brake pads and coefficient of friction

Started by 94touring, December 14, 2020, 05:39:38 PM

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94touring

I've had a few days to kill time at work, so dove into brake pads.  This started as minor brake research on the Vw Bus and ended up in me watching videos of pads being destroyed in laboratories, disc brake test with vents and slots, and eventually learning about codes on the pads themselves.  Usually for the mini, pickup truck, or even Jen's recent BMW brake pad change, I'd just grab a set of whatever was priced about in the medium range and slap them on.  Now I'm rethinking this strategy after watching cheap pads on a fast spinning disc glowing red in some of these test videos.  I may even pull my truck pads and read what the codes say, since I pull the trailer occasionally and have had a couple incidents where hard braking was less than stellar.  I don't think the disc on the truck are slotted, I believe they are cross drilled, but there's actually a right and wrong way to install slotted disc.  Didn't know that.  On the bus my concern was brake fade.  Since it's the heavy camp conversion and hauling a mini perhaps or at the least a ton of other crap down a mountain, I want the brakes to actually work in extreme conditions.  I know the pads on there have a lot of meat on them, the disc aren't worn down, but I'm sure whatever pads it has are the cheapest pieces of shit some Brazilian guy could find to put on there.  Researching the VW forums as with any forum, you get a lot of well I used xyz brand and they seemed fine.  That really doesn't tell me much.  Then got into organic, semi metallic, and ceramic pros and cons.  After that was all said and done determined for my applications, mini, truck, and bus, that semi metallic is the way to go.  Grips cold, does well with fade, actually grips a bit more with heat to a point, last ok, wears ok.  Probably should have gone ceramic on Jen's BMW as it grips too much cold and I find it to be a jerky pita to drive after driving my other cars (edit they are ceramic, must just be the car or my heavy foot)  Not all pads are created equal.  They have ratings on the pads themselves.  The photo posted shows the chart and some explanation.  Turns out most pads for the bus are rated FE.  The first letter designates how well it does when the disc are cold.  F being higher than E means it grips better cold.  The 2nd letter designates high temps...going down the mountain heavy with only so much engine braking you can do.  This means in the FE example that pad would fade as it heats up.  Not ideal.  A few pads I found for the bus were EE, even worse.  I was able to find a couple FF pads and a set was purchased.  One thing I noticed were some of the Euro pads aren't marked the same as the US pads, and I will assume it's because the DOT has regulations for us to give these designations. 

As far as cross drilled and slotted disc go, they really don't do much for a street car.  Racing application sure.  Several test revealed some interesting things here too.  Side by side a vented, x drilled, slotted disc (fancy disc) to a regular disc in one series of test in a variety of driving conditions, actually showed the fancy disc running hotter.  However, it was also concluded that in this particular test the weight of the fancy disc was lighter and therefor was unable to shed/absorb heat energy as well.  The difference in temperatures were really just a few percent higher but it made sense.  In a racing application fancy disc vs regular the fancy disc did shed more heat by upwards of 150 degrees F.  Now perhaps going down a mountain or repeated hard braking on a hot summer day it would make a difference on a street car.  Doesn't hurt it, but just isn't usually going to help.   

MiniDave

Interesting stuff.

I knew that semi metallic were really grippy when cold as that's what BMW uses (and MINI) and those are the ones that leave your wheels all black.

I ran ceramic pads on Roses '04 Audi and on my blue MINI cause I got sick and tired of cleaning the wheels all the time - I did notice they're not as grabby cold, but they also don't seem to have the same stopping power as the factory MINI pads do, esp. when towing the green MINI. They're perfectly fine tho for daily driving, even in mountains as they don't seem to fade under hard use. I never ran them on the track tho, like I did with the factory MINI pads.

So what did you decide to run on the bus?

Remember - brakes stop the wheels, tires stop the car.
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

94touring

Bosch has some FF pads in semi metallic that should work just fine that I ordered.  Well, my company did cause they sent me an Amazon gift card earlier today.  Couldn't tell if the local ATE pads were FF or not, they actually say AF.  They were about the same price as the bosch and I at least know they're FF.  The Pagid that get good reviews online are Euro and have nothing I can decode.  As far as I know there aren't any GG pads for bus/vanagons.  I just know I don't want EE or FE.

Correct, tires are equally as important.  I have the correct light truck tires with the proper ratio of inflation for the rear and back. 

Jimini II

Great info. I am going to do a brake job on my GMC Sierra tow vehicle and am looking at the different options.
A friend of mine with a Toyota SUV tows a toy hauler and just installed a Bremebo brake kit and he said the difference is amazing.
I was looking at the grooved and slotted rotors but read a lot of reviews that said they are noisy and have a weird pedal feel, other posters have even replaced them and gone back to stock rotors.

