Rear brakes issue
-
? okay so question… why not put drilled discs on a road car? is this due to the lack of heat?
-
@e76fc9e6ac=jamesshack:
? okay so question… why not put drilled discs on a road car? is this due to the lack of heat?
**No. It's because they bring no benefits and some quite major downsides.
I might go a bit "suck eggs" here, so I apologise if you know this already… The primary job of any brake disc is to conduct heat from the friction of pad on disc throughout its body, so that the pad/disc contact doesn't get excessively hot (otherwise the contact isn't as efficient - brake fade), then radiate/convect it away. The secondary job is to provide a surface for the pads to grip. So a good disc is a big slab of very conductive metal and which can get very hot without deteriorating.
With that in mind, let's crack on to what drilled discs do/don't/are supposed to do:
Oft-posited benefit 1 - Drilled discs dissipate heat better
Nope. Discs are made of iron. Iron conducts heat very well, making the heat spread evenly and quickly through the disc, whereupon it can be radiated/convected away. Holes in that are made of air. Air is an insulator. Heat does not spread evenly and quickly through the disc.Oft-posited benefit 2 - Drilled discs effectively remove gas that builds up between disc and pad
Bollocks. Pads haven't outgassed since the 1950s. They're made of steel and copper now. They used to be made of asbestos and glue - heating the glue generated small amounts of gas which could prevent the pad contacting the disc properly. Doesn't happen now, so… what gas?Oft-posited benefit 3 - Drilled discs remove brake dust more effectively
Maybe. But why is brake dust bad?Actual benefit 1 - Drilled discs run cooler
True. They have great big holes in them, through which air can flow. This gives them a slightly higher specific heat capacity - they can hold slightly less heat because there's less metal, but their base temperature is lower. If this particular issue becomes life-or-death on your road car, please surrender your licence before you kill someone.Actual benefit 2 - Drilled discs are lighter
True. Air weighs less than iron. But come on. On a race car where every gram counts, yes - and we are talking grams here.Problem 1 - Drilled discs have less swept area
Yep. Where your pad contacts the disc is what stops the car. Holes don't stop your car. Again, this shouldn't be massively significant on a road car unless you're driving like an arse. On a racer, the benefits of specific heat capacity and weight outweigh the reduction in swept area.Problem 2 - Drilled discs can be badly made
Ooooh yeah, big check on this one. Not such a problem with solid discs, like the MX-3's rears, but with vented ones, very much so. It's amazing how many drill patterns wholly fail to take account of vent patterns - look closely at some cheap discs (or, heaven forbid, homemade ones) and you can see they have drilled clean through a vane inside the disc.Problem 3 - Drilled discs are fragile
Iron is stronger than air. A 10" disc of iron is stronger than a 10" disc of iron with holes in it. But that's not the half of it - discs that are actually drilled (rather than cast with the holes in place - like Porsche's carbon-ceramics) are a catastrophe waiting to happen. Drilling into the metal changes the structure of the crystals around the hole, not only due to cutting them, but the heat generated in the action of drilling. Every single hole drilled in a disc is an added stress point, which you're asking to withstand a tonne of car at 30 metres per second, regularly, and then, because air is an insulator, they become hot spots on the disc. This is a fantastic recipe for shattering a disc. And it happens.So you have a slightly lighter disc which runs a bit cooler than a solid/grooved one. This is good for a racer. You also have a load of stress points and hot spots. This isn't good for a racer, but they only need the disc to last 200 miles and for 400 stops - YOU need it for 60,000 miles and tens of thousands of stops. They don't dissipate heat better and there's no such thing as outgassing pads unless you've come through time in a Frazer-Nash. The benefits are marginal (or fictional) and the potential problems are colossal. Wouldn't touch them on a road car for any reason.
Incidentally, similar things apply to the benefits of grooves, but grooves are all cast and none of the problems apply. I'd put grooves on my car - particularly if the prices are very close - and have. And will again.**
-
Excellent write up there Famine…
I once used a set of drilled discs on a ford ...needless to say they cracked badly so from there on ive used groved discs since but on replacing the disc on the 3 ive stuck to std ones.....
-
FOR SALE
brand new not even recieved yet set of crappy impulse purchase waste of money discs!
Okay I get that they are basically gonna be binned after a few weeks of use cause i drive a damned far distance at high speed daily getting to work, suppose they'd be no issue if i used her as a shoppin trolley…..
before i buy anythin else for my mx i am gonna be bugging u guys for whats best i think......
-
lucky you guys know this cause i was about to order the front set!!!!!!!!!!!!!
-
@43af4feca8=jamesshack:
FOR SALE
brand new not even recieved yet set of crappy impulse purchase waste of money discs!
Okay I get that they are basically gonna be binned after a few weeks of use cause i drive a damned far distance at high speed daily getting to work, suppose they'd be no issue if i used her as a shoppin trolley…..
before i buy anythin else for my mx i am gonna be bugging u guys for whats best i think......
**On the back it probably won't be such an issue. FWD cars have heavy front brake bias and, frankly, the rear discs are just for show. Sports cars with rear drums don't sell well :lol: If you're not shovelling a lot of heat through them, then there'll probably never be an issue.
