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Frankenbrakes and brake improvement discussion

kidwoo

kidwoo

Artisanal Tweet Curator
Aug 25, 2003
42,149
13,358
Squirtin ketchup n' mustard on charred flesh
kidwoo said:
Just got some XT levers on some Cura calipers. Spin around the block indicates possible success.
Click to expand...
So far so good on these if anyone cares. I've been riding these pretty much every day. They've gotten firmer which I think is the unavoidable bubbles that get introduced when removing the syringe from the caliper. Pretty sure they've gotten up to the lever where they should be. With the xt levers they have morphed into the punchy shimano engagement which I was after. And no friggin brake fluid on my pads.

Not sure they're light years better than the stock cura setup but I like the tight lever throw of the shimanos better.
Dh bike is next. For 140 bucks a brake, pretty happy with the curas in general. Just a bitch to bleed cleanly.
 
HAB

HAB

Chelsea from Seattle
Apr 28, 2007
11,589
2,021
Seattle
How's piston rollback on the Curas? That's really my only complaint with the RO Racing. Lever feel is great, power is really good, and I haven't had any real issues yet, but the pad to rotor clearances are reeeealy tight. Getting them to not rub is a bitch.
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,918
1,213
@HAB That was my experience too. IMO that's part of how Formula manage to have decent power and keep the throw nice and short, by running less clearance. Definitely too much of a good thing though, be nice if they had a touch more clearance without going unnecessarily high like Shimano/Hope.

From memory I managed to get mine a bit better by lubing and cycling the pistons, the best stuff is the Finish Line PFPAE if you can get it. For $15 it's worth a shot - I'd avoid using anything else though. NB for anyone else reading, this is for DOT brakes.
 
HAB

HAB

Chelsea from Seattle
Apr 28, 2007
11,589
2,021
Seattle
It was definitely true of the older The Ones I had a while back too. It's annoying but hardly the end of the world.
 
troy

troy

Turbo Monkey
Dec 3, 2008
1,026
785
kidwoo said:
That must be a formula thing because these definitely have that issue too. I was hoping some shimano springs and levers might give some more retraction. Not so much though.

Some ancient cupped out rotors helped a little :D
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Piston seals are responsible for their retraction, not the lever.
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,918
1,213
slimshady said:
Sorry to be the noob here and ask the stupid question, but if I understand your statement correctly, the seals flex when you push fluid through the caliper and thus the pistons move forward. Am I in the right track?
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From memory I explained this a few times over the last few pages, but yes, slave piston seals set the rotor clearance and it's because the square-section seal deforms when you press the lever and then retracts the piston as it returns to its shape. By changing the cross section of the seal and the gland machining profile you can change the rollback.

Independent of that mechanism, the piston can also slide in the seal which is what happens as the pads wear (or if you have a flexy frame), but rollback and thus throw should stay the same over the wear life of the pad (extra fluid is compensated by the lever reservoir). Not always the case sadly.
 
Jm_

Jm_

sled dog's bollocks
Jan 14, 2002
20,067
10,632
AK
Dude, you can just buy new calipers AND brake pads for the same price as brake pads, throw them away after a year. For sure the SLX calipers and finned pads are cheaper than the finned pads at the local bike shop. Freaking ridiculous (yeah, I just ordered a couple because using the cotter pin over time has screwed up my 785 caliper, it works fine, but makes a loud "clank" when I use the brakes as the pad slams into the caliper in the direction of rotation)

Am I missing something here? This price seems totally stupid.
 
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toodles

toodles

ridiculously corgi proportioned
Aug 24, 2004
5,824
5,201
Australia
Udi said:
From memory I explained this a few times over the last few pages, but yes, slave piston seals set the rotor clearance and it's because the square-section seal deforms when you press the lever and then retracts the piston as it returns to its shape. By changing the cross section of the seal and the gland machining profile you can change the rollback.
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Whats the pad spring for then? Serious question.

(bear in mind its Monday morning and my coffee hasn't kicked in).
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,918
1,213
toodles said:
Whats the pad spring for then? Serious question.

(bear in mind its Monday morning and my coffee hasn't kicked in).
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Just stops the pads flopping around, without the spring they'd still drag a bit because they'd be free to float around within that clearance gap. The spring keeps em hard against the piston instead of the rotor.
 
