Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: keithtraffic on August 26, 2019, 02:57:13 PM
-
I have had some issues with the front brake on my 550 so have had to look at the master cylinder.
Unfortunately (as commonly seems to be the case) the internal circlip was badly rusted but have managed to remove that. I was then expecting the whole internal assembly, piston, cup spring etc to simply come out or at least come out with a gentle push from hose connector end, but it seems locked in place.
Should they simply and easily come out or have I missed something else which needs to be removed first? is it possible that perhaps the washer under the circlip has rusted and this is causing the problem? If so how much pressure is it safe to apply to help it out (I have already applied some easing fluid which help release the circlip)
Thanks for any help - would like to get the bike roadworthy again very soon!
-
Have you removed the ring clip that holds the rubber dust cover ? If you have then it is the washer that is holding tight.
-
Yes - that was almost rusted through so will need to get a new one and a new boot - any idea how much force a can safely apply to break the washer free?
-
Use a long bolt through the outlet hole and tap with hammer, piston and all seals/clips are in a rebuild kit
-
Thanks - that worked fine.
One (hopefully) last question for now....
The reservoir has two small holes at the bottom (see picture). The one on the left is clear and goes through into the bore of the master cylinder body but the one on the right seems to be a blind hole or is very firmly blocked. Should it be clear or is it not really a hole with any purpose? If it should be clear how do I clear it (I have tried a very fine piece of wire but if it is blocked the wire can't shift the blockage!).[attachimg=1]
-
Yes, it should be a free route through. Don't enlargen the hole when trying to clean it out....all sorts of problems will occur.
-
I feel your pain! Having just been through the same with my 750. Geting the rear one apart was even worse than the front... as you can't tp out hte piston
-
Thanks All - just managed to clear the hole (it helped to really know that it should be free route through!). I used a small piece of steel wire (about 0.4mm dia) and with a bit of pressure that cleared whatever was blocking it.
Just waiting now for delivery of the rebuild kit and then hopefully all will be OK again!
-
So, Master Cylinder re-furb kit has arrived, but putting it all back together is not going smoothly!
Everything in the kit looks pretty much identical except the Secondary Cup - this came already fitted to the Piston, but it looks slightly different to the original with the end of the cup being more flared. (see Picture). Overall at the very ends it is about 2mm larger in diameter.
Although softer than the original I just can't seem to get it into the Master Cylinder Body!!
Has anyone any experience of this - is it possible its the wrong kit? (although purchased from David Silver against the right bike model!). I maybe could just force it in (say using a vice) but this seems a bit extreme.
[attachimg=1]
-
It will go in easier if you lubricate it with brake fluid.
-
I did give it a good coating of fluid but it still seems too tight - should I force it in?
-
I know it's only from the photo, but it looks wrong to me.
The parallel part of the seal looks bigger than the bore compared to original. That section would not normally compress so it could be giving the problem.
The flare part of the seal will squeeze tight against the bore size but not the straight section.
Have you got a vernier caliper to give you a basic check of that straight section compared to the bore size?
-
Could we have a picture of the side of the mater cylinder as, you may not have a SOHC one fitted ;)
-
Just looked at your intro photo and that's not a Honda SOHC/4 master cylinder you have fitted, unless you have changed it since that photo.
-
Hi All,
Thanks for all the input.
First to dimensions - here they are. The critical diameters are identical (even though the pictures might suggest otherwise), although there is some slight difference in the lengths. The parallel part of the seal is about 13.5mm dia so should fit in the bore without a problem. It is also comparable with the first part of the original one, before it expands out). Just as an experiment to test this I turned the piston around and put it into the cylinder the wrong way round, so that I was not pushing 'against' the flare and it does go in OK!
I have looked at several different rebuild kits supposedly for the 550 and some show the 'flared' secondary cup but others (notably cmnsl) show a cup which is the same as the one I have removed - can they both be correct? I have also seen at least one suggestion that there are two different sizes of kit and one of them is wrong but don't know if this is really the case.
[attachimg=1]
As to the question - is this really a 550 master cylinder, here are some more pictures. Carefully comparing these with the workshop manual and other pictures on line I would conclude that it is but am happy for more expert opinion - This is how the bike came to me, but of course it is possible someone has changed it in the past.
[attachimg=2]
-
All the original Honda SOHC/4 master cylinders are completely metal, yours is plastic, so probably from a later non CB SOHC/4.
[attachimg=1]
[attachimg=2]
[attachimg=3]
-
Thanks Julie, I see what you mean, but is that likely to have any real bearing on the issue I have?
-
Only in as much as you have a kit for an original SOHC/4 master cylinder and your master cylinder is not that original part. To me, this would be a problem as I would only fit the correct overhaul parts to the correct cylinder. I wouldn't know if yours is compatible or not but, personally, I wouldn't risk it.
