Servicing the Honda twinpot brake calipers.
Honda`s twin-pot brakes can be troublesome,but an hour or two of work can have them sorted.
The usual issue is a sticking/binding caliper due to the sliding pins gumming up and preventing lateral movement or corrosion under the piston seals which prevent the pistons retracting easily.In both cases the pads will be dragging on the discs slightly leading to problems such as premature disc wear.Expensive! .Just leaving them unused for more than a few weeks could lead to them needing attention,and winter use with salt/road gunge,a few days inactivity can sometimes result in the onset of grief!
This is how i do mine,and the pics/text may give you an idea on how to tackle you own if you have sticky calipers.
To do a "quick service" remove the caliper and then remove the pads(leave the caliper connected to the hose).
Place a suitable flat piece of material such as some 2-3mm thick steel accross the face of the pistons and pump them out using the brake lever.
One will probably move before the other,hit the steel whereby the other will then come out.
The pistons will not come out completely,when they both hit the steel plate stop.During this process keep the resevoir topped up as the fluid level will go down to fill the void left by the pistons in the caliper body,this will depend on the thickness of your brake pads and the level of fluid in the resevoir,if the master cylinder sucks in air you`ll have to bleed the system.
If the pistons have light corrosion but are servicable,they can be cleaned up using a gentle chrome pollish such as Brasso using a piece of rag wrapped around the piston,but be careful not to remove the gold-coloured plating.
If they are just dirty,clean using brake cleaner/de-greaser or just brake fluid.
Here the pistons have been pumped out,and a ribbon of rag has been fed around the piston to clean off any dirt/muck/light corrosion.
Note that there is no rubber boot protecting the supposedly high-precision hydraulic pistons and they are completely exposed to road dirt/filth and the weather!
OK,so they`re plated because they`re steel, but not one of Honda`s best designs is it?
When the pistons have been cleaned,push them back into the caliper body using a g-clamp - you have to overcome the resistance of pushing brake fluid back into the resevoir through a tiny hole so it won`t be possible to do this with your hands.Do not use exessive force - the pistons have to be *exactly* square to the body or they may bind,and because the pistons are nearly all exposed at this time it is important that if you feel anything that suggests the piston jamming to re-align to the caliper body and try agian.Apply the the g-clamp pressure to the opposite side of the piston to ease it into alignment.Watch that the other piston does not move out too far when pushing the piston in due to the fluid pressure in the caliper - keep an eye on the piston you are not working on in case it starts to move further out,another few mm and it`ll pop out..You could leave the steel plate across the pistons if you wish,but keep switching the clamp from one piston to the other and use only small increments with the clamp to ensure they go in square.
Watch the level in the brake resevoir - it will rise as the fluid in the caliper body is replaced,you may need to use a syringe to remove some if you added any during the previous stage.
Next,on to the "sliding pins" on which the caliper moves.
The long,bolt type one with the smooth shank and flat on one side can be left in place on the caliper - just clean off any old grease and also clean the hole it fits into on the caliper mounting bracket.
The one that gives most trouble is fitted between the two rubber boots between/below the pistons on the caliper body.
Push the pin out - if the brakes have been neglected it may be quite stiff.....
Then remove the two boots.
More than likely,the rubber boots will be perished/holed/split or if the wrong type of grease has been used previously,be swollen to a point where it will be near-impossible to replace them back in the locating groove of the caliper body.
The type of material these boots are made from reacts with certain greases,they will then swell and deteriorate.If they swell enough they will "grip" the sliding pin,impede movement and you will have binding brakes and the associated problems.
Clean the pin,and caliper body grooves where the rubber boot locates (see pic,i use an L-shaped piece of wire held in a pin-vice) - check for exessive corrosion on the pin and wear on the caliper body where the pin slides,remove all traces of old greases to avoid contaminating the new rubber boots if they are to be fitted.It might also be a good idea when cleaning a bike to avoid cleaning the brake calipers with degreaser type detergents in case they react with the sensitive rubber parts.If you are lucky the boots may be re-usable and will fit back into the caliper body.
If not,obtain new boots from Honda - there are two kinds,two of the type for the sliding pin,one for the other longer pin per caliper.
When assembling,use Castrol Red Rubber grease (or silicon grease,but RR is a lot cheaper!) - it is specifically for rubber brake components where swelling and hardening of components is to be avoided.
Grease the hanger hole and boot(longer,fixed type),then install the boot in the caliper hanger.
The other type is a little tricky - especially when everythings greased-up and slippery.
Locate one of the boots in the caliper body - rotate it to ensure it is fully home in the (greased)groove.Place the other boot on the sliding pin orientated in the way it will normally be,then slide it past the locating groove so that it is near to the opposite end of the pin but not sitting in the groove of that end - but close to it.
Now install that boot in the other side of the caliper body - the pin should be sticking out at this stage.
