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- 2022 2.5GT
Well look, all these car manufacturers doing millions of dollars worth of development work have arrived at a point where these cars meet all the legislation on braking, are easy to assemble and dont raise any warranty issues. They use normal cast iron discs, they choose an appropriate pad and work with a system supplier for the hydraulics and calipers. The best thing anybody can do in my opinion is to follow what they did to arrive at this specification. That means that if you need to renew any parts, use a decent aftermarket cast iron disc, one of the branded pads (buy Mazda if in doubt) and follow the guidelines for fitting the parts. Do not use copper based grease - normal high melting point bearing grease is much better.
To answer some of these individual questions.........
Can you use Textar pads? Yes, they are first rate pads and having the German trait of being fairly abrasive will keep the discs in good condition and although you can expect some disc wear, they actually machine the disc true and minimise brake judder.
murky - yes it holds true. If you are fitting new pads to old discs, they need to be inside the limit for thickness and flat enough that the pads make good contact. If they arent, I personally would just stick some new discs on. They are quite cheap and very easy to fit on a modern car. New pads will bed quickly to new discs and meet performance standards straight out of the box. Using old discs will still meet the standards unless they discs are very poor but then other aspects change. Keep in mind that friction is independent of area so if you were to cut a pad down to one tenth of its cross sectional area it will still stop the car in exactly the same way. What it will do is to get very hot very quickly and that effects the rate of wear. The same applies to badly worn or scored discs. If the pad only contacts high spots, it will still stop for a short while but then the contact areas will carbonise and performance will drop off. You guys seem to favour skimming (machining) discs. I question the value of it but as long as it is done right, OK. Like I said, if mine are worn I just put new ones on.
Another consideration is this rate of wear v temperature thing. There is a non linear relationship between temperature and wear. I cant think in degrees F but normal everyday driving will generate about 150-250 deg C. At those temps, you will get very good pad and disc wear - maybe 50000 in a hypothetical situation. If you drive the car hard, live in a very hilly area or carry a heavy load, you will push those temps to double the normal but wear increases exponentially. That might mean only 10000 miles pad life. If you drive like miss daisy, and halve normal temps you could push life out of the roof and get astronomic life but that gives other problems like judder (due to debris not being burned off the disc), poor performance (as the pad doesnt get conditioned and clean off wear debris) and also you tend to get the guide pins seizing up and the pads sicking in the calliper which compounds the situation. The brake is like a garden gate - use it and it will work fine but only go through once in a blue moon and it will start to stiffen up! In summary, the brakes work best when they see temperature and occasional temperature spikes to burn a bit of rubbish off. Vehicle manufacturers do not concern themselves over pad and disc life as long as it is reasonable". However, the demands on performance keep increasing and legislation forces narrower goalposts. They will test the brakes to destruction and they must remain consistent. Modern disc brakes are capable of some astonishing performance without resorting to a racing specification. You can fully load a modern car, put it on a track and knock hell out of the brakes. Because unlike drum brakes, they have a linear output (no self servo action), you can get them up to ridiculous temperatures where they disc and pad is bright yellow. The rubber parts will catch fire and drop off but the car will still stop. That applies to a BMW 7 Series, a Merc SLK and a Mazda CX-5. You would be amazed at what it will do if you subject it to abuse.
So then on to this brake judder discussion. You have to think like a vehicle manufacturer. They want the brakes to work well and they do not want warranty issues that cancel out profit at the drop of a hat. Modern brakes are quite simple. The disc has evolved into something quite reliable and it doesnt need much special treatment. Unobtanium is passionate about wheel not torque and within reason that holds true but look at a modern hub, a modern disc and a modern wheel and they are all designed to be thoroughly compatible. If they are all clean, they will all clamp up snug with absolutely no cause for judder. I personally doubt that reasonable variation ( a mechanic using a wheel brace) would be an issue although air guns are the work of the devil as far as brake engineers are concerned. I use a Milwaukee 18V gun to take nuts off but I only run nuts back on until the very first click of resistance. The rest is done by hand with a torque wrench. However, the type of judder some people are talking about is not from day one due to badly installed discs, it is after a period of duty where the judder starts to develop and particularly under pressure or speed. This is the kind of judder that needs to have the disc machined or renewed. Why does it happen on a CX-5 and not a BMW? I said about half a mile further up the thread, that disc run out is very rare. Run out means that the disc is warped but both sides are warped equally and the disc sways side to side like a pringle with any number of phases. What is not unusual is DTV (disc thickness variation). This is where both sides of the disc are untrue but out of phase. It is almost certainly caused by a phenomena call depositing. This is where some friction material gets left on the disc due to low temperature (not burning it off) or low pad wear (not abrasive enough). A BMW has very aggressive German friction material that is not only high in friction but abrasive enough to self true the disc. The Germans dont give two hoots about wear debris blacking the wheel. The car may also be driven harder that the average SUV. I never have problems with my CX-5 but I do push the brakes. In another situation, the brakes might not see much duty, not much resultant temperature and not generate enough wear to keep the disc clean and true. The fix? Stick some aggressive pads in (we have loads of choice here but Im not familiar with your brands), get the duty up and work the brakes a bit harder or just put up with it and sort the discs out every now and then. Just to close, be wary of brand names. A lot of these brands are only packaging names and often do not make or develop pads. TRW do not make friction material, they buy it in. I wouldnt pay extra for things like slotted or drilled discs or ceramic pads. Id rather at least follow convention with cast iron discs and regular steel based pads.
