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Old 04-09-2012, 11:13 AM
Registered User
Join Date: Mar 2012
Posts: 4
Final stage of vacuum issue?

Hopefully these are my final vacuum related questions folks. Spent yesterday tracking. As frustrating as it can be at times, I have a whole new appreciation for the vacuum and engine design of these vehicles. I will do my best to be as clear as I can!


1.) no shut-off with key. Have to manually shut-down engine.

2.) no door locks. Driver's side is 'normal' after engine on for 10 minutes. All passenger locks are 'stiff'

3.) very hard brakes.

4.) transmission flaring

5.) small amount of oil coming through under ignition key cylinder

6.) ACC unit does not work


1.) Engine shuts down when vacuum applied to brown IP line.

2.) Engine does NOT shut down when door lock lines are plugged.

3.) Main vacuum line out of brake booster reads erraticaly under vacuum.

4.) Yellow/red stripe (lock) line behind driver's door panel holds vacuum at 22 Hg. Yellow/Green (unlock line) does not.

5.) Rear resevoir holds vacuum.

Check valves have been replaced, and all junctions have been inspected for poor fittings.

Whats slightly frustrating is the 1985 wagon seems to have a slightly different set-up for vacuum then the other 123s, which has made cross-referencing schematics difficult. From what I can gather, I think I'm in for a vacuum pump rebuild but would appreciate a final opinion before I order the kit.

FWIW, cruise control works!
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Old 04-09-2012, 11:21 AM
Biodiesel300TD's Avatar
Join Date: Dec 2004
Location: Albany, OR
Posts: 4,845
You might just need a check valve for your pump
Vac Pump Check Valve - Fastlane

You can check whether it's the pump or the booster, but plugging all the small ports on the main vac line using your mity vac gauge on one of them. The run the car. Remove the main vac line from the brake booster, I think it's a 17mm, maybe bigger. Then plug that end of the vac line tightly. See if you vac that still jumps all over or starts to hold steady above 20". If it's still jumpy or reading below 20" your pump needs some attention.
'04 Jetta TDI Wagon
'82 300TD ~ Winnie ~ Sold
'77 300D ~ Sold
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Old 04-09-2012, 11:47 AM
Diesel911's Avatar
Registered User
Join Date: Sep 2007
Location: Long Beach,CA
Posts: 23,341
Hard braking indicates along with the other symptoms idicates a major loss of Vacuum.
The Vacuum Pump Check Valve or vacuum leak/s is most often the issue.

When I had a hard braking removing the Vacuum Pump Check Valve where it screws into the Vacuum Pump and spraying it out with WD-40 fixed it.
Others have found the internals of the Valve damaged or even gone.
84 300D, 82 Volvo 244Gl Diesel
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Old 04-09-2012, 12:06 PM
Registered User
Join Date: Jan 2002
Posts: 18,353
I'd say check valve, bad vacuum pump or bad vacuum brake booster. You need to check the vacuum at the pump outlet with everything disconnected, including the brake booster. There are very few instances on here of hard brakes that pointed to a problem other than a bad booster or a bad pump (check valve).
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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