When the boot is seated properly in the groove(rotate again,this time holding the pin as well,try not to let the boot slip into the groove),you can then carefully push the pin in - it has to go over the resistance of the "seal" part of the boot,then overcome the second boot too - without displacing them from position.Easy does it,firm,smooth pressure with a bit of wiggling....
Check the boots are still in place and push the pin in and out/rotate the pin to ensure all is OK and to distribute the grease.
This pic shows one pin boot in position in the caliper body,the other boot on the pin ready to be inserted into the caliper.Use red rubber grease....!
After you have fitted the sliding pin re-fit the pads/retainer etc and you should be good-to-go.
This mini-service will usually sort out binding calipers most times or is useful if you just want to give the brakes a service when they are working without any other problems.If you want to do a `full service`,recondition,or this has not cured the problem it can be extended to a full re-work: pump the pistons out as previously described,then remove the hose from the caliper to enable working on the bench.Remove the bleed nipple and drain the brake fluid via the banjo bolt and bleed screw holes.If the bleed nipple is seized into the caliper body,be careful.Do not simply apply more spanner force,if the nipple snaps off you have a lot of extra work to do(or have a long delay while you source bleed nipple-equipped banjo bolts).Drain fluid and remove all other parts from caliper body and heat the body local to the nipple screw thread with a gas-torch with a small,localised flame.This will usually free up the nipple - i have saved several calipers this way.
Pull out the pistons the remaining few mm with pliers the jaws of which are covered with cardboard or other suitable material to prevent damage to the pistons.
Use a small flat-blade screwdriver to prise out the dust seal,and then the piston seal.
You will probably find the seal-lands have white alluminium oxidation making the seals too tight a fit in the lands causing the seals to press harder onto the pistons,which resuslts in them not retracting easily when brake pressure (h`bar lever) in released.With a caliper empty of fluid and disconnected from the brake hose the pistons should be able to be pushed fullyinto the caliper body by just using hand pressure.If it takes a lot of effort it`s a sign that the seals are tight.
Make up a wire tool (or pin-vice again) and scrape the deposits from the seal-lands,be careful not to remove any material from the caliper body.Clean/wash/squirt out all the dirt and make sure none is left inside the caliper body.
Inspect the seals - the dust seals usually perish first - replace any that are unservicable,and scrape off any of that white deposit from the surface of them - i have found that in most cases they can be reused succesfully.
This pic shows a caliper body in a seriously corroded state,it won`t be as bad as this in one that has just been removed from a bike but it shows where the oxidation forms under the seals;
After the caliper body has been cleaned up,reassemble the caliper using brake fluid in the seal-lands and on the seals to lubricate and facillitate the replacement of the pistons,and dip the bottom of the piston into clean brake fluid to ease re-fitting.I place a snugly-fitting socket into the piston attatched to an extension and use this as a `handle` to re-fit them into the body,otherwise it can be quite hard to get them in.Using the `mini-service` guide above,reassemble the caliper.
The pic below shows the effect of using the incorrect lubricant (lithium grease,oil,coppaslip etc) can have on the rubber boots - these are the same part,but one has swollen so much that it would impede movement of the sliding pin when in position and would be impossible to re-fit in the caliper housing during a brake service.
This pic shows another example of the sensitivity of rubber brake parts;this master cylinder diaphragm was left in parts washer fluid overnight and the next day it was about one and a half times the size! I brought it indoors to dry out and after a few weeks it shrunk back down to its normal size;
This advise details the work to the calipers - there is another reason why the brakes may be binding,this is when the fluid return-orifice in the master cylinder body is blocked.
There are two small holes in the bottom of the resevoir to allow fluid to flow to and from the piston/cylinder area.One is under a small metal cover which is the smaller of the two,the other is easily seen - make sure both are not blocked.The small one under the cover allows fluid to return to the resevoir and if it is blocked it allows residual pressure to remain in the brake system causing sticky brakes.
If the bleed nipples are seized,i use a concentrated flame from a gas torch on the caliper body around the nipple,and gently turn it back and forth gently with a spanner to release it - be careful the thread doesn`t `pick up` on the soft alloy and damage the thread;
Here`s a few to service when i get the time....!;
Talking of brakes..........
The CX-periment nears completion and it`s time to sort out the front brake system.I need a master cylinder.A quick rummage around the `brake spares` drawer in one of the CX filing cabinets of assorted treasure provides a rather scabby looking plastic-resevoir-type master cylinder of uncertain model/marque or vintage.Its been left unloved for years with fluid oozing out,the paint has fallen off,theres oxidation all over it,it`s looking very sad and it`s seized up.Here we go again...............
I can save it!
First thing to do would be to take the lever off,right? Woah,hang on,things arn`t as easy as that on this one - even the lever pivot bolt is absolutely stuck solid and needed the gentle persuasion and mechanical finnesse that only an impact driver and a 2lb hammer can provide,but several clouts later it yeilds to the prolonged process of percussive persuasion and comes away.I win.
