CB450N brake calipers

kennyv71

kennyv71

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Hi all can any one help with a brake caliper problem. the bike is a cb250n, 1981. but fitted with dual caliper/disks when purchased, from a cb450 i presume. Ive fitted new master, cheap Chinese, new pipe work thin braided pipes. Trying to bleed the system all air appears to be remove, i have clear fluid coming from both bleed nipples, but no pressure on the lever. my thoughts are either the one to in two union, air trapped inside?, or what are the extra bolts fitted fairly close to the bleed nipples, i wondered if air is trapped further inside the calipers. any help would be appreciatedIMG_20260503_182545[1].jpg.
 
Sorry just realized what the bolt head is for, I think to hold a anti squeak plate. still interested in why it might not be bleeding properly. cheers.
 
Initial bleeding of the dual calipers with the splitter takes time. Starting at the master loosen the fitting and bleed 1st. Same thing as using the bleed screw, loosen, squeeze, tighten, release. Do each fitting 2-3 times working down to the actual bleed screw. There's lots of air trapped in the lines and splitter.
When you finally get pressure stop and let it sit for a hour or more. Don't do the fittings again but bleed the calipers a 2nd and 3rd time with wait periods.
 
thanks LDR, will give that a go in the morning. Been doing the caliper ones, maybe 10 times each, no air coming out, but can only just about get minimal pressure. Ill start tomorrow at the top. The brakes have never been satisfactory since ive owed the bike, it has had a front fork upgrade to twin calipers, and ive tonight just seen at the back of the haynes manual, that the 400s had a slightly larger master, so began to think its got the wrong master. It frustrates as i changed the old bleed nibbles for new, but getting the slightest leak from around the threads, so wondered if i could but some plumbers white tape around the thread. Rather than start another thread, would you have any thought about using a 100/90-19 tyre on the front to replace the 3.60s 19s on there at present. Many thanks for your previous advice.. let you know how i get on. The suns out and im getting itchy to get out in the sunshine.
 
If there's a leak of fluid past the threads that means the tapered end of the bleeder screw isn't sealing, probably dirt/corrosion on the seat. Use a Q-tip with valve lapping compound the clean and polish the seat.
You likely have a 15mm or 5/8" master. A 14mm or 9/16" would be correct for the dual calipers.
A 100/90/19 will work just fine
 
Hi all, beginning to loose what hair i have left. I have a 1981 cb250n super dream, but when brought, it had twin front calipers, i presumed from a cb400 super dream. The brakes have always been really poor. Ive serviced the calipers, ive changed the rusty pipes and fitted a look alike master brake cylinder. Bleed the system 50 times over, with not a sign of an air bubble, but can barely get a little pressure at the end of the lever travel, pumping doesn't help. I notice in the Haynes Manuel, page 94, its showing a single piston caliper, total two, one on each side, but on page 119 they show a caliper for the cb400nc, which has 4 pistons, two on each side, these calipers match mine. see picture. any thoughts that the "standard" master cylinder hasn't got enough push to operate all 4 pistons. in which case i need to source two single piston calipers or a CB400NC master. Any thoughts or observations, would be gratefully excepted.

cbfront.jpg
 
kennyv71 said:
Hi all, beginning to loose what hair i have left. I have a 1981 cb250n super dream, but when brought, it had twin front calipers, i presumed from a cb400 super dream. The brakes have always been really poor. Ive serviced the calipers, ive changed the rusty pipes and fitted a look alike master brake cylinder. Bleed the system 50 times over, with not a sign of an air bubble, but can barely get a little pressure at the end of the lever travel, pumping doesn't help. I notice in the Haynes Manuel, page 94, its showing a single piston caliper, total two, one on each side, but on page 119 they show a caliper for the cb400nc, which has 4 pistons, two on each side, these calipers match mine. see picture. any thoughts that the "standard" master cylinder hasn't got enough push to operate all 4 pistons. in which case i need to source two single piston calipers or a CB400NC master. Any thoughts or observations, would be gratefully excepted.
Click to expand...
You already have a thread for this effort, so I moved your newest post here.
 
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The Haynes manual is showing the 1st generation brakes, CB250N(A), with single piston calipers. Your dual piston calipers are correct. You should have a 14mm master according to CMSNL.
Have you solved the leaking fluid past the bleeder screw threads? If fluid is leaking then air is getting sucked in.
 
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Thanks Jim for both the bleed nipple tip and the thoughts re master cylinder. i will try to polish out the nipple connection today when i drain the system again. You suggest a 14mm master and the part number? 100/90/19. Could you just elaborate please. Sorry being playing around with my 3 BSA bantams for years, so not sure what the 14mm refers to. Im going today to short cut the system to one caliper, (two pistons) as not sure of the "original" master, on the bike, or the new lookalike one ive brought is compatible. I noticed on a lot of images of the earlier 400s, they have a master with a white plastic top container. mine is as per.master.jpg
 
Ok, update, success in my mind. Had the right banjo joint to remove one cylinder connection , and reconnect through the one into two box, with just one cylinder connected and sealed. bleed the system in no time, and perfect, the system pressurized up and lever pressure is there. So the conclusion is the master i have isn't up to the job, for a 4 piston setup. Ive also noticed on ebay, certain suppliers give more info regarding a bore size, 14mm and 16mm, or no detail at all. So answers my question what does 14mm refer to. The new master i have is shown as 14mm bore. I will say that my Haynes version, I know Haynes isnt the all and end all of details, but all i have to go with, on page 94/95 suggests that maybe the early CB400N's had twin calipers but single pistons. so Im assuming through the course of time, mines got scrambled. Also its a European bike, so maybe different to say a USA models. Only outstanding question what is the 100/90/19 number, is that a part number. Other than that many thanks for your inputs and advice, after many frustrating hours, I can get out and ride the old girl. Bring on the sunshine.
 
