Why such big, hard cotter pins for brake pads?

[spokewrench]

When I replaced OE brake pads on a Radpower bike in 2021, the cotter pins were reasonably easy to straighten. The pins with the replacements were bigger and harder. It was difficult to bend the ends and worse when I had to remove the pads for cleaning.

Yesterday I replaced OE pads on another Radpower bike. The OE pins were reasonably small but of such hard steel that on the first one, I stopped trying to unbend the ends and tried diagonal cutters made for steel wire. They wouldn't cut it. Again, the replacement pins were very big and hard.

It appears that the cotter pins don't have to resist any braking force. Why are they so big and hard?

 

[PCeBiker]

,.. It appears that the cotter pins don't have to resist any braking force.

I'm pretty sure they do,..

When the brakes are applied, it's the cotter pin that keeps the pads and "spring" from rotating with the rotor.
Not the caliper housing itself.

All the brake force pressure is put on the cotter pin, and into the cotter pin mounting holes.


My brother-in-law showed me how to use diagonal side cutters to straighten and bend cotter pins.
It works great. The cutters bite into the cotter pin to keep it from slipping. You can't cut through them anyway.

It's just a matter of having enough room to get the head of the diagonal cutters into wherever to bend the pin.

 

[E biker]

Probably not a good idea to reuse old pins? Not a good place to skimp.

 

[PCeBiker]

It appears that the cotter pins don't have to resist any braking force. Why are they so big and hard?

I watched a YouTube video about installing hydraulic brake pads, and it looks like the pads slide into a channel inside the caliper.
So it looks like the sides/edges of the brake pads transmit force directly to the caliper housing.

So maybe the cotter pin does nothing more than keep the pads from falling out of the caliper?

 

[mfgrep]

I've read these posts, however, I still do not believe that these cotter pins (or threaded bolts depending on model) sustain any substantial braking loads whatsoever.
These bits merely hold the spring/pads in place within the caliper.

 

[sc00ter]

I've seen someone use a small zip tie in place of that cotter pin, ON A MOTORCYCLE! I still see this person from time to time so I guess the zip tie worked.

 

[spokewrench]

I'm pretty sure they do,..



When the brakes are applied, it's the cotter pin that keeps the pads and "spring" from rotating with the rotor.
Not the caliper housing itself.

All the brake force pressure is put on the cotter pin, and into the cotter pin mounting holes.

Your pics don't show how the pads are aligned relative to disk rotation. On mine, the slots are perpendicular to rotation, so the edges would secure the pads against rotation.

Suppose your gross weight is 350 pounds. Stopping in 20 feet from 20 mph would be almost entirely up to the front brake, requiring 245 pounds of braking on the contact patch. If the tire is 700mm and the disk 160mm, the pads would have to pull 1072 pounds. If a pin had to deal with that 50 times a day for years, I'd want a big, round, lubricated pin, not a cotter pin.

 

[spokewrench]

I've seen someone use a small zip tie in place of that cotter pin, ON A MOTORCYCLE! I still see this person from time to time so I guess the zip tie worked.

I was going to experiment with 0.8mm lock wire, but I have a jar of puny zip ties that would be ideal. In testing I'd avoid streets that might require both brakes. If a little zip tie holds everything in place, a smaller, softer cotter pin would be fine.

Hmmm... maybe the cotter pins are big and hard to discourage reuse.

 

[Urbancowboy]

I've read these posts, however, I still do not believe that these cotter pins (or threaded bolts depending on model) sustain any substantial braking loads whatsoever.
These bits merely hold the spring/pads in place within the caliper.

Exactly
Cheers

 

[rob feature]

Check if the caliper is threaded on one side where the pin goes through. Alot of the time you can swap these for a bolt - usually easier than pins & not everyone has a stash of extra pins lying around. Manufacturers will use pins as a cost-saving measure on lower-spec models, but you may be able to order bolts for these. I know Sram & Shimano sell these separately. Might be a good alternative if you're having to buy pins.

 

[Urbancowboy]

I'm pretty sure they do,..

View attachment 179578View attachment 179579

When the brakes are applied, it's the cotter pin that keeps the pads and "spring" from rotating with the rotor.
Not the caliper housing itself.

All the brake force pressure is put on the cotter pin, and into the cotter pin mounting holes.


My brother-in-law showed me how to use diagonal side cutters to straighten and bend cotter pins.
It works great. The cutters bite into the cotter pin to keep it from slipping. You can't cut through them anyway.

It's just a matter of having enough room to get the head of the diagonal cutters into wherever to bend the pin.

Hmmmmm, I replaced and/or just checked the Brake Pads on my eBike before and found the Brake Pads are actually held in a recess of the Brake Caliper and thus prevented from "rotating". All the Cotter Pin does, is holding the Brake Pads so they don't slip out of the recess. I suspect its the same on your Brake Caliper, perhaps a quick check is in order.
Cheers

 

[Urbancowboy]

Btw. its good practice to bend both ends of the Cotter Pin because if the Cotter Pin fails (which is highly unlikely) both sides will still stay in and hold the Brake Pads.
Cheers

 

[indianajo]

