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Old 09-28-2011, 01:30 PM
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Join Date: Sep 2011
Location: Nashville
Posts: 8
Good Vacuum, Bad Vacuum

The culprit- 81 300sd
The problem- Vacuum is great at the hard line coming off the vacuum pump, I took the brake booster hose off, applied vacuum gauge to the hard line, and received a reading of a strong 23"Hg. When I hooked the booster hose back up, and take a reading from the first tee, or second tee as far as that is concerned, I get a bouncing needle between 0 and 7. Mind this is a brand new booster hose..
I got the same reading with the first vacuum pump.. had an extra one laying around, slapped a rebuild to it, new check valves, seals, etc. put that on the car, and, the same readings. Great pressure at the hard line.. terrible pressure at the tees...

I am at a loss as to what it could be... how can I get great pressure 4 inches in front of a tee, and terrible pressure at the tee?? like i said, brand new booster hose...

any suggestions?!

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Old 09-28-2011, 02:00 PM
Biodiesel300TD's Avatar
Join Date: Dec 2004
Location: Albany, OR
Posts: 4,845
Welcome to the forum.It sounds to me like your booster is leaking. When you are testing is the engine running or are you pulling vac with your MityVac, or runnnig the engine to reading it? The way I do it is to plug the MityVac into on of the T's. The plug the other one. Then start the car. If all is well you'll get over 20" of vac. If not then pull the main vac line off the booster and plug that end. A thumb usually works well, if you can get it to seal that is. If the vac doesn't jump up then the pump is bad, which probably isn't your case. If it goes up then the booster is leaking.
'04 Jetta TDI Wagon
'82 300TD ~ Winnie ~ Sold
'77 300D ~ Sold
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Old 09-28-2011, 02:57 PM
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Join Date: Sep 2011
Location: Nashville
Posts: 8
Bingo. Closed up all the other lines and checked using finger, as gauge couldn't fit on so well. Good suction. Check at each tee. Held a good 17"gf of vacuum at each. Hooked all the lines back up, and turned the engine off via the key, and without hesitation, it shut down. Looks like ill be searching for a new booster, or new to me!

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