Been reading up on the various master cylinder and booster replacement threads. Great reading and tips.

I’ve noticed that my pedal is initially firm, then sinks towards the floor significantly before engaging, and is somewhat spongy thereafter. All original parts, so I’m not surprised that something would be failing. From my reading I suspect the master cylinder, but the spongy pedal makes me think the booster could be going bad as well.

I’m thinking I’ll just do both, since 80% of the work seems to be getting the parts out. I’ll replace the line from the booster to the “sucking jet pump” (great name, by the way) too. The “SJP” is only 2 yrs old as I replaced it with the motor swap. Although I do have a spare as somehow I bought two of those things when ordering parts for the motor change.

Anything else while I’ve got it all apart?

A good excuse to get a good brake bleeder and figure out how to use my new, high speed Foxwell to bleed the ABS module as well. Thanks all.

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Current
Original owner 2002 E53 X5 4.4i to 4.6i swap
2026 G80 M3 6 spd
2025 G06 X5 50e
Former
1972 Audi Fox
1986 Saab 900S
1996 BMW Z3
1998 BMW E36 M3 Sedan
2004 BMW E46 M3
2006 Audi A3 Quatro
1993 Mopar 318 Jeep Grand Cherokee
2015 V6 Jeep Grand Cherokee