Turning rotors leads to warping?

[sixsracing]

Increasing the surface area of the pad will result in a decrease in stopping distance. No difference in pressure is necessary.

If your on a bicycle and you drop a foot to the ground and drag it, how long will it take you to stop?

Now drop two feet to the ground. Any difference?

I'm not questioning the improvement, just the amount of improvement.

 

[ryanjl]

Increasing the surface area of the pad will result in a decrease in stopping distance. No difference in pressure is necessary.

If your on a bicycle and you drop a foot to the ground and drag it, how long will it take you to stop?

Now drop two feet to the ground. Any difference?

I'm not questioning the improvement, just the amount of improvement.

We're getting into 'friction theory' here, but when you drop the second foot, you are also applying additional force with the second foot. Our situation of using a bigger brake pad would be like dropping a second foot with half the force you had used on the first, while simultaneously subtracting half the force from the first foot.

The mathematical equation is that increased surface area alone doesn't affect friction. The 80 series pads apply so much force to the rotor per square inch. Install 100 series pads, and apply the same stopping force through your brake pedal and caliper, and the 100 series pads would apply less force per square inch because it's devided over more surface area.

 

[sixsracing]

We have gone off on a tangent. I understand your statement, I have also done a related test with VW's and swapped pads in a similar scenario with moderate results.

Agree to disagree I hope?

I would not go to the effort/cost of turning rotors that are not warped.

I very rarely advise a customer to turn their rotors. The cost of new rotors is usually very similar to the cost of turning them. (LC's are a little more expensive)

I still would like to see stop test results for both.

 

[CharlieS]

Riley,

In the first post you said:

"I really want better braking but I don't want to buy new rotors OR have warped rotors, that would really piss me off."

If you want better braking than stock 80 pads, putting a new set of stock 80 pads on isn't going to help you.

You clearly have options, but the only way to improve braking performance is to change something. Improve the compound, change the surface area, something.

Assuming that your goals are still the same,namely:
1) improve performance of the brakes
2) do not buy new rotors
3) do not chance warped rotors

Then, you have limited choices.

Based on the experience of others here you probalby can't turn your rotors and put on 100 pads and avoid warping.

You could replace your rotors with new ones and 100 series pads and be in good shape - but you said you didn't want to buy new rotors.

In my opinion, that leaves you with approximately one choice to improve performance - you can put on some aftermarket pads with a different (higher perfomance) compound.

Putting in stock 80 series pads won't going to gain you a thing in terms of performance.

Charlie

 

[e9999]

it does seem that as long as we can get the ABS to kick in regardless of pad, this would mean the stopping ability is the same since it won't get any better than that. From what I read here, it seems like one can brake hard enough to "lock" up with OEM brakes and pads. So seems like stopping ability is not the issue.
So going to the 100 would seem to affect only issues such as pad longevity, resistance to fading when really hot etc.


oh, and btw, saying that turning the rotors down "reduces heat dissipation" is flat incorrect from a heat transfer point of view. The reduction in thickness would only affect the edge surface area, not the faces, which is surely completely insignificant. The mass will be reduced so that in turn could increase the temperature of the rotor but not because of reduced heat transfer, just smaller heat capacity. Again likely insignificant. So it seems to me that this would leave only the possibility of mechanical stresses becoming larger because of smaller thickness. Possible, but again not very likely unless a good chunk of metal is removed.

 

[Riley]

>> Putting in stock 80 series pads won't going to gain you a thing in terms of performance <<

Understood Charlie. The pads need to be replaced likely (because they are worn down). I'm checking them this weekend but likely need to be replaced.

So since I was replacing them with new pads anyway I thought I'd investigate the 100 pads since that's the common solution around here. I was just worried about the rotor warping factor. Since I'm not totally comfortable with the answers I'm getting (and not 100% sure about finding a good shop to turn rotors), I'm thinking of sticking with the 80 series pads.

Dan and others have got me addicted to OEM solutions.