Does that answer some questions?
To answer some of these individual questions.........
Can you use Textar pads? Yes, they are first rate pads and having the German trait of being fairly abrasive will keep the discs in good condition and although you can expect some disc wear, they actually machine the disc true and minimise brake judder.
murky - yes it holds true. If you are fitting new pads to old discs, they need to be inside the limit for thickness and flat enough that the pads make good contact. If they arent, I personally would just stick some new discs on. They are quite cheap and very easy to fit on a modern car. New pads will bed quickly to new discs and meet performance standards straight out of the box. Using old discs will still meet the standards unless they discs are very poor but then other aspects change. Keep in mind that friction is independent of area so if you were to cut a pad down to one tenth of its cross sectional area it will still stop the car in exactly the same way. What it will do is to get very hot very quickly and that effects the rate of wear. The same applies to badly worn or scored discs. If the pad only contacts high spots, it will still stop for a short while but then the contact areas will carbonise and performance will drop off. You guys seem to favour skimming (machining) discs. I question the value of it but as long as it is done right, OK. Like I said, if mine are worn I just put new ones on.
Another consideration is this rate of wear v temperature thing. There is a non linear relationship between temperature and wear. I cant think in degrees F but normal everyday driving will generate about 150-250 deg C. At those temps, you will get very good pad and disc wear - maybe 50000 in a hypothetical situation. If you drive the car hard, live in a very hilly area or carry a heavy load, you will push those temps to double the normal but wear increases exponentially. That might mean only 10000 miles pad life. If you drive like miss daisy, and halve normal temps you could push life out of the roof and get astronomic life but that gives other problems like judder (due to debris not being burned off the disc), poor performance (as the pad doesnt get conditioned and clean off wear debris) and also you tend to get the guide pins seizing up and the pads sicking in the calliper which compounds the situation. The brake is like a garden gate - use it and it will work fine but only go through once in a blue moon and it will start to stiffen up! In summary, the brakes work best when they see temperature and occasional temperature spikes to burn a bit of rubbish off. Vehicle manufacturers do not concern themselves over pad and disc life as long as it is reasonable". However, the demands on performance keep increasing and legislation forces narrower goalposts. They will test the brakes to destruction and they must remain consistent. Modern disc brakes are capable of some astonishing performance without resorting to a racing specification. You can fully load a modern car, put it on a track and knock hell out of the brakes. Because unlike drum brakes, they have a linear output (no self servo action), you can get them up to ridiculous temperatures where they disc and pad is bright yellow. The rubber parts will catch fire and drop off but the car will still stop. That applies to a BMW 7 Series, a Merc SLK and a Mazda CX-5. You would be amazed at what it will do if you subject it to abuse.
So then on to this brake judder discussion. You have to think like a vehicle manufacturer. They want the brakes to work well and they do not want warranty issues that cancel out profit at the drop of a hat. Modern brakes are quite simple. The disc has evolved into something quite reliable and it doesnt need much special treatment. Unobtanium is passionate about wheel not torque and within reason that holds true but look at a modern hub, a modern disc and a modern wheel and they are all designed to be thoroughly compatible. If they are all clean, they will all clamp up snug with absolutely no cause for judder. I personally doubt that reasonable variation ( a mechanic using a wheel brace) would be an issue although air guns are the work of the devil as far as brake engineers are concerned. I use a Milwaukee 18V gun to take nuts off but I only run nuts back on until the very first click of resistance. The rest is done by hand with a torque wrench. However, the type of judder some people are talking about is not from day one due to badly installed discs, it is after a period of duty where the judder starts to develop and particularly under pressure or speed. This is the kind of judder that needs to have the disc machined or renewed. Why does it happen on a CX-5 and not a BMW? I said about half a mile further up the thread, that disc run out is very rare. Run out means that the disc is warped but both sides are warped equally and the disc sways side to side like a pringle with any number of phases. What is not unusual is DTV (disc thickness variation). This is where both sides of the disc are untrue but out of phase. It is almost certainly caused by a phenomena call depositing. This is where some friction material gets left on the disc due to low temperature (not burning it off) or low pad wear (not abrasive enough). A BMW has very aggressive German friction material that is not only high in friction but abrasive enough to self true the disc. The Germans dont give two hoots about wear debris blacking the wheel. The car may also be driven harder that the average SUV. I never have problems with my CX-5 but I do push the brakes. In another situation, the brakes might not see much duty, not much resultant temperature and not generate enough wear to keep the disc clean and true. The fix? Stick some aggressive pads in (we have loads of choice here but Im not familiar with your brands), get the duty up and work the brakes a bit harder or just put up with it and sort the discs out every now and then. Just to close, be wary of brand names. A lot of these brands are only packaging names and often do not make or develop pads. TRW do not make friction material, they buy it in. I wouldnt pay extra for things like slotted or drilled discs or ceramic pads. Id rather at least follow convention with cast iron discs and regular steel based pads.
Does that answer some questions?
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