Topic: CB 550 Master Cylinder Question

[christianr]

Hi All,

I have a dragging front brake and I'm pretty sure I need to either rebuild or replace my master cylinder on my 76 cb550 (It's got a leak in the area where the lever applies pressure). If I bleed the system really well, the brake works for a while and then it begins to tighten up after a day or so of riding. I'm thinking that the master cylinder is letting air into the system slowly as I use the brakes. I took the calipers apart the other day, and the piston was clean (no pocking) and the seal looked good (but I didn't replace it)

The master cylinder rebuild kit would probably do the trick but would there be any benefit in replacing the master cylinder with something like this?



Is there something better or cheaper? I would like to spend as little money and time on this as possible.

Am I going in the right direction?

Thanks!

-Christian

[ws6transam]

Shoot Christian, you asked the very same question that I wanted to ask!
..except for me it's because I have extra mushy brakes after checking the calipers and bleeding the system.

I hope someone can answer the question. I *do* know, however, that whatever master cylinder you choose, you want to make sure it has comparable piston diameter and stroke to the old one. Otherwise your brake pad pressure (relative to lever pressure) will change.

[christianr]

Shoot Christian, you asked the very same question that I wanted to ask!
..except for me it's because I have extra mushy brakes after checking the calipers and bleeding the system.

I hope someone can answer the question. I *do* know, however, that whatever master cylinder you choose, you want to make sure it has comparable piston diameter and stroke to the old one. Otherwise your brake pad pressure (relative to lever pressure) will change.

That part (above) is for a Cb550 nighthawk. It says that it has a 14mm bore. It is selling for $39 bucks. The rebuild kits are about 25 plus shipping.

Does anyone know of any compatible MC's from other models? Maybe off a newer sport bike?

[Bodi]

Newer sport bike MCs will work fine.
I have fitted a 5/8" bore early GSXR600 MC, it looks fine and works well plus it has an adjustable lever angle The hose has to come around the fork tube rather than inside it because the business end is shorter. Mounting the reservoir is a bit tricky - all the sportbikes have separate reservoirs. I can add a pic if you like, I had to drill and tap through one of the clamp bolt holes and use a spacer and long bolt. The reservoir hose is a bit strange looking but it works. There are some Honda ones that adapt to look a bit neater, but you still need to do some drilling and tapping to get the reservoir on. I just used what the wrecker had at hand.
Most of these have an integral brake light switch so you can ditch the pressure switch junction block and run a single line straight to the caliper or hard line without needing a switch banjo.
Cruiser ones have integrated reservoirs, but the ones I checked are too long and the banjo would be in my speedo with low bars.

[78 k550]

some how it isn't letting the pressure back out. glogged line or blocked return hole in resivor. Could be a bad piston in the caliper.

Paul

[TwoTired]

I have a dragging front brake and I'm pretty sure I need to either rebuild or replace my master cylinder on my 76 cb550 (It's got a leak in the area where the lever applies pressure).

Whatever you do, do it soon. Brake fluid entering the switch control pod WILL destroy the starter button switch.

Cheers,

[Jinxracing]

I've read tons of articles in magazines and online about how critical it is to match MC piston area to caliper piston area to achieve proper brake feel and effectiveness. The general tone of these articles seems to be, "If you don't get the ratio just right, your brakes ain't gonna work". Being a logical and scientific kind of guy, I've always assumed that to be true. However, I've seen at least half a dozen posts here in the forum and quite a few bikes in real life that use master cylinders that "shouldn't work", yet the owners say they work just fine. I don't recall seeing a single post here about someone who fitted a MC that didn't work because the piston ratio was off. Perhaps all the hullabaloo about MC/caliper piston ratio is a fine point that only rears its ugly head while riding at 10/10ths on track days when you'd need every last ounce of braking feel and feedback?

I think you should buy a cheap '90s-era sportbike MC from eBay and try it out (carefully of course). Most of them still have an integrated reservoir, and based upon people's experience here I think the odds are in your favor that it will work fine. Of course, getting the ratio as close to optimum from the get-go wouldn't hurt either. 

[christianr]

Whatever you do, do it soon. Brake fluid entering the switch control pod WILL destroy the starter button switch.

Cheers,

I already found this out the hard way. I lost all of my front lighting (Headlight, position, gauges). I tried to track down the electrical problem for a long time before I found that the problem was the constant contact in the ignition switch. I was able to clean it up and it's been working fine again...

As soon as I figure out what to do, I can get it done right away.

Thanks.