They do need to be replaced. Sorry that my posting was clear enough above. If I don't replace them, I'll be dead (or my family will). Better braking was a nice to have requirement, having some brakes is a mandatory requirement.

 

[sjcruiser]

Warping is a possibility but IMHO, most of the brake vibrations are results of pad's material buildups, either from improper breakin period, or over heated by sudden braking, or different pad's materials itself. If post-machined rotors are still within specs then I wouldn't be worry slapping 100 series pads on (which is what I did last year or the year before).

 

[e9999]

yup, also seems to me that the claimed "need" to machine the rotors for the 100 is just to address the edge of the worn-by-80-pads faces with a bit of elevated rusty surface. Not obvious to me what damage putting on the 100 pads on there without machining would do. Would indeed likely wear both the metal and the pad very quickly. Oviously, at the beginning you'd brake with only a sliver of pad, which is not good, but wouldn't that be gone very quickly, likely by the pad wearing out real quick there and then the metal slower later on? I would not hesitate to try it out, but would drive *very* carefully at the beginning...

 

[Riley]

so both E9999 & sjcruiser - did you observe much improved braking with the 100 pads on?

 

[sjcruiser]

Since my brakes had always been done by a private mechanics; and had always been sh*tty afterwards, I'd say it's more than 100% improvement, especially I've done it myself. Did it when the truck had about 69Kmiles on it (10/03); now closing to 84Kmiles, still stops very well with ZERO shakings/vibrations; and the pads looks like they're installed last month - no kidding!

Of course I'm only a lazy shade tree wrencher so I'm speaking from my own experience - so no scientific measurements whatsoever...

Frank.

 

[CharlieS]

E99999
You said:
"oh, and btw, saying that turning the rotors down "reduces heat dissipation" is flat incorrect from a heat transfer point of view. The reduction in thickness would only affect the edge surface area, not the faces, which is surely completely insignificant. The mass will be reduced so that in turn could increase the temperature of the rotor but not because of reduced heat transfer, just smaller heat capacity."

It has nothing specifically to do with surface area - it is all about mass.

The mass of the rotor is related to it's ability to abosrb energy in the form of heat. A rotor absorbs mechanical energy transformed into heat energy and then releases it slowly. The more mass, the more heat energy it can absorb wihtou changing the state of the material.

This may not be exactly correct, but as I recall in a high speed braking situation a rotor will increase in temperature 100 degrees per second and cool at 10 degrees per second (per a Skip Barber instructor at BWM performance driving school at NHIS).

If you keep hammering your brakes without giving them adequate time to cool you will do several things, you will boil your brake fluid, burn up your pads and you will warp your rotors. almost GA-RON-TEED.

So in that situation you brake late and give the brakes time to cool between corners. You don't want to exceed the heat capacity of the rotors and calipers (yes the calipers absorb heat).

At some point the rotor can absorb too much heat energy and the state of the material changes from a solid toward a liquid (have you ever witnessed F1 brake rotors glowing orange?). If you heat a rotor up too much and it becomes soft(er) and you apply mechanical braking force you will deform (warp) the rotor.

Brakes become more succeptable to warping when they become thinner because they have less mass.

Anything that says That "rotors warping" is just experiencing a transfer of pad material to the rotor is filling you full of pure BS as far as I am concerned. I am not an expert, but I call BS.

Charlie

 

[cruiserdan]

DO NOT RUN 100 SERIES PADS ON 80 SERIES ROTORS THAT ARE NOT PERFECTLY FLAT............The contact surface is just too different. I would not consider it for my own vehicle.

I suggest that you select the 1997 model year 80 series pad, 04465-60110, and run that until such time as you are prepared to replace the rotors. If your rotors are iffy, the front axle service is a perfect time to replace them and upgrade to the 100 series pads.

Anytime you do a front axle OR a rotor replacement is THE PERFECT TIME to combine both operations, if your billfold can take the hit.