With that done lets try the notorious-for-seizing resevoir cap screws.It doesn`t look good.Someones already had a go at them and the rounded-off screw heads suggest some work with tools other than just a screwdriver may be required.
Sure enough,two of the screws came out OK but the others would not budge and the rusty heads just rounded off.I already had the drill prepared......
I bored into the heads a few mm with increasingly-sized drill bits until the heads popped off.I win again.You can`t let these mechanical objects get the better of you...
Once all the fixings were off the first really exiting part of the overhaul was imminent - what would be revealed once the cap was removed?
Actually it wasn`t as bad as i thought,there was still fluid in there which was still,err,fluid,it`s always been a gelatinous mass on all the other MC jobs i`ve done.
With the cap off i could extract the remainder of the screws by gripping the protruding shanks with pliers.Look at those threads,no wonder it was seized.
The resevoir cup was a really tight fit on the body - i couldn`t shift it with just my hands i had to use a lever to ease it off.
With the resevoir off i was not dissapointed in my jello fix as there was a nice fresh supply undeneath.A brake overhaul just isn`t the same without it..
Now to the next troublesome stage;removing the piston-retaining circlip.
After teasing the rubber dust seal offand scraping away the fluffy crud i could just about make out the circlip hidden in the depths of the recess.I haven`t got a decent long-reach set of circlip pliers so what i tend to do is use the prong of just one side of the pliers to locate the hole at each end of the circlip,lever it out of the groove and then `walk` it up and out of position alternating between each end of the circlip so it doesn`t bind.
When this circlip is removed the spring in the cylinder should push everything else out,but of course on this one it wont because it`s stuck.
You could hold the MC vertically and apply some penetrating fluid and let it soak for a few days but previous experience has shown it didn`t make any difference so i`ll skip to the next stage - getting the recalcitrant piston gubbins out.
The piston seizes in the `released` position so there is room for the piston to be pushed down the bore which should un-seize it.
Tapping the end of the piston lightly with a small hammer in short-shock strokes is usually enough to free them up and they`ll retreat further down the bore before freeing up completely where the spring pressure will push them back up again.You have to be careful not to tap the piston too far down or you won`t be able to reach the dust boot groove on the end of the piston which is handy for putting a screwdriver in and gently levering the piston and seal assembly up and out once it`s loose enough.
Well,thats it dissasembled,does it look salvageable?,yeah no probs,and without spending any dosh,too..
Here it is after clean-up,everything looked fine,even the dust boot was intact - they usually perish first.
What i do with the master cylinder body after scooping out most of the muck/jelly is to bring it indoors and put it on a radiator,heater or somewhere else warm.This`ll dry out the jelly and leaves just a white deposit which can then be scraped/rubbed and picked out and then cleaned using a piece of fine Scotchbrite pad.
Then using some steel wire in a pin vice clean out the o-ring and circlip grooves.
Master cylinders that have reached this condition invariably have the tiny fluid return port blocked or fused together,it`s only about 15 `thou or so in diameter and it`s easy to overlook if you don`t know it`s there,and will cause problems if left blocked.A piece of smaller steel wire again cleans it out.
With everything cleaned up and checked it was just a case of putting it back together with new res.cap screws.
.......so that i could start on the calipers.
Here we go agian,how many times have i had to do this over the years.Bloody brakes.I`ve got four bikes and eleven calipers to look after....
I did the basic brake service first,and noticed the tell-tale coppery smugde of a previously applied lubricant on the slider pins resuslting in greasy grief - all the pin boots were swollen.......No bother,i had a spare `pattern` set here i bought via Ye Olde Interwebbe Spares Shoppe.The immaculate sliding pin was a surprise though,i`ve never seen one in so good a condion.There was just the one though,the others were the usual...The master cylinder performed without problems and bled easily.
Bench set-up for a brake cleaning session:master cylinder mounted on a piece of tubing held in the vice and hooked up ready to pump the pistons out of a caliper
After doing a basic clean on both these front calipers i wasn`t sure if the pistons were completely free,they pumped out OK with hydraulic pressure and i was able to push them back with the g-clamp,but they still gripped the piece of steel i was using to prevent full travel when i released the brake lever,so i took the hose off and drained the fluid out to try something else;
I fitted a Schrader valve to the bleed screw threaded hole and blocked the banjo bolt hole off with a suitably threaded bolt.
Using a foot-pump i had to virtually jump up and down on the pedal to get the pistons to move and noticed the pressure gauge on the pump reading up to about 70/80psi.That didn`t seem right so i pumped them out as much as poss and removed them,cleaned out the seal lands and seals (medium oxidation found) and reassembled.
With that done i hooked them up to the foot-pump again and found i was able to push the pistons out much more easily by just using hand pressure at about 25/30 psi.Good job i didn`t wait until fitted back onto the bike and found they were sticking on and have to strip them all down again..
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