Can't spin wheel after bleeding brakes

[mrmacmusic]

My rear brake was bled on Saturday (by the LBS, not me) and new pads fitted. Rode the bike home afterwards and it was fine. Went for a short 5 mile ride with the kids yesterday, and by the time I got back home, the rear brakes were binding – if I try and spin the wheel, it won't even do one revolution!

Now I watched the chap fit the pads and do the bleed, and he clearly wasn't 100% happy with the brake operation at first – I saw him take a small amount of fluid out a couple of times. Once done, I asked him if he was happy with it now as he clearly hadn't been at first, and he said it "suddenly just felt better, with proper modulation" and that he hadn't felt that at first after the bleed....

I'm wondering if there is still too much fluid in the system, and whether I should attempt to remove a little myself? Perhaps I should just go back to the LBS next weekend?

The brakes are Hayes Stroker Ryde – I had contacted Hayes directly a few weeks back asking about play in the levers, and they kindly sent new pins and master cylinder kits in case they were needed. The LBS fitted the pins which helped alleviate some play, but weren't keen to strip and rebuild the levers with the new pistons... is this a job I could (and perhaps should) do myself?

 

[Linford]

A hydraulic brake system is a failry simple setup. I can tell you what is most likely wrong with it as I have done loads of them on motorcycles over the years, but you won't like what I've got to say - substantially easier on a cycle than a m/cycle though.

 

[mrmacmusic]

A hydraulic brake system is a failry simple setup. I can tell you what is most likely wrong with it as I have done loads of them on motorcycles over the years, but you won't like what I've got to say - substantially easier on a cycle than a m/cycle though.

Hit me with it Linford...

 

[Linford]

The brake system is basically a piston in a bore pushed on by a lever at the bar end (master cylinder), and sealed with a one way O-ring type seal which allows fluid to be drawn in from the reservoir and then squeezed down the lines to the slave cylinder on the wheel end which then pushes a piston in the bore and that squeezes the pads against the disk. The slave cylinder usually uses a dust seal O-type ring (square edged though) and a similar but thicker fluid seal, and both sit in series in turned grooves in the slave cylinder bore. The pistons don't actually touch the bores on either end of the system, but float on these rubber seals.

What happens to cause disk brake binding is that road salt - or salts from mud, get splashed onto the seals in the slave cylinder with use, and this solution ingresses into the seal groove, gets behind the seal, and when it dries (with heat cycles of brake use), starts to grow salt crystals which interfere with the tolerancing and pinch the seal hard against the piston as they get bigger and bigger over time.

The only way of curing this is to pump the piston out of the slave, remove the rubber seals, scrape out the salt crystals from the seal grooves with a jewellers screwdriver or similar, and then reinstall them using a bit of red rubber hydraulic grease (never an oil based grease) before re filling and re bleeding the system with Dot 4 brake fluid.

A single piston caliper sytem on a cycle is straightforward, but my old m/bike had twin 6 piston calipers linked together off a single master cylinder, and it was a bit of a challenge to get all the pistons out of the calipers in one hit before you could start, and when seized in were a real pig to sort.

 

[Crackle]

It's quite new isn't it, in which case I'm not sure Linford's advice applies here?

 

[GilesM]

Quick question, are both pads binding on the disk, or just one side?

 

[mrmacmusic]

Thanks for that explanation Linford

Is it possible that there's just too much fluid in the system? The mechanic appeared to struggle to get the wheel back on after fitting the pads, and looked like he had a couple of goes at pushing the pistons back in... Clearly he wasn't happy with something, and took fluid out more than once after bleeding the system.

The brakes weren't binding before they were bled, there was just no braking power and the lever seemed a bit spongy - now the lever is brick hard!

 

[mrmacmusic]

It's quite new isn't it, in which case I'm not sure Linford's advice applies here?

Well, it's a few years old... whilst Cubist maintained it, I think Larry (theLoafer) won't have done any brake maintenance in the year/200 miles he owned it. Wouldn't have thought it would need a major rebuild.

 

[mrmacmusic]

Quick question, are both pads binding on the disk, or just one side?

I'm at work just now GilesM, so I'll need to check later... why do you ask, and what significance is there if it is just one pad or both pads that are binding? Are you thinking if it's just one that I need to reset the caliber, and if it's both, then it is indeed a 'pressure' problem (too much fluid)..?

 

[Linford]

Run a m/cycle through a winter with salted roads, and this happens. I've no doubt it can happen to a cycle If they can't get the pistons to retract under thumb pressure, then they are seized. The system is an open one when the lever isn't pressed so any fluid would run back into the reservoir when the pads are pushed in.

Cars get around this by having an extra exterior rubber gaiter which stops any water/mud getting to the piston seals.

 

[Moodyman]

Sounds like the pistons (that push the pads) are too far in.

Over time as pads wear out, the piston which pushes the pads onto the rotor, moves inwards. This way you alway get strong braking.

But when you change the pads, you should use a screwdriver or similar to prod the pistons back out. Your new pads will be a lot thicker than the ones you repalced so the pistons needs pushing back to avoid the rub.

 

[Linford]

I'm at work just now GilesM, so I'll need to check later... why do you ask, and what significance is there if it is just one pad or both pads that are binding? Are you thinking if it's just one that I need to reset the caliber, and if it's both, then it is indeed a 'pressure' problem (too much fluid)..?

Single piston calipers float on a slider pin which equalises the pressure on both pads as they squeeze the disk. The calipers are ally, the slider pins are steel, you get an electrolytic reaction if not greased well, and they seize/fur up. This is not the same as a piston sticking in the cliper though, but can exagerate the need to sort the problem out if this is the case. If they can't retract the piston easily, then it needs stripping.

 

[Linford]

Sounds like the pistons (that push the pads) are too far in.

Over time as pads wear out, the piston which pushes the pads onto the rotor, moves inwards. This way you alway get strong braking.

But when you change the pads, you should use a screwdriver or similar to prod the pistons back out. Your new pads will be a lot thicker than the ones you repalced so the pistons needs pushing back to avoid the rub.

Runout in the disk faces knock the pads back out a fraction when you release the brakes when the pistons aren't sticking. this stops them rubbing al the time. It is miniscule and can be caused by slight warpage, play in the wheel bearings etc. It is all normal. If they are knocked too far back, you end up with excessive lever travel at the bar.

 

[GilesM]

I'm at work just now GilesM, so I'll need to check later... why do you ask, and what significance is there if it is just one pad or both pads that are binding? Are you thinking if it's just one that I need to reset the caliber, and if it's both, then it is indeed a 'pressure' problem (too much fluid)..?

If only one pad was binding, it would be that the brake caliper was not central to the dissk, however as you have written that the lever is rock hard (I am assuming this means virtually no play), centreing is unlikely to be the problem, it does sound like the pistons just need moving away from the disk, see if you can do this, it could be there is too much fluid, but I would be surprised.

 

[mrmacmusic]

So... assuming I don't need to rebuild, and the pistons aren't seized but just weren't pushed back enough before bleeding and there is now too simply too much pressure in the system, would I be best rectifying this by opening up the bleed nipple and then pushing the pistons right back in?