Slotted/Drilled Rotors vs Solid

[cruiserdan]

I am puzzled by 80 rotor warpage. Maybe I have been lucky but I have not experienced that problem ever in my vehicle. My original front rotors went over 96,000 miles without a hitch before I changed them as part of my front axle housing swap. In fact, one of them still lives on installed on a friend's 80. I replaced pads on them at about 22k mile intervals and I NEVER turned them. They did have a noticible "lip" at the outer edge when removed. My current set of OEM rotors have just passed the 30k mile mark with OEM 100 series pads. The friction surfaces are nice and flat with no aparent ridges AND the pads have about 50% remaining. My rear rotors are original and un-cut at 126k miles.


D-

 

[Scamper]

Dan - It may be my faulty memory, but I recall seeing a number of posts here and on other boards regarding warped rotors. But I too have never had this problem, even though I tend to abuse my brakes when towing.

Turbo - I think you misunderstood part of that thread's discussion on cross-drilling. The guy's point was that even though cross-drilling did cause some additional cooling to the rotor, the reduction in mass of the rotor (which reduces the effectivness of the swept surface to be cooled) is more significant. BUT, they were also talking mostly about racing car use where the pads and rotors don't get a chance to cool down between periods of exteme braking.

 

[cruiserdan]

Your memory is fine. Many folks have reported pulsation issues that appear to be related to warped rotors. I am un-able to identify a pattern.

 

[Cruiserdrew]

I had warped rotors on mine by 50k miles. I bought it with 39k I think, and they(Toyota) did a brake job as part of the pre-sale service, machining the rotors like the books say. I don't brake that hard or often, but I had major warpage problems front and rear. DBA's went on at least 20k ago with absolutely no problems since. I have the slots and no holes. Raven's pics made me run out to the garage, but they look perfect. One of my friends bought the DBA's that had the holes and was very proud of them. Our first trip out together he got a rock in one of the holes that made an aweful noise and tore up his brake pad. Lesson learned.

 

[Bear80]

Raven, if you had Midas put the rotors on did they set the torque on the hub correct? Many mechanics use the american car technique that you only tighten the nut finger tight. This will cause the steering wheel to shake under braking. My 80 had this problem when I bought it and it had new rotors put on not to long before my purchase. This will warp the rotors...you can do a quick check, pull the front wheels off and pull on the top of the rotor disk. If you notice any play at all the hub was not installed correctly, as far as I can tell there isn't any bearing damage but it sure itsn't good for them.

 

[RPG]

In my other life I race a Porsche. All OE drilled rotors (Brembo or otherwise) on a Porsche are drilled. Nobody, as far as I know, casts holes into the rotors- this is one of those strange internet rumours.
Any Brembo engineers that have been consulted on this have chuckled and replied: "Can you imagine the casting? Not a chance!"

Coming from personal experience, the quality of the metal in a rotor is FAR more important than anything else done to it 'after the fact'. As you can imagine, some OE rotors tend to be much more warp resistant(and rust resistant) to any OEM/aftermarket ones (of the same size/spec). Reducing the mass of object will not help in heat dissipation.
I have used drilled and slotted, slotted only, and OE rotors on my Porsche. I only use OE rotors on my Porsche now.

The two most influential variables in any vehcile braking system is the type and specification of the brake pads and the tires. Contrary to popular belief, bigger rotors will NOT necessarily reduce braking distances- they only really affect heat dissipation/fade resistance. If you want a shorter braking distance, buy grippier tires. If you want less rotor warping, go for bigger rotors and change brake pads.

The #1 factor I've seen in warpage problems has been driver habits. Coming down a long elevated exit ramp real fast, slamming on the brakes, and then SITTING at a traffic light with the brakes locked up is what really causes warpages.

 

[RavenTai]

Raven, if you had Midas put the rotors on did they set the torque on the hub correct? Many mechanics use the american car technique that you only tighten the nut finger tight. This will cause the steering wheel to shake under braking. My 80 had this problem when I bought it and it had new rotors put on not to long before my purchase. This will warp the rotors...you can do a quick check, pull the front wheels off and pull on the top of the rotor disk. If you notice any play at all the hub was not installed correctly, as far as I can tell there isn't any bearing damage but it sure itsn't good for them.