[croquesaveur]

Some brake drag is normal.  A normal amount being that if you raised the front wheel off the ground and spun it, it would slow down and stop faster than if no brake were installed.  Unacceptable drag would be where you can actually notice the drag when you are coasting with the clutch pulled, or if the front brake gets hot after you've ridden around for a while without using it.

If the drag you're talking about is more like the former example (the wheel has a tiny amount of drag that is only noticeable when it's spun by hand) then that's normal.

I think the general consensus is that CB brakes are spongy all the time.  Switching to stainless steel brake lines helps a lot.  A CB will never stop as well as a modern bike, but it should certainly stop better than the average car.

Any brake fluid leak is serious and should be fixed immediately.

[snyquist53]

http://www.sohc4.us/forums/index.php?topic=21938.msg226894#msg226894
  this is an old post bout those levers

[christianr]

Well, I went with the rebuild kit since I found a discount one in town. I should find out tomorrow whether this did the trick or not.

You guys were right about that circlip, what a pain in the @#$

Anyway, I finally got it out with the use of a screw in some vice grips, it got in the hole enough that I could pull that sucker out.

I will probably put a newer MC on at some point but hopefully this will get me back on the road.

[jjoves]

Hi Christianr,

I saw this post since I was having the same issues w/ my caliper on my CB500.  The caliper would increase it's pressure over time and eventually the bike would have so much drag (even in neutral) that I would have to release the bleeder valve tension.  How did your results turn out?  I was going to get some SS lines ($110) and a rebuild kit (~$30).  Any recommendations? 


Thanks,
James

[bryanj]

Both people asking the questions:-
FIRST thing to inspect is the caliper swinging bracket pin as they corrode and sieze for a passtime
SECONDLY check the tiny return hole in the master cylinder
THIRDLY strip out the caliper, clean the seal groove and fit new seal
FORTHLY, and only if the bike has been standing for some time, check the hoses are clear.


Thats all for dragging brakes, Mushy brakes might need new master cylinder seals

[Jay B]

I replaced the master cylinder on my 550 with one of the eBay units pictured to gain more clearance for my drag bars. Glad I did, even with all stock componenets the front brake feels a lot better than before, and my old MC was in good shape.

[rlarkin70]

FORTHLY, and only if the bike has been standing for some time, check the hoses are clear.

What's the best way to clear out a clogged brake hose? I have one that is in good shape, but it's plugged. I think there is some old crystalized brake fluid in it. 


Hey Jay B-  You used one of those just like the picture at the top? From a CB550 Nighthawk? I have drag bars on my CB50 too, and plus I like the clean look of that MC.

-Ron

[Jay B]

Ron- I used a stiff peice of wire to clean out a brake line once, it worked but it was a PITA. The MC I used was a new unit sold on eBay, aftermarket. Search CB550 Master Cylinder and you should probably find one. I think the bore on mine was 14.5 mm if I remember right.

[OldSchool_IsCool]

What's the best way to clear out a clogged brake hose? I have one that is in good shape, but it's plugged. I think there is some old crystalized brake fluid in it. 

-Ron

Disconnect the hose from the caliper (if it's the lower hose that's plugged) or the brake switch manifold (clogged upper hose).  Now pump your master cylinder to push out any craption that might be in there.  If you can't clear it with pressure from the M/C, then really really consider replacing the hose, no matter how good the outside looks.

[rlarkin70]

Ron- I used a stiff peice of wire to clean out a brake line once, it worked but it was a PITA. The MC I used was a new unit sold on eBay, aftermarket. Search CB550 Master Cylinder and you should probably find one. I think the bore on mine was 14.5 mm if I remember right.

Is this the MC you have on your bike? 

http://cgi.ebay.com/ebaymotors/FRONT-BRAKE-MASTER-CYLINDER-CB550-SUPER-SPORT-CM450_W0QQcmdZViewItemQQcategoryZ35592QQihZ002QQitemZ120183261039QQrdZ1QQsspagenameZWDVW#ebayphotohosting

Do you have any photos of how it looks with the drag bars, and the clearance up at the top of the forks? My problem is, the stock MC will hit against the top cap on the right fork. I can clear it by either tilting the controls back towards me, but then the level is sticking up a bit high. The other option is to tilt the bars down (ie. the rotate them towards the rear of the bike).  This changes the angle of the brake lever, but then gives me problems on the left side clearing the clutch cable. Also, like that, the controls can bang against the tank at full travel of the bars. I broke off the horn switch put a little scratch in my tank when I learned this the hard way.

