odakyu Posted December 14, 2008 Report Share Posted December 14, 2008 I have a pair of Hope mono trials and i can't seems to centralise the caliper pistons. I have tried re-positioning the caliper with the shim washers and also prised the the pistons back. But the brake pads are still brushing the rotors.Can someone please help or advise? Quote Link to comment Share on other sites More sharing options...
Sidehop Stuart Posted December 14, 2008 Report Share Posted December 14, 2008 I'm not too sure but if the brake pads are brand new they may need time to wear in.Just a guess. Quote Link to comment Share on other sites More sharing options...
Ben John-Hynes Posted December 14, 2008 Report Share Posted December 14, 2008 Loosen the bolts that hold the caliper to the adapter, pull the brake on and tighten the bolts while still holding the lever. Quote Link to comment Share on other sites More sharing options...
Muel Posted December 14, 2008 Report Share Posted December 14, 2008 Loosen the bolts that hold the caliper to the adapter, pull the brake on and tighten the bolts while still holding the lever.Mono Trial brakes don't have post mount, they're IS.Push the pistons back into the caliper with a screwdriver. Also check you havn't got a dry seal, which would cause the piston to stick.If you've got a dry seal, I.E. one of the pads doesn't move when you pull the lever, hold the piston that does move into the caliper with some pliers and squeeze the lever to force the sticking pistonout, then spray it with some WD40, wipe the caliper out really thoroughly and push if back in with a screwdriver, it should then be sorted. Quote Link to comment Share on other sites More sharing options...
sstein Posted December 14, 2008 Report Share Posted December 14, 2008 Slight bend in the rotor? Quote Link to comment Share on other sites More sharing options...
odakyu Posted December 15, 2008 Author Report Share Posted December 15, 2008 Both pistons are moving at the same time but one is touching the rotor earlier than the other.Is there any method to centralise the pistons?Mono Trial brakes don't have post mount, they're IS.Push the pistons back into the caliper with a screwdriver. Also check you havn't got a dry seal, which would cause the piston to stick.If you've got a dry seal, I.E. one of the pads doesn't move when you pull the lever, hold the piston that does move into the caliper with some pliers and squeeze the lever to force the sticking pistonout, then spray it with some WD40, wipe the caliper out really thoroughly and push if back in with a screwdriver, it should then be sorted. Quote Link to comment Share on other sites More sharing options...
odakyu Posted December 15, 2008 Author Report Share Posted December 15, 2008 How do i check if there is a bent? Is there a way to flatten it back?Slight bend in the rotor? Quote Link to comment Share on other sites More sharing options...
Muel Posted December 15, 2008 Report Share Posted December 15, 2008 Both pistons are moving at the same time but one is touching the rotor earlier than the other.Is there any method to centralise the pistons?Not that I know of, I suppose you could pull one piston in with a pair of pliers then squeeze the lever to push the other one out, I've never done it though.Spin the wheel round, you'll be able to see the rotor waving about in the caliper. If it is doing then it's bent, and you can easily straighten it with an adjustable spanner. If you're careful enough you can get it perfectly true. Quote Link to comment Share on other sites More sharing options...
odakyu Posted December 15, 2008 Author Report Share Posted December 15, 2008 i think the rotor is very slightly bent as the brake pad rubs the rotor only at certain point. However, i can't find where is the bent...it bent is definitely not obviousNot that I know of, I suppose you could pull one piston in with a pair of pliers then squeeze the lever to push the other one out, I've never done it though.Spin the wheel round, you'll be able to see the rotor waving about in the caliper. If it is doing then it's bent, and you can easily straighten it with an adjustable spanner. If you're careful enough you can get it perfectly true. Quote Link to comment Share on other sites More sharing options...
Dan6061 Posted December 15, 2008 Report Share Posted December 15, 2008 If you're going to be poking it with screwdrivers and spanners, make sure all the tools are CLEAN, as you don't want to contaminate the pads/rotor with dirty, greasy tools.I thought Muel would mention that, being a disc bummer! Quote Link to comment Share on other sites More sharing options...
odakyu Posted December 15, 2008 Author Report Share Posted December 15, 2008 i am thinking if the wheel is misaligned or the rotor is bent...but i can't seems to find where the problem is....the brake pads are still rubbing the rotordoes this happened to anyone before? Quote Link to comment Share on other sites More sharing options...
