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Old 06-27-2008, 12:18 AM
awsrock's Avatar
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Vacuum issue severity

I have a guy offering me an 87 300D with 134k, for $1500. According to him, it has vacuum issues, hard shifting trans, and won't turn off when the ignition is cut. Otherwise he says it is good. If he doesn't know anything about these cars, I could be in for a deal...maybe

Paint is in rough condition as well : \

I'm going to assume that the trans issue may also be vacuum related, but my question is, is working on the vacuum system something that is easy to do? I know in some of these threads that it sounds like it can be a pain.

Also, if I were to take it in somewhere to have these things repaired, would it be reasonable? I am looking for a $4000 car and can't imagine some vacuum issues costing 2500.

I'll update this after I actually go look at it. Anything to watch for?

Last edited by awsrock; 06-29-2008 at 11:01 PM.
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Old 06-27-2008, 01:14 AM
compress ignite's Avatar
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Could be:
1.Bad Vacuum pump (2-3 hundred)
2.along with a bad vacuum fuel shut off switch ($35)
3.'Hope the tranny issues are also vacuum related

I'm going to guess ('Know what that makes me!) either vacuum leaks or pump
are causing the problems.

YOU need to read GSXR's pre-purchase inspection on his website...


This only applies to the 1987 300D/TD, not all 124's in general. Some
of the items may apply to other 124's, for example the A/C information.


1- The cooling systems are notoriously problematic. If the car hasn't
had a recently replaced radiator and/or fan clutch, watch the temp
gauge closely. It should almost never exceed 100C except in extreme
conditions (blazing heat, A/C on, climbing a mountain.) A new
radiator is ~$350 from Rusty, or you can send yours out for a rebuild
at Reseda Radiator for $125 + shipping. I haven't seen great results
with rebuilds... and since the old radiators don't have metal
reinforced necks, AND the plastic can get brittle, I'd lean towards
a new Behr (not Nissens!) unit if possible. "Normal" operating temps
are between 80C-100C. Don't freak out if the car runs at 90-95C all
the time, that's fine, as long as you can't make it go past 100-105C
under high loads. Mercedes says temps above 110C are excessive, and I
have the TSB to prove it. Damage should not occur until temps pass
~120C but I'd have the heater on 'max' long before that point!

2- Fan clutch: This is probably about worn out after 15 years. If the
fan has metal blades, it's the old style clutch, and may need
replacement. The new style clutch requires a new plastic fan (from
the 606 motors.) Total cost ~$250 for both parts. If the old clutch
has a good bearing, it can be re-filled with silicone fluid. If the
bearing is bad (fan blade moves front to back more than maybe 5mm),
you must replace the clutch. Don't be too quick to condemn the clutch
as not working - it requires hot air to engage it! That means the
radiator cannot have a cold spot in front of the clutch, and cannot be
plugged with bugs & dirt, because if it does, even a NEW clutch won't
engage. To test the clutch (after making sure the radiator is clean &
hot), get the engine to 100C or higher, and kill the engine while
watching the fan. It should stop immediately, or within 1-2
revolutions. If it spins 5-10 times, it was not engaged. Compare this
to how it acts a warm or cool (40-80C) engine. And yes, the fan does
do a lot at freeway speeds, the ram air effect at 70mph IS NOT enough
to cool the engine with a bad fan clutch!!!

3- Electric cooling fan: There is a 3-prong electrical switch at the
water outlet, near the upper radiator hose, on the front of cylinder
head. The 2-prong connector triggers the electric fan on high speed
when the temp exceeds 105C. To test the fan, short the two wires
together (with the engine on), and the fan should run on high. This
switch is almost always bad and should be replaced on principle. The
original switch is usually blue (and rated 105/128C), but I recommend
replacing it with the gray-colored switch (rated 105/120C) from the
W126, which costs half as much (order part number 006-545-61-24,
about $30). To test the low speed fan, find the green or red pressure
switch at the AC receiver/drier (behind the left headlight), and short
the wires together - the fan should turn on low speed. (If you ever
open up the AC system, replace the green switch with a new red one!)

