Set the lever in the bleed position, bleed port at 12, mc body basically parallel to the ground. Cycle the lever and see if the spongey feel goes away. If so, likely a bad bleed, possibly a bad bladder. If the feel stays the same, check the brake line for any kinks, especially where it moves over any suspension linkages/components. Brake lines aren't indestructible and can develop internal leaks that weep between the layers of the hose, so it's leaking just not visibly. You can also check for this while the lever is in the bleed position with the cup attached. Add about 15mm worth of fluid to the cup and cycle the lever very slowly. If the lever goes to the bar and the fluid level drops with each pull til there's less fluid in the cup than what you started with the line's ruptured. If the lever goes to the bar but the fluid level rises slightly as you hold it to the bar then returns to the original level on release, you have a bad MC piston or mc bore.
(FWIW, the term spongey can mean diff things to diff people. Someone may take it as the lever feel gets softer during actuation while another takes it as the lever goes to the bar without much effort. May seem like splitting hairs, but the problems described can have way different causes.)
April 19, 2022, 11:46 a.m. - JT
Set the lever in the bleed position, bleed port at 12, mc body basically parallel to the ground. Cycle the lever and see if the spongey feel goes away. If so, likely a bad bleed, possibly a bad bladder. If the feel stays the same, check the brake line for any kinks, especially where it moves over any suspension linkages/components. Brake lines aren't indestructible and can develop internal leaks that weep between the layers of the hose, so it's leaking just not visibly. You can also check for this while the lever is in the bleed position with the cup attached. Add about 15mm worth of fluid to the cup and cycle the lever very slowly. If the lever goes to the bar and the fluid level drops with each pull til there's less fluid in the cup than what you started with the line's ruptured. If the lever goes to the bar but the fluid level rises slightly as you hold it to the bar then returns to the original level on release, you have a bad MC piston or mc bore. (FWIW, the term spongey can mean diff things to diff people. Someone may take it as the lever feel gets softer during actuation while another takes it as the lever goes to the bar without much effort. May seem like splitting hairs, but the problems described can have way different causes.)