Author Topic: vacuum pump replacement: 300sd  (Read 2605 times)

delux68

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vacuum pump replacement: 300sd
« on: 14 July 2006, 04:39 PM »
hi everyone, i finally got a used vacuum pump for my '79 300SD. i took one from a junk yard and have a new gasket but i am unsure of the procedure for replacing one. i thought i would use some gasket sealant and just take the old one off and put the new one on. is that it or do i need to do something else along with that?
thanks in advance

116.025

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Re: vacuum pump replacement: 300sd
« Reply #1 on: 15 July 2006, 10:22 AM »
I don't think you'd really need the gasket sealant, but it may not be a bad idea.  Re-installation will be much easier with the engine at TDC(and, I think, 180 degrees from it), as you will not be fighting the spring pressure, since the piece that drives it will not be trying to push it outward.
Chad Johnson

'77 280SE Euro (4-Spd) Sold 1/5/09
'71 220D (4-spd)
'77 280SEL Euro (4-Spd) RIP
'89 420SEL
'78 350SE Euro
'86 300E 5-Spd RIP by Chevy S10
'83 380SL
"Don't Worry, Bobby, even a worn out Mercedes is better than a 2010 cracker-jack box

delux68

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Re: vacuum pump replacement: 300sd
« Reply #2 on: 17 July 2006, 09:03 AM »
ok, how do you get it to top dead center? i had no idea i needed to do that.

116.025

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Re: vacuum pump replacement: 300sd
« Reply #3 on: 17 July 2006, 10:41 AM »
ok, how do you get it to top dead center? i had no idea i needed to do that.

Well, you don't absolutely have to...I've done one with the engine at TDC and one without...

Back to your question, there's a bolt with a twenty-odd (at least, I'm pretty sure it's under 30mm) millimeter head on it that keeps the crank pulley on.  Put a socket on that with a large ratchet/breaker bar on that bolt and spin the engine in the normal direction (clockwise I think, but someone else should chime in if I'm wrong, or you can crank the car and see which way it spins).  It seems you have two options for the purpose of this project to tell when you're at TDC(or where you won't be fighting the spring during reinstall).  The more complicated (but precise) would be to take your valve cover off and line up the mark on the camshaft just behind the sprocket with the notch in the cam tower.  I think you could also start removing the vacuum pump and if it starts coming off of the engine as soon as you get all of the bolts loosened, spin the engine until the pump moves freely back to being flush with the block.  I think you might also be able to tell by the marks on the crankshaft pully, someone else will have to chime in to confirm or deny that one.
« Last Edit: 17 July 2006, 10:44 AM by 116.025 »
Chad Johnson

'77 280SE Euro (4-Spd) Sold 1/5/09
'71 220D (4-spd)
'77 280SEL Euro (4-Spd) RIP
'89 420SEL
'78 350SE Euro
'86 300E 5-Spd RIP by Chevy S10
'83 380SL
"Don't Worry, Bobby, even a worn out Mercedes is better than a 2010 cracker-jack box

delux68

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Re: vacuum pump replacement: 300sd
« Reply #4 on: 26 July 2006, 08:07 PM »
what a pain in the booty, the pump from the junk yard came out in about 40 minutes. i worked on mine for at least two hours. i cant get to the bottom bolt and i think the top one is stripped from a previous vacuum pump replacement. any tips for getting stripped allen (hex) bolts out.
i am saving $450 by ding it myself and getting the part used. that is my motivation. and i am still unsure of how to get the engine to TDC.

cipha

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Re: vacuum pump replacement: 300sd
« Reply #5 on: 26 July 2006, 08:29 PM »
Top dead centre (TDC) is the position of a piston in which it is furthest from the crankshaft.

Top dead centre is the datum point from which engine timing measurements are made. For example, ignition system timing is normally specified as degrees before top dead centre (BTDC) although a very few small and fast-burning engines, require a spark just after top dead centre (ATDC).

Top dead centre for cylinder one is often marked on the crankshaft pulley, the flywheel or dynamic balancer or both, with adjacent marks showing the recommended ignition timing settings as decided during engine development. These timing marks can be used to set the ignition timing either statically by hand or dynamically using a timing light.

Knowing this it may help you understand what you are trying to achieve.

Thus turn the engine manually [and of course do not have the ignition switiched on as you try to rotate the engine] until you verify that it is at TDC [or close enough as is OK in this example: you will need more accuracy for other engine work].