Brake problem-thoughts please

[tanman]

Evening all. This happened a couple of times last year then stopped, but has happened frequently over the last few days- any suggestions would be appreciated as to what it is.
When I go out in the Elise the brakes are fine (a tiny little bit of play at the top of the brake pedal- like there has always been). Then after a few dabs of the brakes, the pedal feels like pressing a stone, additionally when I finish my journey the discs are very hot (especially the rear ones, but fronts hot too) despite not really breaking coming home. When I go out again they are fine before the cycle starts again.
My initial thoughts were that the callipers maybe binding on, but obviously they can’t be as they free off soon after the car is stopped and allowed to cool down. Could it be the brakes need bleeding and new brake fluid put in? It’s a 52 plate car, done 20k, pads are fine and has always been serviced on time if this helps.
Thanks for your thoughts.
Tanman

[Extra 300 Driver]

Master cylinder not letting the pressure go.

Thats what it sounds like to me. Does the car coast ok?

[GreenV8S]

The master cylinder is not opening fully when you come off the brakes. There needs to be sufficient slack in the pedal to bring the master cylinder back far enough to open the port to the reservoir. If you take all the slack out of the pushrod then the brake circuit remains a closed system, there's nowhere for the fluid to go when it heats up and expands, the brakes will apply themselves. If they get hot enough then this can turn into a vicous spiral and the brakes can sieze completely.

[tanman]

Cheers guys, will drop it into the garage and get them to look at this. Extra 300 driver- yes it will coast fine at the beginning of the trip then after a few dabs of the brakes no, thats why i initially thought it was the callipers binding. i guess i need a new master cylinder? is it expensive?, how long does it take to replace?

>> Edited by tanman on Thursday 6th April 22:09

[GreenV8S]

It's very likely to be an adjustment problem rather than a terminal problem with the master cylinder.

[iccees]

I would go along with the previous, although I've not had experience on Lotus brake problems, your cars symtoms would suggest an adjustment is required to the rod that enters the master cylender, as per, fluid heats up, expands and applies brakes. Why this rod became out of adjustment is another question.

[Extra 300 Driver]

Well we all agree. The job shouldnt take long but remember that the brakes will have a different feel after.