Thank you so much for your detailed reply and advice - that is very helpful. I've got a plan now!As Mike says above, it's almost impossible to guess how long a particular set of pads is going to last, just too many variables. I've tried to be "helpful" in the past when asked by a valued regular customer and then subsequently catching a big cold when they turn up on the forecourt with a "horrid grinding noise". It's worth also considering that many mechanics will recommend a pad change some time before it's strictly due in order to avoid exactly that problem. Also, with long service intervals now a days, many will recommend a pad change even though plenty of material is still present because they feel they genuinely can't be sure the pads will last another year, 18 months or two years or whatever until the car is next in the workshop.
People such as us can do an inspection whenever we like so allowing us to get a lot more life out of our friction materials. I'd caution against trying to run things too close to the bone though, personally I'd not go much below 3mm and I wouldn't be setting off on one of our trips to "the deep south" unless my pads had considerably more than that on them.
Thickness of new pads does vary a bit - I'm not really in the habit of measuring new pads so can't be specific and I wouldn't be surprised to find they vary a bit from one manufacturer's vehicle to another - ie. thickness on a Jag or Range Rover might be different to a Mini or Seat Ibiza? However I'd take a guess (Mk 1 eyeball) that, on common every day stuff, it's going to be around 1/2" (13mm) give or take. One I did recently was my older boy's Punto (see pictures above near the beginning of this trhread). I serviced it towards the end of last summer - when it was still nice and warm weather wise - and noticed the pads were low enough for me to say to him that we ought to be doing them "soon". The Punto is his daily work car doing a half hour there and half hour back journey into the city roughly 5 days a week (he does shifts) with one very steep hill of approx a mile in length which has traffic lights at the bottom so needs a hard stop at the bottom of the hill so not all that friendly for the brakes. He eventually let me have the car to do the brakes about a month ago and I doubt if it had taken more than around a mil off the pads in that time. I just measured them (they are still in my box of stuff to go to the recycling centre) and they've got about 4mm still on them and, although they would have done another month or so, I'm very happy we changed them when we did. Why? because you have to be aware that when the friction material gets very thin it doesn't deal with the heat so well and will fade more quickly under arduous conditions. It's also more likely when the friction material is thin and especially if the pads are quite old - I suppose maybe over 6 or 7 years since fitting, but difficult to be specific, let's just say "old" as in "not in the first flush of their youth" that the friction material may separate from the metal backing and give you instant metal to metal contact, which will quickly ruin the discs to say nothing of reducing braking efficiency!
So if a new pad has around 13mm (1/2") of friction material and yours were reported with 6mm still on them it's tempting to think of them as half worn? But no! If we take it that they need changed when they get to around 3mm then at 6mm they are 2/3 done, yes? so still got quite a bit of safe running in them - my boy would have gone through to next summer if his had measured 6mm at the end of last summer - so no need to "panic" immediately but a check after a month or so and compare how much has degraded in that time against how much is left will give you an indication of how long you can afford to leave them. Oh, and remember to check the pad depth on all 4 pads because wear can be uneven due to differing disc surface smoothness and stuff like siezed/partly seized caliper sliders and pistons etc. It's not all that unusual to find inner pads wearing quicker than outers so don't just look through the weel spokes at the outer pads on each side and assume the inners will be worn the same.
When I was younger it was much more of a thing to regularly check pads because if you caught it early enough all you would need would be a set of pads and it was not unusual for you to get two or even three sets of pads worn out before a disc change was needed. Today it's not all that unusual to change discs and pads as a set every time and certainly you'll be very lucky to get more than two sets of pads worn out before renewing a disc.
Technical Brake disc, a ring of rust
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Technical Brake disc, a ring of rust
Thank you so much for your detailed reply and advice - that is very helpful. I've got a plan now!
That disc is in a pretty poor state. You may think the brakes are Ok but you'll get a shock if you have to do a bit of serious emergency braking. It's only the bright shiny bits that are doing any braking so i guess only about 50% of that side of the disc is effective. It's not unusual to find the back of a disc is in worse condition than the front so I think someone should take a look at the other side of that disc right now. If it was my car I'd be putting new discs and pads on it tomorrow.
