Brake failure in hot weather

[johnw1327]

I am at my wits end with this issue. After standing in the sun, my x350 petrol experiences complete servo failure with an incredibly hard pedal and virtually no retardation. The servo has been changed twice, once by a main dealer under parts warranty but the problem persist and I stress only when left in the sun.

Please any ideas.
Thanks

John Wharf

[BrianG]

Have you checked the vacuum line from the throttle body to the servo? I found recently when changing out a faulty fuel pressure sensor, this has the same size vacuum line connected and is connected to a branch joint on the throttle body (at least on the 3.5 V8 it is). The plastic pipe material used becomes incredibly brittle and can crack just by moving it slightly!

[johnw1327]

Thanks for that Brian. I have changed the throttle body which had no effect but haven't changed the pipe which is apparently no longer available and it doesn't seem sensible to fit an old used one. I might fabricate a replacement in metal and try that. By the way mine is a three litre V6.

Regards,
John

[BrianG]

Hi John,
You're right - I even checked with the JLR classic parts site - "no longer available" what do they expect owners to do?. The tubing is small overall diameter but very thick walled so that the vacuum doesn't collapse it, but that seems to make it brittle with age. The short section from my fuel pressure sensor literally snapped at the rubber junction adapter into the throttle body so I would check there first (I noted that the JLR site showed a replacement pipe section along with the sensor and I thought nah, why would I need that?!) Metal tubing is probably a good idea (brake line?) if you can make suitable couplings or adapters at the ends. Good Luck!