Hmm. The loss of brake power appears to be entirely random. I did a little more tests, and here's what I found:

* Let engine "build up a charge" of vacuum power. Put car in reverse, hit brake pedal. Booster kicks in, and the car stops on a dime. Hit the brakes again, slightly less effective. Third time, and I was operating off manual brakes, no boost.

* Checked vacuum off of the main hard plastic line (Main Vacuum Line?). The "small" split-offs appear to be as follows:
- First split reads 15hg, constant. Engine revving doesn't change anything.
- Second split reads 5-15hg, and seems to vary with engine rpm's.
- "thick" connector to the brake booster itself, reads 15hg sometimes, but will randomly climb to 25hg (which is what my pump put out, when I tested it), and seems to "prefer" 15hg.

I know that the brake booster is probably fine. I don't leak any brake fluid, and when the booster has vacuum built up, it brakes without any issues. I'm wondering if the check valve in the main vacuum line is broken (even though it's a new part), or if my vacuum pump is acting flakey.

Tomorrow, I'll put the mityvac on the vacuum pump, and see if it holds 25hg constantly, or if the vacuum fluctuates. So far, it doesn't appear to fluctuate, and 25hg leads me to believe that the pump was either replaced by the PO, or was recently refurbished, since it seems to put out a good vacuum. Any ideas, with this added info?

Thanks for all the help.

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(Oo{=|=}oO) 1983 MB 300D USA, 212,000mi. 80's yellow/white. "Gunther"
(Oo{=|=}oO) 1984 MB 300D Euro, Turbo Added in Germany, 186,000mi [SOLD] Missing her dearly.
(Oo{=|=}oO) 1984 MB 300D USA Turbodiesel, 269,000mi. [SOLD]