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Paul Beazer
24-01-2005, 11:11 PM
I have recently spent a lovely saturday fiddling about with my brakes / disks. Basically just cleaning off some rust around the inner and outer edges where it had built up a bit. My main concerm is regarding the rear disks themselves. The wear pattern was such that rather than having a 2" shiney surface I had a 1" surface with about 2/3" on the inside as rust and about 1/3" on the outside. Obviously this means that there is nearly 50% braking surface that wasn much use! I carefully chipped off the rust on both inner and outer edges (the inner had built up to 2mm in places) Obviously its going to take a bit of time for the pads to wear in to the rustless disks, but im hopeful this will help the rear brakes to work more efficiently.
Can anyone shed any light on why the rust had built up so much in the first place? I thought the pads as they wore down would "polish" the braking surface and prevent such build ups? Would it be worth getting the disks "skimmed" to tidy them up, or will the pads start polishing again? Or do i really need to replace the pads and disks as a set? :dozey:
Kieran???
Help!

Paul

PS They do seem to have a bit more "bite" than before!
PPS Its a 2000 V6 Sport in case that helps!

Kieran
24-01-2005, 11:25 PM
Hmm....

When you say 'Inner' and 'Outer', do you mean each side of the disc, or just the top and bottom one one side?


If you mean that both sides of the disk (ie, the one facing outwards and the side you can't normally see), then I would change the pads and have the discs skimmed.... If they're pitted, the pads will never get an even contact on the disc again, even if you do chip the rust off. It may also be worth making sure that the caliper assembly is 'floating' properly and that the pistons aren't stuck.

I did an article about the rear brakes some time ago, but it's in the member's area.... They're not difficult to strip though. :)

wirdy
24-01-2005, 11:36 PM
Your rear calipers sound like they're seized Paul. That would give the wear symptoms you describe.

Did you undo the pivot bolts and slide the calipers off to clean up the disks?
If the ridge is 2mm as you say then I fear you need some new rears- fitting new pads to unevenly worn disks is a false economy. You may get away with a skim - check your owners manual for minimum disk thickness then get a vernier on the shiny bit of the disk to see if you've got enough material left to successfully skim down to.

The rears don't do a lot of braking compared to the fronts but you need to know they're there and functioning properly when you have that first 'fully locked up -ABS pumping- heart stopping-panic emergency stop'

In it's current state it would probably fail the MOT too. :sad3:

Paul Beazer
25-01-2005, 08:56 AM
Your rear calipers sound like they're seized Paul. That would give the wear symptoms you describe.



The rears don't do a lot of braking compared to the fronts but you need to know they're there and functioning properly when you have that first 'fully locked up -ABS pumping- heart stopping-panic emergency stop'

In it's current state it would probably fail the MOT too. :sad3:

Im pretty sure they arent seized, they're not dragging, but there is a fair amount of c**p on the calipers.
I dont need to worry about the MOT as it passed in the start of dec (Thanks Nick!)

Will need to look at a skim and new pads i think...... :sad3:
Paul

colVR4
25-01-2005, 10:43 AM
I had the same problem on my 2000 V6 Sport when I first got it, thin strip of braking surface on the rear disks. No problems since I changed to the new disks and pads. The only thing is that now when I put the brakes on at low speeds around town I can hear them hitting/slapping against the disks.
Do I need the calipers adjusting or is there something I need to get checked out?

wirdy
25-01-2005, 01:47 PM
Im pretty sure they arent seized, they're not dragging, but there is a fair amount of c**p on the calipers.
I dont need to worry about the MOT as it passed in the start of dec (Thanks Nick!)

Will need to look at a skim and new pads i think...... :sad3:
Paul

They won't necessarily drag Paul, it's not the brake pistons seizing that I meant, but the bolts that the caliper slides back-and-forth on. Mine were all seized and needed a good deal of freeing off to make smooth again. until you do this your brake caliper is acting like a trapezoid when you push the brake pedal down. If you get a vernier on your pads I'll wager they are not the same thickness across the whole pad?

