Brake pad bed in - serious heat
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This is a discussion on Brake pad bed in - serious heat within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; (I posted this question in the Tutorials section also, which was probably the wrong spot, sorry). My 2005 WRX has ...

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    Brake pad bed in - serious heat

    (I posted this question in the Tutorials section also, which was probably the wrong spot, sorry).

    My 2005 WRX has about 49k miles on it, so I swapped out the pads just now with some Hawk ceramic. The bed in process was pretty clear from Hawk, however, it seems like the front pads are so thick, that they are hanging a bit.

    After seating the new pads in the front calipers, and pushing the pistons all the way back into the calipers, there was some serious jiggling to get the caliper back over the disc/pads (no tools, but had to smack it a few times with my bare hands). I checked the brake fluid level frequently when compressing the pistons, no real problems there. The old pads still had about 5k miles left in them, and the rotors were in really great shape.

    When I did the bed-in, about 5 miles, the disc is *extremely* hot, probably due to some "dragging" due to the tightness in the caliper, and you can hear the fronts drag a bit even coasting under no-brake. Is this normal for a short period? I'm thinking of getting out on the highway, and it seems like they could overheat and warp the older rotors on the fronts. I've done plenty of brake jobs before, just never had them drag quite this much out of the blocks - and that's a lot of heat.

    Is this normal? Are these discs going to go into melt-down?

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    Moderator Donkey's Avatar
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    Quote Originally Posted by KryptoNyte View Post
    (I posted this question in the Tutorials section also, which was probably the wrong spot, sorry).

    My 2005 WRX has about 49k miles on it, so I swapped out the pads just now with some Hawk ceramic. The bed in process was pretty clear from Hawk, however, it seems like the front pads are so thick, that they are hanging a bit.

    After seating the new pads in the front calipers, and pushing the pistons all the way back into the calipers, there was some serious jiggling to get the caliper back over the disc/pads (no tools, but had to smack it a few times with my bare hands). I checked the brake fluid level frequently when compressing the pistons, no real problems there. The old pads still had about 5k miles left in them, and the rotors were in really great shape.

    When I did the bed-in, about 5 miles, the disc is *extremely* hot, probably due to some "dragging" due to the tightness in the caliper, and you can hear the fronts drag a bit even coasting under no-brake. Is this normal for a short period? I'm thinking of getting out on the highway, and it seems like they could overheat and warp the older rotors on the fronts. I've done plenty of brake jobs before, just never had them drag quite this much out of the blocks - and that's a lot of heat.

    Is this normal? Are these discs going to go into melt-down?
    Not really normal.When I do brake jobs I re-polish the caliper pins to remove all oxidation and brake dust.Then I grease the pins and the where the pads sit to allow them to move freely.Did you clean the calipers and regrease?
    Last edited by Donkey; 09-21-2008 at 05:10 AM.
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    Hmm. I didn't think about the pins, normally I do wire brush those and grease 'em. Honestly, this is the first caliper I've done where the pin doesn't actually pass all the way to the opposide side (it's a very short pin in the WRX).

    Could there be a problem with excessive brake fluid pressure, in just one caliper? The pistons seem to compress the usual way (I did not bleed the system).

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    Quote Originally Posted by KryptoNyte View Post
    Hmm. I didn't think about the pins, normally I do wire brush those and grease 'em. Honestly, this is the first caliper I've done where the pin doesn't actually pass all the way to the opposide side (it's a very short pin in the WRX).

    Could there be a problem with excessive brake fluid pressure, in just one caliper? The pistons seem to compress the usual way (I did not bleed the system).
    I would try the pins and maybe bleeding.The WRX uses a certian bleed sequence because of the ABS module and how the lines are run.Factory chassis manual:
    http://ken-gilbert.com/wrx/mans/5%20-%20CHASSIS.PDF
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    Thanks, Donkey. You know, when I put them back together, I noticed the Hawk pads already had a backer spacer (fronts) built into the pads, so the only backer pad plate that I reinstalled is the stainless plate that the pistons actually press against on the inside pad. I had tried at first with all four backer plates (from the original pads), but it the pads/plates/disc final assembly was simply too thick for the caliper to be reinstalled properly. Now I'm thinking that I just didn't spend enough time making sure the caliper travel mechanisms were sliding well enough.

    I have tried bleeding brakes once, alone, and I ended up taking it to a shop to have it power bled soon after as I couldn't seem to clear the air in the line. I'm trying to avoid the bleeding at all costs.

    Do the pins (part no. 3 and no. 9 on PDF page 375) actually come out? I can't recall a way to get them out ...
    Last edited by KryptoNyte; 09-21-2008 at 05:35 AM.