4- Serpentine belt tensioner: The pivot bearing tends to fail and lean
at an angle. Look at the tensioner pulleys near the water pump, if they
don't look perfectly straight, you likely need a tensioner. ~$100 in
parts, not a bad job if you have the tools to R&R the fan clutch
quickly. Also the belt shock tends to have it's bushings fail and it
causes a rattling noise. Press on the shock body with your fingers with
the engine running to see if it quiets down. It will be obvious if it
does. Get a new OE dealer "Genuine Mercedes" shock if it's bad, the
aftermarket ones seem to have shorter life spans - the OE part is
~$60, the aftermarket shock is ~$30.

5- Oil leaks: hopefully you don't have many. Cost and location vary
widely. Depending on the severity you may choose to ignore them. The
oil level senders tend to seep oil through the body. This is ~$50
and simple to replace at oil change time. Also, the tranny cooler
hoses at the front of the engine tend to leak too, just replace them.
The injection pump often leaks oil from all over, you can pull the
pump and re-seal it for about $30 in gaskets, and 4-6 hours labor
(not a fun job but it's nice to have a dry pump!). The turbo also can
leak oil externally, but that's expensive to repair, so try to ignore
that leak if possible. A leaky front crank seal will cost ~$200 to
have a shop fix it (don't try that at home). The 603 engine does not
suffer from the severe oil leak problem at the turbo oil drain, like
the older 617 engine did.

6- A/C system: This can be expensive to fix. The manifold hose (the
main hose assembly) tends to weep oil *through* the barrier, making
the outside of the rubber hose wet and oily. Yes, it's actually
refrigerant oil! This is the big hose near the ABS pump. If it's
oily, you will need to replace it eventually. I just did mine, it's
a massive unpleasant job. The hose is ~$350 new from Rusty or you
can have your old one rebuilt for about $100. Stick with R-12 if the
system hasn't already been converted - please! - and don't ever
convert an R-12 system to R-134a, or any other refrigerant that
requires PAG/POE oils. You'll be sorry in the long run. If the car
has already been converted, well, cross your fingers and hope it was
done properly. If the evaporator is leaking, it's a massive job
(15-20 hours) to replace as the dash must come out - see next
item (#7, below).

7- The center vent vacuum actuator is often broken (ruptured
diaphragm.) Put the A/C on max and see if you get a constant stream
of air out the center vents over 10-15 minutes operation. If it EVER
stops, the actuator is bad. There's a diverter flap (NOT the recirc
flap) that allows air out the center vents, but this flap cycles
during normal operation- hence the intermittent airflow. When the
center vent flap is open, you can look into the center vent itself
with a flashlight and just see the aluminum evaporator down below.
If you can't, the door is shut - because the flap isn't open! To
replace this $20 part, you must R&R the dash - a 5-10 hour job.
NOT fun. I've done this on both of my cars, and my sister's car,
and most early 124's need this done. If you pull the dash, replace
EVER vacuum pod, not just the center vent pod! You will not want
to pull the dash again to replace the next failed one a year later,
believe me. To test all of them, pull the glovebox out, and use a
MityVac to apply vauum to all 7 of the vacuum lines at the manifold.
All should hold 25" vacuum. If not - if they leak down, or don't
hold vacuum at all, that pod is bad. DO NOT bother with the rebuild
kits sold by Performance Analysis... that kit only works properly
on the center vent pod, and on one of the two chambers in the
dual-chamber pods. Just get new ones from Rusty, it's NOT worth
pinching pennies here.

8- See if the ELR (idle speed control) is working. There's a black
trim plug near the fuse box, with the engine idling pull it out,
turn it to a different number (1-7), and push it back in. The idle
speed should change. 1 is slowest, 7 is fastest, 20+ RPM per number.
If it's not working, it could just be a bad connection.

