Front Calipers Rebuild

[Okie2ee]

Tried searching forum for brake calipers and came up with everything but.............I'm looking for recommended methods to the remove the pistons from the caliper body............several of the pistons are locked in with the o-ring partly sticking out...............is there a tool for removing them.................tried air pressure and they didn't budge...........they've been sitting for several years...............any and all suggestions are welcome............don't want to go in with the vise grips just yet...........thanks

 

[dannymax]

Air pressure has always worked for me but I have heard of guys using grease gun pressure...maybe look into that.

 

[Fire-medic]

dannymax is correct. If the pistons are not frozen in the cylinder then an air compressor @100 psi should pop 'em-out. If that doesn't do it, try more air pressure. Be aware that if you use air pressure, and you are careless about it, you may end-up 'painting the walls' with DOT 3 or 4! As the pistons pop-out you may end up releasing the remaining brake fluid in the caliper. I usually try the air compressor first, and I'll use something like a screwdriver blade between the caliper pads, to stop their excessive movement where one side pops-out before the other, a common occurrence.

I also use a shop rag or an old bath towel around the caliper to prevent the splurt! of rapidly-propelled brake fluid going everywhere.

If you're a novice around DOT 3 or 4, they are great at removing paint, so have plenty of paper towels or clean shop towels to wipe-up any that spills onto painted surfaces.

I have a post about using the grease-gun on the opened bleeder valve, to remove stuck pistons. A hand-pump grease gun can develop nearly 2,000 psi so twenty-times an air compressor's pressure. Yes you have to clean the caliper's inner passages of grease but I've never had a caliper not release a piston or pistons.

A vintage SOHC Honda 750-4 surrendering to my grease gun.


Probably 40 year-old crystallized brake fluid.



A rig to test the rebuild before replacing it on the bike.

 

[Radioguylogs]

My first choice is to use the rear MC to push them out. Since there are 2 pistons in the Gen1 calipers, you have to block one side somehow so you can put pressure behind the other piston.

Sorry, I can't remember how I got both pistons out. I might have clamped one side when it was out "far enough", or I might have figured how to block the fluid passage, or I might have blocked off the opening after removing one piston.

My other choices are already mentioned....air or grease. Grease works better than air, but it's messy and little wasteful.

 

[Fire-medic]

A couple of C-clamps can hold one side of the caliper's pistons so the force goes to the stuck-side's pistons. A couple of pieces of flat bar stock say an inch wide by 1/8" or 1/4", where one goes inside the caliper (where the rotor would be) and one goes on the outside-back of the caliper, with the C-clamps holding them so the piston(s) on that side of the caliper are immobile, will transfer the pressure to the other side of the caliper's piston(s).

In this picture it appears to be a single thick brake caliper pad actuated by the pistons, and a much-thinner stationary brake caliper pad to the right of it.




pardon my crude drawing, there would be another C-clamp on the same side, below this one, and the caliper should have 4 pistons (two pairs of opposed pistons), instead of a stationary plate opposite the pistons as shown here. The blue line represents a flat piece of steel bar stock. The second piece of flat bar stock would go where the thick brake caliper pad is.

 

[one2dmax]

I broke down and bought an actual caliper piston tool removal kit. Came with multiple size "sockets" to tighten inside of a piston giving the ability to twist and pull to get them out. Works very well and quicker then the air pressure did for me.

 

[Fire-medic]

There are multiple sizes of plumbing tools which are 'internal-expanding' splined tools for removing pipe from being stuck in a female fitting, those would work, you'd just have to ensure you got the proper size for the pistons' I.D. you have.


https://www.homedepot.com/p/Husky-I...VxKlaBR3kKg9BEAQYBSABEgKRafD_BwE&gclsrc=aw.ds
$12.48 the set.

• Use to install and remove pipe nipples without marring, scratching or denting pipe surface
• Expandable knurled cams for an easy internal grip
• Use with an adjustable or standard wrench
• Long-lasting, durable solid steel
• Backed by a Lifetime Warranty. If your Husky product ever fails, bring it back and we will replace it for free. Click here for details.
• Includes 3/8 in., 1/2 in. and 3/4 in.
• Breaks loose pipe when threads are damaged

Another one, for larger pistons.


https://www.amazon.com/RIDGID-31405-Internal-Wrench-2-inch/dp/B0015B9SF6?th=1

$73.24

• Designed to hold closet spuds and bath, Basin and sink strainers through 2-inches
• Use to install or extract schedule 40 1-inch through 2-inch nipples
• Jaws expand by eccentric action and are reversible for various sizes
• 4-1/2-inch (113 mm) internal wrench has a 1-inch to 2-inch (25-50 mm) pipe capacity
• Ridgid covers its products with a lifetime warranty against defects in material or workmanship for the life of the tool

These two sets should cover any motorcycle pistons you have.

