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Rob750SRAD
moped
Joined: 02 Mar 2008
Posts: 55
Location: South Shields for collage but Essex is home
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 Posted: Thu Jul 17, 2008 2:09 pm Post subject: Srad brakes |
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For the past few weeks i have suffered from spongy frount brakes on my 750 srad! I put this down to old standard lines so was gonna get some braided lines when money permitted.
2day i wanted to have another look just in case, anyway took the pads out and had the callipers off aswell, checked all pistons are ok and not seized and they all look good.....until.....
I put the pads back in and left the metal plate off and grabbed the lever, i could see the pistons move in which im sure thay should, but as i let off the lever i could also see the pistons move back out i very small amount!!!!
I think i have heard of tthis before and think it may be the piston seals not sliding or somthing???
Can anyone correct me on this or has any1 had a simular problem?
Cheers in advance |
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Martin_K
Tech Bod
Joined: 20 Jul 2007
Posts: 452
Location: Redditch, Worcs
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| Posted: Thu Jul 17, 2008 3:49 pm Post subject: |
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They will move back a fraction.. thats normal, else they would bind/squeak/get hot, when not using them 
Mine do anyway, and mine feel great.
Spongy? Does the lever hold in place when applying a firm pressure to it? Have you changed the fluid lately or done any work on them? Id give them a good bleed just incase you have air in there before anything else.. will do it good in any case if the fluid is old, even if it doesnt solve your problem. |
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Rob750SRAD
moped
Joined: 02 Mar 2008
Posts: 55
Location: South Shields for collage but Essex is home
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| Posted: Thu Jul 17, 2008 3:51 pm Post subject: |
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| Ok sounds ok, I have put new fluid in and given them a VERY good bleed many times to try and solve the problem but i gues it is just a case of old standard linse bulging when the brakes applied? |
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Martin_K
Tech Bod
Joined: 20 Jul 2007
Posts: 452
Location: Redditch, Worcs
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| Posted: Thu Jul 17, 2008 4:03 pm Post subject: |
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Could be.. I presume you bled them due to this problem, and it didnt suddenly arise after bleeding? When you say youve suffered with it the past few weeks, did it suddenly feel worse one day or what?
Standard lines to expand more than braided ones, so it will give it a firmer feel. Best to go through the basics first though(sounds like you have) just incase you have a problem, rather than just compensating with new lines. |
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Rob750SRAD
moped
Joined: 02 Mar 2008
Posts: 55
Location: South Shields for collage but Essex is home
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| Posted: Thu Jul 17, 2008 4:44 pm Post subject: |
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I,m not sure when it started! Since i go the bike about 6 months ago it has always had spongy brakes but not as bad!
and i did bleed to correct the problem and didnt cause the problem.
I think i have covered about all of the posible problems just though the seals may be not seated properly but i gues there ok so i will get some braided lines and again refresh the fluid and see what happens.
Cheers |
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renthalryan
Ghost Rider
Joined: 29 Apr 2008
Posts: 611
Location: notts / over the hill
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| Posted: Thu Jul 17, 2008 9:22 pm Post subject: |
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| best bet is to junk the 6 pots, there s***. had probs before, and on zx9r too as they are the same. 600 4 pots drop straight on |
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radiodave
scooter boy
Joined: 31 Dec 2005
Posts: 18
Location: Hampshire
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| Posted: Mon Aug 11, 2008 10:47 am Post subject: brakes still soft? |
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This is abit long but it is all important.
Soft brakes fully bled still soft maybe even after new seals new pistons etc.
This is the problem.
All the shit from the road corrodes the caliper but only around the outer seal.
This results in the grove for the outer seal being half round (not square) due to the crap that has built up down the sides and behind the seal.
The outer caliper seals MUST sit a square grove in the caliper just the same as the inner seals.
Problem being is that the outer seal is now tighter on the piston than the inner one.
The inner seal is sitting in a nice square grove as never seen any road crap.
But the outer seal is being pushed out by the crap making it tighter on the piston than the inner seal.
Is this Ok?
No but it is (maybe) the cause of your problem.
Operation of the brake (current soft operation).
So when you pull the leaver the pistons push the pads up to the disks all ok.
When you release the leaver the pistons move the pads away from the disks.
This is normal?
NO.
What should happen is:
Correct operation of disk brakes (this why we use them).
When you pull the leaver the pistons push the pads HARD against the disks.
When you release the leaver the pads no longer push HARD against the disks but relax.
The disk and pads sort the friction thing out themselves as the system is hydraulic the fluid will go back (only a little bit) to the master cylinder (that’s why we must have it).
In normal operation you should only just (and I mean only just) see the pads moving.
Think about this.
Front brake operation.
You pull the leaver and this pushes a piston that is about 9mm diameter and you can move it about 15mm if you pull the leaver to the bar.
This will never stop you.
This tiny piston needs to push the big pistons in the caliper and the pads onto the disk and stop you without crushing the two fingers that you are holding onto the bike with.
My bike has 12 pistons so this tiny little piston (as above) will stop me from whatever speed I am doing and it works always even with just one finger.
All ok so far?
So what is the problem with your brakes?
If you can see your brake pads moving then all your braking effort is going into moving the pistons and pads up to the disks and NOT STOPPING YOU. And when you release the leaver you can see the pads move back then you need to clean the outer seal groves.
So what is the problem?
The outer rubber seal is forcing he pistons back into the caliper when you release the brake leaver due to the crap that has built up behind the outer seal.
So when you pull the leaver all of the effort is going into pushing the pistons and pads to the discs.
