Giant MPH hydrolic disc brake jammed on..

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james_h
Posts: 40
Joined: 8 Jan 2007, 11:05pm

Giant MPH hydrolic disc brake jammed on..

Postby james_h » 16 May 2008, 8:58am

Hi...

My wife's Giant MPH back brake: The pads have gradually been moving in closer to the disc (over months) initially causing mild drag, but now the wheel will hardly turn round.

(These particular brakes have a dial to adjust the pads in and out, which is currently in the most "out" position.)

Any suggestions on how to remedy this? I wondered about taking the wheel out and trying to push the pads back in with a tyre lever?

The bike is about a year and half old, and the brakes have never been bled (or had any maintainance). And the bike doesn't get much use either..

Thought I'd post on here first before I started fiddling with it..!

Cheers,
James

orangechimp

Postby orangechimp » 16 May 2008, 12:42pm

i'd try pushing them back in to start with

gilesjuk
Posts: 3270
Joined: 17 Mar 2008, 10:10pm

Postby gilesjuk » 17 May 2008, 9:57pm

I've got these brakes, the brake lever doesn't always spring back fully, you can check that first and lube the lever.

Otherwise it would sound like time for a rebuild of the caliper. New seals, check for rust and stiffness.

TBH, I'd replace them with something better. I'm going to do this asap.

james_h
Posts: 40
Joined: 8 Jan 2007, 11:05pm

Postby james_h » 19 May 2008, 2:24pm

I had a look at them this weekend, but the problem has "gone away"... The day they were jammed on was very hot, I wonder if that's got anything to do with it?

I tried pushing the pads in, but they didn't want to move. Turning the pad adjuster thing on the handlebars would move them in ok, so I guess they're not seized.. ?

gilesjuk
Posts: 3270
Joined: 17 Mar 2008, 10:10pm

Postby gilesjuk » 19 May 2008, 10:10pm

Probably the fluid. Try changing the brake fluid.

eyepic
Posts: 2
Joined: 21 May 2008, 12:59pm

Postby eyepic » 21 May 2008, 1:09pm

I have seen this problem before.

A mate of (recently single lady not very confident with anything techy), came and asked for help.
All the shops I contacted said they had never experienced the problem before.


I suspected that as the brake fluid was 3 years old that it needed replacing...so I did. problem resolved until the next hot day when it happened again. I suspect that with warm weather the hydrolic fluid was expanding and squeezeing the brakes on.
The solution was to open the top bleed screw, squeeze the brake a little, let out a little hydrolic fluid, do the screw back up whilst still keeping the lever slightly squeezed (so as to stop air getting in).

Worked all last summer no worries.... Then winter came along and I had to bleed the brakes to top them back up again. Needless to say I am expecting a call soon to let a bit out for the summer. Now that I know what I am doing it takes only 5-10 mins to bleed both brakes and this way she gets new fluid each year.

When winter came along

james_h
Posts: 40
Joined: 8 Jan 2007, 11:05pm

Postby james_h » 22 May 2008, 10:46pm

Spot on - thanks! I undid the screw on the top of the reservoir while gently putting pressure on the lever, and a bit of liquid brake fluid came out. I nipped the valve back up again, and now I actually have some travel in the lever! Horah! Thanks folks!!

:D

gilesjuk
Posts: 3270
Joined: 17 Mar 2008, 10:10pm

Postby gilesjuk » 24 May 2008, 1:53pm

Interesting. Sounds like expansion and contraction in the system? so you need to expel some fluid.

eyepic
Posts: 2
Joined: 21 May 2008, 12:59pm

Postby eyepic » 2 Jun 2008, 8:18am

My feeling is that it is a little more complicated than that.
I belive that there are some replaceable seals in the MPH brake systems(because I have some kits for replacing them ...I think). Whilst my mate's was jamming on it was also impossable to change the clearence (there is a wheel adjustment on each brake revevoir). I think that after a year or two the seals or something like that start degrading so that you can no longer adjust the brakes enought to account for the change in temperature .... then the expansion and contracton due to temteratre causes the brakes to jam on ....or in the case of winter become ineffective.

james_h
Posts: 40
Joined: 8 Jan 2007, 11:05pm

Postby james_h » 2 Jun 2008, 12:00pm

I did read elsewhere that dot brake fluid is hygroscopic meaning that it absorbs water. So could it be that the volume of fluid in the brakes has increased because of this over time?

