Manual disc brakes

[ntsqd]

While I'm thinking about it there are related things that are worth knowing if they aren't already.

Pad size. The area of the brake pads on the rotors has little influence on how good or bad the brakes work*. In calculating all of the various things that can be calculated about brakes, the area of the brake pads is not in any of those formulas. The geographic center of the pad area is in a formula or two, but not the area itself. The friction that the pads generate against the rotors is dependent on only the clamping force and the friction material's Coefficient of Friction (which varies with operating temperature). wilwood used to publish pad compound Cf vs. temperature graphs, I don't know that anyone else does this.

Drilled Rotors. They aren't necessary or even a good idea. They used to be, in the 60's and early 70's. They weren't a great idea then either, but they were used because they fixed a bigger problem at the expense of a shorter life. The friction material would generate a gas when they got hot enough and that gas would build up between the pad and the rotor. Which caused the brakes to fade. The problem was that the gas could build up faster than it could escape around the perimeter of the pad. The holes sped up getting the gas out of the way. When I said they weren't a great idea then either what I mean is that drilled rotors crack earlier and have a shorter service life than non-drilled rotors. It is sad that some Marketing person decided that we all need drilled rotors. Probably;y so that they could sell us more rotors.
Slotted rotors could have the same cracking problem, but do not appear to be quite as bad. In off-road use the slots are thought to provide a wiping mechanism that cleans dirt & debris off the face of the pad. I'm not convinced, but it's a good argument and it wouldn't surprise me.

Rotor width or thickness. This is brake fade factor, heavier vehicles will have thicker rotors for two reasons. More thermal mass (slower to heat up) and increased airflow thru the vents (faster to cool down). Thicker rotors increase the flywheel effect.

*With one exception that is a theory of mine that I've not (yet) had a good vehicle to experiment with it.

 

[gnpenning]

The 76 and 77 Broncos were available with manual disc or power assist disc brakes.
Depending on what was ordered. With manual brakes, there was a spacer between the master cylinder and the firewall. 1 inch thick if I remember.
So yours may or may not have been swapped out at some point. Might’ve come from the factory that way.

This is how my 76 came from the factory. Did the same basic thing when I converted my 74 to disc brakes back in the early 90s.

 

[ssray]

Lots of math in brakes....a little perusing the Wilwood site the other day found some 16" rotors the biggest they list. Would help in the MA part of the equations and likely heating at the expense of rotational mass. Would take bigger wheels, probably over 18"? Some of their calipers look low profile but I really have no idea how much they need for clearance. OEM calipers are space hogs just from what I've seen.
Something else Ive seen mentioned is dual calipers. Sounds good until you go back to the formula and have to add area to the master which then requires more pedal pressure to maintain line pressure. The 4 piston calipers are likely doing something similar by creating more pad pressure. In theory doubling caliphers would double the stopping force but thermal capacity would come into play along with the factors above. Of course you could have smaller piston area on double calipers and still increase braking over a single. Hope I've got this right and am making sense.
I wonder if anyone has tried some kind of cam based mechanical system at some point in time. Fast ramp at the start for good feel under low braking with a lower ramp rate after to give a higher MA as you push at the expense of travel. If pedal pressure was still increasing though with travel would it reduce the mushy feel that a higher ratio system gets? I have to wonder if the math in this would even work. Fortunately we have boost systems for larger capacity brake systems.

 

[ntsqd]

General Rule of Thumb is the largest rotor that will fit in a given wheel size is 3" smaller than the wheel. A 12" rotor for a 15" wheel, a 13" rotor for a 16" wheel, etc. There are always exceptions, but that rule will get you thru most of it. One of the exceptions is the 12.188 rotor in a 15" wheel. It is caliper choice sensitive, but generally it works.

Haven't seen dual calipers done in years, and the last one that I saw was a Vintage racer so it was decades old then. If the m/c bore is scaled up appropriately to give the desired Total Ratio nothing really changes except that now the rotor has two thermal input zones and a smaller thermal rejection area. I recall being told that they really didn't work as well as expected, but I don't recall the details of why. Assuming that I ever knew them anyway.

I wasn't directly involved, but I did watch my mentor doing R&D on a mechanical caliper for an OEM application. Those get ugly really fast. If you design it to have a reasonable lever movement you very likely will not have much clamping force. If you design it have enough clamping force the lever's motion range will be large.

 

[nvrstuk]

Math- that's why I like brakes...

 

[Speedrdr]

Math- that's why I like brakes...

