RWD - master cylinder rebuild??

Volvo RWD 900 Forum

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master cylinder rebuild?? 900 1993

Did the MC fail on your over time. Or were you using it to bleed brakes?

What color is the brake fluid. I hope not black or very dark brown so light passes through the MC reservoir. Is the MC original?

1993 940 has ABS, yes?

I've not seen an MC rebuild kit in a very long time, yet have not looked. If the MC is factory original, wear of the bore or the piston may occur? Also, if the brake fluid is not regular flushed with new DOT 4 like every two years or so, corrosion may form outside the piston seal travel. That corrosion may require, I guess, some sort of machine shop to treat? I'm uncertain. I'd not ever rebuilt a brake master cylinder. I've disassembled failed MCs usually on 100 and 200 series on occasion. A few times when I stupidly used the brake pedal to bleed the brakes. Don't do that.

Use a Motive or like power bleeder to flush the brakes at like 15-20 PSI with new DOT 4. One quart may do it yet have a second quart or at least a pint on hand.

If ABS, not need to run the ABS pump. Brake pedal pressing a few dozen times may move the fluid around from inside the ABS pump chamber a bit. As I bleed, I may slightly, ever so slightly, press the brake pedal to move fluid around a bit. Also, to feel the pedal when nearly finished with the bleeder nipples closed.

Use brake parts cleaner with the red straw to remove remaining brake fluid from inside the bleeder nipples and around them. Restore them rubber bleeder nipple caps as the nipples will otherwise corrode from the inside, sometimes. Though some corrosion occurs at the threaded interface between the outside of the bleeder nipple and inside the threaded caliper material bleeder nipple bore.

If you do not have ABS, and I guess you do, the fuss-budget non ABS may require a repeat bleed, or you may perform a fluid bleed that requires at least two and sometimes three, maybe four, bleed circuits in order.



My post about bleedin' them brakes with new fluid using the Motive pressure power bleeder and such:

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New master cylinder rebuild?? [900][1993]
posted by  Dom's940  on Mon May 13 11:35 CST 2019 >

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