Thanks ancientdad, my head was so full of front brake problems, i'd totally forgot i'd asked about Tyre sizes. Its age related. Interesting with the brakes, some of the earlier master cylinders had 16mm bore masters. Idealy id like to put one on mine to see if it would drive both twin piston calipers. but i can only find ebay/uk/itm/281254500769 having 16mm, and on a USA site, sorry im in the UK. At least i can ride for now with the one caliper, after the sites help. Cheers again.
 
Pretty accurate description of bore sizing for the master
How Bore Size Affects Brake Feel
  • Smaller bore: Pushes less fluid volume but generates higher pressure with less lever effort. This yields better modulation, more "feel," and a longer, softer lever pull.
  • Larger bore: Pushes more fluid volume, resulting in less lever travel (a shorter pull). However, it requires significantly more hand effort to generate the same clamping force, which can make the brakes feel "wooden" or stiff. [1, 2]
 
Ive now purchased a pair of 400 front calipers and a stock? master with the plastic reservoir. Help please, first the plastic reservoir, with the lid and rubber seal out of the way, do you just prise the plastic reservoir from the body, to get to the o ring, and secondly the two caliper disc pad pins, mine are screwed into place, and are fighting hard not to come out, do i need to use the same screwed in pins or do the push in and retain with split pin ive seen on ebay work as a replacement. thanks for any advice.
 
kennyv71 said:
Ive now purchased a pair of 400 front calipers and a stock? master with the plastic reservoir. Help please, first the plastic reservoir, with the lid and rubber seal out of the way, do you just prise the plastic reservoir from the body, to get to the o ring, and secondly the two caliper disc pad pins, mine are screwed into place, and are fighting hard not to come out, do i need to use the same screwed in pins or do the push in and retain with split pin ive seen on ebay work as a replacement. thanks for any advice.
Click to expand...
I moved your post from another member's thread to your existing thread here.

It would appear the cap and reservoir body are held to the master cylinder by the 4 screws that go through both of them into the metal body of the master cylinder. The o-ring sealing the round bottom of it where it enters the master cylinder body is likely the resistance you feel.

1780066906735.png
 
ancientdad said:
I moved your post from another member's thread to your existing thread here.

It would appear the cap and reservoir body are held to the master cylinder by the 4 screws that go through both of them into the metal body of the master cylinder. The o-ring sealing the round bottom of it where it enters the master cylinder body is likely the resistance you feel.

View attachment 58007
Click to expand...
double thanks, for that, my plastic tank has only 2 screws through top, maybe 250, and my thoughts are if you remove the screw and that removed the pressure on the o ring the reservoir would leak when topping up. So on your picture (Haynes) does 25 and 26 hold the reservoir in place, but only on the 400. I have no 25 or 26 on mine so assuming a snap fit? or something to keep pressure on the o ring.
 
kennyv71 said:
double thanks, for that, my plastic tank has only 2 screws through top, maybe 250, and my thoughts are if you remove the screw and that removed the pressure on the o ring the reservoir would leak when topping up. So on your picture (Haynes) does 25 and 26 hold the reservoir in place, but only on the 400. I have no 25 or 26 on mine so assuming a snap fit? or something to keep pressure on the o ring.
Click to expand...
Not sure why you're referring to a Haynes manual instead of simply looking up the CB250N master cylinder at places like CMSNL, Partzilla and others. It's all in this link I've supplied to everyone in my Welcome Package of links to help members find things themselves easily.

Tips for identifying and locating parts

Lots of people new to the vintage Honda motorcycle world are unfamiliar with how to identify the parts they need and where to look for them. The question is often asked: "Where can I find a (part name)?" The first step to finding any part for any of our favorite Hondas is to properly identify...
www.vintagehondatwins.com www.vintagehondatwins.com

This is the 250 master cylinder fiche, seems to be the same except with only 2 long screws as you suspect.

1780068179473.png
 
Thats magic Ancientdad thank you, i may where the master is concerned, be back where i was, a 250 master driving the duel calipers, that the guy sent me, all as one lot, saying they came from the same bike. I think ill service the calipers and then run thro the masters i have, stock and aftermarket, to see how they run. still seeking an answer to the pad retaining pins and do i take a deep breath and try to prise the plastic reservoir off. Thanks again Ancientdad
 
Something I just remembered.
At the shop, I always had a section of old handlebar handy to clamp in vice.
It makes life a lot easier than working 'on the bike' or loose on bench, particularly if complete front end is 'off bike'
You can orientate caliper so base is level or very slightly tilted a few degrees and air can't get trapped anywhere, same with calipers put something between pads 1/4" thick and you can move things around to make bleeding 10 minute job.
It doesn't work so well if you can't get hose routing 'back on bike' though because fork legs are in place, but, often, it's still quicker to unbolt M/C from bars and mount to a shorter section.
There were a lot of 'tricks' not in service manuals that sound like they should take longer but were actually much faster so not 'intuitive'.
Had one acquaintance who had 'wasted' two days and about half gallon of brake fluid before he called me, ten minutes after I got there he had brakes.
He was so pissed he threw screwdriver at garage wall, found out between garage and kitchen was only two layers of wallboard, his wife came in ranting because screwdriver just missed her.
They were divorced a few years later.
 
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