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- 5/20/00
- Jon,
I have a 1990 Mercedes Benz 300 E with approximately 100,000 mi. on
it. At
its 90,000 mi. mark I had it serviced. Since that time or shortly
thereafter, whenever I start up the car and it is cold, the fan
belt
squeals loudly for a few seconds. Physically checking the tension on the
belt, it feels slack.
I decided to try to adjust the tension. I loosened the tensioner
bolt, and then turned the adjuster nut, but the adjuster nut did not seem to
change the adjuster pointer on the triangle scale. In fact, it looks like
the adjuster nut has come loose or has been stripped from the threaded
rod. It looks to me as if someone tried to adjust the belt tension
without loosening the tensioner bolt and stripped the threads, either on
the rod
or the internal threads of the adjuster nut. It seems that to repair this, I will need to remove the fan shroud,
the fan (probably), the radiator and probably even some pulleys. The
adjuster nut seems to be pressed into the bracket with some sort of spherical
bearing
on the underside. If it is the adjuster nut, does this have to be
purchased
as a whole unit (with bearing and bracket)? And the rod...is it
attached in a way that it can be removed separately or does it have to come
assembled with attachments?
I'm a fairly competent mechanic...is this something you would think I
could
do, or would you advise me to take it to a Mercedes dealer?
Thanks in advance for your help. I really like your web site....many
helpful hints there! :-)
Regards,
Steve N.
- Steve, Sorry about not hearing from me, it seems like I run out of time
and
get nothing done anymore. The problem that your having is a common one.
Most
mechanics don't understand the technique around the belt tensioner and
adjustment rod on the MB. It may not be the mechanics fault because
they can
fail on there own. There are two scenarios, the first is that the
adjustment
rod was moved with the center locking bolt tight. The adjustment rod
should
only be moved after the center bolt is loosened. Failing to do this
rips the
rubber. The second is that the tensioner bolt was left loose. The
tensioner
itself is held tight by the center bolt, usually a 17, or 19 mm bolt
(some
of the late model MB's it is an allen). The belt tensioner shock which
bolts
from the front of the head to the tensioner dampens the vibration (
these
also fail a lot and causer a rattling sound . From the center section
that
is held tight by the bolt comes a layer of rubber, then comes the main
body
of the tensioner. This rubber layer breaks loose and causes the belt to
flop
and lots of noise in general. Some time the car stops charging because
of
the loose belt. You need a new belt tensioner assembly, adjustment rod,
(sold separately) and a new belt tensioner shock. I always change the
shock
when I am in there. Let me know if you want the part #'s. Let me know
when
you get it fixed. If I was unclear let me know. JON
- Jon,
Just an update to my belt tension problem... as you first suggested, it was
a faulty tensioner. What kept leading me astray (after a couple of attempts
to just replace the adjuster rod/nut), was that I could NOT make the
tensioner fail (slip) in a bench vise. In other words, it seemed completely
tight as I couldn't make it appear to rotate when I applied torque by hand)
So I assumed that the tensioner was OK. But after two more rods ruined it
just didn't seem to make sense that I would be left with just a couple of
threads that the nut was engaged with, and still wouldn't tighten the belt.
So I got a new tensioner, shock and adjusting rod/nut and put it all
together and it made it all work like it was suppose to....purring like a
kitten now! :)
Thanks Jon for all your input!
Steve
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