Thanks,
-Ron

[tsflstb]

I had problems mounting a similar master cylinder with my clip-on bars.  At the risk of being called an idiot, I'll share what I've done.  Seriously, think it through and do this at your own risk.  I was trying to mount the thing and running out of ideas, and I wanted to just do something temporary to get the brakes bled.  I took some 7/8" diameter wood (think broom stick), cut a 1" long piece off, cut that in half so you have a half circle and put that in between the master cylinder clamp and the bars.  I've seen some bar risers that mount in handlebar clamps that do the same thing.

It spaced the reservoir off just enough to clear the fork leg.  I will get hold of some 7/8" round aluminum stock and re-do this, but it works fine as is.  I filled in the space where the longer bolt goes with a piece of foam I had laying around.  This was all intended to be temporary and I'm not proud of it, but it's held up well.

[Jay B]

Ron- That's the same one I have. It's shorter than the stock one, things are still a bit tight in that area, but it works well. My switches will hit the tank on my '77 k model also, I don't think it's an issue on pre-77 k bikes. tsflstb- Nothing wrong with your spacer that I can see.

[rlarkin70]

I had problems mounting a similar master cylinder with my clip-on bars.  At the risk of being called an idiot, I'll share what I've done.  Seriously, think it through and do this at your own risk.  I was trying to mount the thing and running out of ideas, and I wanted to just do something temporary to get the brakes bled.  I took some 7/8" diameter wood (think broom stick), cut a 1" long piece off, cut that in half so you have a half circle and put that in between the master cylinder clamp and the bars.  I've seen some bar risers that mount in handlebar clamps that do the same thing.

It spaced the reservoir off just enough to clear the fork leg.  I will get hold of some 7/8" round aluminum stock and re-do this, but it works fine as is.  I filled in the space where the longer bolt goes with a piece of foam I had laying around.  This was all intended to be temporary and I'm not proud of it, but it's held up well.

Yeah, I noticed that if I spaced the MC off the bars, it would clear OK. The idea of a spacer came to mind, I'm glad to hear it has worked out well. I like your setup with the clip-ons. How's the position of the brake lever? Does it seem to far forward, or is it all there when you go to grab it?

Ron- That's the same one I have. It's shorter than the stock one, things are still a bit tight in that area, but it works well. My switches will hit the tank on my '77 k model also, I don't think it's an issue on pre-77 k bikes. tsflstb- Nothing wrong with your spacer that I can see.

Jay B- Thanks, that's good to know. I like the look of that MC, and if it is even a little bit shorter it would work. I think what I'm going to do (since I just ordered a rebuild kit for the stock MC) is to put it on the bike and try a spacer. If that doesn't work out, I'll go with one those eBay ones from USA Motorcycles. I have done some searching, and they have a bunch that look like they would work.

-Ron

[MoTo-BunnY]

I replaced my old stock master cylinder with one of these eBay units - just like the one starting this thread. It was one of the single best improvements I have done yet - BIG improvement in braking.









P L U S

(copy/paste from old reples I have made a few times now - since this keeps coming up)

If you want to upgrade your master cylinder to one that will support one OR two discs (and REALLY improve your braking), you can get this style off of feeBay:






This is apparently a very close copy (and a very good one, at that) of the Nissin master cylinder? (it could even be made by them but there isn't any manufacturer markings anywhere on either of the ones I bought) This company sells them and I have bought and installed two of them on two different bikes ('73 CB500 & '79 CB750K) with fantastic results: The style I used were 14mm piston - works great for our Hondas - the stock brake hose and mirror even fits the threads - and the brake switch hooks right up if you extend the wires and change the wiring connectors)

usa-motorcycles-inc

However, they seem to be running fewer of these at auction than they used to and are jacking up the price. (I bought both of mine at $39.95 each - now the same style is $49.95+)

You don't have to be particular with what brands they post in the title as long as its the 14mm piston model and it looks like this picture. .  .they are all the same. I have noticed bidding wars over $80.00 on one that says "VTX" or Shadow or something while the exact same part in a different auction goes for beginning bid ($49.99) . . . . lol.

[rlarkin70]

However, they seem to be running fewer of these at auction than they used to and are jacking up the price. (I bought both of mine at $39.95 each - now the same style is $49.95+)

You don't have to be particular with what brands they post in the title as long as its the 14mm piston model and it looks like this picture. .  .they are all the same. I have noticed bidding wars over $80.00 on one that says "VTX" or Shadow or something while the exact same part in a different auction goes for beginning bid ($49.99) . . . . lol.

Yup, I noticed the same thing. I just did a search on "front master cylinder" in Motorcycle Parts on eBay, and a whole bunch came up from that company. Some were starting at $29.00, some at $49.99...but for the most part they seemed to be the same thing.

