Brakes feel spongy? Lever pulling all the way to the handlebar? 99 times out of 100 it’s NOT because the OEM brakes are bad, it’s because there is air in the line! Does pumping the lever help? If so then there IS air in the line.
- My GF: “Babe I made you some lunch…wait what are you doing? I thought you JUST worked on your brakes!”
- ME: “Yeah I did but that guy Matt wanted to know how to do it so I told him I’d post a how to.”
- My GF: “You must really like this guy!”
- Me: “He’s the one with that adorable little daughter.”
- My GF: “Ah no wonder you’re doing this. OK lunch is ready.”
First and foremost I HATE when people try to tell me how to do something. Or worse they feel THEIR WAY is the BEST WAY. So I’m posting this to tell you how I do it. How you do it is up to you.
If you don’t want to do a full bleed, a simple way I maintain my brakes is to just remove the top mushroom screw, insert the plastic syringe into the hole, fill it about halfway with oil and pump the lever. As time goes on the bubbles move upward toward the brake lever and they’re easy to remove with this method. Up to you. Just be sure to adjust your brake lever so that it’s level to the ground and you’ve turned your handlebars so that the respective lever is higher than the lowest part of the brake line.
Another easy hack is to tie your brake levers to your grips with a zip tie or something similar. Leave it that way overnight. The next day remove the zip ties and then perform what I’ve described above. Tying down the levers forces the air up to the top of the lines.
Here is the kit I purchased to work on my MTB and Sur Ron brakes:
I always remove the brake pads from the calipers no matter what I’m working on. Dirt bikes, MTB bikes, on road race bikes. I never want any contamination of the fluids to hit the pads or rotors.
- Step one is to remove calipers from the fork leg and the rear swing arm. I think it’s a 5mm hex but I can’t remember. Easy.
- Remove the pads from the calipers. Just use a number 15 Torx and unscrew the pin that holds the pads in the caliper. You’ll need to remove the small retaining safety clip on the end of that threaded pin. BE SURE TO INSERT A BRAKE PAD BLOCK INTO THE CALIPER!
Unlike motorcycle master cylinders the Sur Ron’s are tiny. Hence they use tiny screws too. On motorcycles I would draw the fluid from the top down. With the Sur Ron I push fluid from the bottom up. I like it better since it moves air bubbles up rather than down.
- Pick which brake you want to bleed first. Loosen the brake handlebar 5mm bolt and adjust the lever so that it is level with the ground. You should turn the handlebar to the right all the way if you’re working on the left brake. This will allow the brake line to be as high as possible.
- In this case go to the back caliper and remove the teeny tiny 15 Torx screw which is the ‘bleed’ screw. Don’t worry if mineral oil starts to leak out. Place one of the threaded hose fittings (the one that fits from the kit I use) into the bleed port on the caliper. Attach the hose. Fill the syringe ¾ of the way with mineral oil and attach it to the fitting.
- Undo the very small mushroom screw and place an empty syringe into the opening. Be careful to notice if the rubber washer is on the screw or left in the threaded hole. Place the non-threaded syringe into the hole.
- Go back to the caliper and start compressing the syringe with the ¾ amount of oil. You will see the syringe on the brake handle start to fill and you will see bubbles too. That’s what causes the mushy feeling when you brake. Stop when you have about ¼ inch of mineral oil left in the caliper syringe.
- Then pull the oil back through the line by drawing the caliper syringe back until the one on the brake handle is about 4mm from the bottom. Reverse the procedure and again push the mineral oil back into the line.
- Doing this removes more bubbles than just doing it once. Once that’s done place the pushing rod slightly into the top of the brake lever syringe. Not too much, it’s just to keep the fluid from flowing out of the caliper fitting once you remove that syringe.
- Remove the syringe, nipple and replace the bleed bolt.
- Use the caliper syringe to suck out the majority of fluid out of the brake handle syringe after removing its plunger.
- Replace the mushroom bolt, do NOT over tighten.
- Wipe down everything with a rag and alcohol. (Not the kind you drink) The caliper, the brake handle, anything that has oil on it.
- Remove the brake pad block and reinstall the brake pads and be sure to align the spreading spring properly as to NOT be in front of the brake pads.
- Reinstall the caliper. I use Blue Loctite on the threads.
- Remove the mushroom screw and reinsert the plastic syringe without its plunger.
- Fill it halfway with mineral oil.
- Pump the handle. This is to remove any remaining bubbles. If some remain, you will see them rise up from the brake handle. Do this for about three minutes.
- Reinstall the mushroom screw and adjust your brake lever to where you like the angle.
The brake levers are also adjustable for reach, although it may not be readily apparent. Using a 2mm hex wrench you can adjust the reach to be further or closer to the handlebar with this small screw:
Another important screw to check is the one that holds the lever onto the master cylinder. It is secured by a small 2mm set screw. Be sure to check it occasionally or you may find yourself without a brake lever….not so good!
Shortening your brake lines
I found that both the rear and front brake lines were about 5 inches too long. So I shortened them to what I feel is the proper length so they don’t catch on brush or branches. Like most mountain bike hydraulic disc brakes the Sur Ron uses Mineral Oil for hydraulic fluid. I have tons of that from changing my ebike brakes. Just use a sharp pair of cutters to cut the lines and buy some brake Olive and connector pieces. Bleed the brakes and you’re all set!
Removing the brake sensors and trimming the brake lines made the front end very tidy!