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Old 08-02-2011, 07:49 PM   #76
henrymartin OP
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Originally Posted by squish View Post
I know of what you speak on those brakes.

Thankfully they are a real easy system to work on. My suggestion is if everything is still togther work on getting all the pistons to move. I've had to use a C-clamp and blocks of wood to hold pistons that move, and use the hydralics to force stuck pistons to move, the idea is that you want to get the pistons to move, but you don't want them to pop out.

If you have already taken the system apart, you may find that when the loose piston comes out that it's near immpossible to get the stuck one out.

The process that has worked for me over the years.
Again with the C-clamp push the now freed piston back into the caliper, just enough for it to seal against both seals.
Then using your force of choice, I use an air compressor with a blow nozzle and a rubber tip)
Get the other piston to pop out.

Sometimes these things comeout with a bit of force, so use a rag to keep the pistons from getting damaged.

Dental picks work very well to clean the grove of the piston seals after you get every thing out.
I plan on doing that with the front (had done almost the same thing in the past), but the rear has a stuck piston and leaking master. The perfect combo. I'll have to rebuild the master first, to force the piston out.
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Old 08-03-2011, 07:27 AM   #77
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Quote:
Originally Posted by squish View Post
I know of what you speak on those brakes.

Thankfully they are a real easy system to work on. My suggestion is if everything is still togther work on getting all the pistons to move. I've had to use a C-clamp and blocks of wood to hold pistons that move, and use the hydralics to force stuck pistons to move, the idea is that you want to get the pistons to move, but you don't want them to pop out.

If you have already taken the system apart, you may find that when the loose piston comes out that it's near immpossible to get the stuck one out.

The process that has worked for me over the years.
Again with the C-clamp push the now freed piston back into the caliper, just enough for it to seal against both seals.
Then using your force of choice, I use an air compressor with a blow nozzle and a rubber tip)
Get the other piston to pop out.

Sometimes these things comeout with a bit of force, so use a rag to keep the pistons from getting damaged.

Dental picks work very well to clean the grove of the piston seals after you get every thing out.
A plus for this particular year is the calipers are single piston, so no one piston out the other still in monkey motion.

When my 750 came back into the family, I had to unstick all the calipers. I was able to just remove all the pistons, carefully remove the seals, clean the corrosion out of the cylinders and off the pistons, wipe the seals off and reinstall everything. They all work fine--no leaks or sticking.
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Old 08-03-2011, 07:44 AM   #78
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Originally Posted by brucifer View Post
A plus for this particular year is the calipers are single piston, so no one piston out the other still in monkey motion.

When my 750 came back into the family, I had to unstick all the calipers. I was able to just remove all the pistons, carefully remove the seals, clean the corrosion out of the cylinders and off the pistons, wipe the seals off and reinstall everything. They all work fine--no leaks or sticking.
There is hope then

When I priced new caliper pistons, seals, and rebuilt kit for the rear master, I almost fell over. Ended up getting only the rear master kit and one caliper rebuilt kit - just in case.

Parts'n more lists pistons for $21 but won't let you order it. All other places are triple and above that price.
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Old 08-05-2011, 10:39 AM   #79
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Ran into a glitch last night that will require some sorting out: When I played with my seat pan and the tail section, I dry-fitted it and it worked fine. Now, however, when i tried mounting some aluminum flat stock to act as a seat holder up front (would slide under the tank mounting point to prevent the seat from lifting, it does not fit right. Well, it does fit too loose and it fails to press the pan down enough to follow the tank contours. I'll have to figure something else out.

Also started on reinstalling the wiring harness, after repairing a few rubbed-through wires. Anyone ever tried running the harness inside the frame? Looking at it, it appears too bulky in its stock form and that would require a large hole in the frame tubing -- something I do not wish to do. I just want to hide it as much as possible.
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Old 08-05-2011, 02:39 PM   #80
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In regards to the calipers. I had issues getting pistons for my CBX750FE, honda themselves supplied the wrong ones. After arguing with several vendors who told me my bike was wrong and also the spares I had were also wrong I gave up.

I measured the piston, stuck the size into google and bought them that way, for much cheapness.

As for the wiring, the wiring loom can be cut down a lot.

The standard loom earths everything through a single point. If you earth things near the component you have lost the earth return wires, thats half the loom almost.

As a side effect you get better performance of the electrics, of course assuming the earth points are suitably grounded.
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Old 08-06-2011, 08:40 PM   #81
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CB750F Project: part VIII


Brake time!

When I first brought the bike home, the rear brake was completely stuck. The Previous owner drained all fluid from the reservoir, and took the bleeder out of the caliper. That's about it. He neither investigated further, nor attempted to fix the issue.

A week after I ordered two rebuilt kits the parts finally came, and I was able to get to the bottom of it. I started on the rear brake, as that was the one in the worst shape.






This is what 30 year old brakes hide under the dust seals
Ah...nothing like a broken circlip to make this easier. It was locked in place with rust, and took some heavy pounding to move.
And a little surprise underneath the flange. I swear, this fluid looks like the original, 30-year old fill.
Well, about 30 minutes of playing with a Dremmel and some brake cleaner, and things looked much better.


