Turning rotors leads to warping?

[CharlieS]

Bruneti-

Yes, the 80 is not a race car and I do not drive it like one, but the mechanical principles are the same on the 80 as they are on a track car.

The race car takes it to the extreme, so it is a simpler illustration.

Whether your heat buildup is from flying around a track ina 2000 lb car or going down a mountain road in a 6000 lb vehicle, the same issues come into play.

I have followed other large passenger vehicles (suburbans, pickup trucks) on mountain roads and wached their pads literally go up in smoke as they braked. Your 80 can do the same thing with all that mass. you don't need a sports car to exceed the capabilites of your brakes.

RavenTai - I always bed my pads - I'm not sure of the procedure you mention for the 80 since I haven't done it like that yet.

On my other vehicles I have done it when I have changed pads. As I understand it, the bedding burns off the volatale compounds in the pads and beds the surfaces of the pad to match the rotor.

I have always been told to, pay particular attention to cool down cycles. You can do more damage than benefit if you just keep overheating those brand new rotors and pads without cooling them in between braking sessions.

Your instructions suggest not cooling the rotors between braking steps. I would worry about htat for the health of your brakes. I agree, that procedure seems designed by someone trying to sell brake parts.

Also - if this is directed at me:
"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."

You may be misreading what I said. I KNOW rotors warp. What I disagree with was some mention that what peole think is warping is just a buildup of pad material. Rotors can and do warp. 80 series rotors are heavy duty but they WILL warp.

Charlie

 

[miked]

thats it.
i'm cutting a hole in the floor and going Flintstones style!!

heres what i've got going on. first few stops in the morning are fine. city, not heavy. by the 5th or 6th stop i have the pulsing. then a 20 mile highway drive and it always pulses at the end. i'm thinking a pad is not retracting. now i'm wondering if the heat build up is warping the rotor OR does the pad material build up have a more pronounced effect when warm or hot? for what it's worth, i put in new oem 80 pads last night and bedded them with the 10 stop method. the first 5 stops shuddered worse than ever but by the 10th it was much better. i followed by a long highway drive to cool them, and it was smooth after that. not sure what i pulled out of there as far as pad brand but they definitly weren't OEM pads. the real test will be in about an hour as i leave for work.
one last question... if a rotor is warped it's warped right? i mean do they warp and straighten with temp? because mine are fine in the morning for the first few stops. hmmm. this is leading to it being the "pad material build up" it seems.
this has been an interesting thread thanks to all who are posting here.

 

[CharlieS]

miked,

This may be a long shot, but have you ever bled your brakes?

You may have localized boiling your brake fluid as your brakes heat up.

"Normal" DOT3 and DOT4 brake fluid is hydroscopic (not sure if that is the right word) - but it means that is absorbs water. Water boils at a much lower temperature than brake fluid.

The gas formed (steam) is more compressible than the liauid.

When the brake fluid boils it loses its ability to transmit force to your brake pistons->pads.

That is one reason why it is important to flush brake fluid every couple of years.

Just a long shot....

Charlie

 

[Bruneti]

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).

Hoser,
Not that it matters to this topic anymore, but Car & Driver had two other seperate tests where the mkiv Supra stopped in 149ft. from 70-0. It is this distance that they have listed year after year as the best 70-0 braking distance of any production street car.
Car & Driver 10 Best Performers 1997
Car & Driver March 1997: Toyota 2000GT vs. MKIV Supra TT
The real point was, Toyota brake engineers know what they're doing.

Many sports cars & supercars have better brakes for high speed track specific purpose with repetitive extreme temp braking. But most of these test poorly in 70-0 cold brake performance. For daily driven street performance the C&D 70-0 test is very legitimate. Toyota was balancing street performance with track performance in the brake system and pad material. For serious track use the car needs higher temp pad material, high temp fluid, and brake ducts. These items are needed by any race car.


That said, I agree that everyone wants to stop their rigs as quickly and consistently as possible. If the 100 series pads help provide this, then I'm all for it. I personally would like to compare front 100 series pads from Toyota, Axxis, and Performance Friction. The Axxis and PF are probably both higher temp compounds than the OEM pad, which has some tradeoffs for cold braking performance, but should help the severe duty braking performance.

