New Disc Warped

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cavalier1990
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New Disc Warped

Post by cavalier1990 »

Hi

I put new GM discs on front and just after putting back on road there is a chiff chiff pulsating noise as I slow down at lights as I am pulling back on braking force. Jacked car up today on drivers side, wheel off, put in 2nd gear and let the disc spin. Clearly the disc was pulsating back and forth about a millimeter or two, using caliper holder as a reference point. I could also see the pad pulsating in and out slightly.

Removed disc to check the hub mount never had any crap on it or chips. There was one little bit I filed down where I think it had a blow from a hammer at some time. Other than that fine, hub tight, brakes tight, bearing fine etc. but still it pulses and makes this chiff chiff noise when spinning.

I'm going to try the old disc on it to see if it is pulsating as well, if not then confirms new disc is faulty, else back to drawing board. Only other thing I can think if is hub is warped but it would take some hit to do that.

Any thoughts or anyone had similar issue?

Cheers

Andrew
kimi sri
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Re: New Disc Warped

Post by kimi sri »

Have you checked the backing plate is not rubbing on the disc
colin1
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Re: New Disc Warped

Post by colin1 »

Start with the easy ones, as Kimi says try pushing the splash plate back off the disc, it might just be as simple as that

Did you wind the pistons back far enough?
93K C20XE Cavalier SRi Hatchback Spectral Blue Metallic
94M X20XEV Cavalier SRi Hatchback Flame Red

96N C14NZ Corsa B 4-dr Flame Red'ish
cavalier1990
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Re: New Disc Warped

Post by cavalier1990 »

kimi sri wrote:Have you checked the backing plate is not rubbing on the disc
Yes, it is new backing plate and is a good few millimeters from disc even taking into account the wobble it has. Only happens when letting off brakes.
cavalier1990
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Re: New Disc Warped

Post by cavalier1990 »

colin1 wrote:Start with the easy ones, as Kimi says try pushing the splash plate back off the disc, it might just be as simple as that

Did you wind the pistons back far enough?
Yes otherwise wouldn't have got new pads in. I can hear the noise right at the pad and can see sliding caliper move in and out. Once I get time I'm going to put old disc back on and see if that does it as well.
thegriffin
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Re: New Disc Warped

Post by thegriffin »

It's unlikely the new disc is warped.I don't like the sound of a hammer blow on the hub.
The hub has probably had a thump in the past and it has probably bent the flange.
I had a bent rear hub on mine causing the drum to run out of true by a previous owner.
I'd remove the disc and check the hub for runout. A small amount would be magnified by the larger diameter of the disc.
cavalier1990
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Re: New Disc Warped

Post by cavalier1990 »

thegriffin wrote:It's unlikely the new disc is warped.I don't like the sound of a hammer blow on the hub.
The hub has probably had a thump in the past and it has probably bent the flange.
I had a bent rear hub on mine causing the drum to run out of true by a previous owner.
I'd remove the disc and check the hub for runout. A small amount would be magnified by the larger diameter of the disc.
I put old disc back on, it certainly doesn't have this side to side wobble. I used caliper bolts to go into wheel nut holes, furnished with about 8 big fat washers to press the disc right on to the hub, and stop the extra length of the caliper bolt hitting the inside of hub, basically emulating the wheel being on and tightened. I see a marked difference with new disc. Yet I still hear this scrape scrape noise. There is nothing rubbing on disc.

If driving along normally you can hear this shh shh shh pulsing noise that increases with speed, it's not loud but I can hear it. If I then press brakes lightly it goes away and as I press harder and slow down more, then start backing off brake when coming to a stop, I can then hear it return.
colin1
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Re: New Disc Warped

Post by colin1 »

If you put the new disc on a flat surface, a kitchen worktop for example, with the contact between disc and surface at eye level and slowly rotate the disc, do you see any intermittent increases in gap between worktop and disc?

Judging by the amount of warp you're describing, you should be able to.

My policy with new discs and pads is to take them for 5 or 10 minutes reasonably aggressive braking to bed them in (somewhere where no-one's going to pile into the back of you obviously) - have you tried that?

Is it an OE disc or some high performance aftermarket gear? I've never seen a warped (new) disc before.
93K C20XE Cavalier SRi Hatchback Spectral Blue Metallic
94M X20XEV Cavalier SRi Hatchback Flame Red

96N C14NZ Corsa B 4-dr Flame Red'ish
cavalier1990
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Re: New Disc Warped

Post by cavalier1990 »

colin1 wrote:If you put the new disc on a flat surface, a kitchen worktop for example, with the contact between disc and surface at eye level and slowly rotate the disc, do you see any intermittent increases in gap between worktop and disc?

Judging by the amount of warp you're describing, you should be able to.

My policy with new discs and pads is to take them for 5 or 10 minutes reasonably aggressive braking to bed them in (somewhere where no-one's going to pile into the back of you obviously) - have you tried that?

Is it an OE disc or some high performance aftermarket gear? I've never seen a warped (new) disc before.
Hi Colin

It was GM discs new. I was suspecting the hub because I though ok why would a new disc be warped, but as I put on the old disc the movement became a lot less, but is still slightly there. Making me think perhaps the old disc has kind of bedded itself into the offset and when new one is on the hub warp is amplified.

I've now just kept the old disc on it and put up with it, actually haven't thought about it until I heard it a wee bit the other day. The old disc actually wasn't that old it was about a year old GM discs and had rusted a bit from the car lying.

Andy
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