This one, I'm not sure what sizes it covers, but it says 'up-to 3-1/2"' so much-bigger than any bike piston. Maybe something to check-out before purchase, probably available at your local plumbing supply shop as it's a Sloan brand.


$51.64 list price

 

[Okie2ee]

Thanks to everyone for all the great suggestions....................I also found a YouTube video which showed a socket being placed in the piston and then a rod along side the socket inside the piston and then the rod would be rotated and cause the socket and rod to lockup against the piston............didn't work for me. Finally decided on the grease method..........started looking for a grease zerk to replace the bleeder screw and after several trips to the hardware store I realized that the grease gun will fit the top of the bleeder screw.............this is all information I didn't have and would have been nice to know............so I hooked up the grease gun and sure enough one of the piston started to move and I realized I have to limit the motion of that piston to maintain pressure on the others.............used wood working clamps to limit the piston travel.............that worked for one side and on the other side I had to block off the fluid passage ports using clamps:


Used a small piece of rubber sheet from plumbing supply section for gasket


Bolt required to hold the clamp from slipping off the casting



Cut off head from sheet rock screw inserted in the bottom of the main fluid supply bolt to block grease.
Once I got the piston to move I was able to pull them out with a pliers taped up not to damage the pistons. I also used air pressure to move the pistons closer to being ejected. What a fun day working on my motorcycle...............thanks again for all the great advice and help..............some of those tools definitely look like the cats meow

 

[cbx1260cc]

VERY INGENIOUS.

Appreciate your sharing your method.

 

[Shuriken]

I found the grease gun method on the bleeder screw side to be astoundingly simple and effective at releasing one piston. I will have to clean the pistons up to evaluate their condition.

I used an m8 zerk fitting from Harbor Freight. Plus a Harbor Freight grease gun.

I also ordered an m10x1.25 grease zerk fitting as well but sounds like I will have to clean out grease from behind the piston and reinstall it and then hold it with a clamp to get the other side out or get some kind of piston extractor.

Can't wait to see how the front end feels with new fork seals, new steering head bearings, stainless brake lines, rebuilt calipers, and new brake fluid. That's my goal for my 85, anyway.

 

[Shuriken]

Cut off head from sheet rock screw inserted in the bottom of the main fluid supply bolt to block grease.
Once I got the piston to move I was able to pull them out with a pliers taped up not to damage the pistons. I also used air pressure to move the pistons closer to being ejected. What a fun day working on my motorcycle...............thanks again for all the great advice and help..............some of those tools definitely look like the cats meow

So you installed this sheet rock screw into the banjo bolt to block grease? Cool!

I noticed that the bolts that hold the calipers onto the forks are also m10x1.25 -- same as the banjo bolts -- so I used a caliper mounting bolt in place of the banjo bolt to block the grease from emerging through the main fluid supply passageway.

 

[Fire-medic]

I noticed that the bolts that hold the calipers onto the forks are also m10x1.25 -- same as the banjo bolts -- so I used a caliper mounting bolt in place of the banjo bolt to block the grease from emerging through the main fluid supply passageway.

Yep, that's an old-time trick in the garage, it goes back to the first OEM hydraulic brake caliper available on a production bike, the 1969 Honda SOHC 750-4. The caliper mount bolt (red arrow) replaces the hydraulic hose, while the bleeder valve is the point of injection for the grease, Neat, simple, and fast.

As-shown in post #3 here:



As a point of interest, MV Agusta used a cable-operated disc brake before that, on a production bike. Count Agusta, owner of the company, also sponsored Agostini as his premier rider, who won many world championships for MV Agusta. In 1974, with a career unmatched to that time, Agostini went to work as a rider for someone-else, Guess who that was?



