothly but a couple of times when moving slowly in a queue I put my foot on the brakes and they are rock hard, solid! The car still stops but why is this, and why only a few times does this happen? Okay the brakes weren't touched yesterday and the car has been standing for a couple of weeks, could they need airing perhaps, maybe something to do with the vacuum pump on the alternator and if so how would I check it, maybe the brake fluid is spent? Any advice before I drive home tonight?

Cheers
Al

Also there are no warning lights that come on.

its the vacuum pump - check pipe connections

I agree the vacum pump.

Mine did exactly this and on mine it was the front of the pump that had come loose 2 bolts had dropped out

Taking into account that the vacuum pump and alternator are going together and u worked on the alternator that is the most obvious explanation..........though with a LR u never know

Okay, I'll give it a go and see if I can see anything down there. Let's get it straight then, I'm looking at three pipes, #1 on the side, #2 which has the 12mm bolt, and #3 with the long spout. Problem is I have put on the fan and all the bits so I don't reckon I'll see anything :-(. Could it also be a split in one of these hoses?

I also took out the pipe to the intercooler (the big un') and the curly metal one above it which I believe one puts on the blanking plate if required.

If the Vacum pump was faulty would it have shown up when it was tested at the auto electrics shop?

Just been out to the car but I haven't any screwdrivers with me so I can't take off the fan cover but underneath I took a peek at the vacum hoses but quite dark hence I'll try again when home...good old torch. I suppose I could use the vacum from the original alternator as well? I really hope this is an easy fix....

Update....It seems that the vacuum pump has been behaving itself for the last few days no problems with the brakes at all. Should I assume the job was a success and put it to bed, or still investigate?

Ta'

I had a problem like this, if I pressed the brakes twice then the pedal went hard and lost vacuum.
It was the small pipe that comes off the main vacuum pipe and runs along the bulkhead to supply air con switch I think (may be wrong on that) any way I blanked this little pipe off and all was well.

Hi landowner, seems you maybe right about this, but according to RAVE I should have put a new O ring on...There wasn't even an old one (whoops) just a metal washer. So should I try putting on an O ring first and if so what size or do you recommend just blanking it off and what's the best way to do this?

Cheers
Al