I'm in the middle of replacing the power brake booster in Guderian. It quit working when I replaced a front caliper.

While looking for an easy way to replace the booster, I found a bunch of threads that start out "after replacing my master cylinder, caliper, brake pads, etc., my booster doesn't work." After the obligatory posts saying that the person must have knocked off a vacuum line and further testing, yes the booster went bad. Sounds familiar. But everyone was amazed at the coincidence of two brake components going bad at the same time.

I happened to look at my "new" 300SD and it had a booster with a junkyard date of 9-25-07. When I got it, the PO said it just had new brake pads front and rear and gave me the receipt. Got it out. 9-21-07. Too much for coincidence.

Theory: A twenty to thirty year old booster diaphram isn't as flexible as it used to be. It can stand a limited range of movement very well, but when the brake pedal is pushed all the way to the floor, it is more than the old diapham can stand.

From now on, its only pressure or vacuum bleeding for me. In one of the posts, I did see a great idea. If you have to do the pumping method, put a block of wood under the brake pedal to keep it going further than it usually did.

I hate to be a Chicken Little, but if I can spare someone the torture of replacing a power brake booster in a 300SD, it seems worth it.

BTW. There is no easy way to replace the booster on a 300SD.

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1983 300SD "Guderian"
1987 MR2
2015 Camry
2015 Chevy Spark
2006 Hyundai Tucson