94touring

I have cars with slotted and drilled rotors but haven't noticed any difference in pedal or noise personally.  I've run them on minis and my rx7 certainly has them.

94touring

There's some history behind slots and drilled rotors actually.  Way back in the day of asbestos and other materials, brake pads emitted gasses.  This would cause the pads to float and you'd get mushy pedal feel and poor braking.  To remedy this they cut grooves and drilled holes.  Today this isn't much of a problem.  Although it's said that grooves will help clear the surface of the pad and keep things clean. 

94touring

Trying to price pads for my Tundra assuming the cheap set on there are junk.  I noticed that the OEM factory pads came in a couple different specs, even with the same part number.  Some are labeled FF and others FG.  There's also an OEM EF pad set.  Brembo makes a GG set in ceramic that may be the way I go, also comes with the rear shoes which I've never changed. 

cstudep

Wow you have really done some research here. I had no idea about any of this stuff but I do know that Toyota OEM pads are some of the longest lasting and least troublesome pads I have ever used on a vehicle so I have always just done OEM with Toyota. Next time I am buying pads for the truck though I am going to keep this in mind as the ones that I got the last time I did them suck, but since I had to do them 700 miles away from home in a campground, I used what I could get at the time.

94touring

Quote from: cstudep on December 15, 2020, 01:48:23 PM
Wow you have really done some research here. I had no idea about any of this stuff but I do know that Toyota OEM pads are some of the longest lasting and least troublesome pads I have ever used on a vehicle so I have always just done OEM with Toyota. Next time I am buying pads for the truck though I am going to keep this in mind as the ones that I got the last time I did them suck, but since I had to do them 700 miles away from home in a campground, I used what I could get at the time.

A few years ago shortly after buying my truck, which was used an it's rather old at this point being a 2003 but had 75k miles, the brakes were wobbling on medium/hard braking.  So I went to trusty ebay and found a disc and pad combo to toss on the front.  I didn't know any of this stuff at the time of course.  Now I find myself annoyed looking up pads and I can't see the DOT rating letters that let me know how well the pads actually perform. 

94touring

One more thing I've stumbled across, arcing drum shoes to fit perfectly to the arc of the drum.  Has anyone ever checked to see the contact patch on their shoes to drum mating surface?  Since no one has these machines readily available to do shoes, another option is getting sticky sheet sandpaper, adhering it to the drum, and sanding down the shoe by hand till it matches the arc.  Curious how the new shoes will match my old drums on the Tundra.  The rear disc conversion on my mini won't allow me to check anything there. 


MiniDave

Yes, this was common practice when cars had all drum brakes, I think today most people just wait for them to wear in together. I use my belt sander - you can hold the shoe next to the drum and see where it needs a little taken off.....

Today's shoes are made better too, so they need less attention to match the drum.
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

94touring

Saw some guys using belt sanders too.  Just something I'd never considered.

tsumini

FWIW When I built up my single LE brakes on the 60 I had the drums trued up and diameters were fairly close. I set the brake adjuster tight (Unable to turn) and backed the adjuster off one flat (1/4 turn) with light drag.
The first run of about 3 miles RT ended with front brakes dragging and slowing the car. Brakes were hot but not excessively. The next day when cooled they were free and weren't adjusted and 2nd run done. This time the rears were dragging and hot. After cooling they also were free and not adjusted. At least for new parts and turned drums I stumbled onto a technique to bed in the brakes. I do recall trying to sand down the shoes with not a lot of success. So far the brakes are firm with good pedal.

jeff10049

Quote from: 94touring on December 14, 2020, 07:47:01 PM
There's some history behind slots and drilled rotors actually.  Way back in the day of asbestos and other materials, brake pads emitted gasses.  This would cause the pads to float and you'd get mushy pedal feel and poor braking.  To remedy this they cut grooves and drilled holes.  Today this isn't much of a problem.  Although it's said that grooves will help clear the surface of the pad and keep things clean.

Around here this time of year odot dumps tons of volcanic cinders on the roads for traction slotted rotors are your friend really helps keep the cinders out of the pad surface they still embed in the engine belts and grind down the pulleys though.

I have a shoe arching/grinding machine this is how a lot of guys got exposed to large amounts of asbestos.

Like tsumini I run single leading on my 60 they will lock the wheels up easy from any speed the car can go.  firm pedal and work great you have to stay on the adjustment but they work very well. I did arch the shoes to the drums.