Author Topic: hard downshift  (Read 7764 times)

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hard downshift
« on: April 18, 2003, 21:02:30 »
I just purchased my 1969 280sl and sometimes on downshift   (especially coming to a stop,it makes a clunking sound.I don't know if I described it right. I quess it downshifts hard any ideas?
thanks

michael bence

Tom

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Re: hard downshift
« Reply #1 on: April 18, 2003, 21:50:25 »
Michael,

This has been discussed a lot on the yahoo site and this reference gives a good summary:

http://autos.groups.yahoo.com/group/W113/message/3952

The idle throttle switch actuates a pressure switch on the transmission.  Adjusting the idle throttle switch may just solve the problem.  Hope this helps.

Best,

Tom
1971 280sl Tunis Beige Metallic

ja17

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Re: hard downshift
« Reply #2 on: April 18, 2003, 22:35:28 »
Hello Michael and Tom,
Bellow is the information Tom refferred to. I edited the original version in a later post. There was a correction concerning the power at the venturi switch. Below is the later post "corrected copy".


If your car has a rough final downshift or no kickdown passing gear you
should check the operation of the three position electrical solenoid on the
transmission;

Please be aware that putting things right may cause running or idle problems
if  previously unaware technicians have made adjustments to compensate for
incorrect settings. So if you correct some linkage settings this may cause
the idle or other linkages to  need adjustment. Read through this before you
get everything out of sink. I'll be glad to help with specifics if needed,
just email me.

The double-acting solenoid responds to electrical input from the accelerator
pedal (both lifting and kickdown) and transmits this information to the
modulator and effects up and downshifting. If you need to check it's
operation, open the hood and find the intake throttle valve (venturi unit).
Make sure the linkage lever is shut tight against the stop screw. You may
have to move the vacume dashpot out of the way depending on year and version
and you may also find it neccessary to pop the linkage loose temporarily.
Now you  can check its basic operation  by turning the ignition on with the
engine NOT running, and manually crack open the throttle. If you carefully
listen you will be able to to hear the  double-acting solenoid switch
activate as soon as the throttle begins to open. If you cannot detect any
reaction find the bakelite switch with two wires attached (on the other side
of the venturi unit). With an electrical tester, make sure you have power at
the switch. With the ignition  on and the shifter in "D"  and the throttle
closed you should have
power at both  terminals . Now if you  slightly open the throttle you
should have power only at one terminal. If
you do not have any power at all to the switch your problem is electrical,
(check the fuses). If you have power only at one terminal at idle follow
these
instructions; The first thing to check is the butterfly valve or venturi
throttle valve on the intake. The 10mm  and stop screw is often mistakenly
used for an idle adjustment. This stop is factory set and normally should
not be tampered with. It can be easily re-set.  Lossen the 10mm nut and back
of the slotted stop screw until the throttle valve just sticks when
activated. Now set the stop screw just enough to keep the throttle valve
from sticking, then tighten down the lock nut. Before re-connecting the
linkage, and dashpot, check the electrical switch attached to the opposite
side of the venturi again. Ignition on, car not running,  transmission in
drive, linkage against stop,
the power should be at both terminals, activate throttle slightly and only
one
terminal will have power. The switch is attached by two 5mm allen screws
and fine adjustments can be made by lossening these screw and twisting the
swich itself. Once you get this far I suggest you hook things back up and go
for a test drive before going onto the next stage. Make sure the linkage
allows the lever arm at the venturi valve to be tight against the stop screw
when the car is RUNNING at idle or all is in vain!

If your problem has not improved after test driving, then the problem may be
at the double acting solenoid, which rests on the very top front of the
transmission. These unit and it's linkage often will rust or get stuck from
inactivity. Lift the interior tunnel carpet and remove the phillips screws
holding the access cover on the tunnel (passenger side foot area). You can
view the operation of the unit through this opening.  With ignition on and
engine at idle running, the solenoid linkage should be toward the rear, with
the throttle cracked open, the solenoid linkage should be centralized. If
you depressed the accelerator pedal to kickdown (full throttle) the switch
linkage should be forward, thus engaging passing gear.  If  it is stuck
manually exersize and lubricate to get it working. Notice that the linkage
has a turnbuckle and is adjustable. I suggest you do NOT tamper with this as
slight adjustment cause radical changes. (best left as last resort or the
experienced). Note: the solenoid is a little stronger with the engine
running since voltage is higher in the electrical system with the engine
running. Getting this working will cause major improvements in the shifting
and drivability of the car. If everything seems to be functioning correctly
avoid tampering. If your unsure and everything seems to function and your
still not happy with the shifting,  try to get a ride in a few other 113's
with automatics and compare.




Joe Alexander
Blacklick, Ohio
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback