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Last set of front rotors I purchased had a couple of metal clips pushed into the vented area. At first I thought maybe just hanging hooks and yanked them out. Then I though maybe for balancing and put them back. Anyone now for sure what these are for?
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The clips must be for hanging, as they're too apt to go flying away to be used for such an important job.
As for balancing, I get Brembo rotors (actually, they're also finished by services -- e.g., cadmium plating, slotting -- from Eurosport Tuning), and I sometimes notice that a little bit of the edge (circumference) of the rotor, here or there, has been ground down. I assume that this is the proper way to balance a rotor, being a bit more permanent than a loose clip.
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"..., and I sometimes notice that a little bit of the edge (circumference) of the rotor, here or there, has been ground down. I assume that this is the proper way to balance a rotor, ..."
That makes sense. I thought perhaps the ground-down bit was there to make measuring wear easier. Your assumption is far more probable.
Erling.
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My 240 Page
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You should find the 'missing bit' - which has been ground away - is the same size as a brake pad.
So when you come to renew the pads, and the circumference has a rusty raised outer edge where the pads don't reach to keep polished, you will be able to rotate your rotors and line up the 'ground away' section with the pads - and slide them out easily.
Others who used lesser brands don't have this facility.
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Interesting thought ... but is it called for?
I always thought that the proper way was to retract the pistons, by pushing the pads apart, before pulling the pads out. Usually, I use a really big set of slip-joint pliers, with a jaw on the "ears" and the other on the caliper, to press the pads (and with them, the pistons behind) back. Rarely, if I have some trouble, I insert a small pry bar under the pad (the pivot is the very edge of the rotor, so it doesn't scratch the rotor surface).
After all, trying to push in the pistons (to accommodate new, thicker pads) without pads in place would compel me to pry directly on the pistons -- this might twist the pistons, or risk bruising the seals that skirt the edge of the pistons -- whereas prying on the faces of the old, worn pads lets them put uniform pressure on the perimeters of the pistons and forces them straight into their cylinders without tearing the seals.
And once the pistons are retracted, the pads slip out readily, regardless of any "raised" edge, so the slot is unnecessary. And, I'm not at all sure if the rotors always have that edge....
So while that edge coincidentally allows you to follow your procedure, I don't know if you ought to, if you're going to have to retract the pistons anyway to replace them with new pads.
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... to my bare eyes, the cut-out seemed shorter than the brake pads. I haven't thrown away the old rotors and pads yet, so I'm going to test this later today. Interesting!
Here's a picture I took when replacing pads and discs, showing the cut away part at the top of the disc:
Erling.
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My 240 Page
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Nice picture!
And clearly, just from the photo, there's no way that short ground arc (compared to the long edge of the pad) would let those new pads be withdrawn, or inserted, through it, even with that bevel on these new pads (older pads, worn so that the bevel is less, would have an even harder time being withdrawn).
By the way, it looks like quite a substantial bevel on the sides of those brake pads! It really reduces area of contact (between pad and rotor) a lot (at least until the pads are almost worn down)! The pads I use (PBR Deluxe) have no bevel, and therefore a lot more pad-rotor contact.
A rough measure, directly off the picture, would suggest that if you used a pad without a bevel, you'd have almost 50% more area of contact -- so even a pad with a more modest bevel would give a lot more area.
Have you considered other brands of pads with a larger contact area?
Best regards,
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Ken;
Firstly, here's a picture of an old original disc and pad. The conclusion should be clear - the ground away section was not intended to make pad removal easier - it's far too short.
As for the pads, now that you mention it I do remember wondering about the bevels first time I replaced them. Never gave it a thought since, but as is apparent, the contact area has increased a lot as the pads have worn. I wonder why Volvo makes them like this? I can't even say I have noticed the brakes getting more efficient either (or less efficient, after the change). Hm. But I think I'll stick to original Volvo pads, I like picking parts out of a blue box-!
Thanks for your comments,
Erling.
