EPP Posted January 4, 2009 Share Posted January 4, 2009 Hi all, After some deliberation I have decided to fix up the 1990 xj600 that was stolen and recovered at the end of last year (some of you may remember the thread I started prior to the bike being stolen). I have managed to get all the parts I need and I'm making steady progress, though it's not ready to ride just yet... My question is whether there should be any brake drag on the front wheel when the brake is not being applied? I can turn the wheel, but it's quite stiff. I have had the RH caliper off (drained the hose) to look at the pistons and they seemed okay. Cleaned up the LH caliper without removing the hose, as the pistons again seemed okay. I probably didn't need to remove the hose from the RH caliper, but that was down to inexperience. I replaced the pads using copper grease in the right places and reinstalled the calipers. I've filled and bled the system, though it might till be a bit spongy. Again, I don't have enough experience to be sure when it's done right! I've tied the lever back and will leave it for 24 hours to see if any more air escapes from the system. It might also just be that the pads need to be bedded in a bit after being removed (both the pads and discs will need to be replaced before long, but that's another story). When the calipers were removed, I tried pulling the brake lever a bit: the pistons moved out freely, and returned a small amount, which I think is what they should do. However, I needed to use a G clamp to push the pistons back enough to get the pads over the discs when reinstalling (it says in the workshop manual this might be required). Am I right in thinking that because the pads are not attached to the pistons, they are not actively pulled back off the disc? If so, is the idea with a disk brake that the pad will back off a fraction just through riding? Obviously there is no return spring, and the anti-rattle spring that sits over the pads seems to actually prevent them from moving freely away from the disc! How much drag is normal after applying the brake to a stationary bike and then trying to spin the wheel by hand? Cheers everyone! Ewan Link to comment Share on other sites More sharing options...
Ttaskmaster Posted January 5, 2009 Share Posted January 5, 2009 I'd suggest first checking your dust seals on the pistons. The caliper (usually) works by squeezing it's two halves together. The pads are affixed to each half and so back off when pressure is released. The pistons just exist to compress them. Things may vary somewhat with differing technology, but that's the layman's explanation. Have you had the bike checked out following the recovery? The caliper itself may be out of alignment, or the discs, or even the forks. Depends what the thieves did to it. If it's only slight dragging, then just make sure you've retracted the pistons completely, bled the system entirely and then give the pads some time to bed in. Link to comment Share on other sites More sharing options...
EPP Posted January 6, 2009 Author Share Posted January 6, 2009 I'd suggest first checking your dust seals on the pistons. The caliper (usually) works by squeezing it's two halves together. The pads are affixed to each half and so back off when pressure is released. The pistons just exist to compress them. Things may vary somewhat with differing technology, but that's the layman's explanation. Have you had the bike checked out following the recovery? The caliper itself may be out of alignment, or the discs, or even the forks. Depends what the thieves did to it. If it's only slight dragging, then just make sure you've retracted the pistons completely, bled the system entirely and then give the pads some time to bed in. I haven't been able to have the bike checked professionally as it is still laid up in the cellar. My plan was to get it running and gingerly take it round to the nearest motorcycle specialist (who are not far away). Nothing looks to be out of alignment, but I know these things can be hard to spot. I've managed to find a bit of info on this question and the consensus seems to be that there will always be a small amount of drag, perhaps enough to limit the wheel to around 1 full turn when you spin by hand. You say the pads are affixed to each half, but this is not the case in my system - the pads are held into the caliper by the retaining pins, but not attached to the pistons. I think this is the typical set up from what I've read. My wheel does not continue spinning at all, but as the discs and pads need to be replaced I'm going to do that first and see how things are once everything is bedded in. Cheers! Ewan Link to comment Share on other sites More sharing options...
Ttaskmaster Posted January 6, 2009 Share Posted January 6, 2009 You say the pads are affixed to each half, but this is not the case in my system - the pads are held into the caliper by the retaining pins, but not attached to the pistons. I think this is the typical set up from what I've read. That is what I'm saying. The caliper has two halves to it. The pistons move the halves together. The pads are attached to the halves. There is no direct relation to the pistons and the pads themselves.... Having said that, the three are all linked in my caliper. My pistons apply pressure to the pads when closing, but it's the fit against the caliper housing that pulls them apart once the pressure is released. Either way, it's not massive drag, so bed 'em in and see how it goes. Do get it checked over asap, though. Link to comment Share on other sites More sharing options...
EPP Posted January 6, 2009 Author Share Posted January 6, 2009 That is what I'm saying. The caliper has two halves to it. The pistons move the halves together. The pads are attached to the halves. There is no direct relation to the pistons and the pads themselves.... Having said that, the three are all linked in my caliper. My pistons apply pressure to the pads when closing, but it's the fit against the caliper housing that pulls them apart once the pressure is released. Either way, it's not massive drag, so bed 'em in and see how it goes. Do get it checked over asap, though. My calipers are fixed rather than sliding/floating, with a piston either side of the disc. The pads sit in front of the pistons and are compressed onto the discs. Sorry if I'm stating the obvious, but it sounds like you might be talking about sliding calipers. There does not appear to be a mechanism to pull the pads apart on mine, just an anti-rattle spring that holds them down against the pins, rather than pushing against the pistons (which would be required to pull them apart). This actually reduces the free movement of the pads! I don't think I can assess anything properly until the discs and pads are replaced, so I'll post back then if there's still an issue. Thoughts from anyone are appreciated in the meantime though! Ewan Link to comment Share on other sites More sharing options...