Here is the first DOHC transverse, alloy inline four-cylinder production bike, with cable-operated disc brakes the 600 GT by MV Agusta. The company didn't want people racing their bike (where they might beat the factory entries!) so it was only offered at that time as a shaft final-drive. It preceded the Honda SOHC 750-4 by three years, the Honda using a single hydraulic disc brake. Behind the carburetor, you can just-see the ignition distributor. Note the finish on the engine cases, they're sand-cast, common on low-production bikes. The first SOHC 1969 Honda 750-4 bikes manufactured used sand-cast engine cases. Those models are highly-prized by collectors, today.



The picture above showing the left side of the bike, also shows the dual mechanical disc brake rotors. All this available in 1966, while Harley-Davidson was still selling flathead V-twin engines, in their Servi-Car. To be fair, they also used a flathead V-twin in the same-year KRTT a 750 cc limited-production engine used at the Daytona 200 by the factory team. The KRTT also used a twin leading shoe front brake.

Her's a great article on the success of the KRTT flathead roadracer, in all of its flathead, drum-brake glory, written by a long-time moto-journalist, racer and enthusiast, Dain Gingerelli:
https://www.motorcycleclassics.com/.../rayborns-harley-davidson-krtt-zm0z23jfzawar/

Details of the H-D KRTT (below):




https://www.yamaha-motor.eu/kv/en/about-us/myyamahastory/racing-legends/giacomo-agostini/

In an interesting juxtaposition, compare this MV Agusta, first offered in 1970, to the earlier 600 GT. Beautiful castings, a traditional distributor for spark management, a 35 mm fork from Ceriani and what's that, a four-leading shoe drum brake. Agostini was one of the riders who preferred a well set-up 4LS-drum brake, because he was able to 'feather' it more-precisely. That was common among more-experienced racers.



Check-out the right side of the drum brake in this picture (below), this is a premium design, as it uses four parallel brake shoes. You can see the leading-shoe levers on this side as-well. Specialized manufacturers made up-to eight leading shoe drum brakes.

 

[Shuriken]

So you installed this sheet rock screw into the banjo bolt to block grease? Cool!

I noticed that the bolts that hold the calipers onto the forks are also m10x1.25 -- same as the banjo bolts -- so I used a caliper mounting bolt in place of the banjo bolt to block the grease from emerging through the main fluid supply passageway.

Alright... however for my next trick, Okie2ee gets all the credit for the idea...

After getting one piston out easily, the other was stuck, and I needed an easy way to get it out with one piston already out.

The only way I could think to do it was to find a way to block grease from flowing towards the caliper with the missing piston, as there would be no way to build up pressure otherwise.

I thought I might cut some aluminum squares and sandwich them between caliper halves and bolt back together.

But that's when Okie2ee's engineering came to me: I cut the shafts off of 4 screws (vice grips and grinder), dropped them into the orifices in both caliper sections, bolted back together, closed the bleeder screw, and used my m10 zerk to inject grease. Flow of course gets blocked at the screws and flows against the stuck piston only.

Pop goes the piston. I should have it all back together for testing in the next few days. Thanks Okie2ee!

 

[Shuriken]

Medic, those are gorgeous bikes. I love seeing the various engineering involved in the brake designs...

 

[Fire-medic]

If you search 'drum brake' you can see some period designs for them, I've previously posted.

The opened-up 8-leading-shoe designs resembles some fossil of a prehistoric bird, showing all the brake's pivot points and the linkages. A Suzuki T500 Titan 2-stroke parallel-twin has a good drum brake often used by period racers. These could be ported to give a Kawasaki 500 two-stroke triple a run for its money.



Suzuki T500 Titan racing achievements:
Art Baumann became the first man ever to win an AMA national championship race on a two-stroke when he won the 125-mile road race at Sears Point September 1970, and Ron Grant was forced out of the lead at Daytona this past year (1970) when he ran out of gasoline on the backstretch. He later won the 125-mile national at Kent, Wash., on the same machine. Most impressive was Cycle World's assistant editor’s qualifying speed at Daytona this year, which was in excess of 151 mph on a modified T500.
https://magazine.cycleworld.com/article/1970/10/1/suzuki-t500-iii

Suzuki T500 Titan 8 inch twin leading-shoe front brake.



The twin leading-shoe has two pivot points so there is more leverage from the two brake shoes' operation. Look for the two linked pivots connected by the lever inside of the left fork slider, on this wheel.

https://www.motorcycleclassics.com/classic-japanese-motorcycles/suzuki-t500-titan/