Sorry if that sounds a bit alarmist and it is a bit difficult to give an opinion based on just one picture, but i really don't like what I see here. The whole of that face, including the rusty bits, should be bright and shiny.
Sorry if that sounds a bit alarmist and it is a bit difficult to give an opinion based on just one picture, but i really don't like what I see here. The whole of that face, including the rusty bits, should be bright and shiny.
Here's the one on the Mazda:
and with the wheel off:
Of course these pictures are of a brand new disc just after fitting but a used disc in good condition shouldn't really look very different. Yes there might be a bit of a lip on the outer edge and a bit of rust around the hub in the middle where the wheel studs are, but the bit where the pads grip the disc face should be bright and shiny.
Ah, here's a picture of one of the old discs which I removed because it was worn too thin. You can see though that the face where the pads rub is still nice and shiny:
The pads can only grip the shiny bits, the rusty bits just act like a cheese grater and wear away the pad without giving any braking effect.
and with the wheel off:
Of course these pictures are of a brand new disc just after fitting but a used disc in good condition shouldn't really look very different. Yes there might be a bit of a lip on the outer edge and a bit of rust around the hub in the middle where the wheel studs are, but the bit where the pads grip the disc face should be bright and shiny.
Ah, here's a picture of one of the old discs which I removed because it was worn too thin. You can see though that the face where the pads rub is still nice and shiny:
The pads can only grip the shiny bits, the rusty bits just act like a cheese grater and wear away the pad without giving any braking effect.
Mike1alike
Established member
Yeap, that disk looks totally worn out.
Yes 100% agree with previous comments, also I would say looking at the rust groove in the centre of the braking area, in it's past the brake pads have been allowed to go down to the metal.
The rust area on the edge is more common and if not attended to gradually takes over the contact area reducing efficiency, but the bit in the centre is purely bad practice when the brake pads were so badly worn to the metal they were replaced but not the brake discs which should have been as well.
The rust area on the edge is more common and if not attended to gradually takes over the contact area reducing efficiency, but the bit in the centre is purely bad practice when the brake pads were so badly worn to the metal they were replaced but not the brake discs which should have been as well.
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Tipotwo
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Emergency braking has been fine. From the time I got the car, the rear pad does not sweep the whole of the disc. The first service I got included skimming the rust off, which the dealer said was normal. They charged me £70, it did nothing to braking performance and the rust was back within a week.
I will get it checked.
Do others have the same ring of rust on their rear discs?
Please take a trip over to the "not grumpy but not smile" thread and see the images I've recently posted as a result of the brake work I did yesterday on my Ibiza. I'm actually quite shocked that your dealer thinks your discs are acceptable. Yes, chipping (not quite sure what they mean by "skimming") off mild rusty bits on the outer edges of a disc is not an unusual practice. mostly done to reduce the possibility of rubbing/grinding noises, but that's a very different thing to trying to "skim"? or buff off widespread corrosion on larger areas of the surface of the disc. I'd be very interested to see what figures your discs would produce on a brake test machine.
Please don't think I'm in any way "having a go" at you. I'm genuinely concerned about you running about with discs that look like that - if the other 3 are in similar condition the vehicles braking must be impaired and you run the risk, if in an accident, of the vehicle being declared unroadworthy which would cause you no end of problems.
Nope see my pics on the first page on what front and rear look like on my car
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An update to the thread. After a few weeks of checking every Tipo I could find, realising many have drum brakes, not discs, I saw only one other with a ring of rust, that was for sale at Arnold Clark Jeep dealership, Linwood. The salesman who saw me and obviously thought I was interested in the car, said he was not aware of any issues. That car's ring of rust was not as large as mine, so I did go ahead with new discs and pads.
It has made no noticeable difference to braking performance, but if I had left it, the garage I use would have failed it on its next MOT. I wonder if an underperforming disc is as good as a drum brake and the Tipo is also available with drums.
It has made no noticeable difference to braking performance, but if I had left it, the garage I use would have failed it on its next MOT. I wonder if an underperforming disc is as good as a drum brake and the Tipo is also available with drums.
