Brakes binding

[svs]

The front brakes on the SV have really started dragging a bit too much lately and this morning was just too bad. I got 5k down the road (no braking) and the disks were hot. So took the bike home, stripped and cleaned the calipers, pistons, master cyclinder and lever in case it was getting gunked up anywhere, changed the fluid and it's still no better.

Tried pads off the race bike to get the pistons sitting in a different spot, but still very tight when you release the brakes.

Any ideas? would new piston/dust seals help? - couldn't do that today being sunday. I'd hate to give up and take it to a shop, but the WOF and rego are due so I may as well get it all sorted.

Oh - and does anyone know where you can get that caliper piston grease - the red stuff that you occasionally get with replacement seal kits?

[wkid_one]

Be careful - you want to get that sorted before you warp the disks.

Try getting brake clean and go mad around the pistons etc.....get some feeler gauges and check that they are the same distance from the rotors as Manu Spec.

Rebleed your brakes (there is a thread on here showing you how - if not go to www.r1-forum.com - they have a how to) and if all else fails take it apart.

[svs]

and if all else fails take it apart.

err. that's what I did this afternoon Just didn't replace any of seals when putting it back together.

pistons are nice and shiney now. There are a few marks and scratches on them, but nothing that I would have thought would make too much difference.

[Motu]

So,did that fix it? If not check the clearance at the lever,you should have some before the lever touches the piston,check for binding as well.It could be the compensating port is not being uncovered in the released position,if not an external problem it will need to be rebuilt or replaced.

[svs]

Everything as far as I can tell looks OK, but the pads are not releasing from the disks properly. Plenty of play in lever ( I learnt that lesson the hard way a few years back - a sticking lever caused me to crash my RGV250 at over 140kph at knockhill ).

I've had everything apart, cleaned, and put back together. The bike's done just over 43k - would anything really need replacing?

Motu - how can I check to see if the compensating port is being uncovered. The inside of the master cylinder looks pretty simple to me. spring- seal - piston with screw like thread - seal.

Wkid - Clearance = 0. At least less than 0.05" which is the finest feeler gauge I've got and the shop manual doesn't mention any clearence as far as I can tell.

Will look into getting one of those master cylinder rebuild kits tomorrow. Even when putting the pistons back in the calipers, the seemed to go in OK. not too stiff.

[stevedee]

Go here http://www.sv650.org/ Have a look at FAQ and spot the brake stuff

[stevedee]

From the site
27/11/00 - HOWTO - UNSEIZE THE FRONT BRAKE CALLIPERS - Ian ian@netgates.co.uk once again supplies 'how to' information...thanks for your effort Ian!!
N.B. Read all of this before you start. If you've not got the right tools or if you're not confident in using a tool kit, then get a professional to do it. it involves the braking system, and you don't want to get it wrong.

Do one side at a time.

Remove the brake calliper bolts and the P clip which attaches the calliper and the brake hose to the fork leg. The calliper will be stiff to pull of of the brake disc. I find that it's easiest to hold the calliper with a cloth and swivel it back and forth until it comes free. Hold the calliper so that you can see into the gap between the brake pads.

At the bottom of the calliper is the pad retaining pin, which is held in place by a small R clip. Remove the R clip with a small pair of pliers and pull out the pad retaining pin. You may have trouble with this, some people have found that the pin is seized solid in the calliper. Mine were fine, because they had been assembled with some copper grease.

Remove the fixed pad by swivelling the bottom out and then sliding it off of the top pad retaining pin.

Remove the moving pad by pulling it away from the pistons, the sprung base plate will make it pop out when it is free of it's retaining lugs.

This is a good opportunity to inspect the wear on the pads and to clean out the wear indicator groves with a small flat blade screwdriver. Be careful not to loose the anti-squeel shim from the back of the moving pad.

Clean the pistons with a cotton bud and some brake fluid. Any Dot 4 fluid is fine, but keep a small bottle purely for cleaning the pistons, NEVER USE IT IN THE HYDRAULIC SYSTEM. It will quickly fill up with atmospheric water and miscellaneous dirt, and will be dangerous to use as brake fluid. Gently dab some fluid onto the
curved surface of the pistons, just enough so that it soaks into the muck and loosens it. Don't use too much and get it all over everywhere, since it will damage paint work. When the muck is soaked, it should come away fairly easily. You probably won't be able to get all the way round the pistons, but the fluid will soak in to the bits that you can't reach. Wipe round the pistons with a dry cotton bud and the muck should just fall off.

You need to press the pistons back into the calliper a couple of mm to allow easy refitting of the calliper to the fork leg. I use a couple of small carpenters G cramps. I doesn't need much pressure, but the G cramps allow you to apply that pressure accurately. Fit one cramp and do it up just tight enough to keep it in place. Fit the second cramp and compress the piston a couple of mm. Then compress the other piston the same amount. If you try it with just one cramp, then as you press one piston, the other will be pushed out, rather than squeeze the brake fluid back up to the master cylinder. Don't push the pistons too far in, otherwise the reservoir may overflow and leak fluid.

