I ride an Enve Fray with a SRAM Red E1 groupset. I performed all steps of bedding in the brakes according to guide from escape collective. The rear brake works perfect. However the front brake ist pulsating unless it gets hot on a long descent. I already cleaned the rotor and used sandpaper to refresh the pads. Nothing helped, so I changed the pads but it still pulsates. The front brake ist aligned properly. There is no disc rub.
Do you have any recommendation what to do? Do you think the disc mount of the fork needs to be faced with a special tool?
While rare, I have come across the occasional SRAM rotor that is uneven in thickness. Try a different rotor, and if that fixes it, send the other one in for warranty replacement.
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Can you feel any change at the lever, or is it just a feeling of the brake slipping and grabbing? Is the brake performing as expected, other than the pulsating feeling?
Unlikely, but worth checking - is the disc concentric with the hub? Occasionally the mounting point isn’t quite in the centre of the disc, you’ll see the edge of the brake track rise and fall as the wheel spins. Not common, but not unheard of, though it generally affects cheaper discs. Had to warranty a few discs for this issue over the years, mainly Tektro but also a Shimano RT800 and a Hope floater. This can cause a slight sense of pulsating as the rotor passes through the pads, though if its more than a few mm out of round, it’ll catch against the top of the calliper, which you would definitely be aware of.
Loose headset can also cause pulsing, worth it to double check that.
The fact that it doesn’t pulsate when the rotors are hot may mean the rotors are warped and need straightening . All rotors warp to some degree when they get hot so maybe when yours warp, they warp in such a way to work against the deflection.
When you have the bike in a stand, and you spin your wheel, you should be able to look between the pads and rotor to see if the gap changes, indicating a warped rotor. It’s pretty straightforward to straighten, although it’s easy to start chasing your tail if you don’t go slowly and methodically. If you don’t have a rotor straightening tool, you can use a Crescent wrench. Be sure to clean your rotors with alcohol after straightening in case some contaminants transferred from the tool to the rotor.
I will check the thickness. By the look of the distance to the pads the thickness looks evenly
I don’t feel anything in the lever. Brake power is good as well. The rotor is concentric to the hub. It’s the sram Paceline x rotor
The headset is also tightened correctly. When I push the front brake, there is no play between the frame and the fork.
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I will check it. The rotor does not look warped. There is also no rotor rub while riding or in the work stand
Thank you for all the replies. I guess I will try to sand and clean rotors and pads. Then I will try to bed them in again. The rear brake works flawlessly. I set them up at the same time. Therefore I am a little frustrated.
I had a similar problem with my new Force build- a disconcerting vibration during harder braking on descents. Headset tight, rotors straight, all good. Jesse at my local shop in Toronto, Blacksmith, suggested using “floating” rotors. Ordered and installed some Hope rotors and the problem immediately disappeared. Needed new pads too, but the price of happy, quiet confidence was priceless.
The thickness variance would be pretty much invisible to the eye. It would require a micrometer or similar measurement tool.
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There is sometimes a reflex to give the brake a quick check too soon after the bed-in process, while the rotor and pads are still very hot, and create just enough of an uneven transfer layer to the rotor to cause this problem. You may not even remember doing it.
I strongly discourage sanding rotors but would suggest aggressively cleaning the rotor with acetone, which will attack the surface and transfer layer better than isopropyl alcohol. If the pulsing is better or gone after that round you know it was a rotor issue. Alternatively, albeit annoyingly, I would advise just trying a completely fresh rotor as others have suggested.
There is a lot of flex and potential for misalignment at the fork and front of a bike compared to the rear so it is much less forgiving to any imperfections in setup than the rear brake with alignment triangulated by the stays and far more heavily supported.
In case this helps,I had this exact issue with a Force caliper; tried cleaning, sanding, blowtorch, new pads, nothing worked. In desperation I finally took it to my LBS and they put the bike on their brake-bedding machine, ran it through the cycle and that fixed it.
Yesterday I did the same. Before I cleaned everything und did the recommended piston Massage. In the LBS the bedded in the brakes with a bedding in machine. Hard braking still leads to a light stuttering of the front. The employee of the LBS said that it’s kind of normal because of the braking power of the SRAM E1 brakes. There is no squealing. Therefore he might be right. The braking power is excellent, however the sounds still annoy me a bit
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If you’re bugged by the sound I’ve had good luck w/ MTX brake pads, completely silent w/ great feel and modulation
I had the same issue with a SRAM rotor. In the end the only thing that worked was using a dial indicator and getting the rotor within .1mm deflection.