Diesel RVs: Re: [diesel_mercedes] Re: 1980 300SD will not turn over after short/long drive

First, determine whether or not it is or is not starting in first. At a stop, put the shift lever into "L"; this forces the transmission into the first gear. Then accelerate. If it seems to have better pick-up, then it is not starting out in first when in "D".

The fix is probably in the vacuum modulator. It's either malfunctioning, or it needs adjusted. It's located on the right (passenger) side of the transmission, just above the oil pan. It has a vacuum line connected to it. You can check it by connecting a hose to it, sucking on the hose, then putting your tongue over the hose hole. If your tongue stays on the hose without the hose falling off, then the modulator is able to hold a vacuum.

To adjust it, you need to pinch the two ends of the clip that holds the cover onto the modulator body. The cover is the part that the vacuum hose connects to, and will lift off (possibly with some difficulty) when the clip is pinched. Under the cover is a sort of screw driver that is held in place by slots in the modulator body. Lift the "screwdriver" from the slots, and it can be turned in or out. It would probably need to be turned in. Turn it a half a turn at a time, then reassemble the cover and do a test drive, until the car starts out in first gear.

If that does not fix the problem, then the valve body in the transmission has some sticky spool valves. A fluid and filter change may (or may not) restore it to proper operation.

Mark in Centennial, CO

From: "john public brad_macaboy1234@yahoo.com [diesel_mercedes]" <diesel_mercedes@yahoogroups.com>
To: "diesel mercedes" <diesel_mercedes@yahoogroups.com>
Sent: Saturday, April 30, 2016 7:32:17 PM
Subject: Re: [diesel_mercedes] Re: 1980 300SD will not turn over after short/long drive

If it was starting out in second gear, what is the fix?

It shouldn't be any
slower than the '81. At least, not by much. Is the
turbo spooling up? They can get gummed up if it's not
driven hard enough.
Also, is
your starting out in first gear?. My '79 does, and it
can easily keep up with any other 5-cylinder
SD.
The jumpy temp
guage is likely a spotty connection for the temperature
guage sending unit in the head.
Mark in Centennial,
CO'79 300SD

From:
"sandtaz@yahoo.com [diesel_mercedes]"
<diesel_mercedes@yahoogroups.com>
To: "diesel mercedes"
<diesel_mercedes@yahoogroups.com>
Sent: Friday, April 29, 2016 4:01:37
PM
Subject: [diesel_mercedes] Re:
1980 300SD will not turn over after short/long drive

Thanks to everyone for their comments, suggestions
and advice. Finally got around to replacing the neutral
safety switch (had 40 mph winds here in southern Arizona the
last two days) and drove it to town and back (30 miles) and
everything seems to be working fine. Shut it off two
different times and it started right up. I will take
Nate's advice and replace the solenoid. Nate, we just
love the car and almost everything works, at least most of
the time. Still have to tackle the jumping temp gauge, right
side windows (motors work but do not operate the regulator)
and the super slow acceleration. This car is much slower
than our 81 300SD. Cleaned the banjo bolt to the ALDI valve
but not any better. At least it gives me something to do
with all my spare time. HA HA. Thanks again and you can be
assured that I will have more questions/problems.