D-

 

[concretejungle]

Only facts i can add to this is that my front rotors were warped pretty bad when i bought the truck. Took them to have them turned while i did the birf job. Put new pads on them and put them back on the truck. Torqued everything to spec. Within 3,000 miles they were just as wobbly as before i had them turned. Purchased new OEM rotors and pads from Cdan, replaced the original turned rotors and haven't had a problem since.

 

[hoser]

it does seem that as long as we can get the ABS to kick in regardless of pad, this would mean the stopping ability is the same since it won't get any better than that. From what I read here, it seems like one can brake hard enough to "lock" up with OEM brakes and pads. So seems like stopping ability is not the issue.
So going to the 100 would seem to affect only issues such as pad longevity, resistance to fading when really hot etc.

Most any car sold today can skid at 40mph. It takes less torque to skid a wheel than it does to hold it at "threshold braking." The objective is not to skid but to get very close to it.

Riley, I recommend that you switch to aftermarket pads with a higher coefficient of friction. I haven't had the opportunity to explore what's available for the fzj80 yet but I am SURE something out there is better than OEM. Try to get a matching set (front and rear) to keep closer to the original brake bias.

 

[Bruneti]

People, the 80 series is not a sports car. If any of you are running this vehicle on the track and building heat in the brakes from corner to corner without a chance to cool, then you've got more balls than brains. Even with a S/C, these beasts accelerate slowly enough that you would have to try pretty darn hard to floor it, slam on the brakes, & repeat enough times to heat up a rotor until it glowed. The only scenario that I could see would be towing a large trailer without proper trailer brakes and having to stop the whole rig in stop & go traffic.

Now I admit, it seems odd that so many have issues with brake pulsing after turning their rotors. But has anyone ever proven it was warp? If you collected all the chips machined off the rotor when turned and weighed it, I would guess that it would be less than 2% of the total mass of the rotor removed. Look at it this way, what if you only replaced your pads and never your rotors. A rotor that is worn right up to the thickness limit would have less mass than a nearly-new rotor that was just lightly turned before using the larger 100 series pads. Why wouldn't that worn rotor (remember-less mass) be warped?

Toyota consistently has the best or near best-in-class braking performance in all vehicle segments. I own a mkiv supra turbo, and this car first sold in 1993 held the shortest braking distance of any stock production vehicle, as tested by Car and Driver, until this past year when the Porsche Carrera GT (at a cost of $443K) with exotic 15" ceramic composite brake rotors finally surpassed it. Many supra owners road race their cars with stock rotors and high temperature pads with excellent results. You CAN warp a stock Supra rotor on a race track with aggressive race compound pads and no brake cooling ducts. However, it's not possible with even aggressive street driving on stock pads. I know the LC is a much heavier vehicle, but I cannot imagine that a rotor turned within spec would lose enough mass to cause warp in nearly every case. That would seem like a serious blunder for world-class brake engineers to make. The stock pad material would be in serious hurt before a stock rotor should warp.

As far as the 100 series pads go, the most likely reason for the perceived improved braking performance (real or not) is likely due to the initial "bite" of the pad material. By providing more braking friction early, the braking will feel more powerful. Normally this means a pad material that is optomized for lower temp ranges. Stressing the pad material above it's temp. range will mean more fade. However, it takes several severe braking occurrances back to back to back without cooling time to build enough heat to fade most pads (let alone warp a rotor).

Wow, a lot said. Not trying to offend anyone here, so please don't take it that way. I just don't buy it that Mr. T's rotor "can't take the heat", so to speak, after a standard brake maintenance procedure. I'd like to see a suspect "warped" rotor measured as proof one way or the other.

 

[hoser]

Bruneti--

We all know our 80's are not sports cars but that doesn't mean we don't need shorter stopping distances, better fade resistance and brake feel. Lots of cruisers here weigh in at 6-7K+ lbs when fully loaded. Many take road trips passing through hills and mountains. You eventually have to go down, right? Panic stops--sure you won't utilize your brakes full potential 99% of the time but when you do need it--you're gonna wish you had a little more than what the OE brakes provide.