Moderator drewpy Posted January 6, 2009 Moderator Share Posted January 6, 2009 what normally returns the pads back is the "rolling" action of the piston seal as it returns to normal state after compression. problems can arise with rust in the brake cylinder affecting this and also the "slurge" hole in the master cylinder blocks up, preventing a return of a small amount of brake fluid from the initial compression of the brakes. Link to comment Share on other sites More sharing options...
Ttaskmaster Posted January 6, 2009 Share Posted January 6, 2009 My calipers are fixed rather than sliding/floating, with a piston either side of the disc. The pads sit in front of the pistons and are compressed onto the discs. Eeeeeeeeeeeeeeeeeeenteresting..... Have you a screenCap from the PDF manual or anything? Link to comment Share on other sites More sharing options...
EPP Posted January 6, 2009 Author Share Posted January 6, 2009 Here's the exploded view from the manual. I'm going to check out the slurge hole too - sounds like a good suggestion as the cylinders don't seem to be seized. I guess the seals could be old and have lost their elasticity. I'd hate to have to take everything apart again to replace those though! Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 6, 2009 Moderator Share Posted January 6, 2009 There should be no drag with your brake, check that the pads are free to move inside the caliper and that the anti rattle spring is fitted correctly and has not become trapped anywhere between the pads and the caliper.. Try using a wood chisel to scrape any rust and old brake dust out of where the pads sit and check for rust build on the edges of the pads Link to comment Share on other sites More sharing options...
EPP Posted January 19, 2009 Author Share Posted January 19, 2009 Just an update to this thread. I replaced the pads and discs (discs were used, but not very worn at all) ensuring the calipers were nice and clean and the pistons retracted slightly after a gentle squeeze of the lever. Used copper grease in all the appropriate places and, once everything was installed, there was certainly less drag than before. I get about half a turn of the wheel with a good shove. I can't bed everything in yet as I still have to fix the ignition and the exhaust, but I'm hoping the drag will reduce and the lever will firm up after a few miles. I'll post an update. Thanks to everyone for their advice - always helpful! Ewan Link to comment Share on other sites More sharing options...
JUST ME! Posted January 20, 2009 Share Posted January 20, 2009 Just an update to this thread. I replaced the pads and discs (discs were used, but not very worn at all) ensuring the calipers were nice and clean and the pistons retracted slightly after a gentle squeeze of the lever. Used copper grease in all the appropriate places and, once everything was installed, there was certainly less drag than before. I get about half a turn of the wheel with a good shove. I can't bed everything in yet as I still have to fix the ignition and the exhaust, but I'm hoping the drag will reduce and the lever will firm up after a few miles. I'll post an update. Thanks to everyone for their advice - always helpful! Ewan Geday mate! Pull all of the pistons out of the calipers and you will be surprised by the amount of crap that is mixed in with the old brake fluid. Clean all the pistons with brake cleaner and scotch brite and reassemble with new seals and dust boots, applying rubber grease to the seals. Short of there being a problem with your master cylinder, it should be as good as new. Just did a friends 600 Kawasaki and it had 6 pistons in each caliper.The pads also get pushed back by whats called-KNOCK OFF- just due to the normal flexing of components and bearing end float. I once had an 1100 Suzuki that used to head shake that badly that you had to pump the pistons back out to where they lived to ensure the brakes were ready for action! HAVE A BLAST! Paul. Link to comment Share on other sites More sharing options...
steve m Posted January 20, 2009 Share Posted January 20, 2009 As Paul Above.......... Also while you have the pistons out of the calipers, make sure you clean out the groves where the seals fit, this is a bit of a faff, but you can get quite a build up of crap in the grooves, this then stops the seals seating properly which in turn makes it harder for the pistons to slid in and out ........ Link to comment Share on other sites More sharing options...
Moderator drewpy Posted January 20, 2009 Moderator Share Posted January 20, 2009 As Paul Above.......... Also while you have the pistons out of the calipers, make sure you clean out the groves where the seals fit, this is a bit of a faff, but you can get quite a build up of crap in the groves, this then stops the seals seating properly which in turn makes it harder for the pistons to slid in and out ........ these groves are they like olive groves? Link to comment Share on other sites More sharing options...
steve m Posted January 21, 2009 Share Posted January 21, 2009 Nopeeeee Orange groves,,,,,,,,,,,,,,,,,lot nicer Link to comment Share on other sites More sharing options...
Moderator drewpy Posted January 21, 2009 Moderator Share Posted January 21, 2009 Nopeeeee Orange groves,,,,,,,,,,,,,,,,,lot nicer you missed a grove in your edit Link to comment Share on other sites More sharing options...
blackhat250 Posted January 21, 2009 Share Posted January 21, 2009 My question is whether there should be any brake drag[ quote] ------------------------------------------------------------------- While on the subject , The RD400 in my shed " when I ran down the drive On it . The rear brake progessivly got tighter +tighter , untill locked solid ?? To me was like the master cylnder not returning fluid. Is it a replacment job ?or is there a kit [seals etc] . coz them cylnders hard to soarce ??? Link to comment Share on other sites More sharing options...
Moderator drewpy Posted January 21, 2009 Moderator Share Posted January 21, 2009 My question is whether there should be any brake drag[ quote] ------------------------------------------------------------------- While on the subject , The RD400 in my shed " when I ran down the drive On it . The rear brake progessivly got tighter +tighter , untill locked solid ?? To me was like the master cylnder not returning fluid. Is it a replacment job ?or is there a kit [seals etc] . coz them cylnders hard to soarce ??? check the splurge hole, its a tiny hole at the bottom of the resevoir and is so that the fluid can return Link to comment Share on other sites More sharing options...
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