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I have a Promax Decipher Hydraulic Rear Brake on a bike I am trying to repair, but no idea how to bleed the brakes. I have tried to find something out there in internet land but the two videos I found are not helpful.

How do I bleed these using the Park Tool BKD-1? Please feel free to respond like I am a child - listing everything. Thank you in advance.

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Generally speaking if a brake has no coherent published bleed procedure, but it does have a Shimano-style reservoir cap on the lever, bleed it like an older (pre-funnel) Shimano brake.

Take out the pads and put in a block. Make the reservoir the highest point and make the cap level. Stabilize the bars. Fill a syringe with the appropriate fluid and hook it to the bleed port on the caliper. Open the caliper port and push fluid up until the reservoir is nearly full. At this juncture you can try working the plunger back and forth to try and draw air into the syringe; this is effective on some brakes and not others. End on a push of fluid and close the caliper bleed port. Remove the syringe and hose. Give the lever some flicks and squeezes and see if bubbles come up into the reservoir. Angle the bike back and forth and repeat. Level it again. Reconnect just the hose to the bleed port, set up a collection bag at the other end, then open the port and let any bubbles drain out. Add fluid to the reservoir as needed to keep it from emptying. Close the bleed port, do some more squeezes and flicks at the lever, and repeat until no bubbles come out. Then with the reservoir fluid level high enough that re-installing the cover will make a little fluid displace and ooze out around it, put the cover back on and fasten it down, wiping up any fluid.

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DECIPHER Hydraulic Disk Brakes Bleeding Manual has the step by step directions you seek. A couple things I'll point out: Do change the rubber washers on the drain and fill ports. The directions do a nice job parenthetically telling the reader to check these and replace as needed. I suggest just changing these for the appropriate replacement washers (size and type of rubber must be correct).

Make sure you replace all the old DOT4 fluid. Over time, DOT fluid will attract water into the system. This diminishes performance. The water can even boil in the a system that is used hard and develops heat. Heat that would be tolerated without performance issues if the DOT fluid is pure.

Be careful with leaks as DOT is very hard on paint. It's not safe or smart to get it on you and not wash it off ASAP. It doesn't do real good if it gets on the pads or rotors.

Back to the bolts, the seal to their openings is complete if there's adequate torque of the bolt and rubber washer. Torque wrench makes it for sure.

I'll leave the rest to your skills and the Promax directions at the link.

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  • Are these DOT? That means promax sometimes use mineral oil and sometimes DOT while most manufacturers stick to one.
    – Chris H
    Commented Mar 30, 2023 at 5:29
  • @ChrisH There are Promax brakes with both DOT and mineral. I haven't seen a new one with DOT in some time so they may have switched away completely. Commented Mar 30, 2023 at 15:59
  • @NathanKnutson the ones I got rid of from my hardtail were oil (solve). It leaked onto the pads. Even new they were nowhere near as good as the MT200s I've got now
    – Chris H
    Commented Mar 30, 2023 at 17:04
  • According to the Promax directions for bleeding (the link in my post), the Decipher brakes utilize DOT4 brake fluid. On the actual Promax website, there are no current brake systems named, "Decipher," which tells me it's an older model.
    – Jeff
    Commented Mar 31, 2023 at 1:23

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