Giant MPH3 Adjuster - Which bits should move?

S_J_P

My front MPH3 brake adjuster won't adjust. I've removed the adjuster assembly from the reservoir, and the adjuster knob just keeps turning but the piston isn't actually moving in or out.

Can anyone tell me whether the piston itself should remain stationary, with the adjuster-wheel rotating the threaded stub (see picture) into/out-of the piston, or whether the threaded-stub and piston are one-piece?

I can see a hex-nut between the piston and the anodised threaded plug, which rotates with the adjuster wheel, and I wonder whether this has broken away from the plug.

If it is broken then I have the choice of a £9.99 adjuster assembly (Ash Cycles), or £40 for a Juicy Five (Merlin, so it's unlikely to be current-spec), using my existing rotor.

S_J_P

I've sussed it myself!

For info, there are two small depressions in the anodised plug at approximately 12 o'clock and 6 o'clock positions behind the chrome adjuster wheel. If you align the holes in the adjuster wheel with these, you can use the ends of needle-nose pliers to unscrew the adjuster assembly from the cylinder housing. Make sure the bike is on it's side, with the adjuster wheel uppermost, otherwise you'll loose (corrosive) fluid.

With the mechanism removed, remove the sealing ring (to prevent damage) by pinching to form a bulge, and then hook out of the depression. Clamp the piston in the jaws of Mole Grips or similar (protecting the piston with a cloth). Use the needle nose pliers again to rotate the adjuster (it's a left-hand thread!) until free.

Remove the piston completely from the threaded stub, clean it, and put a liberal coating of copperslip anti-seize on the thread before reassembly.

Refit the piston sealing ring, and wind the adjuster wheel so that the piston is fully retracted (remember left-hand thread again), then press the mechanism back into the cylinder carefully checking alignment before starting to carefully screw the mechanism in.

Once the adjuster has been turned into the cylinder a turn, rotate the bike upright so that the filling-nipple is uppermost, and slacken the nipple off a little to release the pressure which builds up as the mechanism screws back into the cylinder (use a cloth over the nipple so that you don't loose any fluid onto paintwork).

With the bike in an upright position, the air trapped in the cylinder will exit first, hopefully leaving a system which won't need further bleeding.

Screw the adjuster mechanism all the way back into the cylinder housing, and then retighten the nipple. Screw the adjuster in until the desired braking is achieved. The brakes should now work properly again

Anonymous

what does that adjuster do?

nicklouse

sheepsteeth
sets the pad position.

Mmm copper slip. i would have used brake grease.

S_J_P

sheepsteeth
what does that adjuster do?

The Giant MPH3 brakes are closed, which means that as the temperature changes or the pads wear you have to change the system volume by using this adjuster. By judicious use of the lever-reach screw and the adjuster wheel, pad contact point can be fine tuned over a range of conditions.

nicklouse
Mmm copper slip. i would have used brake grease.

What's brake-grease? I've always used copperslip on the backs of (car) brake pads to prevent them squealing, and it's a great anti-seize compound with a high melting point.[/quote]

Bmjboy

SJP Do you have the stock Giant rotors on your bike?

We have the same brakes, and was wondering if a rotor upgrade to something a bit lighter or bigger would help braking, is that something you've considered?

S_J_P

The MPH3 are Hope C2 clones, and the rotor face is wider than on most other makes of rotor. This means that should you replace the rotor, you may end up with some pad-overlap.

This isn't really too much of a problem, and I have an EBC 203mm front rotor upgrade kit on my bike (see My Album below) which has significantly improved braking efficiency and control, but is way OTT for XC riding and in hindsight I should have gone for the 185mm disc option.

Ash Cycles do sell 180mm Giant rotors for £24.99, which solves the face-width issue. You'll also need a +20mm IS adapter from someone like A2Z too.

Whatever you decide, you'll need to ensure that the forks are warranted for the upgrade you elect to undertake.

