Hi all. I need your help: when I move my bike in a morning - front brakes(Nissin 4 pots) pops(Suzuki TL1000S).There are pad marks on a disks(abe-aftermarket).First I serviced brakes(new seals,cleaned,pads are Goldfren-plenty of meat left)-same.Next master cylinder repair kit-same.Bled the brakes,fluid level- fine. Now run out of ideas. Could the aftermarket disk are cheap metal or maybe pads are crap somehow?... Cheers
Posts 30 | Views 7436
sounds like your caliper pistons are not being pulled back in enough that could be because there is no vaccum in the master cylinder.
1. Remove brake fluid reservoir cap and rubber diaphragm
2. Remove the first front caliper and push the pistons in so that they are flush with the caliper (make sure the reservoir dosen't overflow) also do not pump the lever yet.
3. Do the other caliper and follow step 2.
4. Refit both calipers fitted with pads back to there rightful places
5. Refit the rubber diaphragm and the cap to the reservoir
6. Now you can pump the lever which will cause a vaccum in the system and suck those pistons back a little bit further.
7. Have a cuppa
Vacuum in reservoir
Just getting my head around the idea of a vacuum in the reservoir pulling the pads back as I've never heard that before.
I can see how the vacuum is created but will it be sufficient to pull the caliper pistons?
If that were the case, surely the oil level in the reservoir would always rise to the top and the pads would get pulled further away from the disc as they wore.
Very interesting statement though and definitely got me stroking my chin.
I'd be very careful attempting to, in effect, try and keep the fluid level at its lowest possible level. Could be risky!
Suzuki TL 1000S Year?
I would go with the aftermarket disc's being the problem(not necessarily cheap?)the after market disc's could well be of a higher iron content than the standard equipment.The higher iron would have the disc's a lot more susceptible to the weather i.e. rain and salt corrosion,this combined with the sintered brake pads your probably getting an electrolysis problem happening.Probably need to wash your brake disc's and calipers in clean fresh water and dry them before putting it to bed for the night?,that's just my take on this anyway,not so sure of the other fix?never tried it Good Luck
hi arthur this is the correct way to set up the braking system, as the brakes will work fine without the rubber diaphragm but the pistons will not retract enough without it. diaphragm is there doing a job for a reason.
so if you bleed brakes with the cap and diaphragm removed (which is the only way because you need to keep adding fluid) and you get a good lever you should follow the steps above. otherwise the diaphragm is not doing it's job at all.
Just my two penneth, but I tend to agree with kcmc with regard to your "problem".
If it is just a "click" first push of the bike in the morning it is probably not much to worry about as long as the discs rotate freely after the first push. I've had the same symptoms on most bikes over recent years, although not usually just overnight. But it has always coincided with water being involved the last time I used the bike.
There was a time when cast iron discs on European bikes greatly out performed those of the stainless discs found on jap bikes. So iron is not necessarily a totally bad thing. Cast iron is actually a reasonably good material for brakes. But it rusts! And is heavy!
Things have moved on.
Sorry, but I was typing just as you submitted your post. I didn't mean to necessarily disagree with you. Only that I agree with kcmc as to the likely cause.
In fact I'm very interested in what you have said.
But surely we could have a vacuum above the oil without needing a diaphragm? Just a good seal against the top cap (sealing against atmosphere) would allow a vacuum to occur?
I thought about this and reckoned the diaphragm must be vented. Then it would all make sense.
Been out to the garage and checked three brake reservoirs. They're all vented.
The way they achieve this is that under the screw on cap there is a large plastic washer. This looks innocuous enough, but a careful look reveals three little radial slots..
These will vent the top side of the diaphragm to atmosphere.
Sorry, but it looks like no vacuum.
As long as these little slots remain clean, the top side of the diaphragm, and therefore the fluid in the reservoir, is at atmospheric pressure. It looks like the fluid in the reservoir can never be anything else.
I'm not saying i'm right and your wrong.
But what i am saying is i had this problem a couple years ago where my pads were sticking to my discs so bad it was causing rust spots/pitting on two pairs of discs. as you can imagine i was very upset to see this.
so after a lot (and i mean a lot) of chatting to motorcycle techs about it i was told to try this method and it worked for me at least. Now this is how i do it all the time and the wheel spins more freely.
But yes i do see the vent holes youre on about.
just one more thing if there is no vuccum how does the diaphragm get pulled inside out. also i do see your point but as i say this does work on my bike...
**Balanced diaphragm **
Quote: "just one more thing if there is no vuccum how does the diaphragm get pulled inside out"
I can explain that.
