Started having the usual problems (hard brakes, delayed shutdown, etc)

So far, I've plugged every tee'd point at the end of the hard vacuum line by the brake booster so that the ONLY thing that should be drawing vacuum is the brake booster itself.

Fired it up and measured a VERY slowly climbing vacuum of about 16in. It may have gone higher but it took about 2 min already just to reach 16in.

Next, I disconnected the brake booster connection and plugged that line. I hooked up a mighty-vac and see if everything was tight and if it would actually hold vacuum. I was able to easily and quickly pull 25in. and it held rock steady.

So now, I disconnected the mightvac and reconnected the vacuum gauge and fired it up again (plugged brake booster this time). It got up to 18in. fairly quickly this time but didn't look like it was going any higher.

At this point, my info says that I should be seeing 20-23in....so I'm already low here.

Next, I reconnected the brake booster line back up and fired it up again. Again, it took a LONG time and I finally stopped the test after it reached about 16in.

My question now, is it normal for the vacuum level to take this long when the brake booster is connected? Intuitively, it seems like it might be normal since the pump has to evacuate the volume of the brake booster.

Other question is....should I REALLY be expecting to see 20-23in of vacuum or is the 18in that I was able to produce at one point normal? (or the 16in when the brake booster connected)

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Chris
1985 300SD - 'Grace' (198K mi.)
2018 Honda Civic Sport
2018 Honda CRV LX
2010 Honda Fit Sport (RIP)
2013 Honda Accord Sport (Sold)
1996 Lexus LS400 (Retired)
1995 Ford Contour SE (Retired)
1976 Porsche 914 (Sold)
1972 Datsun 240Z (RIP)

It seems there was a vacuum thread a while back and the guys problem was a faulty check valve in the vacuum pump.

you should be getting around 23in of vac. last time I checked my 300D, I was getting 23.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

It sounds like your brake booster is leaking. It should only take a few seconds for it to reach max vac when you start the car. If its not doing this or can't reach 20" or higher with the booster hooked up then your booster is leaking.

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If it should take only a few seconds to come up to the full 'available' vacuum, then this would seem to indicate a problem. It DEFINITELY took more than a few seconds though. Would love to hear from anyone else who can vouch for this! Anyone want to time their system?

But, like I had mentioned, I can only get to about 18in. even WITHOUT the brake booster connected (and nothing else connected either)....so it seems like there's also an issue with the pump too...unless of course it's not unusual to have about 18in from a pump....which is sort of why I'm asking all this.

If it appears that the pump is not up to par, then it looks like I'll be doing a pump rebuild. Not that I mind....after all the car is as old as dirt so it had to go sometime.

I miss read your post. If the pump is only pulling 18" with everything plugged you are on the verge of needing a pump rebuild. I would start with that and see if that fixes the issue. Especially since a new booster will cost you one left arm and one right leg.

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I guess then that a good test, that I haven't tried yet, is to pull a vacuum JUST on the brake booster and see if it would hold. If it's in good condition, should I expect the booster to actually hold a steady vacuum?

Yes you should be able to pull vac on the booster and have it hold. It will take some pumping to get the vac up to 15 or 20". It will hold as long as you don't press the brake petal. Once you hit the petal the vac will drop.

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The Check Vlave is what the main Vacuum Line attaches to at the Vacuum Pump. It can be unscrewed and cleaned.

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84 300D, 82 Volvo 244Gl Diesel

I know of the check valve you're referring to....but, how would this check valve cause a reduced vacuum level?

Just popped the vacuum line off the top of that check valve and took a look down in there.
Very weird. I could see what I thought was a small spring standing up vertically but wasn't sure. So, I took something small and poked at it. It was in fact a small spring (about a 1/8 - 1/4" long and about twice the diameter of the ball point pen spring). The spring fell over on its side. Other than that, this check valve appeared to be completely pass-thru.

Should I have seen something inside the valve itself (it's a valve, after all!)

Actually that is not an easy question to answer because it is hard to visualize a vacuum as something that is moving.

Think of a Piston in a Cylinder and think of a spring loaded Valve at the top. When the Piston goes down it creates a negative pressure behind the Valve and the Atmospheric Pressure pushes the valve open.

When the pressure equalizes the spring closes the Valve (this is the Check Valve). When the Piston goes up a different spring loaded Valve opens and expels the Air in the Cylinder as the Piston Moves to the top.

If the Valve at the top (the Check Valve) cannot close/seal completely due to being gunked up it will be difficult to keep the negative pressure going.

In Fact besides the Check Valve the Piston type Vacuum Pumps have 3 valves that can get gunked up. The Check Valve is the easiest
to get at.

A sorter explanation is that the Vacuum pump works the opposite of an Air Compressor. The Vacuum Pump pushes the pressurized Air into the Crankcase the other end of the pump creates a negative pressure because for the most part it is sealed off.
Without the Valves there would be no 1 way flow through the Vacuum Pump (because both Diaphragm and Piston type Vacuum Pumps have parts that cycle back and forth and no or less of what we call vacuum would be created.

I hope someone else will take a stab at an eplaination.!

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the explanation Diesel911.

I'm still curious though about what I saw when I peeked inside the exterior check valve.
Should it have looked completely empty? What is that little spring I see just freely moving around inside there?

I actually do not recall entirely. I did not remove mine but sprayed inside with WD40 to clean it and after that it worked. So I assumed the valve was not seating inside and the WD40 washed away something as my Vacuum problem went away after that.

There is supposed to be a Disc in there that the spring pushes against otherwise there would be no reason to have a spring. It should be one way and only be able to blow through it from one side.

In any event when you put it back on the Vacuum pump check and see what the Vacuum Pump is putting out right there at the Check Valve. Some Vacuum Pumps come with a Cone Shaped Rubber Adapter to push into the hole to test it.

I did a quick look in the Manual for a picture but could not find one.

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84 300D, 82 Volvo 244Gl Diesel

That's sort of along the lines of what I figured should be there. Apparently, my check valve is one of those that you hear falling apart.

I've gone ahead and ordered a rebuild kit....as well as one of these rediculously expensive check valves. (geez, you'd think these things were made of solid gold for what they're charging for them)

I figure that if the check valve has gone, it's probably worth rebuilding the pump too (not the mechanical rebuild kit). Looks like the hardest part of that job is going to be accessing all of those hex bolts holding the pump to the block.

Pump rebuilt.
Found the little round disc, plastic piece, and spring inside the pump. These were all the little parts that were suppose to make the exterior check valve do its thing. What's weird is that from what I had read, if your exterior check valve disintegrated like this, you were supposed to have lost ALL vacuum. In my case, I still had some vacuum...just a little low.

In any case, easy job. Taking the power steering pump off and laying it to the side certainly made accessing the bolts holding the pump on...a LOT easier! Well worth the 5 minutes it took to unbolt the PS pump!

Haven't reinstalled the pump yet....that's today's project. But before I do that, I need to spend a couple hours in there doing some major grease/oil cleaning in that front area. (I really want to pinpoint where all the oil is coming from in the first place and fix it!)