The rotor’s were installed about 6 months before I bought the cruiser, don’t know what torque was used but they were tight when I did the birf repack, I am up for tire rotation in about 500 miles (next weekend or the one after). I'll give them a wiggle then.

Feels like warped rotors, I assume loose rotors would make noise?

 

[Bear80]

nope, infact the wagon should drive fine and have no noise, but only when you brake the steering wheel shakes. When the job is first done, you won't notice it until the rotor becomes warped and causes the shakes.

oh if you already did a repack then I'm sure you put the hubs on correctly and now there is no way to know for sure if it was due to incorrect seating of the bearings/hub nut by midas.

 

[Beowulf]

I don't think you'll find any race team that will use "drilled rotors." As stated above, "drilled" rotors are actually cast not drilled into a solid rotor.

In my other life I race a Porsche. All OE drilled rotors (Brembo or otherwise) on a Porsche are drilled. Nobody, as far as I know, casts holes into the rotors- this is one of those strange internet rumours. Any Brembo engineers that have been consulted on this have chuckled and replied: "Can you imagine the casting? Not a chance!"

I think I'll believe RPG. This makes much more sense than what Bear80 is telling us.

-B-

 

[IdahoDoug]

I'm with Cdan on this and his experience almost exactly mirrors mine down to the miles when the original rotors were removed, etc. However, I also have around 15,000 miles of towing a 6000lb trailer and have had two memorable 65-0 full on panic stops with the trailer with. I believe a properly maintained brake system (regular proper flushes, no sticking calipers, pads in good nick, etc) will provide at least the same margin of performance improvement as upgraded pads and rotors do.

Turbo - not intended to insult you, but did you do instrumented testing with your and your Dad's 80s, or is this a seat of the pants assessment of the changes you've made? I ask this because I really feel that instrumented testing and measuring are the only real way to evaluate mechanical changes like this. I've participated in a lot of instrumented testing as a Product Planner for both GM and Lexus and for something like braking performance there's simply no substitute.

I've offered before to compare my stopping distances to anyone's "improved" braking system and got no takers. As RPG aptly stated above, grippier tires will make a FAR (like twice the impact or more) greater impact on braking distance that any brake improvement will. One last comment on brakes is that many people who have larger diameter tires on complain about their brakes. This is a change that directly leads to less effective brakes. These larger tires are also generally offroad traction oriented, which is the opposite direction to go for good braking.


DougM

 

[turbocruiser]

Turbo - not intended to insult you, but did you do instrumented testing with your and your Dad's 80s, or is this a seat of the pants assessment of the changes you've made? I ask this because I really feel that instrumented testing and measuring are the only real way to evaluate mechanical changes like this. I've participated in a lot of instrumented testing as a Product Planner for both GM and Lexus and for something like braking performance there's simply no substitute.
DougM

Hi Doug, no insult taken at all and thanks for going out of your way to make that so, you're a gentleman and scholar.

To answer the question this is the seat of the pants method. So you are absolutely right in saying that what my father and I perceived as improved performance is not quantifiable. It was something we both perceived though so it is probably not placebo effect, but you are absolutely right in saying that its indeed impossible to know til measurements are taken with all other factors equal.

Some factors that were totally unequal is the weight of these two 80's - my father's was bone stock since he got it and he had Michelin LTX 285's - mine has slee sliders, slee tc skid, arb bullbar and GoodYear ATS 285's. I assumed the LTX's would be much better for braking than the ATS and I know that my rig weighs more so I assumed if braking performance was equal, his would stop faster. Again by the seat of the pants method, even with the differences, my 80 consistently stops faster.

I'd love to be able to hook the measurement tools up and see exactly how much, if any, the DBA rotors improve brake performance over OEM. I would be surprised but willing to work with it if the tools showed no improvement. At least with the measurement my mind could convince my ass that there was no difference, instead of my ass convincing my mind!!! This is a cool thread. Keep the thoughts coming!