Letting a few drops of fluid out of the reservoir seems to have corrected the problem, for now anyway!

nomad1960
Posts: 1
Joined: 18 May 2009, 9:12pm

Re: Giant MPH hydraulic disc brake jammed on..

Postby nomad1960 » 18 May 2009, 9:32pm

[color=#400040]
I bought a giant xtc carbon 18 months ago and i had the same problem start last summer,draining a small amount of fluid did resolve the problem for a short time.
I replaced the the hydraulic pipes with Goodrich braided hose, it was a bit in the expensive side to do but it worked a treat... and a piece of cake to fit.
Just a word of warning the difference in in braking performance is amazing, nearly put me over the bars 1st time out :oops:

prm
Posts: 180
Joined: 7 Apr 2009, 11:15pm

Re: Giant MPH hydrolic disc brake jammed on..

Postby prm » 23 May 2009, 2:08pm

A common problem with Giant/MPH discs locking on.

The bolt attached to adjuster knob is prone to jamming onto the L/H threads of the internal piston. Rather than increasing or decreasing the master cylinder internal volume with adjustments, the piston just rotates, and fails to move.

Slight rotational taps, in both directions on the adjuster lugs, may free the piston

To gain access to the piston. Remove the complete end cap assemble by inserting two pins (old spokes work well) into the holes on the adjuster knob, rotate, pressing pins forward, which should engage with two corresponding holes in the reservoir end cap.
Keeping pins parallel and pushed forward, using the flat jaws of an adjustable spanner, unscrew the complete assembly - normal R/H thread.

Once dismantled, hold piston between two pieces of soft wood to avoid marking piston body and rotate adjuster. L/H thread,

Apply a small amount of brake fluid to thread, piston, and end cap before reassembling.

Laying bike down with adjuster uppermost, helps to retain a large proportion of the fluid, possibly avoiding a complete system bleed.

Once refitted, unscrew adjuster fully, top-up master cylinder, and expel any air by slowly operating brake lever.

Hope this may help.

Regards

wildinga
Posts: 2
Joined: 1 Jul 2009, 11:07pm

Re: Giant MPH hydrolic disc brake jammed on..

Postby wildinga » 1 Jul 2009, 11:25pm

Thanks prn, so gald I read down the e-mail trail!

I've had the same problem, found the rear brake binding, adjustment wheel wouldn't rotate, I undid the end cap a little to release the pressure which got me home (nearly 30'C today which didn't help!) and then this evening I lay the bike on its side to remove the end cap fully without spilling too fluid.

What I found was that the adjustment wheel ad plunger rotated free in the end cap but the plunger didn't move in or out. I couldn't see what was broken or how it managed to adjust the pressure until your post!

I'll take it out again tomorrow, clamp the plunger and rotate the wheel to try and release thread, I'll confirm when it's fixed :o

Thanks again!

prm
Posts: 180
Joined: 7 Apr 2009, 11:15pm

Re: Giant MPH hydrolic disc brake jammed on..

Postby prm » 2 Jul 2009, 8:53pm

Hi Wildinga

Pleased you’ve been able to investigate the disc brakes.

One additional point that makes refitting the piston/end cap assembly slightly easier, when the calliper pads are extended/jammed. Would recommend keeping pads and rotors in place during repairs, to avoid over extending the hydraulic pistons.

If you release some way, the reservoir filler screw, or ,remove totally, this avoids over pressurising the fluid chamber and possibly rolling out the end cap O-ring seal when refitting.

Regards

wildinga
Posts: 2
Joined: 1 Jul 2009, 11:07pm

Re: Giant MPH hydrolic disc brake jammed on..

Postby wildinga » 2 Jul 2009, 11:25pm

Hi PRM, fixed it in 5 minutes this afternoon :o)

Did as you'd said and with a little twist of the plunger and wheel with the left hand thread the plunger then moved in and out lovely. I just lay the bike on the floor to take the cap off then putting it back together again i set the plunger to almost fully retracted and once the end cap was in a little was I stood the bike up so I could let any pressure out from the screw at the top.

Fantastic, I thought I was in for a new system! Thanks again :O)