First of all imagine there is no top on the reservoir, so it is more like an open tank, as you might have in your loft. Then as the pads wear over several thousand miles the fluid in the tank would go gradually down.
The diaphragm is put there precisely to let this happen, but at the same time exclude any contact with the (humid) air above it. Brake fluid is extremely hygroscopic, meaning it readily absorbs water contained in the atmosphere. This has at least two very undesirable effects on brake systems so has to be kept out. Water boils a lot easier than pure brake fluid and obviously water also corrodes aluminium and steel, two materials used in critical instances in both master and slave cylinders.
The diaphragm (or bellows might another good name for it) allows atmospheric pressure to keep acting on top of the oil in the reservoir, whilst excluding any contact with the atmosphere.
Actually, the cap on top of the reservoir needn't be a cap at all. A ring would work fine, but it wouldn't be very practical at keeping debris out or damage occurring to the diaphragm.
Make any sense?
Do the brakes bind on, or stick at any other time? Or are they merely sticking onto the discs due to residual water/salt left over from the previous ride??
If they free off as soon as you move, and stay free, then it's normal.
And FWIW, goldfren pads are shite.
Hi all, thanks for your advice.Lots of replys I've been told that spring in a master cylinder pushes oil back not a vacuum. And i also feel its not the vacuum what causes sticking. It's not a big deal-just my other bikes never used to do.The rest of the times brakes are not sticking or binding. Also its sticks even it wasn't raining. Maybe salt.I probably need to read a bit about iron vs stainless... And yeah i heard Goldfren are shit but they came in with the bike. Will see, better weather soon, when its time -will replace with other brand pads. Thanks again
To push or pull?
Yes there is a return spring in the mater cylinder, but to say that it pushes oil back is not entirely accurate, as far as I can see.
There is a very good diagram on page 158 of Kevin Cameron's Sportbike Performance Handbook 2nd ed as well as his description of what actually happens. I can recommend this book as a tenner well spent, if you want to brush up on all aspects of a motorcycle.
There will be a combination of factors, some of them tiny, which ultimately contribute to the system returning to "original state", but the main factor seems to be the springiness of the caliper piston seal. This is what seems to push the oil back. The spring in the master cylinder , in my eyes, assists by returning the master cylinder piston, thereby opening up the tiny hole into the reservoir above.
If a brake pad decides to stick itself to the disc, there is nothing in the hydraulic part of the system to get it off.
If the diaphram's
Only Job was to pull the pads back you would find when bleeding your brakes that your brakes would be binding ...... make sure someone hasn't modified the pawl that pushes on the mastercylinder hasn't been packed out or modified to improve lever feel..... i have seen this before .....very dangerous also on the opposite side some cheap pattern levers can be the wrong profile causing poor lever feel
my bet if the bike moves ok once initially shifted try some different pads abe will probs reccomend a certain compound pad ....
Hi Swen, you said you serviced......
The brakes, replacing seals.
This might be obvious but you sure you fitted them correct way round?
They are usually tapered on the outside edge.
Worth a check in your manual.
Edit: Oh yes, and I agree with eatcs01, those Goldfren pads are for the bin.
The master cylinder seals have a pronounced taper on them, but if they were fitted the wrong way around nothing would happen. No oil (or certainly very little) would be pumped. The "cup" would fold in on itself. The lever would return very very slowly as the piston would be trying to pump on the return stroke and push the oil through the tiny hole.
Besides, if both master cylinder cup seals were fitted wrong way around, oil would leak out the end and quite copiously when the lever is pulled.
Regarding the caliper piston seals, I'm not sure if they are all tapered? If there is a taper, then yes, you would have return problems, but I suspect you'd have severe oil leak problems too.
I'm pretty sure you'd know in both cases.
Going back to the second post and the vacuum scenario. If there are still any doubters then consider that the diaphragm is more like a bellows. It is made to extend itself freely. It is unable to provide any mechanical support.
tapered caliper seals
Caliper piston seals
Are some caliper piston seals wedged (tapered) on the outer diameter? Fitting the wrong way around in that case would lead to problems with sticking perhaps?
It might tend to squeeze the seal a bit tighter? Dunno.
The seals are meant to deform without necessarily sliding so is this wedge shape done for that reason or some other reason? Seems that this deforming characteristic is the main factor which will return the piston after lever pressure is released. As the seals straighten back again.
listen to bad advice by crusty poo pants he ain't got a clue
Crusty poo coo coo cah choo
Maybe, maybe not. But are the seals wedged shape or not? That is the question.
LAR LAR Land
come on now lads get a grip caliper seals are not wedge shaped and master cylinder rubber diaphragms don't pull caliper pistons backand the moon isn't a balloon.