9- The outside temp sensor can be a problem. If it's always WAY
off, you can replace the sender ($40?) but even after I did this,
it always reads way too high in the summer. It's more accurate in
winter. Poor design. If it really bothers you, it's possible to
retrofit the newer type, which "holds" the last temp reading at
low vehicle speeds, to prevent it from climbing when stopped in
summer traffic. If the display is "blacked out" you must replace

it - about $300 for a new one (!), or a good used one will be
$75 from salvage yards.
'84 300SD sold
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Old 06-27-2008, 01:17 AM
compress ignite's Avatar
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10- Check the sunroof, power windows, cruise, locks, seats, etc.
Often it's just a switch (cheap) but the sunroof can cost a fortune
($1-2000) to repair. Don't attempt DIY sunroof repair - it requires
special tools and experience. Most dealers only have one or two techs
in the shop who can properly fix the sunroof. If the cruise doesn't
work, make sure all the brake light bulbs are good; if so, it probaby
needs a new cruise amp (~$175 for a rebuilt unit, $50 for a used one).

11- Performance: The 1987 300D is NOT slow. Check it with a stopwatch
from 0-60. Factory spec is a little under 11 seconds. Faster than
12-13 is probably acceptable if it drives OK otherwise. Much slower
than that and you have a problem. The wagon is one second slower than
the sedan. Could be as simple as a plugged boost line to the ALDA
(free fix), or a bad turbo ($500), or an injection pump ($500-$1000),
or both. An engine with bad compression (shot engine) will likely
have other symptoms like hard starting, lots of smoke, and high oil
consumption. If the car is very sluggish off the line (off idle),
the IP is low on fuel delivery at low RPM. This can be compensated
for by adjusting the ALDA (remove it, add shims OR turn the setscrew,
re-install). If the car launches hard but runs out of breath past
~3000rpm, either the turbo isn't working (stuck wastegate? damaged
impellers?), or there is an exhaust restriction. This assumes all
filters are clean, brakes are not dragging, etc. At high elevations,
say over ~3000ft above sea level, the car may be sluggish off idle...
this is normal and you can't really do much about it. Adjust the
ALDA richer until you don't see a power gain, then turn it back
leaner slightly, that's usually about perfect. If you can feel the
turbo "kick in" at 2000-2500rpm or so, that is another indication
the IP is too lean, and you need to richen the ALDA. There should
not be any "kick", the engine should have strong power off idle,
and build power smoothly to the redine (5000rpm).

12 - Smoke should be minimal. Smoke at hot idle is not a good sign.
Constant smoke all the time is also not good. Smoke only at WOT means
the car might need to be driven hard ("Italian Tuneup") to clean out
the carbon buildup, especially if it has been driven sedately for the
prior months or years. After a few full throttle runs on a GOOD
engine, smoke should be almost non-existent in sunlight. Ignore smoke
at night in headlights, you will always see that, even with a perfect
engine. Black smoke is usually excess fuel, blue is oil, and white can
be coolant (or unburned fuel, in some cases.)

13- Oil consumption should also be low. Mine uses about a pint per
4000-5000 miles, with 250k on the clock and Delvac-1 5W-40 diesel
synthetic. A quart per 4000-5000 isn't bad. When you start using a
quart in 3000, or 2000, or worse... something is NOT right. Always
use xW-40 or xW-50 viscosity oil that is diesel rated (CG/CH/CI/etc).
Mobil-1 5W-40 'Truck & SUV Formula', also known as Delvac-1, is my
favorite. Amsoil and Red Line are excellent as well but a little
more expensive.

14- Trap oxidizer: The cars came from the factory with a catalyst
called a 'trap oxidizer'. It's a huge round metal can above the
turbo, about 10 inches in diameter. This has been replaced under
factory recall with a straight pipe that looks like a shiny
foil-wrapped iron log, about 4 inches in diameter. If the car still
has the trap, go visit your dealer and Mercedes will replace it for
free, and you'll get a whole new exhaust system too! The new exhaust
includes a small oxidative catalyst which will be downstream of the
turbo, about under the passenger seat. You will see a noticeable
increase in power and MPG with the trap removed.

