TIL a simple brake bleed trick that saved me 3 hours of frustration

I was working on an old Freightliner last week, the rear brakes were spongy no matter how many times I bled them. I tried the standard two-person method, then a vacuum bleeder, still felt like mush. Finally a shop foreman walked over and told me to crack the bleeder screw at the master cylinder first before doing the wheels. I felt stupid but I tried it, and sure enough there was air trapped right at the top that was never getting pushed out. After that, the pedal was rock solid in like 20 minutes. Has anyone else dealt with air pockets hiding in weird spots on these older trucks?

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coleman.jamie2mo ago

Dang, that master cylinder trick is a lifesaver! I had the exact same problem on an old International 4900 a couple years back. Spent hours with a vacuum bleeder and even pressure bleeding it, pedal was still garbage. Finally my old man stopped by and told me to loosen the lines at the master cylinder itself. He said sometimes on these older trucks the fluid gets a little thick or the reservoir has a weird angle that traps air right at the outlet. I cracked the front line just a hair, let a little fluid and bubbles dribble out, then tightened it back up. Did the same on the rear line and after that the brakes bled out perfect in maybe fifteen minutes. It's one of those things you just don't think about until someone shows you, you know? Now I always start with the master cylinder on anything older than like 2000.

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bethcarr2mo ago

Yeah, isn't it wild how something so simple can save hours?

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