If I hadn't just ordered a MC rebuild kit from Sirius ($28 shipped) I would just buy one of those newer MCs and be done with it. The additional appeal for me is that I will be going to a dual front disc setup soon, and the new MC will handle it.

Oh well. Maybe I will just buy one, and sell my un-used MC rebuild kit on ebay.

[edbikerii]

I just installed a new 14mm master cylinder from ebay seller usa-motorcycles-inc.com.  This appears to be the same master cylinder referred to by both Moto-Bunny and rlarkin70.  The pictures in the ebay listing were identical.  The master cylinder is exactly as advertised, and is quite nice.  I like the fact that it is shorter in length to the end of the banjo bolt, so it gives me more clearance next to my gauge with my shorter GP bars.  I like the built-in brake light switch, but I'm not using it yet.

But alas, all is not perfect.  Since the piston size is 14mm -- exactly the same as the stock unit, and the lever appears to have basically the same leverage ratio as the stock unit, there is very little, if any, improvement in braking feel.  I feel as though the lever may be slightly firmer, but there is no noticeable improvement in braking performance.  It is still basically impossible to lock up the wheel.  I even wonder if the firmer feel may be due only to the fresh GT LMA DOT4 fluid I put in.  My old fluid was several years old (yes, I know, I'm a lazy bastard, but the old fluid was only a little yellowed).

Yes, my entire braking system is in perfect working order.  If anything, it is better than when the bike was new.  I've got braided stainless lines.  I've cleaned and adjusted the caliper.  I've got stock OEM pads with plenty of meat on them.  I recently rebuilt my original master cylinder with Honda OEM rebuild parts, so I'm making a direct comparison with the stock system. 

I could see how replacing a defective master cylinder, replacing old moisture-laden fluid, or  simply purging air from the old system while bleeding after replacing the old master cylinder might lead one to believe that this master cylinder was superior to the stock unit.

Since the ratio of master cylinder piston area to caliper piston area hasn't changed, I'm not surprised.

For those interested, the 77 CB550 I'm working on has a stock 38mm single piston caliper, 14mm master cylinder, 10.75" disk and 19" rim, with a tire diameter of about 27".   All components are stock except the stainless lines (and now the new master cylinder).

These stock components, and this ebay master cylinder, provide a 7.37:1 caliper/master ratio.  According to the master cylinder ratio advice offered on Vintage Brake's website http://www.vintagebrake.com/mastercylinder.htm, "single piston calipers are much happier in the 14:1 to 12:1 range".

This would mean that a 10mm (14.44:1) or 11mm (11.93:1) ratio would be optimal with the stock 38mm single piston caliper.  Ratios lower than optimal (like our 7.37:1 ratio) result in a "wooden" feel:  "a toggle switch effect: nothing happens until the wheel locks".

Now noting that I don't think I've ever been able to get the front wheel to lock on my CB550, combined with the fact that the ratio is so low (7.37:1), it would seem that one would have to apply a ton more force to get the wheel to lock.  This amount of force is excessive, and probably impossible without breaking the brake lever, as anyone whose ridden a CB550 knows.  I've read elsewhere on these boards that Honda deliberately designed these brakes so that it would be nearly impossible to lock up the front wheel.

So, if I want the braking feel of a more modern motorcycle, I'm starting to think that a change in the master cylinder piston size to 10mm or 11mm is in order, if I'm to trust the experts at Vintage Brake.  That would result in a softer feel at the lever, but more "feel".

Has anyone made such a change on their CB550 or CB750 with single piston 38mm caliper?

Thank you,

Ed

[MoTo-BunnY]

I just installed a new 14mm master cylinder from ebay seller usa-motorcycles-inc.com.  This appears to be the same master cylinder referred to by both Moto-Bunny and rlarkin70.  The pictures in the ebay listing were identical.  The master cylinder is exactly as advertised, and is quite nice.  I like the fact that it is shorter in length to the end of the banjo bolt, so it gives me more clearance next to my gauge with my shorter GP bars.  I like the built-in brake light switch, but I'm not using it yet.

That's the same seller I bought mine from - they list a lot of these master cylinders under all different cycle types.

I surprised you didn't find it better than the stock one. On my bike, the OEM unit WAS way visibly corroded and leaking fluid. I guess the comparison wasn't fair since the OEM one was old and worn out? I still found the braking improvement dramatic though and its now going on like a year and a half on near daily use and still working great! (prolly 3000+ miles, maybe)

I like the look of the replacement unit better too - the OEM one kinda looks like a little cold cream jar sitting there or something?. . .