15- Emissions junk: With the trap removed, the Air Recirculation
valve (ARV) on the turbo is not needed. Find the small vacuum line to
the turbo (not the large rubber wasgate line!) and plug it with a BB.
Do the same with the EGR valve. This can increase part-throttle power,
as well as MPG, and also may correct a cruise surging problem. If you
want a cleaner engine compartment, all the solenoids under the air
cleaner can be removed, along with the three vacuum lines that go
across the top of the radiator. Don't forget to plug the unused ports
on the 5-way splitter above the vacuum pump, or replace it with a
3-way splitter. The large black line is a vent to the passenger

16 - Cylinder head: The original heads were flawed. The casting was
too thin in some areas and they will crack under high heat loads.
(The trap oxidizer is thought to exacerbate this issue.) Look behind
the #2 injector for the casting number, in the format 603-016-xx-01.
If "xx" is number 14, the head is original. If it is a number higher
than 14, the head has been replaced. Numbers 17, 20, and 22 are the
new, stronger heads. The early symptom of a cracked head is high
pressure in the cooling system when the engine is cold. In the
morning, with a cold engine, squeeze the upper radiator hose. It
should have low, or zero, pressure - perhaps even slight vacuum. You
can squeeze the hose together easily. If the hose has HIGH pressure,
so much that you can't pinch the sides together with your fingers,
that's bad - it could be an early sign of a cracked head. A soft hose
only means the head is good IF the cooling system can retain pressure.
If there is a leak, a soft hose means nothing. No oil or coolant will
have mixed, you cannot pronounce the head "good" based on clean oil &
coolant. As the condition gets worse, you may start "burning" coolant,
and at that point the car should NOT be driven until it is repaired -
otherwise the block can get damaged from steam/corrosion, and require
a new or used engine (used = $2500+, new = $6000+). If you replace the
head, never install another #14 head, always get a #17 or newer head.
A used #17 (from a 1990-95 3.5L engine) usually costs $800-$1000, plus
another $500 in assorted parts & tools, and 15-25 hours of DIY labor
with the factory shop manual in hand. A new #22 head is $1600-$1800
and does NOT include valves, springs, lifters, or camshaft. Shop labor
will usually be 10-15 hours at $60-$100/hour. A car with the updated
head is, therefore, worth more than one with an original #14 head.
(At least IMO, anyway!)

17- Oil in the coolant (or vice versa) usually means a failed head
gasket, and not *necessarily* a cracked head. But if the head is a
#14, don't be surprised if it's cracked when you take the engine apart.
The plastic coolant tank may be yellow in color from age. If there
are dark, or black, splotches inside... that means it at one point
had oil in the coolant. A new tank should be installed ($50), AFTER
fixing the head or gasket problem. The new tank will be white/clear
and has a silica pack to help control corrosion. Never, ever use
"green" or "orange" coolant. The Mercedes coolant (also sold as
"Zerex G-05") is light yellow in color, almost clear. This is the
ONLY anti-freeze to use!!!

18- Check all the usual wear items - brakes, suspension, yadda
yadda. The rear torque arms are usually shot. They're about $60 for
both and take 2 hours to replace.

19- Rough idle may be engine mounts, they rarely last more than 10
years or 100kmi (usually a lot less). They are about $60/each and
aren't too hard to replace. If the rough idle persists, it is
probably related to the fuel system - dirty injectors, etc - try a
Lubra Moly 'Diesel Purge' treatment first. If that doesn't help
have the injectors pop tested at a diesel shop. If they are fine,
next item could be injection pump delivery valve seals.

