Author Topic: Finally . . . the seized brake piston is unstuck (Read 1499 times)

kyle750 · « **on:** January 31, 2025, 06:52:59 PM »

This was my very first task with my Honda CB750 restoration and it took a long time. A very slow start.

When I bought the bike it had been sitting for 9 years and the brake piston was totally seized. First we tried new brake fluid and pressure from the master cylinder - did not work. Then we tried carefully sealing and compressed air - did not work. Then we tried the grease gun method at a car repair shop - did not work. So . . .

I threw the brake caliper into a closed container of diesel (to try to loosen it up) and let it sit for a few weeks. I then saw a very old machine shop that looks like it has been in business for a very long time. Perhaps more experience and better tools? I showed them the caliper with stuck piston and they immediately took a blowtorch to it. Clamped the caliper to a heavy duty vise and then took heavy duty vise grips and pulled the piston out. It took over 15 minutes of heating and pulling before they finally got it out

The black paint was melted so I stripped both sides of the caliper down to the aluminum with regular paint stripper and a small brass wire brush. Paint came off easily. Inside the caliper the cavity is now smooth and clean and the groove for the piston gasket ring has been cleaned very well. I ordered a replacement stainless steel piston and piston gasket.

My question is what should I do with the caliper? Repaint black or can I just use as is?

I quite like the look of the silver aluminum of the brake caliper.

bryanj · « **Reply #1 on:** January 31, 2025, 07:20:04 PM »

Early ones were alluminimum not black anyway

BenelliSEI · « **Reply #2 on:** February 01, 2025, 05:08:31 AM »

Given the way parts corrode in your environment, I’d paint it. Black is “original”, but silver works too!

MauiK3 · « **Reply #3 on:** February 01, 2025, 08:18:52 AM »

I've used Duplicator caliper paint, it has a soft sheen and is supposed to be resistant to heat etc. Seems to work, not sure if you can find that there.

BenelliSEI · « **Reply #4 on:** February 01, 2025, 01:34:59 PM »

Any good quality paint works well. Careful with brake fluid. It will destroy virtually any coating!

kyle750 · « **Reply #5 on:** February 01, 2025, 05:00:35 PM »

Thanks. Caliper is just sitting here waiting to decide. Corrosion is a big problem here. I can get good quality heat resistant spray paint here (black or silver).

I'm continuing with the inspection of the brakes today. Very surprised to find that the rotor seems to be in decent shape. As is usual with almost everything with this bike the top edge of the rotor has rusted but the surface has stayed rust free. Is the Honda CB750 rotor typical cast iron? Rotor does not appear to have any deep grooves but I'm not sure if it is OK to use? It would be very easy to just sand the rust off the top edge so it looks better.

I have ordered both organic and semi-sintered EBC brake pads so I can test both and see how they perform. Nobody likes squealing brakes. As the Honda CB750 front brakes have a reputation for being adequate but not very good - the stopping power and steadiness of the brakes is going to be VERY important to me.

As a rider I place Safety first - Always!

RAFster122s · « **Reply #6 on:** February 01, 2025, 05:12:52 PM »

SOHC4 rotors were stainless steel, not ideal material

kyle750 · « **Reply #7 on:** February 01, 2025, 05:17:50 PM »

Thanks mate. I did not know the rotors were stainless steel. With the rust on the top edge I am also wondering if they are not very high quality stainless steel??

RAFster122s · « **Reply #8 on:** February 01, 2025, 05:30:41 PM »

Staining possibly. Scrape it off to see if it is stained or something dropped on edge or it is rust.

kyle750 · « **Reply #9 on:** February 01, 2025, 06:53:53 PM »

WD-40 applied to the top edge and is soaking now

kyle750 · « **Reply #10 on:** February 01, 2025, 07:30:59 PM »

Easy

bryanj · « **Reply #11 on:** February 01, 2025, 08:17:23 PM »

Also remove, clean and grease the pivot pin in the bracket the caliper bolts to

dave500 · « **Reply #12 on:** February 01, 2025, 10:38:55 PM »

you can buy cast iron rotors for 750s and 500/550 here in Australia,i have one,just so much better,stainless has a crap frictional coefficient.

PeWe · « **Reply #13 on:** February 02, 2025, 01:12:10 AM »

There are paints made for brake calipers.

I have a good looking caliper with a stuck piston.
Even the threads for pipe and bleeder valve had dried brake fluid. Hard as old 2k glue.

Deltarider · « **Reply #14 on:** February 02, 2025, 02:22:44 AM »

Mine is partly black because of scars from accidents and I'm proud.

MauiK3 · « **Reply #15 on:** February 02, 2025, 06:45:48 AM »

Some get their discs drilled (I did), I won't speculate on the pros and cons but it does remove a little weight and might aid in water shedding. I like the look. Otherwise, just carefully remove any stains, iron discs in your area will turn to rusty discs right away.

kyle750 · « **Reply #16 on:** February 02, 2025, 07:15:43 AM »

I should not be surprised to learn the brake rotor is made of stainless steel. Seeing how the other metal parts on this bike rusted if the rotor was cast iron it would have turned to a heap of rust. For where I live in a hot and humid country and living near the ocean a stainless steel rotor would be the better choice. Perhaps not the best stopping power but definitely less corrosive.