 

[turbocruiser]

Turbo - I think you misunderstood part of that thread's discussion on cross-drilling. The guy's point was that even though cross-drilling did cause some additional cooling to the rotor, the reduction in mass of the rotor (which reduces the effectivness of the swept surface to be cooled) is more significant. BUT, they were also talking mostly about racing car use where the pads and rotors don't get a chance to cool down between periods of exteme braking.

Naah, I understood the thread, I think maybe you misunderstood what I wrote. What I was saying is that there are two advertised reasons for crossdrilling - reducing weight and increasing heat dissipation. I was also saying that the amount of weight saved with drilled rotors while we at the same time work 33" plus tires is insignificant to the point of possibly being immeasurable ( I mean whats a few grams when your tire and wheel are weighing in at 50 plus pounds?). So in the case of our 80's the primary significance of drilled rotors is the extra heat dissipation. IOW I was not saying that is the most important performance advantage of drilled rotors, JUST that it is probably the only added advantage to drilled rotors, on 80 LC's.

I looked super closely and carefully at all four rotors today while I was replacing my tires. They are in perfect shape: so smooth that you cannot feel any good grooves in them, absolutely no discoloration or stress cracks or anything, not even a lip from where the pad misses!!! Still, the next time I get new rotors, probably another 75K from now, I'm gonna get the slotted only style. There are enough examples here already for a person like me to not opt for the drilled again - I mean I'm a worry wart first of all and secondly my terrian is frequently lots and lots of granite gravel. So again, this thread is super cool and has convinced me that my holes are perhaps an advantage I should not really rely on - I mean if I'm getting the rotors so hot that I need the extra marginal edge of the holes, I'm probably pushing the rig harder than any 80 is supposed to go. Very cool thread though, thanks.


BTW, some strange reason, even though I posted above and the thread was listed as two pages, I could not go to page two, and yet, my post was not showing on page one either. Doodoodoooo Twilight Zone man.

 

[reffug]

BTW, some strange reason, even though I posted above and the thread was listed as two pages, I could not go to page two, and yet, my post was not showing on page one either. Doodoodoooo Twilight Zone man.

Damn that was happening to me too..............

Thought it was just my puter f-ing up.

Turbo, in your previous story was the wife with you? :whoops:

Nice write up dude.

 

[Arleaux]

What timing, NOW you guys have a rotor seminar

Here are my slotted rotors I put on last night.

 

[Beowulf]

How about turning on some lights in the garage.

There, that's a little better.

You need to get some real jack stands before you get under that thing. Seriously.

-B-

 

[turbocruiser]

Damn that was happening to me too..............

Thought it was just my puter f-ing up.

Turbo, in your previous story was the wife with you? :whoops:

Nice write up dude.

No, thank goodness, she did stay home that time that I got so stuck. Normally she's wonderful 'sept when I decide to do something stupid, then she mentally magnifies my mistake for me forever!!! Gotta luv em heh???

 

[Arleaux]

You need to get some real jack stands before you get under that thing. Seriously.

-B-

Give me an example -B-

 

[Beowulf]

Or a pair of these 6-tons at Harbor Freight for ~$25

 

[Arleaux]

Thanks,
My Dad & I have been using the jack stands you see in the pic for years.

He's got a birthday comin up

 

[Jim_Chow]

I have those same Lincoln 6 ton stands for the front (Lincoln 3-ton stands for the rear axle), along w/ a Lincoln 3-ton floor jack. My frame is about 18" off the ground, so I still have to extend those stands quite a bit. If you're lifted quite a bit, you might consider the Lincoln 10 ton stands. Had I known, I might have gone w/ the 10 ton ones instead.

I'm running slotted brembo's...best rotors I've ever used. No signs of cracking. So far, I have 55K mi on them, running kevlar/carbon 0-1000F pads (not recommended if you live in a cold climate, though). I had cheapo unslotted rotors before (Napa?), but they warped in < 1 yr. This experience leads me to believe the warpage problem is due to cheapo metal/construction methods. I called up Wilwood, and the tech told me that drilled rotors really don't do anything other than for looks. They only help w/ out-gassing with the old-type organic pads. You also lose quite a bit of rotor surface area w/ holes, and those holes are prone to stress cracks. I like slotted rotors since it keeps the pads from glazing, and gets the water off fast when you submerge the rotors.