Time to get the new piston, seals, and spring in.
And voila...final assembly. I lubed the seals with fresh brake fluid prior to installation.

With the master cylinder rebuilt, I was able to use the hydraulic force to push the stuck piston out of the caliper. Except a hardened seal and some decent corrosion inside, the caliper looks good and can be reused. the piston, however, has some decent-size pitting. I'll have to look for a replacement.

Tomorrow I'll tackle the front.
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Old 08-11-2011, 08:00 PM   #82
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CB750F Project: Brake Saga Continues


As stated in the previous post, I started working on rebuilding the brakes on my CB. There has been a slight delay, however, as the original OEM pistons were not up to the job. Yes, I could have probably polished them and called it a day, nevertheless, I don't like doing things half-ass.

And this is where I ran into a small problem: The rear OEM piston appears to be discontinued by Honda, and all the kits available on-line show three pistons of the same size - 38mm diameter by 35mm length. The rear piston, however, measures 38mm diameter and 41mm length. There were some pistons of the proper size available via Google.co.uk, but as with anything "reasonably" priced these days, the country of origin is likely China. Forgive my snobbery, but when given the choice, I'd rather not rely on Chinese made cast brake pistons.

The solution? I asked around, and ultimately found a machine shop willing to work with me on creating a set of brake pistons to match the OEM size. Not only these will be the correct length, but I could also specify the material. So, instead of ordering the questionable quality pistons on-line, I chose to order a set of stainless steel pistons made locally. The availability of stainless steel makes for a product that will last much longer than the traditionally chrome-plated pistons which are prone to pitting.

I always believed in supporting the local community whenever possible, and this was the perfect occasion.

The machinist had the new pistons ready for me the day after I ordered them. Frankly speaking, I spent more time searching for a set online, and driving around numerous parts stores, than it took to have them made.

And here they are, right next to the pitted OEM ones.




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Old 08-11-2011, 11:13 PM   #83
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Quote:
Originally Posted by henrymartin View Post
CB750F Project: Brake Saga Continues

The availability of stainless steel makes for a product that will last much longer than the traditionally chrome-plated pistons which are prone to pitting.
Those are some good looking pistons.
I wonder if the dissimilar metal thing is going to be an issue with stainless steel pistons in aluminum bores...
I wouldn't think so with the pistons being surrounded by brake fluid, but seeing some of the corrosion that happens to brake systems, I keep on top of the fluid changes.
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Old 08-12-2011, 05:25 AM   #84
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Those are some good looking pistons.
I wonder if the dissimilar metal thing is going to be an issue with stainless steel pistons in aluminum bores...
I wouldn't think so with the pistons being surrounded by brake fluid, but seeing some of the corrosion that happens to brake systems, I keep on top of the fluid changes.
I wondered the same, BUT:

a) Chrome plated metal pistons are what they are in aluminum bores.
b) Stainless steel usually does not rust unless in direct contact with carbon steel (ie guns, internal parts touching stainless frame, left in high moisture area for long period - seen that)
c) OEM rust and the stainless should last a lot longer
d) Aluminum is constantly oxidizing anyway

Plus, Carpy (the cafe guy) sells stainless steel pistons on his site, so I guess I'm not the only one using the material.

If you think about it, you have an aluminum master, steel banjo bolt, copper crush washers, steel-lined brake line, another steel banjo and bolt, more copper washers, aluminum caliper, steel bleeder, and a stainless piston. You would think that with all those metals, and DOT3 sucking in moisture, your brakes would generate enough electricity to start the bike up without conventional battery.

Same at home; Copper plumbing, brass fittings, steel faucets... somehow it works.
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Old 08-12-2011, 07:55 AM   #85
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Good on you for spending your money on the local guy instead of the cheap imported sh--er--stuff! I go that route whenever possible.
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Old 08-14-2011, 08:21 PM   #86
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CB750F Project: Part IX


Somehow it happened, that I spent the better part of this weekend working in the garage. In the end, however, I discovered some new issues, which leave me quite puzzled.

With the new brake piston and a rebuild kit, I was able to complete the resurrection of the rear brake. Everything went back together smooth, and the new piston fit in perfectly. I replaced the old, rusted piston on the master cylinder, changed all seals, and put it all back together. On the caliper, I got away with a thorough cleaning, replacing the old seal with a new one, and lubricating the sliders. I then bled the brake on the bench, which was quite easy, and prevented me from spilling brake fluid all over my newly painted frame and swingarm.
Fitting the brake assembly on the bike was somewhat challenging, and I had to remove a few pieces off the bike to get it in there right, but in the end it worked out. I did not take any pictures of the process, but what I had to do was to remove the aluminum passenger footpeg mount and assemble everything off the bike. Then it went back on as one piece. To mount the brake reservoir, I also had to remove the lower rear fender. For the brake lever pivot, all it took was to brush off the old, dried grease, polish the inside of the bushing, and apply clean, new grease. It now operates like a dream.


