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.