You also won't run into the problem of drilling through vanes - it's not a vented disc, so no problem.
And since the problems are much more diminshed, at least you have lightweight rear discs :lol:**
-
Just to provide some balance to this…
I've had my drilled and grooved discs on my daily driven ZE car since it was on the road. Same discs for just under 2 years so far. I've had no problems, no cracking, no premature fatigue, no stress cracks. All that plus the big brakes/twin pots from the xedos 9. I've seen one of them glow with heat when my wheel bearing failed and still fine. I bought them for looks and I got a good deal. However if I were to buy again I would buy solid, grooved or grooved and dimpled, because given the choice it's not worth the risk.
-
@e558373c04=Marco:
Just to provide some balance to this…
I've had my drilled and grooved discs on my daily driven ZE car since it was on the road. Same discs for just under 2 years so far. I've had no problems, no cracking, no premature fatigue, no stress cracks. All that plus the big brakes/twin pots from the xedos 9. I've seen one of them glow with heat when my wheel bearing failed and still fine. I bought them for looks and I got a good deal. However if I were to buy again I would buy solid, grooved or grooved and dimpled, because given the choice it's not worth the risk.
I think cracking with cracking brake discs is a lot about the quality of the metal and manufacturing along with driving styles !!!
OK back to the start, you have bought some drilled discs put them on try them no point buying some others and having them sat around or losing money on them, I doubt you are going to be heavy braking into a right hander from 120mph on the way to NETTO's because they have a special on imported chicken livers.
Because to be honest anyone who reads this is now not going to buy your discs LOL.
I am sure they will be fine as they are rears and wont get the punishment the fronts do, bang a new set of pads in and grease it all up or even invest in a pin kit that will replace all the parts that get worn on the calipers without buying new calipers then you have pretty much a new set of brakes
-
its all good, makin these mistakes is part of me getting the hang of getting this car healthly and happy again.
many thanks for all your input
-
@880f00649f=djmarcopolo:
Because to be honest anyone who reads this is now not going to buy your discs LOL.
**Well, that's certainly true :lol:
It's by no means certain that drilled discs = problems. There's just a lot more potential for problems to occur. You could easily get a normal disc from a shart batch accidentally made from plastic but, on the whole (no pun intended) normal/grooved/slotted > drilled.
As they're on the back, the forces involved are significantly less, minimising your risk pretty much as far as it'll go. In all likelihood, the biggest problem you'll have is explaining why the backs are drilled and the fronts are not. You can say that they're lightweight, racing discs to minimise unsprung mass because the back doesn't need as much braking force. It'll fool most people who ask :D**
-
I spoke to the guy i bought them from and he has shipped them already so too late to change them to grooved….
I figure i will fit them, and when they go I replace them hopefully without much damage to the rest of the hub, now could you tell me if the pin kits are car specific or can i get them from halfords os some place?
-
also…... the little spring magoo thingy were do i get them? or like get a really long paper clip :?
-
@4a1d076a6a=jamesshack:
also…... the little spring magoo thingy were do i get them? or like get a really long paper clip :?
The springs will come with your new brake pads usually, also there is no pin kit for the rear of these, they are quite basic at the back but you can get new bolt kit for them. If they come off ok then keep the originals, if they are a mare to remove then its worth changing them in case you have damaged them, you will have to get them from a motor factors or spares shop, halfords will only stock them if they come with a big sticker with "power force brake power fitted" in the pack
Remember, put copper grease on the bolts you remove, the REAR of the pads (metal side) and on your wheel studs
Here is also a link for the pin kit if you are putting new pads in the front, it will be the best £7.50 you have ever spent on your old brakes when you put in new pads
http://www.fordprobestore.co.uk/store/product_info.php?products_id=754&osCsid=62731669fd84b5a224d91bd8b15a3605
-
and finally, a step by step idiots guide to the removal of the rear calipers, I have had a good look and i am a bit concerned that the small clips could break or bend out wrong…
I know its a lot to ask but you guys seem to know your chicken livers..
-
The rears don't need removing. Undo the top bolt (12mm? I think) and hinge the caliper forwards. The pads will come out with some persuasion.
-
that seems so simple even i could do it and from rereading the responses the discs should just slide off?
roll on the weekend will let you know how i get on….
-
@2d4c4f5b9c=jamesshack:
that seems so simple even i could do it and from rereading the responses the discs should just slide off?
roll on the weekend will let you know how i get on….
To remove the rear caliper undo the 2 bolts that go through the black bits either side that you can see on the inside of the discs and then just let it hang no need to undo everything else and because the hubs have studs fitted the discs are held on with the wheel nuts
-
utter genius! so much thanks!!! :D :D :D
-
Couple of things:
If you just bought them you have a 14 day cooling off period so send them back.
When putting new pads on get a brake pad fitting kit, CES UK usually stock them only £5 think they deliver nation wide now. Its a right pain when old pad springs snap ( seen them get stuck and wreck a disk )
Don't go mad with coppergrease and where gloves or use a brush as its not good for you through skin contact.
-
Again many thanks for all ur input :D
