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  #1  
Old 11-14-2003, 12:29 AM
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Does a vacuum pump pull like a hoover?

I think my vacuum pump suddenly went bad, the effect was loss of power assist on the brakes, and inablity to shut off the car by taking out the key.

My first lesson learned, is everyone with one of these cars should practice the drill of turning off the engine without the key. Once you do it, it is obvious, and triviously easy. Next to the valve cover, as looked at from the driver side, is a lever with the word "stop" on it in Red background. Press it down, the engine turns off.


I was like an idiot trying to turn the diesel off by disconnecting the battery. The guys were all saying, that's weird, you disconnect the battery and the motor kept running. Even though its diesel, and I should have known better, seeing is another story. Then I disconnected the fuel line at the clear filter and waited till the engine ran out of gas. After I learned from another thread, how to turn of the engine, I thought my return appreciation to the list is preach that everyone practice turning off the motor without the key. Try the manual shut off lever the next time you open the hood, or check the oil, you'll be glad you know how, if someday you need it.

What type of vacuum pull should the vacuum pump have? Does a working vacuum pump have power like a "shop vac", like an Orick, Hoover, etc, or is is low level and just be dimpling one's finger when pressed to the line between the vacuum pump and the brake booster?

My vaccum pump is just creating the finger dimpling level of vacuum, and I just cannot imagine that that feeble level of vacuum could make a difference in providing braking assist.


Just in case anyone reading this does not know how to locate the vacuum pump, ( I didn't until I had this problem) it is located at the front of the engine, driver side right near the air conditioning pump and the power steering equipment. The pump is not driven by an exterior belt, rather it is fairly integral appendage to the engine. The pump can also be located by following the path of a single thick metal hose encased with a black plastic cover that runs to the brake booster.

Last edited by Judge; 11-16-2003 at 02:23 AM.
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  #2  
Old 11-14-2003, 07:41 AM
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Well you'll need a vacuum gauge to measure it, I don't recall the exact value off hand but it should be at least 17"hg, perhaps upto ~24"hg. Any oil in the vacuum lines? That is a sign of a failing pump.
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  #3  
Old 11-14-2003, 10:24 AM
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Yes, but as an approximation, should the vacuum pump be making a woosh sound like a hoover vacuum to clean the floor and obviously sucking lots of air, "don't get your tie close to it or it will be sucked in type of power", or is it a mild.

Or what does pulling 23 hg mean in a descriptive sense.

There wasn't oil in the main vacuum line.
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Old 11-14-2003, 10:34 AM
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Whoosh is from a volume, this isn't a high volume pump it is just high vacuum, I'm not sure if it'd whisle but the sound effect route isn't real promising for a means of testing. ~30.3"hg means there is NO air left, equivalent if you were in outer space, 0" hg is atmospheric pressure at sea level.
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  #5  
Old 11-14-2003, 12:00 PM
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It will not move a lot of air, but will a pretty good vacuum. You need a gauge to measure it.

Soapbox time (again)
Everyone who owns a W123 should have, at bare minimum, a MityVac. Please, PLEASE, PLEASE go out and get one before you do anything else to this car. Mine was $26 at Autozone.
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  #6  
Old 11-14-2003, 12:25 PM
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Mine pulls 10" and the brakes, doors, and shut-off all work just fine. I will rebuild the pump sooner or later, but it is working well enough that it's not high on my to-do list.
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  #7  
Old 11-18-2003, 11:51 PM
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Vacuum and Brake Booster

My 87 300TDT pulls 57cm (22") of vacuum, enough to 'tug' your finger without hurting. I measured it tonight to track down my brake pedal travel. It goes to the floor, but I still have 'standard' brakes. No fluid loss and the brakes, upt to a week ago, could be pumped two or three times to firm up, only after run some miles. Now no apparent boost. Gonna try a new booster.

192K and going ...
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Old 11-19-2003, 12:24 AM
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I always thought that the booster just helped the driver by making the pedal softer. It seems like if anything you'd need a new master cylinder as that is where all of the valving for pressures are. If the seals are leaking then if you push the pedal down no pressure is created so the pedal doesn't firm up and the calipers don't make the pads grab. Did you bleed the lines already?
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Old 11-19-2003, 09:28 PM
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Ok, that makes sense then.
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  #10  
Old 12-02-2003, 10:39 PM
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Bleeding the brakes is practically nothing, the job itself doesn't seem like it'd be very bad but myself I wouldn't fret at all over the bleeding. If you can't get a helper to push the pedal down while opening the bleeder or don't care to buy a mityvac, I've just left the bleeder open and let it dribble out the fluid until I was happy enough.
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  #11  
Old 12-02-2003, 10:56 PM
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to rebuild or not to rebuild

I had the same problem with my Vacum pump and since my car is a beater and I do not want to put any money into the car that I do not have to( I know it is destined for the boneyard soon) I try and disassemble and fix whatever prior to buying a new unit. I did this with the vacum pump and cleaned out the one way valves, there are 2 of them and the pump works fine now. If you are going to remove the pump anyway take it apart and clean the valve and reinstall. You maybe as surprised as I was. Saved the cost of the pump. Will have to see if the valves last another 300k miles.
John
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  #12  
Old 12-02-2003, 11:30 PM
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I still have functional brakes. They just dont' grab until the pedal is mostly to the floorboard. For a month I would have normal brakes until driving the car for awhile, then two or three pumps would be needed to get the power assist to firm the pedal as normal. Now no pumping action will restore the normal pedal, but the brakes continue to stop the car. I have not bled the lines, but I am suspecting the booster. I'm tempted to DIY, but I don't like bleeding brakes manually in the garage. I don't do enough of it to warrant buying a pressure bleeder. The booster is about $200 on the Net -- will see what the job runs at my favorite place in Tyson's Corner Virginia.
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  #13  
Old 12-03-2003, 12:21 AM
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wigia, you don't have a bad booster you have a bad master cylinder, and one of these days it ain't gonna pump up and you are going to hit something or someone.

Either rebuild it or replace it PRONTO!!!!!

Pedal that goes the floor but firms up with a pump or two is almost always a master cylinder leaking -- it will also sometimes drop to the floor slowly under light pressre, but stay up under firm foot pressure. Fix it before you have a wreck!

It works at the bottom of the travel because either only one seal is bad and you have to use up all the spring travel on the piston, or the bore is shot and they only work when you get to the good part at the bottom.

Judge:

Check for a break in the main vac line. Usually it's the plastic part with all the vac lines attached -- if there is a large crack there, or one of the nipples is broken off, all the va leaks off faster than the pump can make it. New line is only available complete (from booster to vac pump), about $35 on FastLane.

Peter
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  #14  
Old 12-03-2003, 04:49 AM
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Wigia,

I agree with PSFRED that's not your vacuum booster. Try a new or rebuilt master cylinder first. They cost less too and are easier to replace.



But get it fixed ASAP !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

P E H
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  #15  
Old 12-04-2003, 10:09 PM
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what are you guys talking about? "hg? is that the same as psi? my mityvac only counts psi and atm. i pull 22psi by the way.

thanks
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