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Old 01-31-2004, 02:27 PM
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Join Date: Feb 2003
Location: New York
Posts: 161
Bad vacuum amplifier 85 300TDT ???

I'm getting around 12" entering my blue vac amplifier on my 85 300TDT, only getting under 5" to my trans. When its cold the needle on my mityvac doesn't move when I increase throttle. Could a bad vac. amplifier be my problem? Has anyone heard of them going bad. I understand they are only on 85 and abouve model. Thanks PS I'm getting a reading of 20" off of the main line.
85 300TDT 456,000 orig. miles
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Old 02-01-2004, 12:16 PM
lrg lrg is offline
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Join Date: Jul 2001
Location: San Francisco
Posts: 1,163
I took the readings on my amplifier ('85 TDT) for someone on an old thread. The tread was started by smartin, you can find it in a search under title "quick transmission shifts". I've copied what I think you need to know here in case it helps:

I did some quick checks and I hope I got what you need. I tested both lines coming out of the top of the round, blue amplifier with my mityvac and got these results:

Center line (white/translucent with blue stripe)
at idle:14"
at 2000+ rpm:14"

Off center line (black plastic that looks like it goes to tranny modulator)
at idle 17.5"
at 2000+ rpm 13.5".

As I revved the engine higher the vac dropped but ony marginally. The drop in vacuum appears to be a linear progression as the rpm increases, there was no sudden drop as near as I could tell. Even revving the engine higher (I'm guessing 3,000 rpm or so) the vac never dropped below 12". Also, I never heard a click but I did this test in my garage so it was noisy enough that I probably just never heard it.

I didn't check the line coming out of the bottom as it appears to be a vac source line. I wouldn't put too much stock in the exact mityvac readings because I doubt those gauges are completely accurate.

I have a feeling I may have created more questions that I answered but I hope this helps anyway.

1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold
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