Do I have a bad caliper?
Thread Starter
Team Owner
Joined: Feb 2000
Posts: 51,504
Likes: 6
From: Sacramento CA
Do I have a bad caliper?
I have some brake pulse. More like a brake throb.
When i slow down from 20-5, its like ... pulse ... pulse ... pulse ...
Almost like I'm driving over little bumps 2 feet apart from each other.
After research, I picked up new rotors. Pads looked low, so I grabbed some new HPS pads.
I threw the new pads and rotors on and 90% of the pulse is gone.
I went to toss the old pads and noticed that the left pads were worn slightly unevenly. The bottom was worn just a fraction more than the top.
Is this the cause of my problem? Is this just some anomaly because the pads were so low?
ps- The calipers slide freely.
When i slow down from 20-5, its like ... pulse ... pulse ... pulse ...
Almost like I'm driving over little bumps 2 feet apart from each other.
After research, I picked up new rotors. Pads looked low, so I grabbed some new HPS pads.
I threw the new pads and rotors on and 90% of the pulse is gone.
I went to toss the old pads and noticed that the left pads were worn slightly unevenly. The bottom was worn just a fraction more than the top.
Is this the cause of my problem? Is this just some anomaly because the pads were so low?
ps- The calipers slide freely.
Last edited by Kale; Nov 14, 2009 at 09:33 PM.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
I've been told this and its possible don't hold me accountable for the facts. I was told that if the rotors are hot or even warm and you go to wash the car, the cold water will cause them to warp. Also, brake pads that are wet, it wetter areas of the country will cause rust on the rotors heavily in the area where the pads sit overnight or extended parking, which rust of course is metal thats coming off the rotor. I had lots of trouble with warping rotors on my '99 for years till I broke down and bought brand new rotors, new ceramic pads, all the way around. No more problems past that. The only part I didn't like in replacing all that was that I used AC Delco rotors which turns out the center hubs were not coated with anything to prevent rusting.
Drifting
Joined: Jan 2008
Posts: 1,722
Likes: 138
From: Florida
St. Jude Donor '09
Did you clean and lubricate the caliper pins prior to re-assembly to ensure freedom of movement between both sides?
I'm assuming that if you replaced the rotors, you measured the rotor thickness at several locations and found them to be uneven.
For the record, cast iron rotors do not typically warp. Cast iron usually cracks when exposed to extreme heat cycles.
I'm assuming that if you replaced the rotors, you measured the rotor thickness at several locations and found them to be uneven.
For the record, cast iron rotors do not typically warp. Cast iron usually cracks when exposed to extreme heat cycles.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
Did you clean the face of the hub to make sure that the rust there isn't holding the rotor slighly unevenly?
I had pulsing. I wire wheeled the rotor and the hub mounting faces. I then machined the rotors. No more pulsing and I've gone almost 20k miles since.
As for the pad uneveness, the calipers are known to spread slightly under hard brakng. Could also just be slight variance in the maching of the parts. No big deal.
In theory, every times the wheels are pulled the rotor and hub surfaces should be cleaned because if you loosen up the rotor the rust may not allow it to go back to the position it was the first time. You've got to keep the rotors running true to keep the brakes working well.
Peter
I had pulsing. I wire wheeled the rotor and the hub mounting faces. I then machined the rotors. No more pulsing and I've gone almost 20k miles since.
As for the pad uneveness, the calipers are known to spread slightly under hard brakng. Could also just be slight variance in the maching of the parts. No big deal.
In theory, every times the wheels are pulled the rotor and hub surfaces should be cleaned because if you loosen up the rotor the rust may not allow it to go back to the position it was the first time. You've got to keep the rotors running true to keep the brakes working well.
Peter
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Drifting
Joined: Jan 2008
Posts: 1,722
Likes: 138
From: Florida
St. Jude Donor '09
"Warping: Warping, in my opinion, is the most misunderstood word when it comes to your brakes. Rotors DO NOT warp, they wear inconsistently. Warping can be better described as rotor friction disc thickness variation or “TV”. This is where spots on the friction disc wear faster than others. The first step to combat “TV” is to properly torque your wheels. Improperly torques wheels can lead to devastating “TV”."
http://blog.nurspec.com/?p=41
Burning Brakes
Joined: Mar 2002
Posts: 844
Likes: 11
From: Il
From the article in the link below:
"Warping: Warping, in my opinion, is the most misunderstood word when it comes to your brakes. Rotors DO NOT warp, they wear inconsistently. Warping can be better described as rotor friction disc thickness variation or “TV”. This is where spots on the friction disc wear faster than others. The first step to combat “TV” is to properly torque your wheels. Improperly torques wheels can lead to devastating “TV”."