Refit the moving pad with a little copper grease on the back of the pad. Make sure it is pushed fully against the pistons.

Refit the fixed pad on the top pad retaining pin.

Smear some copper grease onto the removable retaining pin and push through the caliper, through the holes in both brake pads and into the caliper at the far side. The holes in the pads will not line up properly, you'll have to gently press them into the caliper against the sprung base plate. Rotate the pin as necessary and insert the
small R clip.

Make sure that the moving pad is pressed fully against the pistons and that the fixed pad is fully against the caliper body. This will give ample room between the pads to fit over the brake disc.

Fit the caliper over the disk and refit the caliper mounting bolts. Us a little copper grease on the threads and torque them to 28 lb/ft (39 N/m) (thanks RonnieD). Reattach the P clip holding the brake hose.

Do the other caliper in the same way.

Since you pressed the pistons back into the calipers a way, the pads will not be touching the discs. With both calipers cleaned and refitted, slowly squeeze the brake lever. It will easily come all the way back to the bar. slowly release and reapply the brake. After about half a dozen times, the pads will be in contact with the disc and the action at the lever should be firm. Wheel the bike around and check that the brakes work correctly and release correctly.

[svs]

Did that (and a lot more) this afternoon. Cheers anyway. I've stripped the brakes down and rebuilt them as per the shop manual, but they're still not right.

PS - welcome to the site stevedee

[FROSTY:Me]

The lube you're talking about is called rubberlube (no it isn't a sex aid) You can get it from an engineering supply company.
2 Things spring to mind with your brakes --I mean that havent already been covered
1 -the piston seals on the calipers have hardened up and arent allowing the piston to return the 1/2mm the pads need to back off.Try ubberlube If it helps You might be up for a new seal set in the near future
2 You have a replacement brake lever that is slightly preloading the front brakes by pushing lightly on the master cylinder piston

[Motu]

If the compensating port doesn't open then the brakes will start coming on as the fluid heats up and expands,or as the brakes are used the fluid is unable to return to the resivour.Easiest way to check is to take the cover off the top and work the lever - if squirts up and out over the tank then it's working,if you can't see the fluid move them it's not being uncovered.

[vifferman]

I think the seals are partially responsible for helping the pistons to retract when you release the lever, so if you didn't replace them, you may be wasting your time, as they aren't helping to maintain a good seal (so fluid can seep out and air/water could get in). When you release the lever, the reduction in pressure should suck the pistons back in, but only if there's a tight seal, and the pistons can slide freely against the seals. If the seals are a bit old and hard, or if the pistons aren't as smooth as they need to be, they won't move in and out as freely as they need to.
The same applies if there's air in the lines; are you sure they're well bled?

After my initial "clean in place and bleed" exercise didn't do the trick, I did the same exercise as you a few weeks back on my VTR. However, I did replace the seals, even though the ones that were in there looked fine. Cost me $107 for the seal kit, so I felt like I wasted my money. But the brakes don't bind now (although they audibly still rub a little), so it must've done the trick. I didn't use any grease (didn't get any with the kits, so I just 'lubed' em with brake fluid when pushing the pistons in. When I cleaned the pistons, they were a wee bit crappy looking, so I used very fine sandpaper (1200 grit I think), and then polished them on my bench grinder using a buffer wheel and Autosol metal polish.

[pete376403]

The seals are totally resposible for retracting the pistons. They are square in cross section, and when the piston moves out, initially the seal twists. Untwisting is what pulls the piston back again. The seal has only a limited amount of 'twistability", if the piston has to move further (ie to compensate for worn pads), once the seal has reached its twist limit the piston will then slide through. This makes the brakes self adjusting.

[Motu]

The pistons don't get sucked back in any way,it's just the action of the retangular seal - it distorts when pressure is applied then resumes it's shape when released,just that tiny fraction is enough to clear the disc.Seal failure on calipers is not really that common,but don't count it out and replace if in doubt - tight sliders is more common,then gunged up seals,then master cyl,finaly the wierd stuff like restricted hoses.Just work your way through,a bleeding pain eh?

[vifferman]

The pistons don't get sucked back in any way,it's just the action of the retangular seal - it distorts when pressure is applied then resumes it's shape when released,just that tiny fraction is enough to clear the disc.

Oh - OK. I'd heard that was what it was, but I thought the fluid pressure dropping would help pull em back in a bit too.
Thanx for the info, Motu.

[svs]

Plan for tonight when I get home from work least effort stuff first:

1) Swap disks with race bike - Checking to see if disks are straight.
2) Check master cylinder again. Esp. the compensating port - I don't remember any significant fluid flow back into the reservoir when releasing the brakes yesterday.
3) Take everything apart and clean it again. Will also swap lines at this point as I've got some that are a couple of years newer than the original.
4) Kick bike if it still doesn't work.

Any other ideas welcome. Thanks for everything so far. I'm going to run out of brake fluid if I keep taking everything apart like this.

(Fortunately I've got 2 SV's to swap bits round on)