FWIW I test drove a Sequoia and 100 series (both used vehicles) back to back at my local Toyota dealer. The Sequoia's braking felt much stronger than the LC. I can't speak to the condition of either vehicles brakes, if they were oem components, or if this is typical performance of each. But I wonder if there is anything to learn or use from the Sequoia's braking system?

 

[miked]

miked,
This may be a long shot, but have you ever bled your brakes?

You may have localized boiling your brake fluid as your brakes heat up.

Charlie

i have not. looks like it needs to be done though as the fluid looks very old and dark.
the ride into work this morn produced the same shudder at the end of the highway but it seemed less noticeable once i got into the city streets. what i think i really need to do is get in there and inspect the guts of the hub.

 

[Bruneti]

CharlieS,

I agree with your comments about a heavy vehicle decending a mountain being able to stress the braking system. This is the braking equivalent of running your truck on the track. I think the OEM pads are propbably geared more toward the lower temperature ranges to help give them more initial "bite" for street driving. This could be why they get stressed and cause pulsing from uneven material transfer (if that is what is happening). The people who are having issue from overheating their brakes may need to try a higher temp compound and brake fluid. Some simple brake ducts may also be in order.

Did anybody read the article in Sport Compact Car where they tested upgraded pads vs. upgraded pads & rotors on an Evo and a WRX? These idiots stressed the upgraded brake systems by desending a mountain road at high speed. They had one of the high temp race pads catch on fire during the test. Imagine what a $12 pep boys pad would do.

I'm still doubtful that the oem rotors severely warp after being turned once. However, I don't have any data one way or the other. Just my experience that Toyota uses quality parts sources.

 

[ryanjl]

Bruneti, no one here drives their 80 like a sports car, but the same braking principles can apply between a Supra in an autocross and an 80 series with 35"+ tires coming down a mountain pass.

Just based on my personal experience, I had my rotors turned. They worked fine and smooth for a few thousand miles, but then slowly began pulsing when I'd come to a stop. Right before I swapped them out for OEM's, you could hear a rubbing sound at a frequncy in time with the tires when you had the windows down, coming from the rotor hitting the brake pads at certain spots.

Whether this was a warped rotor or not, I'm not sure. But after I replaced the rotors with OEM and 100 series pads, the brakes have been smooth as butter for 15K miles.

Many others have posted the same problems with turned rotors on their 80s, so my recommendation to everyone is "if you don't want to risk the good chance you'll have to do all this over again in a few months, just replace them with OEM now." As I said earlier, my rotors were not ground below Toyota specs, and neither has anyone elses AFAIK.

 

[ryanjl]

Oops, sorry. Didn't see the "80 decsending a mountain" thing had already been brought up.

 

[fzj80kidpen]

Brakes always good for getting things heated up
My 02 cents.
My brakes used to pulse to the point of being annoying.
When I did the front axle grease job I had new rotors ready.
I ended up not using them as I thought the surfaces was in good shape.
I put 80 series Bendix semi-metallic pads on.
FSM calls for metallic but I hate the dust and noise.
Of course I took care to use a lot of brake cleaner on both surfaces on both sides and the pulse was gone.
Stopping distance increased by very little.
When these wear out (its been 15k still no problem) then I will probably replace with Bendix ceramic.
I have also put on 285's which also increased the brakign distance so the ceramics will counteract this.

 

[97 FZJ80]

Something to add to support the larger pad = better stopping power theory. While the frictional coefficient of the pad/rotor interface is constant, there is a limit on the maximum frctional force/surface area that can be generated at the interface, regardless of the pressure exerted. The only way to increase the stopping force without changing the pad/rotor material is to increase the surface area. This is similar to the tire/pavement friction theory. Smaller sized tires theortically will have better traction, but in reality that we have larger tires for more traction.

 

[chip7238]

Formulas and Stuff...

I've been lurking for a little while - great info here guys!

Just thought I'd post a quick note on friction/force/pressure/surface area relationships. Some others have stated this in bits, but I'll put it together and hopefully fill in the gaps.

Pressure = Force / Area

Just do a quick unit analysis to prove it: psi = lb / in^2 (in this case lb = lb force, didn't want to confuse the issue by using slugs )

Okay, it follows that Force = Pressure * Area.

Therefore, with pressure applied by calipers remaining the same, a surface area increase will also increase the total amount of force applied.

