'82 300D loses brake power and won't shut off - PeachParts Mercedes-Benz Forum

cewyattjr · #1 03-08-2007, 04:04 PM

OK, so these two problems happened simultaneously, so I'm assuming a vacuum related issue? The brakes suddenly felt like the 'power assist' went bye-bye. What the heck? Then I turn the key off and get continued running until I hit the big stop switch under the hood.

So I guess my main question for those with more wisdom: Do I have any clues as to the source of the problem given that the brakes are now with no power assist?

Thanks,

Chuck

toomany MBZ · #2 03-08-2007, 04:23 PM

Does sound like vac. Check that big hose between pump and booster. They are brittle. Or could be a connector under hood that has come loose, or broken. Otherwise you'll have to do a Mighty Vac diagnosis. Do your door locks work?

cewyattjr · #3 03-08-2007, 04:30 PM

Thanks for the info!

The door locks don't work, but that preceded this issue. Still could play a role? The car shifts hard much of the time as well. Other than that she's a beaut.

I've been doing some forum reading, and hopefully not the brake booster? I just read those go for over $500.

But I wonder because it was soooo sudden.

It has been really cold here, so that could have possibly aggravated the problem!

-Chuck

holthoff · #4 03-08-2007, 04:45 PM

Try to rule out a cracked or loose vacuum line between the brake booster and the vacuum pump. If it's not that, then your vacuum pump probably needs to be rebuilt.

arcticathlon · #5 03-08-2007, 04:56 PM

its deffinatly vacuum related. i had the exact same issue with my 80 240D. my vacuum pump diaphragm was ruptured and it was not that hard to replace it. i still have a leak in one of my doors, but my car now brakes right, shuts off, but still looses the vacuum 10 mins after i shut off the car.

one easy way to check is to disconnect the door locks, and your cruise control to see if those possibly have a leak.

cewyattjr · #6 03-08-2007, 06:39 PM

I found a thread where WannaWagon describes a very similar "sudden" experience, and it ends up being the vacuum pump, so I'll probably end up replacing it after all is said and done.

What's interesting is that acceleration felt strong if not maybe stronger. Also maybe the hard shifting is less noticeable.

I recently plugged the line that goes to the EGR, hopefully that didn't cause this. Can't imagine it would!

sarthur9 · #7 03-08-2007, 07:00 PM

I had the same problems with my 84 300SD last month and it was the vaccum pump.

You can check my post to see the thread on it, that will give you all the information on how to trouble shoot yours. I puchased my vaccum pump off ebay for less than half that amount brand new. Installation is not that much trouble.

Good luck!

cewyattjr · #8 03-09-2007, 06:12 AM

BTW, does the vacuum system relate to the tachometer as well? That's one of the several non-functioning items on my 300D.

Dang it is nearly zero degrees here this AM in New England, so won't get to trouble shoot this puppy until we get some higher temps, but should be coming this weekend.

Thanks!!

Chuck

tangofox007 · #9 03-09-2007, 08:50 AM

Quote:

Originally Posted by cewyattjr

BTW, does the vacuum system relate to the tachometer as well?

No.

cewyattjr · #10 03-09-2007, 09:39 AM

OK, so I've located the vacuum pump on the front of the engine. Shouldn't be too bad to replace. Do I need to remove the belts to pull it out and install the new one? That would be a bigger pain.

tangofox007 · #11 03-09-2007, 09:45 AM

Quote:

Originally Posted by cewyattjr

Do I need to remove the belts to pull it out and install the new one?

Loosening the power steering pump belt will make the job a lot easier.

I would recommend inspecting the pump inlet check valve first. It's inside the fitting where the hard line attaches to the pump. The check valve can fail and cause a sudden vacuum loss. You can remove the fitting while the pump is still installed.

toomany MBZ · #12 03-09-2007, 07:12 PM

You may be able to check air pump, to see if that is your problem, with a Mighty Vac. I did it once, can't recall exactly what I did. Stay warm.

kerry · #13 03-09-2007, 07:16 PM

I wouldn't plan on replacing the vacuum pump without doing some basic troubleshooting. Hook a vacuum gauge (Mity Vac) to the system and check the vacuum level before proceeding further.

cewyattjr · #14 03-10-2007, 09:54 AM

OK, advice heeded. I'm checking with my MityVac this AM. The "post" check valve vacuum is only 15 mmg on acceleration. I've not yet managed to remove the check valve to check "pre" check valve readings. The check valve is hard to remove? Seems very, very tight!

-Chuck