The US Army Ordnance Officer's basic course, instructed us in 1974 that mechanics we supervise, should always cut cotter pins , and never reuse them.
Those Army cotter pins were mil-spec and probably actually steel. 100% of the cotter pins for sale to me now come from a country where 99.99999% of ferrous metal contains copper, tin, zinc, lead from scrap. Only purchasers that maintain a foreign inspector in that country 24/7 have any chance of receiving parts made of steel. One poster on this website, who was such an inspector sent to that country, was assigned to watch batches of engine block metal to determine how glass was getting into the engine blocks. He observed a cleaner pouring floor sweepings, including glass from bottles & jars, into the melt.
After a decade of only tools from that country being offered for sale to me, now even my corner auto supply offers tools from Taiwan or India. I have had no trouble with those tools. However the box of cotter pins still comes from China. Fortunately brake pads from Shimano come with the pins, and have a chance of having been inspected for proper material before being boxed and shipped. Shimano has big enough operations there to keep an inspector on site 24/7.
As for cotter pins that will not cut, I suggest an 8" diagonal cutter from Chanellock. Still made in USA of US steel, for mechanics that want to do the job once and be done with it. Klein tools has a good one, made in Mansfield TX.
The quality of US Steel from the company of that name, became established in WWII when the plant manager and QC manager of their works went to jail for supplying the "steel" that made the keel of an ore boat that cracked in two and sank.

 

[Urbancowboy]

Some of the best Cotter Pins are made of Stainless Steel soft enough so one can cut them with Side cutter Pliers. I certainly would not want to use "Steel" meaning hardened Steel. I would thing most Cotter Pins on the Bikes are made of "mild Steel" meaning they can be bend easily. As you mentioned best practice is don't reuse a Cotter Pin but if one does as I have done many times in a Pinch, not even once I had a problem.
Cheers

 

[PCeBiker]

As for cotter pins that will not cut, I suggest an 8" diagonal cutter from Chanellock. Still made in USA of US steel, for mechanics that want to do the job once and be done with it. Klein tools has a good one, made in Mansfield TX.

Knipex is another quality brand of diagonal cutters.
I can squeeze the handles with both hands, and all my might, and I won't damage the cutting edges.
It cuts brake and shifter cable so cleanly that the wire will feed back into the casing without fraying.

 

[PCeBiker]

,.. I suspect its the same on your Brake Caliper, perhaps a quick check is in order.
Cheers

Yeah, I'm sure mine are the same.
I haven't done my brake pads yet, so I haven't inspected the mechanism.

 

[spokewrench]

Check if the caliper is threaded on one side where the pin goes through. Alot of the time you can swap these for a bolt - usually easier than pins & not everyone has a stash of extra pins lying around. Manufacturers will use pins as a cost-saving measure on lower-spec models, but you may be able to order bolts for these. I know Sram & Shimano sell these separately. Might be a good alternative if you're having to buy pins.

I now realize zip ties would be bad in case the caliper got hot. I wondered about safety wire, which is good enough for aviation. I read that in aviation, cotter pins are used for more shear strength than other methods. That wouldn't be a problem with bicycle brake pads. Then I noticed that a cotter pin should be the fattest size that will slide in easily.

Doh! Probably a cotter pin should limit the radial bouncing of the pads. The holes are 3.25mm and my fattest safety wire is 1.5. That could let a bouncing pad change position as much as 1.75mm between brake applications, and maybe that would mean poor performance and fast wear.

Some cars use a snug-fitting pin with threads under the head. For brakes like mine, 3.0mm is probably standard for cotter pins. I guess the last ones I installed seemed fatter than before because they were so hard to bend. For under $7, I can get fifty 3.0mm galvanized cotter pins from Amazon. It doesn't say how stiff they are, but it seems to me that galvanized wire bends easily.

 

[indianajo]

For under $7, I can get fifty 3.0mm galvanized cotter pins from Amazon. It doesn't say how stiff they are, but it seems to me that galvanized wire bends easily.

People love coatings. Harbor Freight is full of garbage tools like drill bits coated with cobalt or titanium. .000001" of some expensive metal as a coating makes US consumers salivate. I buy my US made steel drill bits at mcmaster.com. Not even the Dewalt sold at Home Depot last as long.
The actual element content of mixtures like steel matters. The heat treat history matters, too. Unless you get an alloy report as mcmaster ships with steel bars & rods, you have no idea what you are buying. Unless a brand name like channellock. Or a country of origin, which in the case of China guarentees garbage unless it comes from a brand like Shimano or Caterpillar with serious on site QC. Boeing had such problems with their joint venture factory in China they scrapped it before it opened.
One feature of US law, is that a purchaser is not allowed to know what country of origin he is buying for any internet, mail order, or phone order purchase. The stockage of goods in stores where one can inspect the label is obsolete. Really annoys me.

 

[spokewrench]

Knipex is another quality brand of diagonal cutters.
I can squeeze the handles with both hands, and all my might, and I won't damage the cutting edges.
It cuts brake and shifter cable so cleanly that the wire will feed back into the casing without fraying.

Knipex says it good for up to 2mm. The cotter pins are 3mm.
Here's what I tried.

Amazon.com

They have longer handles. I squeezed hard. The cutting edges weren't damaged, but neither was the cotter pin.
I have some more powerful cutters that wouldn't fit. The other day I used them to cut up 7 gauge (4.5mm) steel wire for disposal. I didn't know what such fat wire was doing here unless 125 years ago my grandfather used to mount rubber tires on wooden wagon wheels.

 

[indianajo]

Amazon.com

They have longer handles. I squeezed hard. The cutting edges weren't damaged, but neither was the cotter pin.

The adjectives ultra tough and durable come free. The $9.99 price ought to tell you something. The Ican looks just like a real tool.
The Channellock 8" cutters are $45, the Klein are $48.