Elliot Posted December 15, 2008 Report Share Posted December 15, 2008 i am thinking if the wheel is misaligned or the rotor is bent...but i can't seems to find where the problem is....the brake pads are still rubbing the rotordoes this happened to anyone before?To me it sounds like you just havnt aligned the caliper quite right. I would suggest you space the caliper out in the direction of the piston that is touching the disc firstIf you also have a bent rotor (which you would be able to tell if you spin the wheel and it moves more/less freely in one place) you can straighten out the bend by using an adjustable spanner and gently bending the rotor until you take out the bend. Best to bend slowly/gently and keep checking rather than bending it hard (phnar phnar) and screwing up the rotor more. But try and get the caliper aligned right first, because if its only a slight bend thats just touching the rotor and doesnt affect performance too much its porbably not worth screwing with. It may also be that you have one piston that moves more slowly than the other, as muel said it would be worth cleaning it off (I would also use a cotton bud to put some dot fluid around the piston before you push it back in just to moisten the seal a bit). If this doesnt work then you may have a piston with scratch/gouges on it, which would rub against the seal as you press the lever, stopping the piston moving over the seal easily. This takes a fair bit more buggering about to sort, but its only likely to be the problem if someone has been really f**king around in the caliper with the piston extended and scratched it up. Bear in mind though, the pads often rub against the disc a bit, and according to the manual, this is normal, providing it doesnt slow the wheel down much when it spins. Quote Link to comment Share on other sites More sharing options...
Muel Posted December 15, 2008 Report Share Posted December 15, 2008 (edited) If you're going to be poking it with screwdrivers and spanners, make sure all the tools are CLEAN, as you don't want to contaminate the pads/rotor with dirty, greasy tools.I thought Muel would mention that, being a disc bummer! Well I tend to think that's just common sense, and at the moment my Hope is on the way to Hope, so I have a maggy on the rear, bitch. Edited December 15, 2008 by Muel Quote Link to comment Share on other sites More sharing options...
sstein Posted December 15, 2008 Report Share Posted December 15, 2008 You sound like you have a slight bend, but also the caliper is misaligned, if putting spacers in makes it worse you may need to reface your barke mounts, though tht should only be done be a mechanic if you are not too sure! Quote Link to comment Share on other sites More sharing options...
odakyu Posted December 15, 2008 Author Report Share Posted December 15, 2008 actually i didn't put any spacers for the caliper as the rotor is too near the frame. Instead, i put a spacer between the hub and the dropout...anyway,i placed another spacer at the other side so this is not the cause of the problem. The problem is the brake pad touches the rotor only at certain position ( i mean the wheel )If what Elliot said is correct [the pads often rub against the disc a bit, and according to the manual], then i am not so worried... Quote Link to comment Share on other sites More sharing options...
Elliot Posted December 15, 2008 Report Share Posted December 15, 2008 actually i didn't put any spacers for the caliper as the rotor is too near the frame. Instead, i put a spacer between the hub and the dropout...anyway,i placed another spacer at the other side so this is not the cause of the problem. The problem is the brake pad touches the rotor only at certain position ( i mean the wheel )If what Elliot said is correct [the pads often rub against the disc a bit, and according to the manual], then i am not so worried...If the wheel spins and is not overly slowed down by a dragging pad, and the brake works, then I wouldn't worry about it.How thick are the spacers you are using though? You should be looking to make fine adjustments with .25mm shims Quote Link to comment Share on other sites More sharing options...
odakyu Posted December 16, 2008 Author Report Share Posted December 16, 2008 yeah, the brake pads are brushing the rotors only at certain pointI couldn't put any shims for the calipers, the spacers were for the hub axle so that the rotor is further away from the frame Quote Link to comment Share on other sites More sharing options...
odakyu Posted December 20, 2008 Author Report Share Posted December 20, 2008 now i can see that the rotor is bent but i can't find the correct spot to bend it back. The bent is not sharp enough for me to bent it back with a spanner. Any ideas? Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.