I've recently had my car serviced and on the day (it was cold) they could not find the problem I have. When the temperature outside reaches 30+C my brakes will slide to the floor. This does not happen at all below that temperature.
The service guy said I needed a new wheel cylinder, but I've read here on the forum that replacing this made no difference to some with this problem.
Any ideas?

 

You probably need a new brake master cylinder. It probably has an internal seal leak, you won't see any external leak of fluid. When the cylinder piston seals go bad, the fluid bypasses the seals. One of the symptoms would be the brake pedal sinking on hot days.

 

Red-bull1 gave you a pretty good place and idea to ask your mechanic..he's got good advice in here.

By the way, I have 1/2 doz relatives who live in Brisban..they love it there..

WheelBrokerAng

 

Thanks guys. Oh well here we go spending more money.
Re Brisbane, I used to live there as a child. I loved it. Swimming every day. Now I live in freezing and very hot Melbourne. It can get to 45C here. Lots of bushfires. Not where I'm living though.

 

Yes I meant Brake cylinder.......

 

The classic symptom of a bad brake master-cylinder is the pedal will sink slowly & smoothly to the floor while you're holding light pressure (for example at a traffic light). It leaks back into the reservoir so it doesn't leak OUT.

The wheel cylinder (caliper) can't cause this, because it has no way to leak back into the reservoir.