Just a 19mm? (I think) socket to undo the pivot bolts (they're bloody tight though!) and some copaslip will put your mind at rest. You don't even need to remove the caliper, it stays in place if you just do one bolt at a time. I do mine every time I change the oil......it's a long story but one of my front bolts was seized and sheared off last year, so well worth the preventative maintenance.. takes all of 5 minutes to do the whole lot now, while the oil is draining.

Paul Beazer
25-01-2005, 06:26 PM
[QUOTE=wirdy]They won't necessarily drag Paul, it's not the brake pistons seizing that I meant, but the bolts that the caliper slides back-and-forth on.
Just a 19mm? (I think) socket to undo the pivot bolts (they're bloody tight though!) and some copaslip will put your mind at rest. QUOTE]

Already done! Mine were ok, although 1 bolt was a bit manky, but clean and shiny again now, with plenty of copaslip! Sheared bolts would be a nightmare!!

BTW its 17mm for the caliper bolts on the front and 14mm on the rear.
Yes you are correct the pads are now rather convex! They'l do for now though, will get some new disks and pad in the spring when the weathers better!
Any suggestions for good disks and pads? I gather EBC arent the ones to go for from other threads! I would rather stick with plain disks rather than drilled and grooved, unless they cost similar and offer some sort of advantage!
Paul

Big Ian
25-01-2005, 11:07 PM
there are a few make's for "after market" disc's and pad's..and also in the member's section you will find a few different shop's that supply a discount to club vr4 member's :D i'll also be up-grade'n my disc's and pad's soon (now that i'll be keeping it as my number 1 car?)

Kieran
25-01-2005, 11:14 PM
That's a point.... If you do change your pads/discs, consider upgrading them - the Standard V6 ones are ok, but you'll be amazed at the difference some uprated discs and pads will make! ;)

Paul Beazer
26-01-2005, 09:14 AM
there are a few make's for "after market" disc's and pad's..and also in the member's section you will find a few different shop's that supply a discount to club vr4 member's :D i'll also be up-grade'n my disc's and pad's soon (now that i'll be keeping it as my number 1 car?)

Think its about time I joined up proper like. Been frequenting these forums too long not to!

Cheers for the advise etc guys!

Paul

colVR4
26-01-2005, 10:38 AM
The Black Diamond pads and disks are good value. They have definately improved the stopping performance of my car. I would probably only go for the grooved in future though and not bother with the drilled.

I-S
26-01-2005, 10:46 AM
I have the drilled-only BD discs on the front, and will get the same for the rear at some point. The grooved will eat pads faster. The drilling should allow for some improvement in heat dissipation (since I had badly warped mitsu discs previously, I felt it worthwhile). The BD discs are cheaper than the mitsubishi ones.

colVR4
26-01-2005, 12:35 PM
I have heard mixed reports about drilled vs grooved. Apparently the drilled, unless done to a very high standard are at a greater risk of cracking under prolonged, heavy braking. I think that BDA had experience of this.

There are also reports that the drilled disks were designed to allow the release of gases vented off from the pads causing a cushion between the pad and disk degrading braking performance. With new pad design this is not a significant factor.

The grooved do eat pads, but isn't this due to them keeping the pads from glazing over from the heat build-up under heavy braking? I am sure that I have seen an article somewhere on the site about all of this.

Sorry if this is a bit off topic. I could be talking a load of hoop but I looked into it when I changed my disks and pads.

I-S
26-01-2005, 12:51 PM
There's reasonable arguments for both. For road driving I can't see grooves giving any benefit. I only went for drilled as the choice was between drilled, grooved or both, and it most closely matched my needs. I wasn't suggesting that grooved was the "wrong" choice, just giving what info I have.

I figure that there are reasonably sound reasons for drilled discs as they're standard on 911s, M3, etc. I don't for a moment think that my GLS is capable of placing the same demands on brakes as those cars (nor do I place strong demands on my brakes often), but if they keep warping at bay better than the mitsu discs, I'm happy. The better stopping power of the BD setup is a bonus.

Jimbo
26-01-2005, 11:50 PM
Over Xmas I "warped" my front discs, but not though heat build-up. I believe it was down to washing my wheels only an hour or so after driving the car and then leaving it standing for about a week in the garage.

