Serpentine Belt Tension
 

Can you get to the 19mm bolt to loosen the tensioner without taking off the fan clutch, etc?

I have a loose belt which probably means a bad tensioner... but I want to tighten the belt once to see if I will be ok.

This is on my son's 1989 300e.

I should have put in a new tensioner when I did the water pump...

you can try, but I'm sure it would be easier to just take the fan blade off. Realistically you are only talking about another 5 minutes tops on either end of the task you are undertaking, esp. if you have a fan shroud that comes in 2 pieces and not just 1.

You can loosen the tensioner bolt without removing the fan. You will just have to remove the clips that hold the fan shroud and move it out of the way.

Tension bolt needed?
 

Well we need a new tensioner. It just won't tighten. Is it necessary to get a new tightening rod bolt as well?

Tensioner is on order

What state is the malfunctioning tensioner in ? If it is in a state that it is loose and wont let the regular size belt on, I may have an easier solution. Get a longer belt. The belt I have used and works great is Dayco Poly Cog, 5060915, 6PK2325. What you do is loosen the top bolt on the alternator, remove the bottom bolt, put the belt on and push the alternator down in place, and finally insert and tighten the bottom bolt, and tighten top bolt too. I could have also used 2320 length but this one is not available, only Bando makes it and only comes stock on one american car. But this one works fine so far on my 87, 260E, and I can tell from the A/C working great.

It would be foolish not to replace the rod and bolt while you are there. You may find that your real problem is that rod bolt is stripped.

There is no need to replace the nut and rod. Unless you break it, they are just fine.

I'm going to be doing my tensioner for the second time in 5 months. I tried to go the cheapy route and buy the tensioner off ebay. The first one I got was DOA but I didn't realize it until a year later when I went to put in the part. A quick check for a good tensioner is that the pulley is in line with the 2 flats of the aluminum bushing. I complained to the seller and he sent me another one at cost, ~$50. Both appeared to be the same correct part number but with the manufacturer insignia ground off. I installed it 5 months ago and it just failed. Hope I have better luck with a unit I got from Autohauz for $100.

glenmore
1991 300CE
1990 LS400
2000 C280

Yikes... i almost always got to Arizona ********.... but I am going the ebay route... this is for my sons car... and i was trying to save him some bucks..

i guess we will have to wait and see.

You are! Unless you charge $100/hr like MBZ!

glenmore

I replaced my 5 month old tensioner with a unit from ********. The rubber bushing was gone and as with the original I replaced before, it started leaking grease. Another cheap part of the equation is the pulley was also throwing a bit of grease. One key difference in putting on the new unit was as you tighten the belt and you watch the marker move up the ramp, the torque required was only modest. With the defective unit, it took a lot of torque to get the belt fully tensioned.

glenmore
1991 300CE
2000 C280
1990 LS400

Lee,

You can inspect the old/new tensioners by clamping them in a vice and deflecting them 30 degrees. Bad ones stay there...

If you look at the flats on the aluminum shaft of the old one, you will find that they are worn, and maybe also those on the steel adjusting bolt plate, but much less so. The problem is one small section on the shaft.

One trick that got me home and lasted quite a while is to reverse the order of the bolt plate and the spacer when you reinstall. (You might need to flip the plate over, but it is symmetrical.) Reversing the installation order will put the plate on an unworn section of the shaft. It will wear again, as that aluminum is a dumb choice of materials for the shaft, but this will give it a second life...

Gerry

Even though my tensioner failed, the car seemed to drive fine, except for the brief belt screech at startup. I'm guessing this is the fail safe function of the tensioner shock that keeps some tension on the belt.

glenmore
1991 300CE
2000 C280
1990 LS400

Tensioner shock
 

Had the car in the dealership for servicing the other week and the rep. told me the tensioner shock was bad. Wasn't replaced at that time as I missed his call during the day and needed the car at 5:00 to get home.
Couple of questions:

Where is this critter?
Is this a do-able replacement for a halfazzed ;)diyer? What's involved? Cost of this part?
I looked for this part here without luck. Could only locate the tensioner itself. Did I miss something?
Thanks for your help.

The repair is straight forward but what can take long is the usual: 1) getting your hands in there, 2) dropping bolts, getting it in the right position to start the screws, etc.


Here's a drawing. It is the thing directly above the tensioner.

http://www.performanceproducts4benz.com/drawings.aspx?bmid=89


At FastLane it is under cooling system and is called a acc. belt tension damper.

glenmore
1991 300CE
2000 C280
1990 LS400