http://blog.nurspec.com/?p=41
"Warping: Warping, in my opinion, is the most misunderstood word when it comes to your brakes. Rotors DO NOT warp, they wear inconsistently. Warping can be better described as rotor friction disc thickness variation or “TV”. This is where spots on the friction disc wear faster than others. The first step to combat “TV” is to properly torque your wheels. Improperly torques wheels can lead to devastating “TV”."
http://blog.nurspec.com/?p=41
Last edited by abigfoot; Nov 19, 2009 at 10:56 PM.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
I read a really good article about C3 brakes that described the "warping". A very small run-out in the rotor when new causes the rotor to have places with heavy wear on one side and corresponding lighter wear on the other surface directly across. This makes it appear to be "warped". With a C3's fixed calipers, this worn rotor causes the pistons to pump all the time (braking or not) which wears out the calipers and causes them to leak.
The general recommendation was to make sure the rotor and hub mounting surfaces were completely clean and that the rotor ran true when first installed. Something like 0.004" runout maximum measured at the outside of the pad surface if I remember correctly.
I tend to believe this description of wear, it doesn't make sense that the rotor would just warp when it doesn't get to the temperature required to deform.
Peter
The general recommendation was to make sure the rotor and hub mounting surfaces were completely clean and that the rotor ran true when first installed. Something like 0.004" runout maximum measured at the outside of the pad surface if I remember correctly.
I tend to believe this description of wear, it doesn't make sense that the rotor would just warp when it doesn't get to the temperature required to deform.
Peter
Drifting
Joined: Jan 2008
Posts: 1,722
Likes: 138
From: Florida
St. Jude Donor '09
I tell you what. If you have ever cut a rotor you can see the runout (wobble)when you start them spinning. When you mic. a rotor you check the thickness. I have never seen a rotor no matter how bad it was gouged that mic.ed with any serious difference of more then a couple thousands around the rotor face. If the runout is bad you can't true them up without taking to much meat off the rotor. when you mount the rotor in the lathe it rides on the wheel bearing races. Its not hard to do or hard to screw up. One thing that does happen in brake drums as well as rotors which you may be confused about is hard spots. I'll give you that. A hard spot is caused by excessive (hard Braking) and or bad iron (cheap rotors). They dont wear and will be thicker. you can have 1 or 100. They can be the size of a pea or quarter. A hard spot must be ground down with a grinding wheel. First you cut the rotor to true it up. You can hear a rotor with hard spots when its being cut makes a lot of racket. After its trued up you mount a high rpm grinding wheel in place of your cutting bit and set it to move across the face like the cutting tool. I used to cut 100 a week. They warp believe me
High and low spots, yes; uneven wear, yes; out of round hubs, yes; uneven pad material deposition, yes; warping, I don't think so, we'll just have to agree to disagree.
Last edited by ipuig; Nov 20, 2009 at 08:02 PM.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
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From: Van Buren Arkansas
Wounded Warrior Escort '11
I think those of us who don't know all the in's and out's of the metals and machining techniques, use the term "warped" loosely since we have no clue what the real cause is. It "feels" like something warped out of shape to us, therefore the term used.
Racer
Joined: Mar 2007
Posts: 307
Likes: 2
From: Port Orange Fl
I used to manage a pump and valve repair facility with a machine shop, I know my way around lathes and mills. I'm not a machinist by trade but I know enough about materials that the term warping to me implies that the material's modulus of elasticity has been surpased to the point that it's deformed that it takes on a new shape, this is unlikely with grey cast iron, it typically breaks before that happens.
High and low spots, yes; uneven wear, yes; out of round hubs, yes; uneven pad material deposition, yes; warping, I don't think so, we'll just have to agree to disagree.
High and low spots, yes; uneven wear, yes; out of round hubs, yes; uneven pad material deposition, yes; warping, I don't think so, we'll just have to agree to disagree.
Mike
Safety Car
Joined: May 2008
Posts: 4,237
Likes: 11
From: Lacombe Louisiana
What about normal, true rotors that all of a sudden develope a pulsating pedal after diving into deep standing water(common down here)?Is this wear?I think not.We have to true them up alot for just that reason!
Racer
Joined: Mar 2007
Posts: 307
Likes: 2
From: Port Orange Fl
High and low spots, yes; uneven wear, yes; out of round hubs, yes; uneven pad material deposition, yes; warping, I don't think so, we'll just have to agree to disagree."
Your statement isn't true, cast iron can warp under normal conditions if the heat/cool cycle happens quickly...like here in the south where the rotors can get very hot and cooled quickly by an afternoon shower.
Mike