740 Tutbo Estate - brakes come on when hot

Try fitting a heat shield under the master cylinder and reservoir.

Have you tried bleeding the brakes or changing the fluid? It may have water vapor in it.

Besides the fluid, as others have mentioned, it could be the valve in the booster leaking as though the brakes were applied. Disconnecting and plugging the vacuum line for a test (warning - the brakes will be too stiff to drive safely that way) with the engine hot will tell the difference. Problem goes away, bad booster or adjustment. Problem stays; bad fluid.

Or you can bleed the brakes until the fluid runs clear and see if that helps ;-) Couldn't hurt.

BTW, the engine shouldn't show hot on the guage at idle, even under the worst conditions. If it does, the viscous fan clutch is probably bad. They are expensive but effective. In Phoenix a new one kept the temperature guage at center even when the outside temperature was above 110F and the AC was on high. Before I replaced it the guage would touch the red in a few minutes and drop quickly after we got rolling.

Mike

In article , Michael Pardee writes

Thanks for the input from everyone, I'll give it a go.

BR Don C

They're not hard to find at junkyards, though you never know exactly what you're getting. Another option is an electric fan conversion, price is comparable to a new fan clutch depending on where you get the stuff and you get the benefit of a much quieter fan. Not for everybody but it's something I plan to do on mine if the clutch ever fails.