It's probably not worthwhile, or possible to upgrade the rear brakes though.

nicklouse

S_J_P wrote:

sheepsteeth
what does that adjuster do?

The Giant MPH3 brakes are closed, which means that as the temperature changes or the pads wear you have to change the system volume by using this adjuster. By judicious use of the lever-reach screw and the adjuster wheel, pad contact point can be fine tuned over a range of conditions.

nicklouse
Mmm copper slip. i would have used brake grease.

What's brake-grease? I've always used copperslip on the backs of (car) brake pads to prevent them squealing, and it's a great anti-seize compound with a high melting point.

[/quote]

Brake grease is a grease that is mixable with brake fluid and should be used where there are greasing requirements that may come in contact with the fluid.

S_J_P

You live and learn!

So long as the piston-seal remains intact, there shouldn't be any fluid in the chamber between the piston and plug where I've copper-slipped the thread, so I should be ok!

Bmjboy

S_J_P wrote:

The MPH3 are Hope C2 clones, and the rotor face is wider than on most other makes of rotor. This means that should you replace the rotor, you may end up with some pad-overlap.

This isn't really too much of a problem, and I have an EBC 203mm front rotor upgrade kit on my bike (see My Album below) which has significantly improved braking efficiency and control, but is way OTT for XC riding and in hindsight I should have gone for the 185mm disc option.

Ash Cycles do sell 180mm Giant rotors for £24.99, which solves the face-width issue. You'll also need a +20mm IS adapter from someone like A2Z too.

Whatever you decide, you'll need to ensure that the forks are warranted for the upgrade you elect to undertake.

It's probably not worthwhile, or possible to upgrade the rear brakes though.

So "if" I was to upgrade, then something like THIS would be right if the rotor face was the same width as the current spec?

S_J_P

That's exactly the sort of kit which would suit you, with bigger rotor and the caliper mount adapter. You may need a few 0.25mm washers too, to align the caliper with the new rotor, but they are available for pennies from a bolt-shop/Screwfix.

Bmjboy

But I feel the need for a bot of bling 8) , is there no wavy or styled design other than a dull ol' round edge? I understand it all about the braking surface, surely there must be something with a bit of styling!!??

S_J_P

If you don't mind paying for them, there's a wealth of choice (see CRC's rotor selection

How about one of these:-


Use it with an appropriate adapter (such as this one).

Bmjboy

Now those are blingy rotors! - Maybe too much! 8)

Im quite tempted to convert front and back to 180mm as I only do XC, although I do attack the downhills and Im a big unit!

Will performance be THAT better that its worth doing?

I found this rotor yesterday:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=110275952173&ssPageName=ADME:X:RTQ:GB:1123

And am thinking of getting in 180mm format, the braking face is 18mm, so ideal for my pads which are approx that.

2 rotors and correct IS adaptors comes in at around £41, is that good?[/b]

S_J_P

You probably won't be able to fit 180mm rotors to the rear due to clearance issues, in any case the improved power won't be worthwhile.

At the front the upgrade should make quite a difference. The MPH3's aren't the best brakes in the world, and the increased effectiveness resulting from the increase to diameter will make a worthwhile difference.

If I remember correctly, standard Giant rotors are either 21mm or 25mm face width. On my non-standard EBC disc, there's approximately 2mm overlap at the pad top, and 1mm at the bottom. This isn't really too much of a problem though, but do make sure you take your time in setting the +20mm adapter up to give the maximum pad/rotor contact.

Bmjboy

Yeh, my spare pads from Superstar here are 19mm by 23mm so 1mm difference isnt going to effect anything I doubt.

I would need to buy a 160 wavey rotor for rear to match my new front, but thanks for the input, I will stick to the same size for the rear.

We're off to Wales soon, and Im a stickler for bad luck, so I dont think I will upgrade until Im back from Afan! as at the moment, it aint broke, so Im not fixing it!!

Thanks for the advice, will be going for a new 180 front and a matching style 160 rear.