StiHacka

StiHacka

Compensating for something
Jan 4, 2013
21,560
12,508
In hell. Welcome!
Jm_ said:
Dude, you can just buy new calipers AND brake pads for the same price as brake pads, throw them away after a year. For sure the SLX calipers and finned pads are cheaper than the finned pads at the local bike shop. Freaking ridiculous (yeah, I just ordered a couple because using the cotter pin over time has screwed up my 785 caliper, it works fine, but makes a loud "clank" when I use the brakes as the pad slams into the caliper in the direction of rotation)

Am I missing something here? This price seems totally stupid.
Click to expand...
Yes, they suck, like all newish Shimano calipers.
 
Jm_

Jm_

sled dog's bollocks
Jan 14, 2002
20,067
10,632
AK
StiHacka said:
Yes, they suck, like all newish Shimano calipers.
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But this time, I'll go after the 2yr warranty (had expired with my XT calipers). If they change them out like they did with my M9000s, I'll be happy, like when you break a crank brother's pedal and they happily give you new ones. The plan is that eventually they'll come out with decent ones, or I'll just swap calipers every time I need a new set of pads.
 
troy

troy

Turbo Monkey
Dec 3, 2008
1,026
785
toodles said:
When you squeeze the lever the magnets flip, repelling the pads into the rotor to creating braking force. Duh.
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Unless You are riding Your new 29" dh e-bike. They use electromagnets. That's all I can say for now.
 
profro

profro

Turbo Monkey
Feb 25, 2002
5,617
314
Walden Ridge
So, I had a XT level crap out yesterday while on my vehicle in the sun. Level pulled in and would not return. Brought inside and eventually it freed up and worked again. Crapped out again on the way to trail. After a couple minutes on the trail it started working again. Then the lever pulled to the bar and and stayed that way fpr a couple miles eventually to pop back out and start working again. Ugh.

I miss my old The Ones I ran on my DH bike. They were finicky to properly bleed but they were powerful and repeatable.

I guess my option is to get a new XT brake at $89?
 
Nick

Nick

My name is Nick
Sep 21, 2001
24,865
16,405
where the trails are
profro said:
So, I had a XT level crap out yesterday while on my vehicle in the sun. Level pulled in and would not return. Brought inside and eventually it freed up and worked again. Crapped out again on the way to trail. After a couple minutes on the trail it started working again. Then the lever pulled to the bar and and stayed that way fpr a couple miles eventually to pop back out and start working again. Ugh.

I miss my old The Ones I ran on my DH bike. They were finicky to properly bleed but they were powerful and repeatable.

I guess my option is to get a new XT brake at $89?
Click to expand...
Shimano warranty. Boom. New brake.
 
Olly

Olly

Monkey
Oct 1, 2015
157
76
profro said:
Even if they are the older M-785s? I would think they are well out of warranty?
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It's probably worth a try anyway, they seem to be pretty good about it. Otherwise it's new lever time. Someone posted super-cheap levers the other day - bolt them on, flush the system through with fresh fluid and you're golden.

Mine did exactly the same thing last summer, and the summer before, so it's probably due to happen again soon. Yay.
 
jonKranked

jonKranked

Detective Dookie
Nov 10, 2005
88,673
26,912
media blackout
profro said:
So, I had a XT level crap out yesterday while on my vehicle in the sun. Level pulled in and would not return. Brought inside and eventually it freed up and worked again. Crapped out again on the way to trail. After a couple minutes on the trail it started working again. Then the lever pulled to the bar and and stayed that way fpr a couple miles eventually to pop back out and start working again. Ugh.

I miss my old The Ones I ran on my DH bike. They were finicky to properly bleed but they were powerful and repeatable.

I guess my option is to get a new XT brake at $89?
Click to expand...
Nick said:
Shimano warranty. Boom. New brake.
Click to expand...
what level xt?
 
Olly

Olly

Monkey
Oct 1, 2015
157
76
profro said:
I'm confused... Is the problem in the lever or caliper? I've heard both.
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If only it were that simple ;-) Some have issues with leaky calipers, but you and I have been struck down by lever death syndrome. Yay!
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,918
1,213
profro said:
I'm confused... Is the problem in the lever or caliper? I've heard both.
Click to expand...
If you can't get warranty, there's the deals people posted recently:
http://www.jensonusa.com/Mountain-Brake-Levers/Shimano-M640-Zee-Hydraulic-Brake-Lever?cs=Black
http://www.jensonusa.com/Mountain-Brake-Calipers/Shimano-SLX-BR-M7000-Disc-Brake-Caliper?cs=Black

Whole brake working for $45 with new pads, just swap the hose n bleed.
Shimano is definitely disposable these days, but for these prices, why not I guess.
 
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