Can you guess?

I will pay for breakfast at the Gooseberry for the first member who tells me why this rotor has so many holes....and no answers like just to fit on!!

It was intentional to disapate heat

taken from on line - but I cheated to find answer so the breakfast goes to the first new member that rides with us if you feal I hit the answer --
"The "basic" lesson:

Ok. If I am trying to boil a pot of water with 2 gallons of water in it. It will take a lot of heat to get all of that water up to boiling temperature. Right? Now, if I remove 1/2 the water and with it, 1/2 the mass used to absorb heat, it will now be easier to get that water to boil since there is less mass to absorb heat. Make sense?

Ok, If I take a 3 lb chunk of metal and a 6 lb chunk of metal and set them both over a small torch, which one do you think will heat up first? The lighter mass will see a more rapid temperature rise (it will get hotter, quicker). Correct?

Now, if I take a brake rotor that weighs 20 lbs and begin making "panic stops" with it, it's temperature will increase. Easy enough.

If I now take the same rotor, drill holes in it reducing its weight to 17 lbs and make the same "panic stops", would it not make sense (from the above examples) that the lighter rotor will end that stop with a higher temperature? Less mass to absorb heat will cause a more rapid temperature rise.

Many will say "cross drilled rotors cool better". Hmmm. If you really look at it, how much air do you think can blow through those little holes? Add the fact that they are spinning at a reasonably high speed and the cooling argument becomes even less believable. In fact, the holes could, in theory, disrupt the natural draw of air from the center of the rotor to the outside edge. That is the flow that actually cools the rotors.

The reason:
Rotors were originally drilled to eliminate something known as "green fade". The best way to explain "Green fade" is to relate it to an air hockey table. The puck is suspended on a cushion of air that prevents it from touching the table, this reduces the friction between the puck and the table.

A long time ago, pads were made with the best resins we had available. Many of those resins would produce gas as they cured. When a pad was used the first few times, the heat would "cure" the resin which would cause it to produce vapors. This was known as "out gassing". The vapors would build up between the pad and the rotor and lift or "force" the pad away from the rotor (like the puck in air hockey). This caused the brakes to be very ineffective, even though they were not yet at the maximum rated operating temperature. The holes were drilled to allow that gas a place to escape. So, it is correct to say that rotors were cross drilled to eliminate fade, but not for the reasons you would think. The good news is that today's resins no longer suffer from these problem and the modern race pads are so good that this is really no longer an issue. So, by cross drilling rotors, you will only manage to shorten the lifespan of that rotor (it now has less surface area to wear against the brake pad and will wear more quickly as well as a reduction in weight that will cause the brakes to operate at a higher temperature).

Another problem with cross drilled rotors is the potential for cracking around the holes. The holes become a stress point in the cast iron that can more readily allow cracks to form in the rotor surface. This requires that you pay close attention to the rotor surface for signs of cracking. Some small cracks, known as "surface checking" are acceptable, but anything that resembles a crack would be a reason to replace that rotor. When looking at slotted rotors keep in mind that the slots should not be milled off of the edge of the rotor. This is a great place for cracks to form, and they will. The slot should be ball milled in the rotor face and originate and terminate on the surface of the rotor without exiting the rotors edge. The goal is to eliminate sharp edges that cause stress risers on the rotor surface. This will reduce the possibility of cracking. If you see slotted rotors with slots that are milled off the edge of the rotor, shop for another brand. Slots that are not cut through the edge of the rotor are a good sign that the manufacturer of that rotor knows what they are doing. This is a good indicator of parts made by a brake company and not a machine shop that happens to drill and slot rotors.

Many years ago, when I ordered my first brake kit from Baer Racing, they told me that drilled rotors would typically last 20% less than an equivalent solid rotor. This was why they always recommended solid rotors for extreme use. Baer has changed their stance on this since discovering there was a large amount of money to be made selling "Eradispeeds" (they are very pretty brake rotors). This change in their marketing strategy has caused me to feel that they have gone from "supporting the racing community" to "making maximum money". And, I guess I can't blame them.....

If you are truly looking for upgraded braking performance for your car. I suggest, as a first upgrade, that you leave the stock size rotors and upgrade the pads. Try a set of Hawk HPS pads or something from Larry at Carbotech Engineering (www.carbotecheng.com). You'll think you put "big brakes" on all 4 corners (compared to stock).

If you must go bigger, look at the G-stop kit from LG Motorsports. It will let you use a C5 Corvette rotor. Bang for the buck, the LG kit is an excellent choice. There are larger kits and they increase in both cost and braking ability. Only your needs and your budget are the limit."


Tires:

I'd also like to take a moment to address the impact that tires have on braking performance.

While it is true that the tires have the "last word" with the pavement when it comes to how the car accelerates, turns, and brakes. There are a few things that tires can and can't do. While it is true that a car on wide, sticky tires should and will out brake the same car on thin, non-grippy tires (all other things being equal). And, while tires are extremely important. They become less important on the 5th or 8th stop or the 3rd lap of a road course. By then the brakes (depending on rotor size, cooling, pads, etc) may be so hot that they can't lock up the skinny little tires, much less the wide, grippy ones. This is where upgrading the brakes pays dividends. This is not meant to minimize the tires role in braking performance. Simply, you must remember to weigh the tires limits against the brake systems limits. You are working with a "package" and changes in one can impact the other. So, while tires will be the limit on the first few stops, they will play a less important role as the brake system temperatures increase. Remember, just because you can lock up the tires on the first stop does not mean that you can't benefit from brake system upgrades."

I'm gonna say 5 on 4.5 and 5 on 5.5. What is that off of.

It looks like its the drum/rotor to the 8.8 Its drilled out to the new 5 on 5.5. That leaves the stock wheel stud holes for the stock 5 on 4.5. it was dont to save money and match the front Dana 44.

Allium.. I dont think you would want to disapate heat from the hat of the rotor. Slotted rotors are actual slots in the surface where the pads contact the rotor..

Matt you are on the right track...why would a rotor have both bolt patterns???

makitupthehardway wrote:

It looks like its the drum/rotor to the 8.8 Its drilled out to the new 5 on 5.5. That leaves the stock wheel stud holes for the stock 5 on 4.5. it was dont to save money and match the front Dana 44.

You got it.. but have you ever seen a rotor with both bolt patterns??

I havent and I have been in the business for 21 years..

That is the actual rotor off the back of the cherokee which has a 8.8 from a 95 explorer. I pulled the wheels and almost had a heart attack... I knew soon as I saw it that he had machined the 5 on 5 1/2 when the moser axles were ordered. I called the guy in Indiana and asked and he said he forgot to tell me about that...LOL...I started to take it a local machine shop but wanted to get it done today.. I took the old rotor and clamped the new one too it and put it on a drill press.. Worked perfectly.. I couldnt believe how easy the metal was to cut.. Then when I thought I was almost done the brake hose on the side that Tina broke had to be machined down also at the block..

Brakes are done and its ready to go..

We might be able to twist my arm and change the breakfast at Gooseberry to drinks at Oneals.... Just dont twist too hard..

If not they sell BEER at the Goose

Either one will work for me....LOL...