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My 240 Page
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posted by
someone claiming to be jorrell
on
Sat Feb 18 13:14 CST 2006 [ RELATED]
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Erling:
The reason the edges of the factory pads are tapered is to prevent chatter/squeal. Back in the late 80s/early 90s, Volvo had issues with squealing front pads when they changed pad material, that was a painful period to live through... I'm claiming resultant hearing loss! The only down side of a tapered pad is that they wear more quickly in the beginning, but then as the contact area of the pad to rotor grow, the wear slows down.
Technically, the braking force is the same from new to worn pads as the clamping pressure is distributed across the contact area as the pads wear, ie, no change in performance.
On other cars that I have had brake squeal issues with, I have beveled the edges of the pads significantly, and the noise went away.
jorrell
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I'm with you about wanting "blue box" original equipment on almost everything I put in my cars! I certainly never go to something else to save a few dollars -- in years past, I've been "burned" for that in the long run!
The only exceptions are when I want something I know is better for some specific reason. IPD's bars and poly bushings being good examples; the rotors I get (as I described in another reply), and as for the PBR brake pads ...
These PBR pads do leave less black dust (and I hate dirtying my Hydra summer wheels so much), and in my application (using slotted rotors) I don't feel the need for the slot (I believe, for gas escape) in the middle of the pad (PBR's doesn't have that, either, along with not having the bevels) that your OEM Volvo pads have, either. Admittedly, if I didn't use slotted rotors, I might have second thoughts about not having a center gas escape slot.
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Hmmm - looks like my theory doesn't hold up then, as Erling used Volvo replacement rotors IIRC. My own original Volvo rotors had a longer ground section (which followed the curve of the edge - ie the thickness of the area ground away was constant) and the reason I surmised it must be for pad removal, (apart from the fact that the pads fitted the 'notch') was that both front rotors were the same, so it seemed unlikely they would have been equally out of balance.
I haven't used Volvo rotors since then, Girling equivalents instead, which had no discernable grinding.
Are yours done differently on each wheel?
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I don't have a good view of the rotors (I've got steel wheels and wheel covers, for snow tires, on my cars right now; instead of my summer wheels with big holes, Hydras).
But my vague recollection* is that the rotors vary in their grindings -- sometimes they've just got a little bit, sometimes more, and I've think I've gotten rotors without any grinding (could be wrong about this).
[ * My recollection, admittedly, is just a very casual glance -- I never attributed a critical function like a pad slot to them, so I've never looked at them much more than I would examine a mere wheel weight.]
For the record, however, they're all marked Brembo -- and they bear not only the Brembo name but also the part number (as I recall, VO and then some number like 305 or 505 or some _05 number in front, and maybe _06 in the rear??? All these numbers are just a vague recollection, and I could be off on the digits too. Sorry.
I get my rotors, by the way, from Eurosport Tuning and Brakes -- I get them with slotting and cadmium plating. The slotting (IMHO) reduces fade and cleans the pad face for better initial bite (again IMHO), and the cadmium plating I've found really does prevent rusting. Here in NJ, there's a lot of wet weather and humidity, and before I used cadmium plating I'd get rotors with rust spot imprints of the pads, and these spots would give the same disconcerting feel that you get with "warped" rotors -- bouncing pedal. I haven't had this problem since using the plating.
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Hi GM;
You are correct, I replaced the original rotors with new Volvo ones. Funny, the old rotors had equally short ground sections (see pic above), and the new ones had equally longer sections. They looked like matched pair, but the new ones came in separate boxes.
Cheers,
Erling.
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My 240 Page
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I have seen this before and it was indeed for hanging the rotors on a hook. But also be aware that I was told years ago on an american car that the metal clips were to balance the rotor, I am in serious disbelief this is true though. I would tend to think that the clips could come out at higher rotation with added viberation from road contact with the wheels. A sugestion would be to take them to a tire place and put them on a tire balancer and check them with and without the clips. But i really think the hanging explanation I got years ago makes more sense. :) >> Max
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Max..1989 244 DL 5 Spd., V15 Phase II Cam Bilstein HD, Turbo Swaybars, Poly Bushings all round, Turbo Wheels, Black leather interior, Electric mirrors, LED dash and gauge lights and now NEW ECODES with the turn signals, 1992 black 244 next project
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