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Brake pads and warped rotors


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7 replies to this topic

#1 Aubrey

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Posted 04 August 2004 - 06:20 PM

Hello again,

I've had a lot of trouble with the rotors on the my 91 Legacy Turbo warping. Last summer I bit the bullet and got four new OEM rotors. Now it seems that I'm starting to get that telltale shaking again when I brake moderately to hard in the 80 to 100 kph range. Now, I don't drive like a manic and/or ride the brakes. I drive over a lot of mountain passes on the highway but I always gear down and try to minimize braking. I've never seen another car destroy rotors like this! I think my pads might be the problem, since I discovered that they're aftermarket (installed by previous owner) and pretty hard (I haven't had to replace them yet). Do you think they might be overheating my rotors? Should I go get the pads changed back to OEM and hope that stops my rotors from warping again?

Thanks,
Ian
91 Legacy Turbo (too fast for its brakes!)

#2 aba4430

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Posted 04 August 2004 - 06:53 PM

I would get the runout on the rotors checked. If they are warped, then you could get them resurfaced if they are thick enough. I also recommend that the caliper bracket (to hub) bolts as well as the caliper to bracket bolts be hand torqued to specifications. If you are going through this trouble, you could go ahead and replace the pads with OEM pads (I am not sure of this though. I would if it were me). Finally, have your wheels balanced and lug nuts hand torqued to specification. Thereafter, insist on hand torquing the lug nuts. Using an impact wrench is very often the cause of rotor warp. I have assumed some things in my response, i.e. your lugs nuts are not hand torqued for example.
Regards,
aba4430

#3 SevenSisters

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Posted 04 August 2004 - 07:25 PM

Hand torquing with a torque wrench is good advice but only seems to go so far with these cars. Too much weight to stop with limited brake hardware.

Rust or other build up on the rotors can also cause vibration.
I finally started to buy Chinese rotors and Advanced Pep Zone etc. pads. More frequent changes but no more rust problems and less loss of performance between changes.
Lower over all cost too.


#4 Aubrey

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Posted 05 August 2004 - 12:52 AM

So it's probably the lug nuts being overtorqued and not the pads huh? Well they've never been hand torqued, at least I've never done it or seen it done by hand when it was in the shop. I guess I'll try that, but I don't understand why it makes a difference. Can anyone enlighten the not-so-mechanically inclined? :)

#5 Setright

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Posted 05 August 2004 - 02:55 AM

The pads could be suspect. I would recommend Mintex standard pads over Subaru pads.

The lug nut torque is very important! First of all, they must be tightened in small increments in the right order. If you tighten one all the way, with the others "loose", the rotor and wheel will not be centered.

Too high a torque value (I use 98Nm, check your owners manual) will squeeze too hard on the rotor and will not allow movement for expansion when it heats up, causing warping, but only at high temperature. Usually goes away when the brakes cool. However, uneven brake pad deposits can result from this and cause juddering - even though the rotors will measure up straight when cold.

#6 BAN SUVS

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Posted 05 August 2004 - 03:43 AM

"Warped" rotors are almost always the result of pad deposits rather than physical warpage of the discs from overtorquing. The trouble with automatics is not being able to lift your foot off the pedal when you come to a stop, especially from higher speeds like you see on rural highways that have the occasional traffic light on 55 or 65 mph roads. Even a single high-speed stop can fade inexpensive pads meant for long life. If you can remember to bed your pads in properly and try to stop smoothly and gradually, and let the brakes slip just as you come to a stop, you can reduce pad deposits.

#7 LosDiosDeVerde86

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Posted 05 August 2004 - 06:59 AM

I would get the runout on the rotors checked. If they are warped, then you could get them resurfaced if they are thick enough. I also recommend that the caliper bracket (to hub) bolts as well as the caliper to bracket bolts be hand torqued to specifications. If you are going through this trouble, you could go ahead and replace the pads with OEM pads (I am not sure of this though. I would if it were me). Finally, have your wheels balanced and lug nuts hand torqued to specification. Thereafter, insist on hand torquing the lug nuts. Using an impact wrench is very often the cause of rotor warp. I have assumed some things in my response, i.e. your lugs nuts are not hand torqued for example.
Regards,
aba4430


using a gun can (theoretically) warp a rotor, but only if the tech doesn't use a torque stick. if they just use an impact socket than the lug nut is going on anywhere from 200 to 700 ft/lbs. the torque stick only allows it to go on up to it's specified number, usually, i believe 80ft/lbs. also, if the lugs are put on 1,2,3,4,5 there can be rotor warp. if they are put on (the correct way) 1,3,5,2,4 than there is less chance of the rotor being warped. but really it all comes down to the rotor quality, as well as number of vents in the rotor.

#8 Setright

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Posted 06 August 2004 - 01:56 AM

You can release the brake pedal in an auto, just flip the selector into Neutral - don't need to press the button for moving from D to N to D - pull the handbrake!




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