Rear drivers side wheel - extremely hot

[NCS XC90]

Hi,
My car doesn't do that many miles and generally short trips. The other day after a long trip ~40 miles I got out the car to find to the smell of hot metal/ brakes. Putting my hand near the rear drivers side wheel there was a massive amount of heat coming from it. Nothing unusual felt on the other wheels but the back drivers side was quite alarming.
I've jacked the car to check for the normal bearing wear (rocking wheel top to bottom) and nothing. I took the wheel off and checked the handbrake which is good and not rubbing when disengaged. The foot brake pads on the caliper do seem to drag on the disk slightly but nothing I would normally get concerned about (but definitely slightly more drag than the other side).
At this stage I can rule out the handbrake as fully working and then fully disengaging when released. Would very slight drag on the normal pads cause this (it passed the MOT 2 weeks ago with the same drag – in fact I think I remember the drag being the same 2 years ago when I changed the pads). Could this be a symptom of a wheel bearing even if I cannot feel the play in it?
In addition I believe about 6 weeks ago I feel I could hear a change in the transition noise on the car. Nobody else could hear it, hard to describe other than wheel rotation related (same in neutral as drive) rather than engine linked. Came in at around 45mph and goes at around 55mph (possible doesn't go but wind noise hides it at 55mph). Best described and a low droning noise but hardly noticeable.
Does this ring a bell with anyone? Any suggestions welcome. Its a 53 plate car with 88k miles on clock.
Neil

[corbsxc90]

Hi Neil, If your handbrake shoes are free then I would be looking at possible tight pads in carrier,sticking piston on caliper,collapsing brake hose not allowing fluid to return. If its a binding brake and the disc got really hot due to binding brake I would expect to see the outer edge of the disc red, i.e. the outer most diameter of the disc that corrodes slightly. If the disc got that hot you normally get oxidisation of the corrosion. If the caliper piston can easily be pushed back this would discount a faulty piston or hose problem. Check the caliper sliders for seizing this could be another cause.
With regard to the slight droning, this could be start of a wheel bearing or even a slightly worn tyre, some tyres, especially rears can have uneven tread wear on the tread blocks on the inner edge of the tyre, you sometimes get alternate blocks wearing, sometimes a few, if you jack up the car and turn the wheel you can normally see the "rippling" if you look across the tread area. This can cause a humming about 50mph.
Hope this gives you something to look at,if you want any further help PM me.
Kind regards,
Chris

[NCS XC90]

Thanks Chris,
Makes sense. I had the caliper off last night and the piston seemed free enough. I had pads out as well but did not check if they could be catching in the carrier. I'll have a look at this first and double check the piston.
The heat is definitely from the disk although it could be the bearing passing heat though to the disk. I may be over exaggerating, the disk is not getting hot enough to get the outer part red. It is however way hotter than it should be. So hot that its actually difficult to keep your had on the wheel. Touching the disk would melt your skin without doubt. This whilst the other side is normal (wheel is ambient temp and disk is touchable for quite a few seconds).
Having read past posts I can see the noise does have similarities to bearing noise and/ or tyres as you suggested Chris. No mention of a bearing giving off excessive heat so I'm not jumping to the bearing just yet and will continue on with caliper and pads.
Thanks for your help,
Neil

[corbsxc90]

The pads should fit quite freely in the carrier without the need for any excessive force to fit them, if they are tight in the carrier then this is possibly your fault and remedy is normally to clean the build up of corrosion from the carrier and pads and refit using copper grease or similar heat resistant grease. If your pads have been getting hot the friction material normally shows signs of this. With you saying that the wheel has slightly more drag than the nearside, if you remove the wheel and slightly lever the caliper piston back does the disc become free to turn? If so the fault would appear to lie with the pads/caliper sliders. The sliders are the small pistons with concertina gaiters on that the caliper bolts screw in to. these should be quite free. It can be fairly common for one to get tight and cause a brake to bind but this normally causes a pad to wear more one side than the other. If you push the piston all the way back in, with the caliper bolted on you should be able to freely push the caliper back and forth by hand.
regards,
chris

[NCS XC90]

Chris,
Thanks for taking the time (again). Yes thats exactly it - I can move the pads back in the caliper slightly (not very easy but as easy as I would expect) and as soon as a do this the disk is free to spin. I had the caliper off last night and cleaned up the sliders you describe (at least I think these are the sliders). There was a bit of build up on them which I wire brushed and then put a bit of copper grease on them and refitted (these are the things you screw in using the 7mm hex brake spanner). Caliper would move freely in and out on the sliders after I did this so thinking about it the pads would be moving freely in the carrier also (but will check this as I didn't really look at this last night) which now points the obvious conclusion that its the caliper itself. I'm guessing the caliper is sticking (possibly the dust seal broken and allowed dust and rust into the caliper).
Thanks for this - its helped me get it clear in my head what I need to do next. Whats the score with calipers - can they be freed up or are you better just replacing them?

Neil

[Coldrow]

The droning can be the disk resonating when it is hot. If the pad fails to release properly (for whatever reason) then the disk slowly heats up and thus expands which then increases the friction and so on and so on.

Unfortunately this usually leads to the disks cracking and once this has happened the next time the disk gets hot it doesn't expand uni-formally and it is like it is warped which for me transpired as a droning noise in the car.

My disk cracked on the edge of the handbrake lining and when cold looked perfect. It was only on closer inspection I found the crack.

Worth checking the disk very carefully..

[keithC70]

A similar thing happened to mine on the same wheel.

The rubber seal had split, the inner parts rusted, then when the piston was pushed back into the bore to fit new pads, rust was drawn in.

I bought a re-furb kit but it didn't completely solve the issue. In the end it took a new caliper to sort it out.

[corbsxc90]

Hi Neil, Yes the sliders are the 7mm hex screws/bolts. If your piston gaiter is intact and pushes back quite easily I would not have expected it to be a problem. It's difficult to diagnose without physically being there, but from my experience I would be checking that everything free which is what you are doing. A seizing caliper piston is normally quite hard to push back into it's housing.
Let us know how you get on.
Regards,
Chris

[NCS XC90]

Thanks all, will take the caliper off this Sat morning. I haven't disconnected the caliper from the brake fluid pipe so when I say its not hard to push back I'm making allowances for the difficulty of pushing the fluid back which is pretty hard. With the fluid pipe disconnected it will be easier to assess how difficult it is. Fairly happy from all the replies that this will be the problem but will confirm how I get on. Will be sure to check the disk whilst I'm at it. Thanks everyone for taking the time to share experiences and suggestions. Much appreciated.

Neil

[NCS XC90]

Hi,
Some feedback. Took the caliper off yesterday and the piston is very tight in the housing. The outer seal had not split but rust had got in behind this. Cleaned the piston and housing up but still tight. However the bleed nipple is stuck tight. I put a huge force on it (thought it would snap) but it didn't budge.
Think all in all a refurbished caliper is best bet. At least I know what I'm doing now. Rest of my weekend has been working on my classic Triumph TR3A - fitting a hard top. It's so much easier and pleasurable working on a car you don't need as a daily driver

Thanks again,
Neil