Brake Caliper Teardown (yes, with pictures!)

RennieK · Feb 8, 2010

Only the heat from my hand although it's a balmy 7' Celsius here (should be riding). No damage to anything, even the lougheed writing looks undisturbed. Eventually I cupped it in my hand with a rag to isolate my hand/bones ffom the shock.

swooshdave · Feb 8, 2010

RennieK said:
Only the heat from my hand although it's a balmy 7' Celsius here (should be riding). No damage to anything, even the lougheed writing looks undisturbed. Eventually I cupped it in my hand with a rag to isolate my hand/bones ffom the shock.

A little propane would have made it a LOT easier. Doesn't take much with the aluminum.

swooshdave · Mar 6, 2010

Maxxfli said:
It looks pretty bad but you would be surprised what you can turn that into. I cleaned mine up a bit with the wire wheel before drilling it. After the drilling was through I had it turned by a local machine shop. Did the chamfer after that and went to town with a serious wire wheel on a drill for the inside. Cost $40 to have it turned. When its turned the brake surface area will look new. You might want to soak her in naval jelly before tackling the project but i think you can avoid having it blasted. The stock rotor is .260" thick and has to be at least .245" thick to have it turned or ground. Took about 8 hours of work from start to finish on my rotor.

So it got blasted with the other parts to get powdercoated.

Brake Caliper Teardown (yes, with pictures!)

I think I'm just going to hit it with some primer and paint, with primer only on the braking area. Then get the sweep area skimmed when I'm closer to getting the bike on the road (you know, next year some time...) :mrgreen:

acadian · Mar 6, 2010

Hope to get some input by chiming in here with my own caliper issues. Has anyone been able to find a double male fitting with enough length as to allow the end of the brake line to screw directly into the caliper body (bypassing the steel pipe)? Unable to find one, I had to gently file the surface of the caliper around the fitting hole smooth to get a decent sealing surface. It worked, but there had to have been an easier way.

My second issue is with a stainless body plug I purchased, it just wont fit and I've tried it on two separate calipers, heated on both attempts. Has anyone else had this problem with these SS plugs? The last thing I need is to gall the threads, it should go in fairly easily, shouldn't it?

swooshdave · Mar 6, 2010

acadian said:
Hope to get some input by chiming in here with my own caliper issues. Has anyone been able to find a double male fitting with enough length as to allow the end of the brake line to screw directly into the caliper body (bypassing the steel pipe)? Unable to find one, I had to gently file the surface of the caliper around the fitting hole smooth to get a decent sealing surface. It worked, but there had to have been an easier way.

My second issue is with a stainless body plug I purchased, it just wont fit and I've tried it on two separate calipers, heated on both attempts. Has anyone else had this problem with these SS plugs? The last thing I need is to gall the threads, it should go in fairly easily, shouldn't it?

I'd use anti-seize, but there is no guarantee the plugs were made right. Can you compare them to the originals?

medomuffn · Mar 6, 2010

http://farm5.static.flickr.com/4057/441 ... 6eb4_t.jpg
This tool is very easy to make, and it's also adjustable

RennieK · Mar 6, 2010

Now there's a great use for a crescent wrench although if you turned down one end of the pins and made them longer you could have 2 sizes, one on each side.

B+Bogus · Mar 6, 2010

acadian said:
Hope to get some input by chiming in here with my own caliper issues. Has anyone been able to find a double male fitting with enough length as to allow the end of the brake line to screw directly into the caliper body (bypassing the steel pipe)? Unable to find one, I had to gently file the surface of the caliper around the fitting hole smooth to get a decent sealing surface. It worked, but there had to have been an easier way.

Is that a fibre washer? I'd strongly recommend replacing it with alloy or copper for ultimate peace of mind.

This is the hose I got from RGM in the UK - it went on with no issues and wasn't expensive. It came complete with a double-ended male connection; no other parts required.

acadian said:
My second issue is with a stainless body plug I purchased, it just wont fit and I've tried it on two separate calipers, heated on both attempts. Has anyone else had this problem with these SS plugs? The last thing I need is to gall the threads, it should go in fairly easily, shouldn't it?

Simple answer: yes, it should fit fairly easily!
Mine (again, from RGM) went in OK, but was a transition fit, i.e. I had to use a reasonable amount of effort to screw it in to a cold caliper, but it certainly didn't put up a fight as such; it was about the same as the original plug. I used brake fluid to lubricate the seal on fitting.
Galling is only really a problem when two stainless parts are screwed together in my experience, and then only when I've forgotten to lubricate the threads.
Have you tried fitting it without the seal?

acadian · Mar 7, 2010

B+Bogus said:
acadian said:

Hope to get some input by chiming in here with my own caliper issues. Has anyone been able to find a double male fitting with enough length as to allow the end of the brake line to screw directly into the caliper body (bypassing the steel pipe)? Unable to find one, I had to gently file the surface of the caliper around the fitting hole smooth to get a decent sealing surface. It worked, but there had to have been an easier way.

Click to expand...

Is that a fibre washer? I'd strongly recommend replacing it with alloy or copper for ultimate peace of mind.

This is the hose I got from RGM in the UK - it went on with no issues and wasn't expensive. It came complete with a double-ended male connection; no other parts required.

acadian said:

My second issue is with a stainless body plug I purchased, it just wont fit and I've tried it on two separate calipers, heated on both attempts. Has anyone else had this problem with these SS plugs? The last thing I need is to gall the threads, it should go in fairly easily, shouldn't it?

Click to expand...

Simple answer: yes, it should fit fairly easily!
Mine (again, from RGM) went in OK, but was a transition fit, i.e. I had to use a reasonable amount of effort to screw it in to a cold caliper, but it certainly didn't put up a fight as such; it was about the same as the original plug. I used brake fluid to lubricate the seal on fitting.
Galling is only really a problem when two stainless parts are screwed together in my experience, and then only when I've forgotten to lubricate the threads.
Have you tried fitting it without the seal?