And I’M happy that there are folks here that like math and are willing to use it to help them of us who don’t particularly like math. I’m decently good with math and physics but prefer not to get off in the weeds with it. Lol

Randy

 

[Yeller]

Math- that's why I like brakes...

you've not lived until you've driven at a ratio of 200:1

I had never run the numbers on that set up until TS made this thread. That was 3.5" 1 ton calipers front, 3" gm calipers rear, stock 1" bore master. Could push the pedal to the floor with your finger....

 

[nvrstuk]

you've not lived until you've driven at a ratio of 200:1

I had never run the numbers on that set up until TS made this thread. That was 3.5" 1 ton calipers front, 3" gm calipers rear, stock 1" bore master. Could push the pedal to the floor with your finger....

Did you just need 2ft of pedal travel???

I just left having a beer at a pub that opened in 1604 in Bristol, UK.

Totally enjoy the architecture over here...

 

[ntsqd]

I use Excel and make IT do that math stuff....

Send us a pic of their Lucas refrigerators!

 

[Yeller]

Lol nope stock travel. But start pushing and nothing, nothing, nothing, now getting something keep pushing, really getting something, keep pushing, locked up and thump goes the floor🫣

 

[Oldtimer]

Do British refrigerators leak oil like their motorcycles?

 

[ntsqd]

It's easier than a dipstick. If they don't leak, they're out of oil.

 

[ssray]

Lol nope stock travel. But start pushing and nothing, nothing, nothing, now getting something keep pushing, really getting something, keep pushing, locked up and thump goes the floor🫣

Your very example was what got me thinking about a cam follower at the pivot point of the brake pedal. LOL It will take MATH to figure but need a difference in radius from start to end equivalent to the travel of the master plunger. Ramp it in quick at first to take up slack and get some brake feel then taper the ramp rate up to full travel. Full travel so still high ratio, just maybe could be made to feel better. It would take some precision machining and be built well, probably not really feasible but interesting challenge for a good home machinist. If the cam follower had the metallurgy of Brian’s lifter maybe not such a good idea!

 

[nvrstuk]

I'm following these threads watching Audi's, Porsche's & Beamers cruise by while all food & coffee is at least 50% more ... Bristol, UK.

I'll have to quit my whining about high costs when I we get home. (Least for a week). lol

 

[Speedrdr]

@nvrstuk, how is central WA functioning without you there? The state may disintegrate.


Randy

 

[ntsqd]

He's probably out there right now trying to figure out how to get one of those Thames Taxi's to lay some stripes.........
"Nah, it'll do it. we just need a Holset HX30 with it's wastegate wired shut....."

 

[nvrstuk]

@nvrstuk, how is central WA functioning without you there? The state may disintegrate.


Randy

Friends have told me it's much quieter!

 

[Broncobowsher]

As noted above, pad material is a HUGE factor. Long time ago I was playing with another car and was trying out different brake compounds. Just the drivability between 2 different compounds felt like two completely different vehicles. And this was just swapping around parts store organtic and semi-metalic pads. Long before the internet and the availability of finding the plethora of compounds. Last Bronco got a nice blend with a no longer offered Wilwood pad. Had a little more low speed noise than I would have liked and the dust was nasty.

 

[nvrstuk]

As noted above, pad material is a HUGE factor. Long time ago I was playing with another car and was trying out different brake compounds. Just the drivability between 2 different compounds felt like two completely different vehicles. And this was just swapping around parts store organtic and semi-metalic pads. Long before the internet and the availability of finding the plethora of compounds. Last Bronco got a nice blend with a no longer offered Wilwood pad. Had a little more low speed noise than I would have liked and the dust was nasty.

...but they worked good!

 

[ntsqd]

As noted above, pad material is a HUGE factor. Long time ago I was playing with another car and was trying out different brake compounds. Just the drivability between 2 different compounds felt like two completely different vehicles. And this was just swapping around parts store organtic and semi-metalic pads. Long before the internet and the availability of finding the plethora of compounds. Last Bronco got a nice blend with a no longer offered Wilwood pad. Had a little more low speed noise than I would have liked and the dust was nasty.

Sounds like those were Compound E's. Excellent low operating temperature performance that didn't badly fade with increased operating temp. I remember them with the same fondness that late 60's era road racers talk about Ferodo's DS11 pads.

Had a set of E's on the front of my '79 Sub. When those were done and I couldn't get any more a friend with a 4x4 shop put me onto CarQuest's "Fleet Service" pad, which were everything that the E's did, but better. Except for the dusting, that was roughly cut in half. Now those are NLA, too. What they sell in it's place isn't nearly as good.
Part of my reasoning behind the brakes that I put on the FSB was to be able to use the lower to mid-level pads (No PF, ST, or EBC needed) and still have more than acceptable braking performance. I do have a set of EBC Yellows waiting for the Wagon because it is stuck with a sub 12" diameter rotor.