Hot rear discs

[john milner]

I replaced my rear discs and pads and gently drove for about five miles. I found that each disc was hot, similar to a central heating radiator on full whack. The fronts by comparison were slightly warm and what I would expect. A couple of hours later I drove home and checked again, one disc was about the same temperature as before but the other although hot was noticeably cooler. I jacked the rear up and the wheels rotate freely. The discs have a dark matt finish and after my ten or so miles most of it is still there. I would have thought that if I had a binding problem that the disc temperatures would have stayed roughly equal and the dark finish would have rubbed off in no time.

The pads are EBC Ultimax2 and have a red break in coating. So could the heat be a short term normal feature of the coating and I just need to keep an eye on the discs or is something definitely wrong?

I am leaning towards taking the calipers off and having another go but if it could be normal I don't want to waste my time.

[Jim 123]

Duplicate.

[Jim 123]

Handbrake adjustment a bit tight? Wheel bearings wearing a little on one side?  Disc rotor slightly out of true? Newest pads not matched to wear pattern on rotors?

I'd be tempted to try and get a good few more miles on the car and use the brakes to bed them in.

[john milner]

Discs are new so most likely perfect and nothing odd with the minimal pattern that there is so far. Bearings are fine. Bad handbrake adjustment is a possible as is the calipers not sliding properly but the wheels turn okay so if either of these are out it must be very slight. It's almost as though the break in coating causes a lot of heat to get the main pad to bed in properly but if that theory was correct Google would have found something easily.

I might go with the idea of giving it another couple of shortish runs before pulling things apart.

[john milner]

I decided to pull it apart before driving it. The handbrake cable was on the tight side as it would only click once. The handbrake shafts move when pushed and spring back when released. The red break in coating on the pads had rubbed off. The slider pins slide. I wound the pistons back. The pads are just about the right size, any bigger they would be too big. I slapped plenty of Copaslip on the edges of the pads that touch and the backs.

I was suspicious of the handbrake cable so aimed to set it slightly light. The "turn the nut until an ear moves" method isn't working for me. I had my fingers on the nearside and watched the offside but felt and saw nothing so just guessed when to stop. Three clicks to get the handbrake on full. Tried tightening the offside wheelnuts and the wheel turned so adjusted the cable a bit more. Now two clicks to handbrake on and the wheel does not move when tightening wheelnuts. Wheels move fine with the handbrake off.

I went for a 15 mile gentle drive and pulled over halfway. The discs were at a similar temperature as the other day, the discs were possibly slightly cooler but hard to be sure as it is a much colder day. Got home and the discs were still about the same temperature so at least they had not much got hotter. I had done very little braking apart from one 20mph emergency stop as a test and when approaching junctions etc.. Not much left of the dark finish on the discs. Easy to push the car with the brakes off even on gravel.

I am starting to wonder if the rear brakes have always been like this and its just that I have never bothered to check as closely.

[Jim 123]

After my build, I started doing a walk around and touch test and was surprised to note temperature on the rears.  Probably your car needs a bit more miles of bedding in and wear?

A few things that I considered, some of which may be open to challenge....... Unlike a tin top, there is quite a bit more airflow around the front discs on a Seven which complicates comparison of temperature with the rears inside the rear arches.  The Seven's low weight and center of mass might dictate that the rear brakes on a Seven proportionally provide a bit more retardation than conventionally expected from a FWD saloon car braking system.. I made multiple chassis fixings for the handbrake cable where it snakes around the back end. This was to stop any road induced wobble in the cable teasing the rear discs on and off whilst driving.  I also worked out that my incredibly flat feet needed a narrow shoe fitting, as I was glancing the brake pedal when I operated the throttle

[john milner]

I've got at least 30 miles each way planned for tomorrow so that should be interesting. If the discs don't get any hotter than they have already I think it must be a design feature. Another thing is that it is possible to have one faulty caliper but two is unlikely. The pads are snug so it's possible they are not backing off enough but the wheel rotating should be enough to shift them sufficient microns. I would expect some heat due to the ratcheting action keeping the pads in fairly close contact with the discs. If you touched a disc for five seconds it would be uncomfortable although not enough to blister the skin. By comparison today the fronts were stone cold. If it is a feature I'm surprised not to have noticed it in over 72,000 miles.

When I first sat in a Seven in the old Caterham showroom it had an S3 body and I hated it my hips and shoulders felt squashed and my right foot was in contact with both pedals. On the other hand I am a perfect fit for an SV. I have found that I can't get most brands of trainers (Adidas worst, Karrimor best) on my feet unless they are several sizes too big so I would have no chance with a narrow fitting.

[Jim 123]

If I get out in the next few days I'll compare mine to what you describe above.

[Jim 123]

Another duplicate.

[7 wonders of the world]

Are you saying the rears are hotter than the fronts after hard braking or when your just driving without braking...?

If its the later then you have a problem as there shoulf be no noticeable heat build up by the wheel merely rotating - something is binding, no set correctly, not releasing etc etc and requires attention before this worsens and induces vapour lock as your driving along - the first you will know about this if you miss the smell is a long or no existent pedal 

[sjl1]

I think this is normal behaviour, the rears do more braking than you expect and are out if the airflow. Mine are always considerably hotter than fronts after a run. 

[aerobod - near CYYC]

The rear brakes on my Caterham get hot sooner and stay hot a lot longer than the fronts. The rear brakes and wheels get hot enough on track that I take off the rear plastic centre caps due to the fact I’ve melted the tabs on two of them and had them fly off, only determined when I was handed one back by a track worker. The front brakes and hubs are cooled far better, I don’t have the tabs melting on the centre caps and keep them on to keep dust off the front bearing seals.

[john milner]

No hard braking just moderate speed smooth driving and only braking when I have to. I can understand how they will get warmer than the fronts but it does seem too much. If something is wrong it is most likely the pad backing plates which only just fit so could be catching especially if they swell when they heat up. A file to the edges might be the cure.