For now I think I will keep the original Stainless Steel rotor and see how the pads respond. My expectations for safe stopping and performance are very low. The disc pad is just too small for such a heavy and powerful bike. Who knows maybe the front brakes will work a little better than I am expecting! I hope to find out soon.

Late Edit: The back drum brake on the CB750 is working extremely well. Quick response and strong stopping power. Very pleased!

BenelliSEI · « **Reply #17 on:** February 02, 2025, 08:10:50 AM »

Quote from: dave500 on February 01, 2025, 10:38:55 PM

you can buy cast iron rotors for 750s and 500/550 here in Australia,i have one,just so much better,stainless has a crap frictional coefficient.

Dave…. I’m thinking of ordering one of those discs. Significant improvement?

bryanj · « **Reply #18 on:** February 02, 2025, 10:05:12 AM »

I fitted one to a 500 back in the 70's, great in the dry but worked too well in the wet, brake locked and threw me off

PeWe · « **Reply #19 on:** February 02, 2025, 11:56:15 AM »

Honda was early with an anti-lock braking system

Wet slippery roads have tought me to take it extra easy.
Roundabouts close to gas stations were often extra slippery rainy days due to splashing diesel from just filled up trucks/lorries. I learned the hard way.

Tim2005 · « **Reply #20 on:** February 02, 2025, 12:48:30 PM »

Quote from: dave500 on February 01, 2025, 10:38:55 PM

you can buy cast iron rotors for 750s and 500/550 here in Australia,i have one,just so much better,stainless has a crap frictional coefficient.

Any chance they do them for CB400Fs too?

kyle750 · « **Reply #21 on:** February 02, 2025, 07:31:17 PM »

The delivery of the brake parts and front fork seals from the USA has been held up in customs. Most shipments sail right through and get delivered quickly. But sometimes packages are randomly selected and the shipper must confirm the value of goods.

From past experience once a shipment is held up in customs it takes a long time to clear (sometimes up to a month).

Frustrating

dave500 · « **Reply #22 on:** February 03, 2025, 12:00:30 AM »

Quote from: BenelliSEI on February 02, 2025, 08:10:50 AM

Quote from: dave500 on February 01, 2025, 10:38:55 PM
you can buy cast iron rotors for 750s and 500/550 here in Australia,i have one,just so much better,stainless has a crap frictional coefficient.

Dave…. I’m thinking of ordering one of those discs. Significant improvement?

with a smaller diameter master cylinder it works great it actually gets better as it gets hot,not visa versa like the stainless one,heres a link,they do drilled or solid,with hub or fit your own etc.https://www.ebay.com.au/itm/273994779212?chn=ps&_ul=AU&norover=1&mkevt=1&mkrid=705-139619-5960-0&mkcid=2&mkscid=101&itemid=273994779212&targetid=2370955762951&device=c&mktype=pla&googleloc=1000339&poi=&campaignid=21766114506&mkgroupid=168279963077&rlsatarget=pla-2370955762951&abcId=10047372&merchantid=7364522&gad_source=1&gclid=EAIaIQobChMIzZLh_YSniwMVPKNmAh0dQAbeEAQYASABEgKn6fD_BwE

kyle750 · « **Reply #23 on:** February 03, 2025, 12:47:17 AM »

The cast iron rotors look very good. Thanks for the link. At a price of AU $150.00 plus AU $70.00 shipping = AU $220.00 total. With currency conversion to $USD = Total $USD 135.00

rotortiller · « **Reply #24 on:** February 03, 2025, 05:01:19 AM »

Lots of bikes with SS discs that stop very well. It is the whole cake mix that works, when the recipe gets messed up we pick something to blame. Back in the seventies they were just learning about disc brakes, pad surface area, disc material and area, fluid pressure etc. Today you can have a bike with a single front SS disc lift the back end off the ground. Unfortunately the SOHC fork lower design is not very conducive to caliper improvements. A 5000 pound car uses two cast iron front discs to stop, so a well designed SS disc should have a very easy job with a 500 pound bike. Now if the recipe is incorrect the results will be bad. I do not like rust so I look at other areas for braking improvement like calipers and master cylinders when possible. If all else fails the cast iron disc seems like a good idea for me. I have had good results increasing the brake line pressure, there is the option for the slightly larger 77/78 caliper for braking assistance. What truly amazes me is how much stress front spores can transfer during hard braking.

Stev-o · « **Reply #25 on:** February 03, 2025, 07:22:36 AM »

Quote from: kyle750 on February 02, 2025, 07:15:43 AM

Late Edit: The back drum brake on the CB750 is working extremely well. Quick response and strong stopping power. Very pleased!

