New rotors = new pads?

MarcusMcRae · **Posted:** Wed Jun 04, 2008 11:05 pm

I am replacing my rotors but the pads have a lot of life left in them. I was going to lightly sand the pads and put them back on with the new rotors.

I am replacing the rotors because I am getting a pulsing from 25-0 and some vibration from 100 when I am braking hard. They have a strange wear pattern that either indicates warping or just uneven brake deposits.

Arthur McDonald · **Joined:** Fri Aug 29, 2003 1:54 am **Posts:** 2052

I guess the conventional wisdom is:

1. New rotors + new pads = OK
2. Old rotors + new pads = OK
3. New rotors + old pads = bad

I guess the reason #3 is bad is that the worn pads won't mate squarely to the new, flat rotor.

I know first hand that sometimes #2 doesn't work either, as it seems that the new pads never bed in on the old rotors, depending on the composition of the old pads. Cleaning the rotors with Scotchbrite may or may not (my experience) help.

I've seen #1 fail to work also, but then, I was working on a Mustang.

Unless you have to spend half the morning repacking wheel bearings and gouging a few holes in your forearm with the grease seal removal tool to swap in new rotors, I'd change the rotors too. New rotors are pretty and the fancy ones won't get rusty for at least a few weeks.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Arthur McDonald wrote:

I guess the conventional wisdom is:

1. New rotors + new pads = OK
2. Old rotors + new pads = OK
3. New rotors + old pads = bad

Actually if the problem is weird pad deposits on the rotors I'd say #2 is bad while #3 is fine. Actually I've never heard of a problem with #3, but I do #1 and #2 all the time with no problems. Hmmm.

CosbyWood · **Posted:** Thu Jun 05, 2008 6:51 am

MarcusMcRae wrote:

blah blah blah...and some vibration from 100 when I am braking hard.

And just where pray tell are you doing 100 at young man?!? :lol:

MarcusMcRae · **Posted:** Thu Jun 05, 2008 7:26 am

CosbyWood wrote:

MarcusMcRae wrote:

blah blah blah...and some vibration from 100 when I am braking hard.

And just where pray tell are you doing 100 at young man?!? :lol:

I'll never tell.

Thanks for the vague answers, you guys are useless.

The pads don't appear to have any tapering.

DanDurusky · **Joined:** Sun Apr 10, 2005 7:31 pm **Posts:** 686

Maybe try scrubbing the existing rotors down w/ steel wool to remove any funk. maybe theyre ok.

MarcusMcRae · **Posted:** Thu Jun 05, 2008 7:31 am

DanDurusky wrote:

Maybe try scrubbing the existing rotors down w/ steel wool to remove any funk. maybe theyre ok.

I actually tried having them turned. No change.

DanDurusky · **Joined:** Sun Apr 10, 2005 7:31 pm **Posts:** 686

well then its unlikely to be the rotor. Are the calipers in good shape? any old/bad bushings or ball joints in the front end?

MarcusMcRae · **Posted:** Thu Jun 05, 2008 7:57 am

DanDurusky wrote:

well then its unlikely to be the rotor. Are the calipers in good shape? any old/bad bushings or ball joints in the front end?

The entire front of the car has been replaced except for the steering rack. Due to the wear pattern I am pretty sure it's the rotors. I can post a pic this weekend.

DanDurusky · **Joined:** Sun Apr 10, 2005 7:31 pm **Posts:** 686

Ok.

Also, what pads? Cold track pads (especially the carbotechs i had) can sometimes poop all over the rotors until they get up to temp.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Sorry for my vague answer.

If I were in your shoes (and I have been) I'd order new rotors from Bimmerworld (cheapest around these days) and use the existing pads.

Turning rotors never works well. "Warped" rotors are actually usually deposits which have changed the friction characteristics (think cementite, FE3C) in local spots. Once this starts happening you're getting weird localized heating and probably making all kinds of different phases of steel in small precipitates. Even scraping a small layer off doesn't guarantee getting it all.

MarcusMcRae · **Posted:** Thu Jun 05, 2008 10:05 am

MikeWhitney wrote:

Sorry for my vague answer.

If I were in your shoes (and I have been) I'd order new rotors from Bimmerworld (cheapest around these days) and use the existing pads.

Turning rotors never works well. "Warped" rotors are actually usually deposits which have changed the friction characteristics (think cementite, FE3C) in local spots. Once this starts happening you're getting weird localized heating and probably making all kinds of different phases of steel in small precipitates. Even scraping a small layer off doesn't guarantee getting it all.

I guess my original post wasn't clear. I already have new rotors. I was just wondering if I could use my old pads(Hawk HPS).

I have been getting most of my parts from RMEuropean. They have free shipping and usually beat BW's price.

Thanks

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

MarcusMcRae wrote:

MikeWhitney wrote:

Sorry for my vague answer.

If I were in your shoes (and I have been) I'd order new rotors from Bimmerworld (cheapest around these days) and use the existing pads.

Turning rotors never works well. "Warped" rotors are actually usually deposits which have changed the friction characteristics (think cementite, FE3C) in local spots. Once this starts happening you're getting weird localized heating and probably making all kinds of different phases of steel in small precipitates. Even scraping a small layer off doesn't guarantee getting it all.

I guess my original post wasn't clear. I already have new rotors. I was just wondering if I could use my old pads(Hawk HPS).

I have been getting most of my parts from RMEuropean. They have free shipping and usually beat BW's price.

Thanks

Run with it. You won't have a problem.

Thanks for the tip on RMEuropean.

Richard Casto · **Posted:** Thu Jun 05, 2008 12:09 pm

MikeWhitney wrote:

Sorry for my vague answer.

If I were in your shoes (and I have been) I'd order new rotors from Bimmerworld (cheapest around these days) and use the existing pads.

Turning rotors never works well. "Warped" rotors are actually usually deposits which have changed the friction characteristics (think cementite, FE3C) in local spots. Once this starts happening you're getting weird localized heating and probably making all kinds of different phases of steel in small precipitates. Even scraping a small layer off doesn't guarantee getting it all.

You know more than I do on this Mike, but I agree on the "warped" rotor comment. I wonder how many "warped" rotors actually measure bad (runout) vs. having non-uniform friction characteristics. I wonder if some rotors have non-uniform characteristics that are a result of the casting process and that they are destined to “warp” issue no matter what you do with them (pad selection, cooling, usage, turning them, etc.)

THSCC Forums

New rotors = new pads?

Who is online