You've done the right thing, those old discs were horrid.
Most of the braking effort is provided by the front brakes, so, as long as your front discs and pads are in reasonable condition your brakes will feel good in everyday driving even if the rears are in poor order. Hand brake holding under duress. perhaps on a steep incline? could be much more of a problem.
If we were talking about front brakes here I'd say discs will win over drums pretty much without question. Mostly because they can deal with heat much more effectively so will tend not to suffer fade when braking repeatedly from high speeds - for instance in heavy motorway traffic - or when descending long steep hills. However here we were discussing rear brakes and, except on very high performance vehicles, the performance advantages you get from a disc, on the rear, are far less needed. I think the main reason why disc rear brakes have become popular is that they are easier to service thus cutting down on labour so the manufacturer can claim lower running costs in their advertising - cynical old me? - They are also arguably easier to "motorize" so they can be driven by an electric parking brake. Performance wise, because they don't do as much as front brakes and thus tend not to suffer from over heating I think there's little to be gained in performance with a disc on the rear. Personally I'd prefer a drum because, when you're doing your own servicing, they are so much cheaper to sort out when they go wrong - compare the price of a caliper vs a cylinder. Unfortunately the self adjusting mechanisms on drums are often a cause of problems but seldom need parts to sort out whereas when calipers stop self adjusting you're often buying a new caliper. The big thing for me though is, as you've discovered, rear discs rust something rotten (pun intended). I believe this is due to the fact they don't have much work to do so don't get "cleaned up" so well by the pads acting on their surfaces but also because all the road grit, water and road salt, which gets turned into a very effective atomized spray by the front wheels, gets sprayed all over the unprotected disc surface and remains, often, still damp when the car is parked - Voila, ideal corrosion conditions! The drum, on the other hand, doesn't have to put up with this as both linings/shoes and friction surfaces are enclosed and protected from the spray. Just remember, if you have drums, to file/grind off the lip which develops with time and use on the inner rim of the drum as this makes it so much easier to remove the drum next time you're in there.
At the end of the day though this is all highly speculative stuff because you're stuck with whatever the manufacturer fitted to the vehicle and you've just got to do whatever is necessary to sort it out when there's problems.
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I became a bit of a drum brake expert, as my first car, an Astra, had drums that kept rusting and seizing. I lived next to the sea, which did not help. The local AA man, who I knew anyway, showed me what to do, so I ended up with properly adjusted, clean drum brakes. That came in handy for my first motorbike, which also had a rear drum brake.
The Panda Nut
Nutty about Pandas Infected by Panda virus and OPD
Your doomed to it! MY THEORY... is on the slider pins are rubber collars. They go soft the caliper twists under loas as the rubber gives more than it should and the brakes apply uneven pressure on the pads facilitating rusting. If the brakes work it will not fail the MOT. I dont know the answer it affects a lot of cars. Only ever use specific brake grease never copper based on such things. I am sick of paying for parts on our Panda. We have a 21year old Seat that doesnt do this. Im thinking of finding softer brake pads to see if this will help.
On customers cars where edge of disc started to form rust scale I used to tap it off gently with a hammer when servicing cars as if left on it gradually migrates towards the rest of the disc /pad contact area meaning they have to replace discs.
It's not a terrible problem down here I suspect as we get milder Winters with less road salt used.
When the discs rust like that, there is usually a corresponding chunk missing from the pads, so even if you remove the rust from the surface of the disc you still need to replace the pads.
Discs and pads wear together the rust tends to be harder for the pad to remove and wear away and the rust then gouges a chunk out of the pads.
You can resurface discs as long as they stay in the thickness limits of the disc (usually written somewhere is a minimum thickness) but very little point in doing this on cheap cars with cheap discs. far cheaper and easier to replace them, but resurfacing is much more common on expensive sports cars and super cars that use steel brake discs.
Discs and pads wear together the rust tends to be harder for the pad to remove and wear away and the rust then gouges a chunk out of the pads.