While I was at it, I installed the rear wheel. Of course, I took it apart first, cleaned all the bushings, spacers, and bearings, and packed them with fresh grease. Sometime in the past, someone busted the threads on the rear axle nut by hammering on it. Well, when I got the bike, the rear axle was frozen in solid. A few squirts of PB Blaster, and a good whack with a rubber mallet loosened it up enough to take it out. After removing the old, dried grease and cleaning the axle with 600 grit paper, it all worked smoothly. I cleaned up the threads on the axle with a file, then got a temporary nut at a hardware store. It is quite difficult to find a new 18mm castle nut, but I have one on order now. In the mean time, a plain 18mm nut holds things where they belong.

With the rear wheel done, I moved on to the front wheel. Same story here, but before installing it, I mounted the front fender and brake hose brackets. Everything was then tightened to the correct torque specs.

Next on the list was to install the wiring back on the bike. This was somewhat of a pain, as the harness is pretty stiff up front, but a few quietly uttered cuss words later it was where it belongs. Tidying everything up inside the headlight bucket was more of a challenge, and time consuming. I took a Q-tip and some dielectric grease, and lubed all connectors as well. Since Im going with lower handlebars, I have an extra length of wiring that has to be tucked away in there as well. Im running out of room, but I hope it will work in the end.

Up to this point, I was making some good progress. Feeling motivated, I decided to tackle the airbox and carburetors. Oh my, oh my, oh my! Between not having enough room to get a finger anywhere, and not wanting to scratch the newly painted frame, it took me over an hour to get it in there. Despite lubing the boots, the carburetor assembly would not go into the cylinder boots, and when it finally did, the airbox boots were all over the place. I tried sliding the airbox over, but for the life of me I could not get all four boots to seat properly. There was always one that ended up crooked. I ended up taking the carburetors off the cylinders again, attaching the airbox boots, and then sliding the whole thing forward. Some cussing and heavy breathing later, it was finally in. What an awful design!

I also installed a new chain. This one has a masterlink, so no more taking the swingarm off to work on it.


After installing the exhaust, I decided I wanted to hear the engine. Well, the truth is, I wanted to rebuild the front brakes, only to discover that the master cylinder cover is beyond repair. Ill have to order a new one. So, with the brakes being a no-go, I decided to hear the engine.

I installed the tank, connected the fuel line, and poured in a little bit of gas. And here the issues begun.

Number 2 carb started leaking from the drain nipple. HmmI cleaned and reassembled the carburetors before taking the bike apart, and I remember testing them on the bike. At that time, there were no leaks.
So, after making sure the drain screw was all the way in, I took the crew out again, and polished the cone-shaped tip. A little oil on the O-ring, and it went back together. No leak since lets hope it stays that way.

Then, I started the engine. Cylinders 2,3, and 4 ran fine, while cylinder 1 only came on with RPMs above 2k. I checked gas delivery and spark, and could not find anything wrong. I also know that the carburetors are clean, and there are no vacuum leaks in the boots. Well, this is one puzzle Ill have to investigate later.
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Old 08-15-2011, 06:59 AM   #87
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Regarding the missing on one cylinder, have you replaced the plug wires & spark plug caps? These were marginal when new, both F bikes I had ran much better after replacing these.

I might have a front master cylinder cover for you, it's for an 82 900F but it might be the same. Let me check.
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Old 08-15-2011, 09:20 AM   #88
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Regarding the missing on one cylinder, have you replaced the plug wires & spark plug caps? These were marginal when new, both F bikes I had ran much better after replacing these.

I might have a front master cylinder cover for you, it's for an 82 900F but it might be the same. Let me check.
Thanks. I'm thinking of ordering an aftermarket, chrome one without a logo. The plastic on mine is cracked and while I thought I would get away with making some flat cap from aluminum and reusing the metal flange that holds the diaphram in place, it is not an option as the metal flange is badly pitted.

I'll get some new cables and plug caps, and see what is what. There is fuel in the carbs, and the first one should have the least amount of issues. Darn.

Maybe I screwed something up when fixing the floats? These don't have the tabs to bend, so I just left the old foil in place after cleaning it.
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Old 08-15-2011, 08:30 PM   #89
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CB750F Project: Front Brakes


I'm finally starting on the front brakes.

This is what I found once I took the brakes apart.
Obviously the front calipers are pretty much oxidized, but cleanable.
The Master Cylinder is in a tough shape.
Other than an old brake fluid of very questionable quality, there is plenty of gel-like deposits. On top of this, someone, once upon a time, decided to seal a leaking O-ring with silicone, liberally applied everywhere.
This is what I was hoping to avoid - a complete rebuild. But, the piston has seen better days, so I don't have much choice.

Right now, I'm waiting for parts: new master cylinder cover (the old one is pitted and rusty, with cracked plastic) and a rebuild kit.
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Old 08-18-2011, 07:57 PM   #90
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CB750F Project: Front brakes part II


Finally got to cleaning out the front brakes. Right now, the calipers are all reassembled and ready to go back on the bike.

In the mean time, I discovered some carburetion issues, so I have to take the carbs apart, again. The cause, at this time, is unknown.

Anyway, here are a few pics of the cleaned calipers and the front master cylinder.







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