The inner seal is still and always will be except in extreme circumstances never a problem.
What can I do about this?
Caliper rebuild.
Not as bad as it seems.
Drain, remove and split the calipers etc.
No not yet.
How do you expect to get the pistons out?
Remove the pads (as this will let the pistons move almost to the limit) pump the leaver and push all of the pistons out to the discs (keep adding fluid).
At this stage if any are not moving keep going and let the moving pistons push up to the discs (use the power of hydraulics) keep working on it until all the pistons are out to the discs.
This will make it easer to remove the pistons.
Once all the pistons are fully out drain and remove the calipers.
Remove the pistons.
This is up to you but as the pistons are almost all the way out now should not be difficult. A good grip with a cloth and a twist should see the pistons out without any problems.
If you have a problem piston go back to above and use the power of hydraulics (this will require bleeding the brakes again) but without the discs in the way. Do it on the bench not on the bike.
I use strips of wood and an electric plane to adjust the thickness of the wood. You may also need to put pistons back and stop them with wood (or spacers) just to get the stuck ones out.
If this still fails as one side is moving but the other is not devise a method of locking the moving piston.
This will take some time but it is worth it and you may need to re bleed the system.
Do not be tempted to pull the pistons out with mole grips it will just bugger them.
With all the pistons out carefully remove the seals and check the condition of all components, replace as required (your decision).
Now look at the seal groves, the inner will be fine but you will see the corrosion in the outer seal.
This must be cleaned out every last tiny bit.
I use a tip from a milling cutter head that is by chance the correct thickness and the cutting end is square. You must be careful not to increase the size of the seal grove.
Once cleaned (and I mean cleaned) along with all other components you can start assembly.
Put some brake fluid in a dish.
Dip the seal and fit remembering the correct order for the seals (solid inner grooved? outer)
Now fit the pistons dip in fluid and push in with a twist.
All pistons should fit without too much effort. If you find that one is tight start over.
Do not use any oil or grease only brake fluid.
If you are happy re assemble the calipers and test the operation on the bench is better than on the bike.
If any pistons are still moving in and out start over.
Note: With all this bleeding you can reuse old fluid as you are going to waste a lot.
Now when you are happy with the system drain the fluid and clean the calipers etc.
Refit to the bike bleed with new fluid.
Enjoy.
I have been trying to finish this document for some time.
Not having read tha above through yet please do not whine about any errors.
This will get finished at some time with photos.
Dave |
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Baldrick
moderator
Joined: 06 Mar 2006
Posts: 4698
Location: Nuneaton, Warwickshire, Home of the Banjo
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| Posted: Mon Aug 11, 2008 6:30 pm Post subject: |
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Well done Dave! A most comprehensive post which should be applauded in these days of vacuous spam and topic hijacking! 
I sorted my brakes this afternoon, bloody 6 pot calipers. At least mine looked recently rebuilt and looked after, just needed a bloody good clean. Fluid next. Looks black. But that's 4 months at Mallory without even checking them.
ooopppppsssss  |
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Kirkeh
moped
Joined: 30 Apr 2006
Posts: 96
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| Posted: Tue Aug 12, 2008 10:22 am Post subject: |
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Great post Dave, I've read so many posts on the internet about tockico 6 pot and 4 pot brakes and how people can't get them to bleed properly, bleeding was/is never the problem. Pistons being drawn back into the calipers is always to blame ! And the culprit is almost always the outer dust seals.
My SRAD 750 has the exact same problems that you describe in your post, I did rebuild my but to no avail, seems I have to go back into the garage and get them stripped again and get all meticulous on them bastards again ! One thing I would like to add though. You say only to rebuild using brake fluid, I've read on the internet and in PB about 'red rubber grease'. A minute smear on the inside of the seals seems to be advocated by a lot of people in the know. You have an opinion on this out of intrest? |
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radiodave
scooter boy
Joined: 31 Dec 2005
Posts: 18
Location: Hampshire
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| Posted: Mon Aug 18, 2008 9:55 pm Post subject: Srad brakes |
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Re: grease and calipers.
I do not know that grease but some others when mixed with brake fluid may change state and may clag up the system.
Look at it this way.
The pistons and seals are almost completely immersed in brake fluid and under a lot of pressure when breaking.
Do you want any other products mixed in with this?
No.
As it is not a good idea.
Brake fluid is the only product that the seals should ever be in contact with on the inside of the system.
On the outside between the pistons and pads some moly grease may well help to keep the crap out.
Chemicals and rubber seals.
Just try soaking any “O” ring in white spirit and see what happens.
It will swell up and go soft but if you let it dry it will return to normal.
Would you still use this to keep the oil in your motor?
No.
Chuck it.
Dave
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garynortheast
BSB novice
Joined: 30 Apr 2006
Posts: 2225
Location: Mid Wales
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| Posted: Tue Aug 19, 2008 3:46 pm Post subject: |
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| The rubberised grease should only really be used on the exposed part of the pistons. It helps to keep the corrosion at bay and doesn't react with the outer part of the dust seal. It's designed specifically for this type of function ie. hydraulic assemblies. |
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Rob750SRAD
moped
Joined: 02 Mar 2008
Posts: 55
Location: South Shields for collage but Essex is home
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| Posted: Thu Sep 04, 2008 5:56 pm Post subject: |
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calipers have been rebuilt and are amazing!!!!!!
Through a set of hel lines on while i was at it cant belive the difference as the bike always had bad brakes since i got it!
Cheers for the advice guys all sorted now! |
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