Shimanxo SLX m7120 brakes not working on new bike.. advice please

[matt43]

Bought a new shuttle am with SLX 7120 4-piston brakes and they are horrible. My other bike is a specialized turbo levo with sram RS brakes. The RSs are true 1-finger power.. I can do endos with 1-finger all day long. The SLX brakes require an incredible amount of force to lock the front wheel (at least 2-fingers). Also, my SLX brakes have pad slop. Stand next to the bike and rock it back and forth with brake locked and the pads clunk as you rock it. These things feel like junk.. I thought Shimano brakes are superior to sram? I bought new pads, roughed the rotors and cleaned with brake cleaner. .. better but same problems. Only thing I love about shimano is they are quiet.. my srams moan.

Full disclosure.. my RSC's have 220mm rotor on front vs SLX with 200mm rotor.

 

[timo2824]

If you're using the metal pads it takes quite a bit of heat to seat them in. Like, find a hill and be ready to make 20 runs to get them hot. I'm running the XT's and they have that big honking heat sink on them, I was really surprised how long it took them to get hot. I've had 3 different avid brakes fail on me, one on a downhill run that resulted in a cartwheel over a berm in the Santa Monica mountains, rental bike. My wife's avids locked up, I'm assuming from seal swell. My old specialized camber pro I had them fail on me, luckily back in Kansas so the hills weren't too bad. Tektro and Shimano brakes haven't failed on me so far, so I'll take a pad that's sucks to seat.

 

[matt43]

If you're using the metal pads it takes quite a bit of heat to seat them in. Like, find a hill and be ready to make 20 runs to get them hot. I'm running the XT's and they have that big honking heat sink on them, I was really surprised how long it took them to get hot. I've had 3 different avid brakes fail on me, one on a downhill run that resulted in a cartwheel over a berm in the Santa Monica mountains, rental bike. My wife's avids locked up, I'm assuming from seal swell. My old specialized camber pro I had them fail on me, luckily back in Kansas so the hills weren't too bad. Tektro and Shimano brakes haven't failed on me so far, so I'll take a pad that's sucks to seat.

Yes i am using the metal pads. You might be right because the caliper never got really hot. No hills here in Florida but i will work on it tomorrow and report back. I do love how smooth and quiet they are. Thank you for responding.

 

[levity]

I’ve used SLX 7120 brakes on several bikes, though usually with resin pads. They provide strong stopping power - one finger nose wheelies and rear tire skids - all with good modulation. As @matt43 said you probably just need to bed them in properly with a series of controlled high speed stops. Alloy rotor surfaces help a lot.

 

[HandsomeDanNZ]

After breaking them in, my SLX with sintered pads are the best 4 piston brakes I’ve ever used. Stopping power is excellent and I’m a heavy dude on a heavy bike.

 

[irie]

Yes i am using the metal pads. You might be right because the caliper never got really hot. No hills here in Florida but i will work on it tomorrow and report back. I do love how smooth and quiet they are. Thank you for responding.

Where you are there is no reason to use metal/sintered pads. Instead use Shimano D03S resin pads which are very quiet and grip instantly. Before use clean any previous pad deposits off the rotors.

 

[matt43]

So I bedded the pads in good.. brakes were very hot and rotor looks good. Braking power is significantly improved but still not as good as my sram RS. Is that because of my larger 220mm rotors on the RS brakes? will 220 vs 200 make a big difference? When I use 1 finger braking I end up squashing my middle finger under the lever when pulling hard. The RS brakes definitely have a more on/off feel than these an much less lever movement. these are brand new brakes. i would assume a bleed isn't necessary?

 

[irie]

So I bedded the pads in good.. brakes were very hot and rotor looks good. Braking power is significantly improved but still not as good as my sram RS. Is that because of my larger 220mm rotors on the RS brakes? will 220 vs 200 make a big difference? When I use 1 finger braking I end up squashing my middle finger under the lever when pulling hard. The RS brakes definitely have a more on/off feel than these an much less lever movement. these are brand new brakes. i would assume a bleed isn't necessary?

On my 2022 alloy Trek Rail (L) front and rear I have Shimano M6100 brake levers + M6120 (4 pot) calipers + Shimano mineral brake fluid + Shimano D03S resin pads + Swissstop Catalyst Pro 6 bolt 220mm rotors. Faultless single finger braking with plenty of feel. Can lock both ends at will. Do a top bleed couple of times a year.

No idea why you have a problem tbh but does sound like there's air in them.

 

[cykelk]

these are brand new brakes. i would assume a bleed isn't necessary?

I wouldn’t make this assumption, I’ve had to bleed brakes on new bikes plenty of times. If you bought from an LBS, go discuss with them? It sounds like a setup issue to me, or you just don’t get along with Shimano lever ergonomics.

Also yes, go to 220 up front.

 

[matt43]

spend some time on it today. I trued up the rotor and re-centered the caliper and overall much better. I can see why such a divided group between Shimano/sram. Certainly a different feel between the two. thanks for all the help

 

[James_C]

check for pad contamination too

 

[Astro66]

Bought a new shuttle am with SLX 7120 4-piston brakes and they are horrible.

I had those brakes on my Merida. They were brilliant. Ran resin pads and topped the reservoir up annually, by connecting a filled top up cup to the reservoir and pumping the levers, till no air bubbles came out.

Always firm, so I could run with single finger braking.