-
First time i have had chance to look at pics and the new seal is what the original would have looked like when new, as to fitting the seal needs to be well lubed with brake fluid WEAR GLOVES. Worries me difference in length.
-
Umm -doesn't sound to good to go ahead with the master cylinder I have - does anyone have a puka 550 one that they would like to sell? I obviously have a suitable re-furb kit for one so could apply that if it was required to bring the cylinder up to scratch.
-
One on Ebay >>> https://www.ebay.co.uk/itm/Honda-CB750-FRONT-BRAKE-MASTER-CYLINDER-LEVER-CB500-CB550-F-Series-K-Genuine/233321059302?hash=item365304d3e6:g:hVwAAOSwu~FdYDg-
Or just buy a replica one from DSS
-
Also look very carefully at the bore. When I did mine I reverted to a copy one from DSS.
My original had very slight corrosion and even after polishing I wasn’t confident it would seal perfectly.
This followed me putting a new seal in the calliper which had very slight corrosion in the seal groove and leaked. So again got a good copy new for £40 after some looking.
Basically the lot is now mostly new, shiny, and works well (with EBC FAO13V pads £33.95)
Cost adds up but it’s the brake!
-
Thanks - have been in contact with DSS who have been very helpful and have tried to match the dimensions of the piston with what they have in stock to see if they could identify exactly what master cylinder I have, but unfortunately they could not really pin it down.
I have concluded that I will now buy a replica master cylinder kit from DSS as the cost is not too high and also (to their credit) DSS have said that if I send the replacement repair kit back to them they will refund the cost - which I think is very good of them!
-
Wise decision, this is your life you are messing with here 👍👍👍
-
So the brake saga continues!
I have received my new replica Brake cylinder from DSS - looks very nice and have fitted it.
Once fitted I was able to pressurise the system and force out the piston from the wheel cylinder (I has suspected that some of my brake issues were down to the pad itself not moving back when the brake was released and therefore binding on the disc). I found that the pad itself was almost held in place by awful looking 'gunk' and would not slide easily on its own.
I am replacing the pads, but does anyone know if the build-up of any sort of 'gunk' around the pad is normal and should there be something to stop it? (I have seen on the packaging of the new pads that it is recommended that they are removed and cleaned every 3000 miles, which doesn't seem a lot, but there isn't any mention of this in the Honda workshop manual I have, nor the Haynes manual).
I have also read about using copper or silicone crease behind the pad but have assumed that nothing should be smeared around the edges of the pad to ensure that there is no possibility of any grease contaminating the pad surface or the disc itself. Any thoughts on this?
Also, does anyone know the mechanism that causes the pad to release once the brake handle is released - is it actually pulled back by reverse hydraulic pressure or is it just naturally pushed away from the disc by its rotation (I know from the manual that the spacing between the pads and the disc is meant to be pretty small (just 0.15mm)!
-
Remove the paint from the outside edge of the pads and the "gunk" inside the hole it fits in, perfectly permissible to use copper greas on the edge and rear.
The only thing that pulls the piston back is the "twist" in the rubber seal, the groove is machined such that the seal becomes diamond shaped and only one corner is on the piston, this means that as the piston moves the seal twists until a max point then the piston slides through, it is this deformation that pulls the piston back on pressure release and only the "looseness" of the pad in caliper that gives clearance
-
[attachimg=1]
A little schematic to illustrate the above, bit fuzzy but shows what happens.
Surprisingly little has changed in caliper concept even since these early types as most current calipers have exactly the same arrangement regarding principle seals.
What generally changes is that most employ a weather resistant seal outboard of the main piston seal operation to keep them clean, hence the need to carry out frequent maintenance on these old one's, especially if used on salted roads.
Silicon grease around that seal to piston interface is as near as possible to waterproof which helps to keep them from corroding.
-
Forgot to mention that the seal groove needs to be scrupulously clean for the seal to work properly. N.B. a dremel brush will only "polish" the crud in the groove you need to dig it out with a dental pick or some such.
That little diagram is ideal except that the seal becomes diamond shaped as the groove is not flat bottomed, even more teason to make sure the corners are cleaned out well.
-
As a measure of effectiveness from working on brake calipers, the rear calipers on many VW cars are almost exactly the same proportion and material in respect of aluminium caliper and hard chrome piston. But with a dust seal outer to the principal hydraulic one, they still eventually seize after about 100,000 miles which you can first feel through the handbrake being ineffective or failing to release. Plus lowered efficiency when mot tested.