It's a copper washer, the seal is good now with the decked caliper surface. The issue was that the male fitting provided was to short to "bottom out" in the plug hole, therefore the sealing surface had to be the flange area at the caliper surface which was not quite smooth.

As for the body plug, I didn't try fitting it without the seal... didn't really think about that to be honest. The resistance I met when screwing in the plug wasn't exactly "squishy", it was pretty abrupt metal-to-metal like. I did use anti-seize on the threads as well. Duane from Commando Specialties has offered either an exchange or refund, I'm not certain what to do. She's buttoned up nicely at the moment so there's no rush.

swooshdave · Mar 7, 2010

medomuffn said:
This tool is very easy to make, and it's also adjustable

acadian · Mar 10, 2010

Well, with the help of some great advice from this board I finally got the caliper completely rebuilt. Fresh stainless bits throughout (pistons, bleed valve, end plug, reservoir cap & brake line). decking the surface of the caliper body at the inlet hole was tedious but resulted in a nice smooth sealing surface. The original stainless end plug I purchased was definitely too big, the replacement sourced from Walridge fit perfectly and thanks to the DIY adjustable pin wrench mentioned in this thread, went in nicely.

medomuffn · Mar 10, 2010

Glad that tool worked for you...made mine years ago....patent pending :idea:

swooshdave · Mar 13, 2010

Painted it. Aimed for the center and edges. Before I install it (which will be a while) I'll get it turned down to bare metal.

Thickness is .260in so I think it's plenty thick enough to turn down. Just a few pits on the front side, back looks fine.

chaztuna · May 8, 2017

B+Bogus said:
As for drilling and tapping....why not drill out the piston instead? they're almost guaranteed to be scrap anyway :wink:
This could be used for both pistons, I guess...

Hi guys,
I'm new here. Just discovered this site. I'm back to tinkering with bikes after a 15 year layoff. I've got a Mk III that sat outside for 10 years. Needless to say, everything is rusted or corroded. I first soaked the caliper in ATF [automatic transmission fluid] for a week. I don't like to apply localized heat if I can help it, as the rule of thumb is that heating aluminum over 300F can cause it to warp. Next I tried heating it to 300F in the oven. That allowed me to remove the outer cover. I used a 3 pound engineer's hammer & a 3/4" diameter brass punch to move the outer piston after soaking the caliper back in the ATF for an additional 2 days. I removed the sealing O-ring and cleaned the exposed bore. As mentioned by an earlier poster, I was able to pry the outer piston out via the slot for the rotor/pads.
I have no functional master cylinder and the hammer & punch failed to move the inner piston. The outer piston had corrosion pitting, so it was junk. I could only assume the inner piston was as bad, or worse. As suggested above, I drilled an 1/8" pilot hole into the center of the inner piston. I then opened the hole to 3/16" and finally to 5/16", being careful not to drill into the back wall of the caliper. I tapped the hole for 3/8 X 16 TPI. I was hoping that the tapping process would spin the piston, but no such luck. I started with a taper tap, then used a bottoming tap, so as not to contact the rear wall of the caliper with the tap.
Using a 3/8" X 16 [coarse] X 4" bolt, I was able to press the piston out. However, due to corrosion and a less than perfect centering of the tapped hole, I could not "safely" get the inner piston through the bore for the outer piston. It kept wanting to cock as it transitioned the opening for the pads/rotor. I measured the rotor/pad opening, then measured the length of the outer piston. I realized that if I could cut the inner piston in half, I could retract each half out of the rotor/pad slot. Using a band-saw & a helper, I was successful doing that.
I removed the bolt from the piston, then re-installed it with a jam nut. This was done to prevent the band saw blade from simply spinning the piston around. After centering the piston in the rotor/pad slot, I guided the caliper into the band saw blade, while my assistant kept the piston from rotating by holding it still, with a 9/16" wrench. Push the back half in with the bolt. Remove the bolt & remove the outer half of the piston. Re-install the bolt to pull the inner half into the rotor/pad slot. Remove the bolt and remove the inner half of the piston. Job accomplished without excessive heat or being able to hydraulically force the piston out. Sorry, I didn't think to take photos. I could supply a photo of the now 2 piece inner piston. Scarring on the inner wall of the caliper was minimal, basically cosmetic, for an area that won't be seen.

chaztuna · May 9, 2017

Caliper Snap On Peg Spanner Outer & now 2 piece Inner Pistons. Long 3/8" bolt still in the back of the inner piston

Rear wall of the caliper, showing minimal scarring to the rear wall. Mark was made by contact from the 3/8" bolt.

This Snap On peg spanner worked quite well for removing the outer cover. The smaller set of pegs fit quite well into the cover.

swooshdave · May 17, 2017

I've never heard of anyone cutting the piston in half. Your assistant must be quite brave to hold onto a wrench in front of the band saw. :shock:

Time to get some SS pistons!

chaztuna · May 19, 2017

swooshdave said:
I've never heard of anyone cutting the piston in half. Your assistant must be quite brave to hold onto a wrench in front of the band saw. :shock:

Time to get some SS pistons!

Actually, he was stationed outboard [off to the outside]of the band saw [30" throat]. He had the 9/16" box wrench held firmly to the saw table to prevent the piston from spinning. It actually worked out quite well. You are right about needing SS pistons!

BrianK · May 19, 2017

I half remember this job....the part I do remember clearly was fabbing a peg spanner by chucking two drill bits into a vice. The part I can't quite remember is how I got enough leverage on the caliper to spin it around the improvised peg spanner. Anyway, I did, and if you're there, you probably will too....