A bit more information;-

Our other car (2 down 2 to go although both off the road at the moment!) has a fault so I used the Jaguar on a 50 mile round trip split over two days.

At around 40-45 I could feel a start of a judder which then went away. On a long stretch with no traffic, after around 3 miles the problem started and became so violent I considered abandoning the journey. However, it slowly decreased to nothing. On the return trip there was no judder on the main roads at all. However, approaching home there was a hint of a recurrence and I thought I could feel slight vibration in the brake pedal. At the same time, I could smell brake linings smell whatever that may be called.

Relating this to a local mechanic, his eyes lit up and he suggested sticking piston and warped disc. That sounds a possibility (I am no expert) but I have tried top invoke the phenomenon by hard braking a while ago without success. There could be a case of positive feedback I suppose.

One of the front discs is markedly more grooved than the other. I guess heat build up could cause an expansion related problem although heavy braking could be thought to invoke it. However, "heavy" might cause a sticking piston to bounce back in.

He will take it on a test drive this week and I will report back.

Now to the Volvo Owners forum for the other one or bring the Lenham MG out of retirement!!

 

I think he needs to remove both front wheels and inspect the brakes.
If you can see marks on the disc I would want to investigate further?
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+1 and of course both surfaces of each brake disc.

 

A bit more information.
A new fault has appeared which may be relevant. At engine start, there is virtually no assistance from the servo. The brakes return to normal after 5-10 seconds. The same mechanic has investigated this and found a leak at a grommet in the vacuum line.

The same mechanic found a hot NS front disc after his test drive. On the ramp, the same wheel was stiff. The previous inspection had been performed with the car cold.

It seems (to me) unlikely this could cause the judder problem but, first things first. Sticking piston seems possible.

 

Said grommet cost was £4.50. A pleasant surprise. However, it was not available. The alternative was the complete pipe assembly - ~£45. Not quite so pleasant. But that was not available either. Solution - complete new servo assembly ~£600.

What to do?

 

Photos'-


The offending grommet - broken

The connecting link.

The offending grommet

 

I would start checking EBay. You have the factory part numbers and there is always plenty of cars being parted out.
If fact I would at least post the part numbers to this forum as there are a bunch of very knowledgeable guys reading things and they might be able to come up with one?
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I have found sources of similar items and have ordered one from AutoDoc (in Germany). The sizes look the same. My mechanic tells me that his net searches have revealed mine is not a unique problem. To aid others I will post the results on here once I find a part that suits. Another snippet he has come up with, is that a similar part failure has caused steering judder!

 

Might be worth adding the car details to your signature or every now and then, as the diesel's vacuum system is unlike the petrols' ones I think.

 

After a thrash round the lanes, my mechanic found a hot N/S disc and the attached wheel very stiff to turn. He changed the calliper and fitted the grommet.

To date, the judder has not returned. Still difficult to understand the intermittent nature.

 

Depending on the temperature (different expansion/contraction of various materials and parts) and the position of the sticking piston, these problems are often initially intermittent until things get too bad.

Glad you got to the bottom of it.