Getting back into the car again and pulling off, I heard that horrible clunk noise as the pads released their grip on the discs and on inspection had left nice chunks of glazed pad on them making it feel very grabby under braking at all speeds.

Hopefully a few big decelerations will clean them off, but I won't be making the same mistake again. Decided it's better to go for a quick drive after cleaning the car to dry the discs and pads out after a major alloy-wheel cleaning session.

I-S
27-01-2005, 12:05 AM
"Warping" is a misnomer anyway. It's nothing to do with deformation of metal, but it's uneveness in the layer of pad material that is deposited on the disc during use.

The following is a piece I wrote on the subject that won me a writing competition on another car forum:


Warp Factor 9!

Warping... travelling faster than the speed of light, boldly going where.... hold on, wrong script.

In the real world (some trekkers, as they wish to be known, apparently have real problems with this concept, but that's besides the point), warping is simply the going out of the plane of an object that should ideally be flat.

A vinyl record should be flat. If it's warped, it doesn't play correctly. And the brake discs on a car should also be flat. If they're warped, the car doesn't brake correctly.

Hold up a minute. Whilst it is relatively easy to understand how 150 grams of vinyl in a 12" disc can warp, how does several kilograms of cast iron manage the same trick?

In truth, the term "warped disc" is something of a misnomer. If we take it to mean that the disc is not true (ie it is not flat), then it is a reasonable description, but it isn't by the same mechanism as the record. The metal of the disc does not warp.

The effect that causes a "warped disc" is in fact to do with the way that a disc brake works. There are two types of frictional force involved; abrasive friction and adherent friction. Abrasive friction is generally how we expect brakes to work. Pads rub on disc, scratching at surface (like a brillo pad), which turns kinetic energy into heat. Fair enough... we know that if we sand something with sandpaper, it gets hot.

However, this is only one method of creating friction with a disc brake. The other is Adherent Friction. As the pad contacts the disc, it leaves a small layer of pad material on the surface of the disc. Next revolution, this comes back into contact with the pad, and it generates a higher level of friction (as well as a lower disc wear rate).

Why does this work better? In molecular terms, abrasive friction is caused by the breaking of molecular bonds. Adherent friction is caused by the breaking AND formation of molecular bonds.

No brake pad works entirely by one or other method. Normal road-car pads are mainly abrasive, while racing car brakes are mainly adherent. Adherent pads don't work well when cold (we've all see the glowing F1 brakes... that's when they work best), and abrasive pads don't work well when they get hot.

Back to the warped disc, what actually happens is that the pad material that is deposited on the disc becomes unevenly deposited. This can be caused by sitting on brakes at a traffic light (so that the pad is clamped to the disc as it cools, so more material sticks at that point), or by letting the brakes get too hot, where the materials start to act in ways they shouldn't, and deposit themselves on the disc more heavily (and unevenly).

Although microscopically thin, this difference in deposition thickness becomes very noticeable, as the car will start to judder under braking.

Strangely, a method to lessen the effect of the warped disc is to go out onto a quiet country road, and stop the car hard a few times once you've got the brakes warm. This will even out the deposits on the disc somewhat (although not completely), and lower the effect.

However, just remember that no matter how good your brakes are, "I cannae defy the laws of physics Cap'n!".

Jimbo
27-01-2005, 12:19 AM
"Warping" is a misnomer anyway. It's nothing to do with deformation of metal, but it's uneveness in the layer of pad material that is deposited on the disc during use.

Yup, that sums up my thoughts too. Too many times in previous cars I've been told "my discs are warped". It's just too easy for garages to say this - I reckon they just love taking money for unnecessary skimming :sad3:

I-S
27-01-2005, 12:22 AM
Well, skimming removes the uneven pad layer, so it does solve the problem temporarily, but no dealer is prepared to tell people that they are driving in such a way as to cause this (sitting on the brakes at the lights is the most likely). If they're telling you they need skimming when they don't, that's just dishonest...

For the GLS at least the price difference between skimming and a new set of discs is minimal.