I own a mkiv supra turbo, and this car first sold in 1993 held the shortest braking distance of any stock production vehicle, as tested by Car and Driver, until this past year when the Porsche Carrera GT (at a cost of $443K) with exotic 15" ceramic composite brake rotors finally surpassed it.

I've driven a few MK4 Supras on the track. The stock brakes have much to be desired. They may stop fast but brake feel and modulation wasn't great. But since you mentioned stopping distance. Here's a copy of a Car & Driver article. The RX7 stopped quicker than the Supra back in 1993 (70-0 no other specs listed). With that said, I do like and respect Supras... but only for their engines.

 

[RavenTai]

Wow lots said here good thread,

I have never looked deep into brake theory just done normal maintenance, but

Anything that says That "rotors warping" is just experiencing a transfer of pad material to the rotor is filling you full of pure BS as far as I am concerned. I am not an expert, but I call BS.

Charlie

Agreed.

I have had and measured brake rotor warp on my 80, the rears on my 80 were warped one .030” and the other .035” IIRC (can’t find the thread now), 30 thousands of pad material built up on a rotor would be quite obvious, they were defiantly warped. I measured the new ones and they were only a few thousands. The FSM gives a spec for runout at .006” (0.15 mm (0.0059 in.) front and rear,

The PO had new rotors put on the front (Midas, $700 bill) shortly before I bought it, pads had about half their life left when I changed over to 100 series pads last summer, there was a slight step where the 80 pads did not contact the rotor, I think most of it was rust. I did not turn them just put the pads on partially used rotors, Saw them last week the step is gone, have about 15K on the front pads they looked almost as thick as new. I noticed a must better brake feel with the 100 series pads over 80 series midas pads, they wear well also.

A few months ago I started getting slight warped feel (no where close to the feel the rears had) in the brakes when light pressure is applied. My 80 is mostly highway, I don’t use the brakes often but there are 3 high speed lights on my way to work, if I get caught at any of them there is a 70->0 MPH stop. Maybe this pad transfer phenomenon could explain this light "warped" feeling I currently have.

Guess I should get it up on stands and measure again don’t know when I will get to it.

Are you guys actually doing this pad bedding thing? 10 repetitive heavy breakings with no cool down? Sounds like something a person who makes his living selling brake parts would come up with.

 

[RavenTai]

The mathematical equation is that increased surface area alone doesn't affect friction.

A few have said the same thing in different ways, basically paraphrased that

"The force of the caliper bears down did not change so braking does not improve from the increased area of the pad alone"

And I do not think I can follow that,

What would happen to a dragster if you put standard width (~7") tires on? The weight of the car bearing down on them did not change? They pay the big bucks for them tires for a reason.

But maybe that is an apples to oranges comparison.

I don’t know what real braking gains are gotten from 100 series pads, or if these possible gains are above what the tire can make use of any way as I have never locked my tires nor kicked in the abs on dry pavement with either pads, but the 100 series pads feel better and last longer, good enough IMO to choose them, I woudl not turn good rotors to use them though, slap them on let them find thier own middle or use 80 series pads for the rest of the life of the rotors.

 

[e9999]

if one has pad stuff sticking to the rotor for this pulsy feel, could that not be removed with some serious scraping/polishing/sanding/grinding home job?

 

[Bruneti]

if one has pad stuff sticking to the rotor for this pulsy feel, could that not be removed with some serious scraping/polishing/sanding/grinding home job?

Yes, one of the links I posted earlier talked about doing this a couple different ways. But the easiest for most is to blanchard grind or turn the rotors. Not too many people are going to want to run a high temp track compound pad for one day on their LC to remove the old pad material.

I guess Cdan's dogs are gonna eat well from all the people that think their rotors are warped. We should arrange a core exchange so those who believe the warp is B.S. can turn the rotors and use them.