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    A brake bleed should always be done with two people...one to open the bleed point and provide the visual and the other to monitor the brake oil level. Works best if you switch to something like Motul blue or red oil...then you can see the color change and know for sure you've passed all the old oil and/or bubbles out of the line.

    I've never heard of your issue before. They shouldn't be dragging like that, even if the pins are dirty. The pistons won't stay compressed like that to cause this issue. Have you tried prying them apart a bit to see if there is enough clearance?

    ps...I've never been a hawk pad fan, but there are those who swear by them. Ferado 2500 S for the win baby!!
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    Quote Originally Posted by KryptoNyte View Post
    Thanks, Donkey. You know, when I put them back together, I noticed the Hawk pads already had a backer spacer (fronts) built into the pads, so the only backer pad plate that I reinstalled is the stainless plate that the pistons actually press against on the inside pad. I had tried at first with all four backer plates (from the original pads), but it the pads/plates/disc final assembly was simply too thick for the caliper to be reinstalled properly. Now I'm thinking that I just didn't spend enough time making sure the caliper travel mechanisms were sliding well enough.

    I have tried bleeding brakes once, alone, and I ended up taking it to a shop to have it power bled soon after as I couldn't seem to clear the air in the line. I'm trying to avoid the bleeding at all costs.

    Do the pins (part no. 3 and no. 9 on PDF page 375) actually come out? I can't recall a way to get them out ...
    The pins do come out.They pull right out of the boots.I generally stuff the caliper grease in the pin boot instead of greasing the pins.I bleed my own brakes with a mighty vac and speed bleeders on all 4 calipers.Don't use the factory steel plates.Just what comes with the Hawk pads.I use a C-clamp to slowly push the calipers all the way open.I usually remove alittle brake fluid from the master cylinder reservoir before opening the calipers to keep fluid from going everywhere.I also realized you have an 05.Here is a link to the 04 wrx/sti manuals(might be more helpfull):
    2004 Subaru Impreza WRX STi
    Last edited by Donkey; 09-21-2008 at 10:11 AM.
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    Well, I took it all back apart this morning (the fronts) and inspected the assembly.

    I checked the caliper pins by moving them back and forth, with one finger, very smooth with no sticking at all, so I left them alone. From what I can tell, the pins are as far in as they can be (the small rubber boot is in it's compressed position), which means the caliper is in the typical position for new pads (full open, pistons compressed as far in as they will go), and I have to really "coax" the caliper back on by lightly bumping it with my bare hands, so needless, to say, it's pretty tight right from the start. That said, I can still turn the front wheels (with the car off the ground) with my hands without trouble.

    One conclusion is that the ceramic brake pads from hawk simply have too much padding and the final assembly of new pad+rotor+new pad is too thick for the stock calipers. Or I simply don't understand how to allow for even more opening travel on the pins. It's one or the other.

    I'm hoping that the pads will come around before the rotors melt-down, or I'll be doing this all over again shortly, but with new rotors. I did notice that the pedal is significantly stiffer and has far less travel now, yet the level in the reseviour seems fine. I also found out that the place where I have my oil changed doesn't check the brake fluid, so shame on me for depending on them for that over the last 40k miles.

    Why is it such a strong recommendation here to completely change the brake fluid on Subaru's so frequently? I've driven almost every car I've ever owned well over 100k miles before changing brake fluid, and I just don't recall that being a serious issue for a daily driver.

    Thank you again for all the assistance and advice. You guys are quite knowledgable, and very helpful.
    Last edited by KryptoNyte; 09-21-2008 at 01:49 PM.

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    Quote Originally Posted by KryptoNyte View Post

    Why is it such a strong recommendation here to completely change the brake fluid on Subaru's so frequently? I've driven almost every car I've ever owned well over 100k miles before changing brake fluid, and I just don't recall that being a serious issue for a daily driver.
    Are you sure you have the right pads?Subaru's maintenance schedule recommends changing brake fluid every 30K miles.Much sooner if you brake hard or track.

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    Last edited by Donkey; 09-21-2008 at 03:43 PM.
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    Well, the pads are identical in outline shape to the originals, but I re-checked the part number anyway. It's the right part, according to the box.

    I have since found a few other posts with folks complaining about over-thick hawk pads, ironically, one of them was a 2005 WRX owner.

    Been so busy working over the past 10 years, paying off student loans and such, that I have spent almost no personal time on my cars, I've taken them to the shop for a while instead. Now that I finally have a few bucks, and a bit more time, I had planned to treat the car to some really great stuff. $200 for pads. I don't think I'll ever make that mistake again.

    If you can't handle a brake pad changeout, car modding just wasn't meant for you!
    Last edited by KryptoNyte; 09-22-2008 at 05:31 PM.

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