Has anybody tried a higher Dot rating than 4 . My rear brake on my 2017 supersport is basically a chocolate fireguard. And bleeding doesnt last 5 minutes
The DOT rating won’t make any difference ie if you go to DOT 5.1 rather than 4. Yes DOT 5.1 has slightly a higher dry & wet boiling point than DOT 4 but I suspect your rear brake fluid isn’t getting anywhere near hot enough to boil even with the DOT 4, unless the routing of the brake line is too close to the exhaust.
You need to get to the root cause of the issue. Maybe it’s due to seized pistons, glazed pads, leaking master cylinder piston, air in the line, etc. Perhaps the brake line is passing too close to the exhaust and perhaps the fluid is overheating and reaching boiling point in which it becomes ineffective. Without addressing the root cause you’ll never cure the issue.
The rear brake can and does work, sure, it’s not going to stop the bike from 50mm h or higher without the use of the front brakes but it can be made so it does lock the rear wheel or cause the rear abs to engage.
BTW never mix DOT 5 brake fluid with DOT 3, 4 or 5.1 it’s silicon based not glycol based and the 2 fluids won’t mix you’ll just render your brakes ineffective.
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I have been through this with my Supersport. Tried bleeding and different brake fluid nothing worked satisfactorily. Then it was solved. There is almost certainly air in the system. The problem is bleeding with the caliper on the bike just builds up an air lock in
the caliper because it is fitted below the disc and the bleed nipple is at the bottom. Unbolt the caliper put something between the pads to stop them closing up. Turn the caliper sideways so that the bleed nipple is nearer the top. Bleed as normal from this position and the caliper will bleed excess air within four strokes of the brake pedal. Re bolt the caliper. My rear brake then worked like a vice with little movement of the pedal.
Hope this helps.
rear brake then operated like a vice with litle movement.
Well done with the stahlbus, great product and I have them fitted on my bikes which don’t have ABS. Do you need to electronically disable the ABS pump to be able to bleed the brakes on your 2017 Supersport? I have to with my 2018 S1000RR and own a purpose made device (Hex911) that plugs into the ODBC port and talks to the ECU to disable the ABS pump to enable the bleed function and then you apply the ABS pump after you’ve finished.
I had a similar “air in the system/brake bleed problem” with a much simpler different make bike (Triumph) with no ABS. It didn’t matter what I did, I just couldn’t get the air out of the calliper, I bought a bigger primary cylinder than stock, raised the callipers above the the primary cylinder overnight etc. Then my son used a brake power bleed system they had at his works (building and repairing exotic race cars). It worked, and the brake feel and bite is just gorgeous, right at the top of the lever pull.
Good suggestion from Tommy58 above too, but if that fails, might be worth investigating if a workshop could help you with a professional system.
DOT 5.1 is a specialised product for race track/track day use where brake fluid temperatures get very high, you shouldn’t need it for ordinary road use and especially for rear brakes which I personally only use in emergency stops or slow maneuvering whilst filtering in traffic or in the car park.