20- Don't forget to check CarFax for possibly odometer rollbacks, I
found a nice looking 1987 300D in San Francisco area with "98kmi",
that actually had a broken odometer that was rolled back, the car
really had well over 200kmi on it. The odometers are another item
that fails - make sure it works! They're not hard to remove (and
send out to have fixed), but it makes the actual milage on the car
hard to determine. Good service records can prove the mileage is

'84 300SD sold
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Old 06-27-2008, 01:18 AM
compress ignite's Avatar
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Location: 32(degrees) North by 81(degrees) West
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Some additional comments from Marshall Booth (MBCA Diesel
Technical Advisor), on the subject of 300TD purchase:

The OM60x engines used in the W201/124/'86+ 126s are much quieter then
the older OM61x engine. Part of that IS the engine and part is the
sound encapsulation used in and under the engine compartment (be SURE
the one you buy HAS these panels - some misguided mechanics throw them
away and they are expensive to replace)! The hydraulic valve lifters
CAN make quite a racket if the car has had a steady diet of
conventional oil. Changing to synthetic oil WILL considerably reduce
and eventually may even eliminate all but an occasional clack/clatter
from these "noisemakers" ;-) The '87 300TD is probably my favorite MB

There are LOTS of little things to look at when buying a 13 year old
car. Ones that I would look for are: AC system - it must produce good
cooling (compressor replacement will usually be well over $1000), the
sunroof must work properly in all modes (sunroof repair can be $1000),
The tail gate must open, stay up and close flawlessly and the "pull
in" motor must engage and pull the gate shut without effort once
contact is made, check that the serpentine belt idler pulley (right
below the horizontal expanse of fan belt at the front to of the
engine) MUST be aligned parallel with the belt - if it's a degree or
two cocked, then it MUST be repaired (the costs could be from
$100-$1000 depending on what is actually worn or broken), the engine
MUST start promptly when dead cold and idle should smooth out within
20-30 seconds! There must be NO evidence of transmission fluid on the
grate at the bottom of the bell housing (where the torque convertor
lives ;-) as that would be evidence of leaking seals (minimum of $500
to fix) and the transmission should shift very smoothly after the 1st
few cold shifts. The power seats should all move effortlessly and all
the windows should work at about the same speed. The cruise control
should be tested! The radio, antenna and cassette player SHOULD work
(though a refurbished radio is available on an exchange basis from
Becker for about $130). Wipers (front and rear) should work smoothly.
Finally, the car should ride and handle about as well as your 300SD -
but just a bit more agile and it should feel more powerful ('cause it

Let me add that the 124 is notorious for having the wires from the "B"
pillar to the rear doors break - seems that the wire was made from
stranded wire with too few strands of wire that was too thick to be
sufficiently flexible. The 201s and 126s made during the same period
did NOT suffer from this failure.
'84 300SD sold
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Old 06-27-2008, 02:14 AM
Cervan's Avatar
Crazy mechanic.
Join Date: Jan 2007
Location: olympia washington
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Man he is detailed, i miss him atleast i got to speak with him on the forum he usually stayed on.
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?

As long as they would add one additional commandment for you to keep thy religion to thyself.
George Carlin (Wonder where he is now..)

1981 240d (engine donor 1983 240d) recently rebuilt engine hurray! - No more.. fought a tree and the tree won.

pearl black 1983 240d 4speed (Converted!@$$%) atleast the tranny was rebuilt.
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Old 06-27-2008, 08:18 AM
awsrock's Avatar
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Location: Tinley Park, IL
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Awesome, thanks!

If there is an indie shop around there I will probably take it in if it turns out to be something I want. However, there may not be one in the area....regardless, these points sure do cover a lot!
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Old 06-29-2008, 10:30 PM
awsrock's Avatar
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Join Date: May 2008
Location: Tinley Park, IL
Posts: 619

Got some pictures, but still have yet to go look at it. The clearcoat looks pretty bad...any ideas on how much a repair might cost? I think this is far beyond buffing it out...
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Old 06-29-2008, 11:48 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,717
How is it for rust and water puddles in the trunk? No sense prettying it up to hide rust and leaks.

My guess is a decent pain job starts at $2500 but you can bring it down by disassembling, prepping and masking it yourself.

I would keep looking if I couldn't live with the way it looks.

87 300D
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Old 06-30-2008, 11:02 PM
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Loose Cannon - No Balls
Join Date: Jan 2006
Location: Northeast Indiana
Posts: 10,767
She does need a re-spray. For the bumpers, go body color like the newer ones.

Gone to the dark side

- Jeff
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