Earlier this week I had a diaphram tear on my 300D's vacuum pump. Rebuilt it and reinstalled per normal.

This AM.... failed again. Tomorrow I will rebuild it, but is there some magic secret that I am missing. It is a pretty straightforward job, a PITA but straightforward.

Any thoughts, this is really getting to me.

JCD

Well , I am really just guessing ... and until you take it apart you won't know the exact cause of the failure THIS time.... if the diagram has ripped or if it involves the other mechanism....
Maybe you should describe what you did earlier in the week on rebuilding it...
Particularly how you made sure the piston stroke was at the proper place before you buttoned it up...

I removed the entire vacuum pump and disassembled it, cleaned it and reassembled it, replacing the diaphram. The valve/spring mechanism was in good shape, fairly new (about 1 year), I inspected it and reassembled.

The armeture fits against a circulating cam, as you know. Lucky or not, I have never had an issue replacing it with the orientation of the cam relative to the armeture inside the vacuum pump. It is flush when it comes off and flush when it goes on.

You are right, it could be another reason for the failure, however, my experience is that when the oil gauge flutters, I have now power breaks and the car won't shut off, it is the diaphram.

JCD

Before you remove the vacuum pump, remove the check valve on the top of the pump. You can do this with the pump on the engine. Failure of the check valve is probably the most common reason for "pump" failure. And it is easy and cheap to replace.

But I know it is the diaphram as it has evacuated some oil through the hose into the air cleaner.

Like MORE oil than normal or?
My engine spurts a little oil over there once and awhile...little blow by and whatnot..
curious.

I think a sharp edge on the washers cut the diaphram.

Brandon,

When there is a large tear in the diaphram, it will evacuate oil from the engine, through the vacuum pump, out of the hose that runs to the top of the air cleaner.

For me, when this happens, it is NOT a little bit of oil, but a pretty good bunch.

It deals with the installation of the diaphram.

The first vacuum failure I had what due to the bolt that holds in the diaphram backing out. It was a major mess.

My recent failure was due to, I think, the sharp edge of the washers on the front back of the diaphram cutting the diaphram. My guess is that I tightened down on the bolt too tight as well.

I find that two things are difficult when installing the diaphram.

1. Getting the bolt cinched down tight enough such that it does not back out, but not so tight that it tears the diaphram.

2. Lining up the holes on the diaphram such that the top cap can be installed.

In every case I used Loctite blue to seat the bolt, but I seem to be in a classic standoff. Tight enough, tears the diaphram.... too loose, the bolt backs out and what a mess.

OK experts, your input please. For context, I have the old style vacuum pump, 1977 300D.

The good news is I can swap out the diaphram in about 3 innings of a Yankees/Red Sox game,,,,,,,, go Yanks.

JCD

I am not claiming to be an expert on this... but I may have some pictures from TCane doing my pump which will help....
Also, for 35 years I have used only Locktight RED... Stud and Bearing Mount... I can see people panicking as they read that... but if you check it out... on a Normal size nut and bolt...it only adds about 5 ft lbs of torque required to break it loose... and it doesn't let go the way you seem to be suggesting the blue did for you..... however, I am old enough to remember the time when this stuff first came out... and they had a cleaner and primer to put on it before the locktight.... so maybe you are not getting your threads chemically clean... that might account for your Blue not setting up.. or you are not giving it overnight to Set... ? Do not put Red Locktight on something like the Flywheel Nut on a VW engine.... a LOT of surface area on those threads... and 200 Ft Lbs installation torque... that takes a real Stud to get it off... or oxy-Acet torch.... LOL
Anyway I will try to find the pictures and post them...hope they are of the same type pump....
One of these is the alignment bolts being used ... the other an allen wrench and 90 degree circlip plyers tightening it up....

Attached Thumbnails

   

Same pump, same approach.

I do clean the bolt with brake cleaner, let it dry, then put on the loctite blue. Maybe I should switch to red for the peace of mind. When the bolt threaded out, it tore the washers to pieces and knocked a hole in the cap. Good thing I bought a used vacuum pump for $40 off ebay and had it laying around.

I also use the bolts, as you did, to make sure the diaphram lines up with the holes so you can install the cap.

Maybe what has happened is just a freak thing. This is one of the weak links in the car, so maybe I am over-reacting. At least now I have replacement down to a science. I just wish that a failure didn't result in a suprise loss of power breaks and a big pool of oil under the car.

Jim