Even with an assisted foot brake they are difficult to push the piston out which shows how much drag any corrosion effect has. I clean these and reassemble using silicon grease for both placing the hydraulic seal into the caliper body, plus reinserting the piston. Most calipers you can just push the piston in with your thumbs when cleaned and greased, they shouldn't need much force to do this and if they do it indicates that some more cleaning of the seal groove is required.
Testing after doing this always shows absolutely equal % on mot rollers plus efficiency at maximum end of tolerance for handbrake, showing effectiveness.
Edit ;- my reasoning for using silicon grease in those locations (Honda states to use it in their manual too) is that it excludes both brake fluid and moisture from that area at which corrosion compromised the piston operation. It gives longer service life like that than I've found with other methods.
-
Many thanks for the comments.
I have seen the note about silicone grease in the Honda manual so have purchased some of that and (perhaps luckily) I had already thought to replace the piston seal so have a brand new one.
It is still quite remarkable that its only this that brings the piston back to move the brake pad away from the disc!
-
It is still quite remarkable that its only this that brings the piston back to move the brake pad away from the disc!
Agree, it's just such a simple elegant solution that could have had any number of complex ideas applied to it. I'd be pleased if I invented that one ;D
On the same basis, I use some thick wall small bore rubber tubing (bought from local car parts shop) that fits tightly onto the bleed nipple, push a bolt in the other end to seal it, then with a scalpel cut a 10 mm long slit just up from the bolt.
You can now open the bleed valve a 1/4 turn and just pump the fluid through as it's a particularly effective one way valve.
I use this on cars too to bleed through systems without anyone at the caliper, just buy a piece long enough to reach down to a container on the floor.
-
You used to be able to buy bleed pipe just like that, it was usually orange in colour and was just a rubber pipe with a slit in it near the end.
You still can and they work very well.
https://www.ebay.co.uk/itm/BRAKE-CLUTCH-BLEEDING-TUBE-PIPE-WITH-METAL-STOPPER-ONE-WAY/254342217928?epid=1130461392&hash=item3b37fa40c8:g:pNQAAOSws29bxgdw
-
I've always made mine longer at about 1 metre so you don't have to balance the jam jar on top of a couple of treacle tins to reach calipers on cars. ;D
-
Those orange brake bleed pipes are rather effective, well worth having. I found a gibsons Eazi bleed kit dead handh on the car what with Abs pumps and convoluted routing but on a bike the orange tube 8s rather effective, other handy trick it that fails is get a drenching syringe with 6mm end, bit of pipe that goes from bleed nipple to the syringe, this can either suck fluid through from the caliper end or on occasion I find a stubborn master cylinder and nothings getting fluid through and pushing brake fluid through from the caliper end ( taking care not to overflow the reservoir) has got things working again.
-
I use this Drapper Brake Bleedind Kit, Works perfect for me...…
-
[attachimg=1]
-
So, I have now completed the brake re-build. Actually bleeding the brakes was not the drama I was expecting and after a few false starts to get the fluid flowing I seem to have been able to get all the air out and the brake seems good and firm when applied, with about the right amount of brake lever play. I will leave it until tomorrow and re-check to see if any more air come out but I am not really expecting any.
Because of the brake binding issues which started this all off, I have very carefully rebuilt the whole caliper bracket and hinge pivot assembly, which now seems much better and swings nice freely before I fitted the callipers. I have adjusted very carefully the caliper adjusting bolt so the fixed pad just drags slightly, then backed it off half a turn (as detailed in the workshop manual), so the wheel spins freely.
However I note that when I apply the brake and then release it there is still a little bit of drag on the wheel - its nothing like what was previously experienced, where the brakes really seemed to bind, but it is still there. Is this normal, particularly with new brake pads or is something still not quite right.
-
There's an imperfect geometry in play that affects alignment generally with new pads. The rear support for the pads ( back face away from friction material) "should " accommodate this but may not fully rectify.
The caliper would ideally have it's pads travelling at 90 degree to disc, but they swing on the arm in that radius. With new "flat" pads it can take a little bedding in before they sit perfectly to the disc face at which point the technical error is effectively built in to the pad geometry.
It may take 30 miles or so to achieve the above, then recheck your setup to fine tune. Assess from there.
-
If the brake pads have paint on the outside edge, remove it. The pad should not be tight in the caliper. Also check that you have the correct gap on the rear pad to disc, this can move when you tighten up the lock nut so, always check again ;) ;)
-
Thanks - have just taken the bike out for a test ride and the brakes seem to be fine - just a little 'squeaky' but maybe that's to be expected from new pads. As suggested I will do a few more miles then recheck the setup as I did notice, even when setting up the first time, that I had to re-adjust slightly as tightening up the lock nut did move things.
Interesting before I re-worked the whole assembly I did notice a distinct 'knocking or clanking sound sometimes from the front brake assembly when I went over significant bumps - but this has now gone away which I take to be a good sign!