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Old 05-26-2004, 05:44 PM
mattdave
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Help vacuum pump upgrade 78sd

I have put a 1978 300sd motor into a 1979 300sd the 1978 uses 3 outlets for vacuum. I want to use the 79 pump with one big outlet. I wish to do this for several reasons one of which is the newer model pump was just rebuilt. The current old style pump is fairly corroded and it just is not a pretty or reliable set up. To do this I have to change the drive mechanism that is bolted onto the injection timer. My concern is that when I unbolt the plate from the injection timer, The two halves of the timer will move causing a realignment problem that will affect ip timing. The plate I have to change bolts across both halves of the injection timer the two halves are hooked to some springs that change the timing the faster it spins. Can I unbolt this plate and put new style plate on with out halving to be locked or realign some how I don’t have a manual that covers this
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Thanks Dave S

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Old 05-27-2004, 10:12 AM
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Join Date: Jan 2000
Location: PA
Posts: 5,440
Matt,

Do you mean by the "injection timer" the timing advance mechanism located behind the vacuum pump?

I have R&R vacuum pumps and it never affected the IP timing. The vacuum pump is run from cam lobes that protrude from a sprocket that is turned by the timing chain. Inside this sprocket are the weights and springs that advance the IP timing with increasing engine speed. But they are not affected by removal of the vacuum pump, al least not in my experience.

P E H
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Old 05-27-2004, 09:03 PM
mattdave
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Yes I do and it worked

Yes the injection timing advance behind the vacuum pump. What I have learned taking out the plate that drives the vacuum pump has no effect on the injection timer. But if you are putting a 1978 300sd into a newer car and want to use the newer type vacuum pump. You can only use the driver that goes on the injection timer from a 1979 300sd. It is the part that turns the vacuum pump. The driver part that bolts onto the injection timer after 1979 does not have alignment holes drilled in it to mate with the injection timer. So if you wanted to use the plate from a 1980 and on you would have to drill 2 holes for the alignment pins that are built into the injection timer. I hope this helps someone some day changing motors from a 1979 300sd into a newer car this was the only problem we encountered. You could use the 1979 pump I think If you plugged the 2 extra outputs but I am not sure it did not work for us but are pump sure looked like it was as worn out as it could be.
Dave S San Jose

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