hot front discs

[guest3735]

got a problem that i can't work out....
go for a drive, even a short one... and the front brake discs end up hot. went to my local tame mechanic and he had a good look round after i'd said that i suspected the brakes were binding, heating the discs up. fluid level was ok. thought it might be stuck pistons on the caliper but encountered no resistance when winding them back in. there is no appreciable drag when driving with the clutch depressed. i'm now in that funny position of not wanting to drive the car in case i set fire to it or something. i've not noticed any problems before (although i had a rear caliper rebuilt last year). i appreciate that the discs will heat up to some degree through use but i'm not sure what to do next. have others here experienced this?
if the caliper pistons wind back in ok, presumably a rebuild is not required.
if the discs heat up, there is friction somewhere. (fuel consumption seems normal)
previous rear caliper rebuild was done after fuel use increased noticeably.

also, i can't work out why both fronts are the same.... if it was the calipers, they wouldn't both go at the same time. even i'm not that unlucky. do others here have hot discs? is it normal? why haven't i noticed before?

advice appreciated. it's driving me nuts

[culzean]

really need to know what your definition of 'hot' is - can you touch and comfortably hold your finger on the disc ? if so it is probably below 60deg C - when I have had a 'hot' disc before you could actually smell it - and when I touched it it went 'pssst !! and I had a blister

discs will normally get warm in service because their duty is to absorb the kinetic energy of the car using friction, this results in wasted energy which always results in heat.   As I said - depends what you class as 'hot'

[guest3735]

wouldn't advise putting my fingers anywhere near kind of hot. my worry is that i haven't noticed it before. might it be binding slightly? the previous rear caliper got hot enough to heat the wheel. don't want that happening again.

had another thought.... if brake fluid takes on water, would that push the pistons out? like i said, i had a mechanic look around. he reckoned he couldn't find anything but then it might be something really simple.

culzean... when you had your hot disc; did you dismiss it as normal? on my test drives i hadn't been caning the brakes. i was trying to be exceedingly gentle.

[madasafish]

If a brake sticks on, you can usually fee it by running on a flat surface in neutral..the car should turn towards the sticking brake.

It could be a fault with the master cylinder or a brake flexi acting as a one way valve and not releasing pressure... (rare but had it due to using a clamp on the flexi pipes..)

But brakes do get hot on just normal stopping..If the wheel near the brake gets hot as well, there is a real problem..

[guest3735]

solution found.
remove front pads.... find rust on back of pads. wire brush then copper grease.
apparently the rust on the pads was stopping the caliper piston retracting fully, so pushing the pad onto the discs, causing the heat.

[culzean]

sometimes when you fit new pads the metal 'tongue' on each side of pad does not fit into its housing properly (very tight) I always file a bit of metal off the tongue till it slides in easily with a bit of clearance, I bet that was the bit that was tight and when it got rusty it didn't slide back anymore.  There is actually no force 'pulling' the pads and caliper cylinders back in, it is just that the pushing force is relaxed     I notice the new pads I just bought for Civic (genuine Honda parts from local dealer) didn't have the normal stainless steel shims, but have adhesive backing on the pads (like double sided tape)  that you have to peel a tab off before you fit the pads - this sticks the pads to the hydraulic cylinder face.

Another thing when changing pads,  check that the rubber concertina gaiter on the caliper is intact and in good condition, this covers the bearings that allow the caliper to centralise on the disc,  and if water gets in it rusts the bearing and shaft and you will probably see that the material on the moving pad (the inboard one with cylinder) has worn a lot more than the outer pad.

[guest3735]

sometimes when you fit new pads the metal 'tongue' on each side of pad does not fit into its housing properly (very tight) I always file a bit of metal off the tongue till it slides in easily with a bit of clearance, I bet that was the bit that was tight and when it got rusty it didn't slide back anymore. 

spot on. front and back pads out, cleaned and greased, then back in. all is sweetness and light with the world again.