Grand Cherokee Laredo 2.5 TD Auto year 2001.
Think this is a WJ (?).
Problem:- Hit the barkes and they work perfectly. But do say 80 mph and gently pump the brake 5 or 6 times then slam them on hard - nothing happens for a while, then braking action comes in slowly. Slightly scary. Mechanic says it's a faulty brake vacuum pump and has quoted 450 euros for a genuine part + fitting+ tax (not reconditioned, the old one becomes rubbish - this is Spain). I can get a unit from England for a quarter of this price from a breakers. So, two questions - (1) do the symptons sound as though they'll be cured with a new pump...do you agree with my mechanic? and (2) how can I get a part number for my particular car to be sure the replacement will fit?
And a huge thanks to anyone who helps me out! I am not a mechanic as you can tell.

 

That could be it. Pumping the brakes uses what vacuum is stored and then the pump is not replenishing it fast enough. If you can fit a vacuum gauge where you can see it and plug it into the line to the brake booster, that should tell you if you're keeping vacuum or not.

The vacuum pump seems to be integrated into the power steering pumps on the diesels. There is also a check valve on the brake booster itself. (It's the 90 degree fitting that plugs into the booster that the supply hose attaches to.) Make sure that is still holding vacuum as well.

I'm going to try to upload a couple pics from my 2001 parts manual for you.

One note: The parts manual is for a 2001 XJ, not WJ, but I'd wager the vacuum pump and booster are similar if not the samefor the 2.5TD motor in each truck.

 

Here ya go.

 

Many thanks for info and for the pix - it confuses me a little more as the mechanic says the fault is with the 'brake pump' for which he's quoting 450 euros.....but there doesn't seem to be a brake pump. The power steering is fine so there's no indication the pump itself is faulty. I'll take your pix to him and ask for a detailed explanation. Thanks again.
Colin