You can resurface discs as long as they stay in the thickness limits of the disc (usually written somewhere is a minimum thickness) but very little point in doing this on cheap cars with cheap discs. far cheaper and easier to replace them, but resurfacing is much more common on expensive sports cars and super cars that use steel brake discs.
Normally I would agree with you, but as in many cases the new brake pads on a new disc don't reach the edge of the disc which is why the rust starts to form as the pad doesn't sweep that area and clean it off at the start and then progressively rust forms and works onto the pad contact area.
I agree where the new pads go to the edge of a new disc it would be as you say as braking efficiency would be affected by the reduced contact area.
Definitely true many cars have discs bigger then the padsNormally I would agree with you, but as in many cases the new brake pads on a new disc don't reach the edge of the disc which is why the rust starts to form as the pad doesn't sweep that area and clean it off at the start and then progressively rust forms and works onto the pad contact area.
I agree where the new pads go to the edge of a new disc it would be as you say as braking efficiency would be affected by the reduced contact area.
I see what you're saying there is always that tiny bit of overlap at the edge where the pad doesn't read. I suppose what I am saying is where rust forms in the sweep of the pads. you can remove the rust but if you don't replace the pads, the old pads will have chucks out of the braking surface that do not contact the new clean disc surface and therefore the rust soon makes it way back to those areas.Normally I would agree with you, but as in many cases the new brake pads on a new disc don't reach the edge of the disc which is why the rust starts to form as the pad doesn't sweep that area and clean it off at the start and then progressively rust forms and works onto the pad contact area.
I agree where the new pads go to the edge of a new disc it would be as you say as braking efficiency would be affected by the reduced contact area.
Doses that make sense? it does I think in my head anyway.
Anyway, the way to avoid this is seems is now many new discs are coming coated with some sort of silver zinc coating which doesn't allow the rust to start on the edges.
We are all on the same page Andy, any rust on the pad contact area the rust will always win, gradually expanding to the point the pads have no shiny contact area to even try to function on, long before that time, the Mot tester or service mechanic should have picked it up.
It is amazing to see the poorly functioning brakes on some cars. Over 30 years ago when my two youngest (twin girls) were being born my wife talking to the lady in the next bed to hers mentioned I was a motor engineer and arranged for her father to drop her Austin Maxi car to me to check the brakes as they were pulling to one side. Once the wheel was off I couldn't believe what she had been driving on, the brake disc had broken away from the driving flange completely, so the pads could grip the disc tight but not affect stopping one iota, consequently the car pulled violently to one side on braking. I showed this to her father/grandfather of new baby shortly to be driven in the car and he refused to have the work done, even though I was so concerned I offered to fit the parts free, just the trade price of the materials. He then took the car away, I issued him my normal invoice stating exactly what was wrong with the car and how dangerous it was, with no charge for my time , purely for my records if there was a subsequent accident and it was suggested it had been to me for repair. I also got my wife to tell the new mother how dangerous her car was!!!
there is a section of Reddit called “askamechanic” which obviously gets a lot of posts from the USA where in many states there is no formal road worthy-ness testing, and so you see some truly horrific things with questions along the lines of “is this a problem”
A recent post I saw asked if “cracks” in a chassis could be welded but the pictures posted showed a chassis rail that was 98% rust and the “cracks” were where there was no longer any metal.
A common one you see are brake discs where the disc has been so worn down the fins in the vented part of the disc have become exposed, or like your example the braking part of the disc completely detached from the hub. Other worrying examples show brake discs welded where cracks.
I’ve also seen LED light strips stapled directly to the fuel tank or mole grips used to pinch leaking break pipes then the grips just left in place with the car continuing to be used.
A recent post I saw asked if “cracks” in a chassis could be welded but the pictures posted showed a chassis rail that was 98% rust and the “cracks” were where there was no longer any metal.
A common one you see are brake discs where the disc has been so worn down the fins in the vented part of the disc have become exposed, or like your example the braking part of the disc completely detached from the hub. Other worrying examples show brake discs welded where cracks.
I’ve also seen LED light strips stapled directly to the fuel tank or mole grips used to pinch leaking break pipes then the grips just left in place with the car continuing to be used.
