Hope M4 hydraulic calipers binding

[VX Foxy]

Hello Chaps, can you give me some advice please?

The hydraulic calipers of my disc brakes are binding on the discs - some days they're worse than others but sometimes it's unrideable. I had assumed that as the bike hasn't been used much this year that this was a problem with the pistons seizing in the calipers. However the chap at the bike shop said they just need 'resetting'. What does this mean? I think he's referring to 'realigning' the caliper with the disc but I don't understand why you'd need to do that with a 4-pot caliper.

Any comments gratefully received!

PS. The bike is a 10yr old Kona Kahuna (full sus) with Mavic rims, Hope hubs, and Hope M4 brakes f+r. Is it worth anything?

[Mr Gearchange]

Wheel off. Knife or big flathead screwdriver between the pads - lever/push them back to their original position.
Don't pull the brake lever until you have the wheel back on.

[Gumstabber]

For preference I use a plastic tyre lever not something sharp and metallic so as not to scratch the pistons

[Smartboy]

Maybe aligning the caliper to the disc will help?

If they are like my Elixir's, loosen the bolts which fix the caliper to the frame / fork, give the caliper a wiggle to make sure it is free, pull the brake lever so the brakes are on, tighten the bolts while keeping brakes applied.
That should centre the caliper to the disc.

Also, check the disk is still true. Only one mm of 'out-of-true' might cause binding.

Also, do your brakes have a pad clearance adjustment? Maybe try tweaking that as well to give a bigger gap between pad and disc?

Failing all that, You-Tube or other bike-specific forums might help.

Failing that, stump up some cash and give it to your LBS to sort out... but if you are like me, you run the risk of impulse-buying more bike-bling when you are in the shop!!!

[joema]

Hope M4s usually require alignment via skinny washers as they arent post mount.

[VX Foxy]

Thanks very much for the replies chaps.

I'm surprised they can be fixed just by pushing them back in! My experience of brake calipers on cars and motorbikes is that once a caliper starts getting 'sticky' it will need new seals and possibly pistons. Also, when you have a multi-piston caliper like the M4 as opposed to a single piston caliper I would have expected it to self centre and not require shimming out to centre it.

[PGM]

I noticed mine get like this when bike left standing in direct sun for a while, the fluid must expand a little. On mine there is a knurled aluminium wheel on top of each reservoir to fine adjust clearance on the move which I undo a bit and its fine.

I expect someone will tell me I'm talking from the wrong end of my body but it works for me!

[dr_gn]

PGM said:

I noticed mine get like this when bike left standing in direct sun for a while, the fluid must expand a little. On mine there is a knurled aluminium wheel on top of each reservoir to fine adjust clearance on the move which I undo a bit and its fine.

I expect someone will tell me I'm talking from the wrong end of my body but it works for me!

You've got Hope C2's (or equivalent). "C" stands for closed which means it's a closed system - when the fluid gets hot it expands and the pads get closer to teh disc. You have to unscrew the adjusters to compensate. The M4's are an open system, so when you release the lever, the fluid can expand back into the reservoir, so they're not prone to binding due to fluid expansion.

Re. the O/P - don't just push the pistons back into the calipers. If they have a film or veneer of dirt on them you'll just make it worse by pushing the dirt into the seals. If anything, you want to remove the pads and push the pistons out a bit, give them a damn good clean with degreaser/WD40/Toothbrush and then try again.

[PGM]

dr_gn said:

PGM said:

I noticed mine get like this when bike left standing in direct sun for a while, the fluid must expand a little. On mine there is a knurled aluminium wheel on top of each reservoir to fine adjust clearance on the move which I undo a bit and its fine.

I expect someone will tell me I'm talking from the wrong end of my body but it works for me!

You've got Hope C2's (or equivalent). "C" stands for closed which means it's a closed system - when the fluid gets hot it expands and the pads get closer to teh disc. You have to unscrew the adjusters to compensate. The M4's are an open system, so when you release the lever, the fluid can expand back into the reservoir, so they're not prone to binding due to fluid expansion.

Re. the O/P - don't just push the pistons back into the calipers. If they have a film or veneer of dirt on them you'll just make it worse by pushing the dirt into the seals. If anything, you want to remove the pads and push the pistons out a bit, give them a damn good clean with degreaser/WD40/Toothbrush and then try again.

Yes they are c2, thanks for the explanation.

[dr_gn]

PGM said:

dr_gn said:

PGM said:

I noticed mine get like this when bike left standing in direct sun for a while, the fluid must expand a little. On mine there is a knurled aluminium wheel on top of each reservoir to fine adjust clearance on the move which I undo a bit and its fine.

I expect someone will tell me I'm talking from the wrong end of my body but it works for me!

You've got Hope C2's (or equivalent). "C" stands for closed which means it's a closed system - when the fluid gets hot it expands and the pads get closer to teh disc. You have to unscrew the adjusters to compensate. The M4's are an open system, so when you release the lever, the fluid can expand back into the reservoir, so they're not prone to binding due to fluid expansion.

Re. the O/P - don't just push the pistons back into the calipers. If they have a film or veneer of dirt on them you'll just make it worse by pushing the dirt into the seals. If anything, you want to remove the pads and push the pistons out a bit, give them a damn good clean with degreaser/WD40/Toothbrush and then try again.

Yes they are c2, thanks for the explanation.

I had them on my old bike - I loved their adjustability, and despite dire warnings about them locking up on long downhills I never once had the slightest issue with them.

[chrisispringles]

Have you replaced the pads recently. If so, I've found that my M4 often needs bleeding after a pad replacement to get the pistons to sit right.

If not, then push the pistons back in to the caliper with a tyre lever as suggested. Use the lever against the pad to avoid damaging the pistons. If the brake keeps binding then you need new pistons. Getting them done isn't too pricey; I can't remember exactly how much it cost too much.

[dr_gn]

Course, if the disc is out of true it'll always bind at some point. Worth checking and adjusting the caliper position to suit if it needs trueing.

[Justin S]

Had some M4's and gave me never ending grief. Resealed them, pistons were mint, pads were a bit hit and miss. In the end chopped them in and bought some Shimanos. I still run mono Hopes and other earlier Hopes without issues, but the M4's were just very fiddly and not that powerful.

[dr_gn]

Justin S said:

Had some M4's and gave me never ending grief. Resealed them, pistons were mint, pads were a bit hit and miss. In the end chopped them in and bought some Shimanos. I still run mono Hopes and other earlier Hopes without issues, but the M4's were just very fiddly and not that powerful.

I know someone who had them and IIRC there was no adjustment on the lever - they felt terrible (lever had to be virtually touching the bars before they locked) and there was nothing that could be done to adjust lever travel.

[VX Foxy]

Thanks for your help chaps. LBS sorted it of £15, inc tstraightening the rear disc apparently , brakes now feel like new but I don't know what they actually did!