Even though the rear brake seems to be working well, I would disassemble and check/replace the rear shoes since the bike has been sitting for 9 years. The brake lining has been known to come free of the metal shoe [most are just glued on]

On one of my project bikes, the shoes were a bit worse than expected!

kyle750 · « **Reply #26 on:** February 03, 2025, 08:02:22 AM »

I will need to remove the rear wheel hub when assembling the new DID rim, spokes, and tire. I will be sure to inspect the rear drum brake shoes at that time. Probably would be best to just go ahead and replace the shoes just to be safe. Living in Thailand I have seen really bizarre things happen to glue. I wear fairly expensive running shoes that I buy ahead of time (hard to find large size shoes here in Thailand). Shoes were never worn and when I went to put them on the glue on the soles just disintegrated and they fell apart. Never seen anything like it.

PeWe · « **Reply #27 on:** February 03, 2025, 10:15:54 AM »

My CB750 K2 with a new David Silver rotor described to be improved. New caliper and MC work fine in legal speeds. EBC FA12V orange pads.

Not much faster for an almost safe stop. Need to be alert and see problems in time, before they happen. Use gearbox too.

My K6 has same rotor but 2 of them, same DSS MC. Stock calipers.
This stops good enough in higher speeds with DSS low priced pads.

I have read about guys here with good single front brake and stock rotor. Maybe different MC only or a caliper too.

https://good-bits.co.uk/product-category/braking/
I see now that they have a caliper bracket for K3-K6 fork lowers (marked 341 on inside) to use AP racing caliper.
Maybe they can do for earlier forks too.

Don R · « **Reply #28 on:** February 04, 2025, 03:39:55 PM »

I've also seen the rear shoe de-laminate, I've had good luck with scuffing the rotor with scotchbrite gasket remover discs and sanding the glaze off of a stock set of brake pads. I do use my large shop vac with a hepa filter to collect the dust in case there is asbestos in them.
My best results came from two F1 calipers and two drilled rotors. I practiced stopping until I rippled the front tire.

Deltarider · « **Reply #29 on:** February 05, 2025, 12:19:12 AM »

Quote from: Don R on February 04, 2025, 03:39:55 PM

I've also seen the rear shoe de-laminate, [... ]

Question is... were they OEM or aftermarket? I have heard of some aftermarket products de-laminating. Mine is still the original and does not de-laminate.

bryanj · « **Reply #30 on:** February 05, 2025, 01:16:26 AM »

Depends on storage and environment, in an atmosphere where you get the white corrosion on the alloy they will all delaminate

kyle750 · « **Reply #31 on:** February 05, 2025, 04:28:03 AM »

It will be a while until I can get to the back wheel so inspecting the rear drum brake shoes is still a long way off. Brakes are so important IMO it is just not worth the risk using old brake shoes. Right now they appear to be working OK but for safety and peace of mind it is better to replace. I am going to order OEM Honda rear brake shoes 06430-393-405 from the same seller in Japan who I purchased the original Honda front fork rubber boot covers. Price on the brake shoes is $54 with free shipping from Japan. First experience with this seller was Excellent +++ with excellent communication and super fast shipping.

Kelly E · « **Reply #32 on:** February 06, 2025, 07:47:08 AM »

I've seen two sets of Honda rear brake shoes delaminate. It was on my 74' CB 550 K0 and the 70' CB 450 DOHC we did a couple of years ago.

bryanj · « **Reply #33 on:** February 06, 2025, 12:54:27 PM »

I have seen a lot as it tends to be damper and colder in UK!

seanbarney41 · « **Reply #34 on:** February 06, 2025, 09:04:55 PM »

lots of damp and cold here in Michigan too, and never seen a Honda shoe delaminate out of dozens. Have seen BMW pads weld themselves to the rotor...only way I could get the front wheel to roll was to remove the whole wheel which ripped the crumbled lining off the backing

newday777 · « **Reply #35 on:** February 07, 2025, 03:51:30 AM »

Quote from: bryanj on February 06, 2025, 12:54:27 PM

I have seen a lot as it tends to be damper and colder in UK!

You probably haven't spent winter's in New Hampshire then. Lots of deep cold and damp here.
In the past 3 years I've had 2 sets that were full delam from lots of moisture, probably left outside and water collected in the hub, rusted spokes and rusted brake contact area. I had to whale on a sledge to get the axle out on one trying to salvage the hub, but decided to scrap it because of the rust pitting. I've also had 3 sets of brake shoes that were partially delam, lots of white powder residue on the shoes from moisture. So yes it does happen, probably the glue let go from improper storage in high moisture induced areas of poor storage of the wheel, maybe immersed in water at times.

BenelliSEI · « **Reply #36 on:** February 07, 2025, 06:44:36 AM »

My cb750K1 has excellent brakes. A few years ago, the rear got a bit “grabby”. When I pulled it apart one of the material strips had completely come away from the backing plate. Installed a pair of new ones from Honda. Should be good for another +50 years?

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Author Topic: Finally . . . the seized brake piston is unstuck (Read 1499 times)