 

[CarolinaCrawler]

When I use 1 finger braking I end up squashing my middle finger under the lever when pulling hard.

To shorten the free throw and prevent this I like to use a small, flat head screwdriver inserted between the pad and piston. I will pull the pad toward the rotor while pumping the lever to advance the pistons. This will shorten up the free throw and make the the lever movement much less.

 

[matt43]

Update... went for a ride after bedding in new pads. Disappointing power. I cannot Endo without 2 fingers and a death grip. I pulled the pads and they are disintigrating on the trailing edge. I am using 203 mm shimano rotors and they appear to have good wear. Any thoughts on why this is happening? These pads are brand new.. just bedded in. Rotor is RT66

 

[Astro66]

The calipers are not aligned correctly to the rotor. The pads are only contacting at the rear.

Loosen caliper retaining bolts slightly.
Pull the brake lever.
With the lever pulled, re-tighten the caliper retaining bolts.
This should parrallel the caliper to the rotor.

Also ensure there is nothing behind the pads, putting the pads out of alignment.

If this doesn't fix it. Take the bike to a bike mechanic. There is definitely something wrong with the caliper, rotor or pads. The pads should have even wear across them.



A Used set of pads should look like this.

 

[matt43]

Yes, did it. I also visually inspected the centering and repeated multiple times to get the best centering. I think I toasted them on bed in because I was thinking that was the only way to get these things to work. I cleaned them up and full 2-finger grab and can't get front wheel to lock no matter how hard I pull. Got on my turbo levo with sram rsc's and 1 finger pull almost sent me over the bars. I think I am going to put my rsc's on the pivot and see how that works out. The only thing I am liking about Shimano brakes is they are quiet. Something must be wrong on mine because they don't have half the power my RSC's have.

 

[Astro66]

I've sold my bike with the SLX brakes. But I could definitely one finger brake in 95% of situations. Maybe in a really sketchy section, I'd put a second finger on the lever. I come from motorbikes, so one finger braking was not my default braking technique.

 

[JP-NZ]

Update... went for a ride after bedding in new pads. Disappointing power. I cannot Endo without 2 fingers and a death grip. I pulled the pads and they are disintigrating on the trailing edge. I am using 203 mm shimano rotors and they appear to have good wear. Any thoughts on why this is happening? These pads are brand new.. just bedded in. Rotor is RT66 View attachment 154930 View attachment 154930

That picture defines your problem. No wonder they work so poorly.. Your only using about 30% of the pads and only getting 30% power.

Take them to your LBS and get them to set them up correctly, looks like you have piston issues. From someone who has ridden the SLX 7120's and Code RSC's the shimano's pee all over codes on power.

Lots of good info here

Part # 1: Shimano Brake System Service

This will be a three part technical article discussing Shimano braking system components, how to service your Shimano brakes and brake system modification on your Rise. Part # 1 will discuss basic maintenance on your Shimano brakes. Part # 2 will discuss brake modifications to your Orbea...

www.emtbforums.com

 

[matt43]

This is a brand new bike/brakes. Pads and rotors replaced. Calipers are perfectly centered and all 4 pistons extend evenly within the caliper. My experience with bike shops is they are only going to confirm what i already confirmed and charge me more than a set of RSCs. The only thing i have not done is bleed them. They are not spongy and they do not go to the handle. they are quite firm.

 

[Astro66]

Did the Shimano brakes work before making any changes ?

 

[matt43]

Did the Shimano brakes work before making any changes ?

No. New shuttle am.. thought i bedded the pads good but no power on my first ride down GA mountain trails. Got back and cleaned, adjusted, and re-bedded them assuming that was the problem but no improvement. Pads looked contaminated so i bought new rotors and pads. Did a very hard bed-in procedure and having the same result. They just don't have good power even with 2 fingers. i just don't know if it is worth bleeding them at this point.

 

[Astro66]

Is there a reason you cannot get it fixed under warranty ?

There is something wrong with the brakes. The pads shouldn't look like that.

 

[Dax]

Give them a bleed. Shimano should be a lot more on/off than sram.

That pad wear shows the breaks not working properly. Sticky pistons, badly aligned or full of air. Eitherway, take it back to the shop you bought it from and tell them to fix it. Maybe it’s different in the USA, but over here shops have to warranty bikes.

 

[irie]

Could be that the caliper mount is misaligned. If so, putting on different calipers will merely result in exactly the same problem.

 

[JP-NZ]

This is a brand new bike/brakes. Pads and rotors replaced. Calipers are perfectly centered and all 4 pistons extend evenly within the caliper. My experience with bike shops is they are only going to confirm what i already confirmed and charge me more than a set of RSCs. The only thing i have not done is bleed them. They are not spongy and they do not go to the handle. they are quite firm.

The wear on the pads you posted says completely otherwise.

 

[James_C]

Definitely bleed them I would suggest, that doesn't look right at all. Strongly suspect your pistons aren't moving correctly.

I would suggest bleed, align and if that doesnt work, claim on warranty and get at a new caliper. Is the back one working OK?

 

[irie]

Definitely bleed them I would suggest, that doesn't look right at all. Strongly suspect your pistons aren't moving correctly.

I would suggest bleed, align and if that doesnt work, claim on warranty and get at a new caliper. Is the back one working OK?

Good point ... if the front and rear calipers are the same then swap them over and try again.