Mmm timely, since I spent all afternoon replacing the rear seat belts
in my w140, so let me cross post this since it explains how Mercedes
manages the locking of the belt.
Last month I got a set of rear seat belts for my W140 sedan, dealer
had a garage sale where I bought a few dozen parts thus getting a
great deal, so today I decided to replace then. There was virtually no
tension in the belts when in comfort mode, so people complained the
seat belt just laid there.
I very carefully broke one clip housing(oh well) when removing the
cover and managed to dropped the spring clip into the speaker
compartment below(sigh), plus the right side belt assembly was a pain
to get out, no idea why, new one just slipped in the housing, and the
left side slipped in and out.
My new seat belts were made in Poland and dated 2005, and 2007. I
guess this speaks to the problem when you can buy a part for a car
last made in 1999 and they've made the replacement last May. Just to
understand things I took one apart. In the top plastic housing there
are two steel clock springs, a large one, and a small one. There is an
electromagnetic plunger that is activated in comfort mode to pull a
cam to engage a ratchet so that the large spring cannot rewind the
belt. Leaving only the small wound steel spring to tension the belt.
Apparently this is the part that fails, the small coiled clock spring
looses it's tension over time, thus no or weak rewinding.
Now in the bottom plastic housing is a complicated piece of plastic
engineering where a large metal ball in a cup assembly allows a
ratchet wheel to move only if the ball is at the bottom of the cup.
Otherwise the weighted pivot lever can't pivot down enough to
disengage the racket. Now if the ball is mostly not in the bottom of
the cup the lever engages a lightweight cam, the cam wheel is
connected to a spring assembly which then rotates and engages an
internal larger sized cam which interfaces to another ratchet which
stops the out movement of the belt. I think the use of the two cams
here is to ensure the force on the heaver cam won't force the ball
assembly closed thus disengaging the cam, thus the reel movement
doesn't directly interface with the lightweight cam assembly.
This seems to imply if your car is on a steep slope, you couldn't pull
the rear belts out. Anyone know if this is true?
Obviously in a rollover the steel ball isn't going to be in the right
place so the belt won't come out, same for a side collision or rear
one because velocity changes are going to keep the ball out of the
bottom of the cup.
In a frontal collision the heavy dual metal cam pivots forward to
latch into the metal ratchet.
PS 35 Nm is the bolt tension, and they also looked like they had red
threadlocker applied? The maintenance DVD doesn't say anything, just
gives the Nm, I used blue threadlocker just in case. I'd doubt it's
red otherwise you couldn't disassemble so must be some factory product.
On Nov 17, 2007, at 12:29 PM, Sunil Hari wrote:
In my new-to-me 1988 Saab 900 turbo, I've somehow managed to lock both
seatbelts (shoulder and lap) in the retracted position.
John
1983 300TDt 384k Kilometers (mobil 1 Delvac)
1990's 300TDt 211k Kilometers (mobil 1 Delvac)
1993 500SEL 200k Kilometers (mobil 1 Delvac)
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