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Old 10-01-2000, 09:43 PM
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Join Date: Feb 2000
Location: Germantown, MD
Posts: 106
The theme for the month seems to be "Things that Leak" on an 85 300TDT.

Any advice/tricks on ferriting out the culprit (patience and determination?). I will be studying the diagrams to get a grasp of the system. Basically the locks are dead, the engine will not shut off except manually, and the transmission seems to be shifting harder than it was yesterday.

Thanks for you time.
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Old 10-01-2000, 10:08 PM
shoe's Avatar
Senior Member
Join Date: Jun 2000
Location: Baton Rouge, LA.
Posts: 583
How's your brake pedal? If it is hard as a brick, then chances are your vacum pump has taken a dump. Just a thought.

Keith Schuster
99 Harley Davidson Ultra Classic
97 Dodge Ram
83 300D
Heavy equipment\hydraulic mechanic 20 yrs
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Old 10-01-2000, 10:23 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Verify vacuum at the brake booster vacuum line. This is the source for the door lock, A/C, shut-off, and the trans vacuum amplifier.

Remove and plug all systems at the supply tees by the booster. Leave just the door locks for the moment. The door locks should be the yellow lines. One goes to the system and one goes to the reservoir. Remove the line to the reservoir and place vacuum gage here (this may be hard to determine if your system is full of holes). The purpose of removing the reservoir is to make all vacuum changes more visable.

Go under the carpet on the passenger floor and find the junction for all the actuator vacuum supply lines. If you have no vacuum you must plug every line till you do. This also may be necessary to determine the reservoir line. The difference between the res. line and the system line (under the hood)is that hooking vac to the system will eventually move actuators and vacuum to the reservoir won't.

Once you have vacuum rising with the engine running, verify the integrity of each side of the system (lock and unlock) by watching how long the vacuum takes to rise on changing direction. Then pull the check valve from the source (saves shutting and restarting the engine after each stage)and watch the leak. The leak will be much easier to see with the reservoir out of the system. Usually the leak is only on one side; lock or unlock.

Once you have seen the signature of the leak pull and cap each tee under the floor carpetting until there is no leak (pull the check valve from the source and watch after each line is plugged). When you have identified which line is leaking run the locks up and down and see which door, trunk or gasflap isn't working and that is the line you have plugged.

If you have many leaks you may have to pull all the lines and get a leak free supply to start. Repair your leaks one at a time and reinstall the vac till they are all working.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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