Do not confuse total amount of force applied with "stopping force", though. The total amount of force applied to brake is connected with the coefficient of friction. The coefficient of friction (in this case, dynamic friction since the rotor is in motion) is a function of pad and rotor materials, wear, heat buildup, and some other things too.

Friction Force = Coefficient of dynamic friction for system * Force applied (from above)

So, as long everything else remains equal, the increased surface area of the 100 pad will make a difference in braking. Of course, it's going to take some comparison data from both to know if everything is truely equal.



Chip

 

[e9999]

I've been lurking for a little while - great info here guys!

Just thought I'd post a quick note on friction/force/pressure/surface area relationships. Some others have stated this in bits, but I'll put it together and hopefully fill in the gaps.

Pressure = Force / Area

Just do a quick unit analysis to prove it: psi = lb / in^2 (in this case lb = lb force, didn't want to confuse the issue by using slugs )

Okay, it follows that Force = Pressure * Area.

Therefore, with pressure applied by calipers remaining the same, a surface area increase will also increase the total amount of force applied.

snip

Chip

Nope! Welcome anyway!
The pressure in the hydraulic system is controlled by the pedal etc.
So let's talk about a given pressure exerted on the caliper. Caliper has fixed surface area, so force exerted by the caliper is known.
It's that force that is exerted on the pads and is a given. So for a larger pad with the caliper and same pedal pushing, the pressure exerted by the pad on the rotor is smaller, even though the normal force exerted by the pad would stay the same.
Of course, one could simply push harder on the pedal to generate a greater force, but this can be done with the smaller pads too.
So, as discussed above, it's not an issue of greater force or pressure that could make a 100 pad better IMHO, it's much more an issue of pad heating, temperature, material properties etc...

 

[Rich]

...
Okay, it follows that Force = Pressure * Area.

Therefore, with pressure applied by calipers remaining the same, a surface area increase will also increase the total amount of force applied.
...
Chip

There is a error in the logic above. And that is that the pressure (I.E. lbs/sqi) that matters is the pressure exerted by the pad against the rotor. With the pressure at the caliper pistons remaining constant, the psi with a larger pad will be less than with a smaller pad. The net result is that the force remain constant across pads of vary size.

 

[chip7238]

You guys are both right - I should have drawn my free body diagram - got force and pressure backwards in my mind. The formulas are still right, but with the wrong analysis.

It does come down to heat dissipation, and some other materials stuff.

I wonder if the larger pad would have a tendency to deflect more than the smaller one. Since the calipers only have 2 cylinders IIRC, then there would be a concentrated force applied to the point on the pad directly inline with that cylinder.

I remember reading an article a couple of years back about an F1 brake design (not sure if it experimental or not), and how it used 8 or 10 cylinder calipers with individual pads for each one to make sure that each pad was used to its fullest - i.e. even contact with the rotors.

Any thoughts on this?

Thanks for pointing out the err of my ways...

Chip

 

[e9999]

OK, Chip ole' buddy, let me guess:
you're a Junior in a Mechanical Engineering degree program...? Close enough?

 

[reffug]

Done Riley.

 

[Riley]

They are 4 piston calipers.

oh and thanks Mr Mod for fixing my spelling error in the title. Man it was bugging me.

 

[hoser]

I remember reading an article a couple of years back about an F1 brake design (not sure if it experimental or not), and how it used 8 or 10 cylinder calipers with individual pads for each one to make sure that each pad was used to its fullest - i.e. even contact with the rotors.

Here is something along those lines.

"The solution is to decrease the braking surface area of the discs as much as possible and mount it on a bigger light alloy hub. The B350 12 pot caliper makes this possible by using smaller multiple pistons to spread the pressure area around the outer circumference of the discs so that much of the centre portion of the discs can be removed.The B350 12 pot caliper does the same job as a massive conventional caliper would but without the weight penalty of a massive disc to go with it.

The other advantage the B350 12 pot caliper has is that on conventional caliper this size pad wear would become a problem as one edge would wear more than the other. This problem has been solved by using four pads per caliper and six pots per pair of pads to evenly distribute the pressure applied.Using six pots per pair of pads also allows different bore sizes to be used to even out wear characteristics ."

 

[RavenTai]

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.

I guess I am so delusional that I am hallucinating the dial indicator moving?

 

[e9999]

I guess I am so delusional that I am hallucinating the dial indicator moving?

eh, you said it! Not us... !