I have a nice '93 300E I've driven now for 2 years. It's my wife's car and it runs great (160,000 miles).
My dad and I replaced the belt tensioner, adjustment rod, and shock about a year ago, but I tried to adjust the rod without loosening the center bolt, and I ruined the tensioner, so now I have to do it all over again, because it is squealing terribly, even after I tried to manually tighten it.

A new one is on the way.

My question is this: How do I put the adjustment rod on THE CORRECT WAY? I think we put it on wrong, and that's one reason it messed up.

Also, what is THE CORRECT WAY to install the belt tensioner. I want to do it for the LAST TIME! It's about to drive my wife crazy, and I know it's not good to drive around like that.

Please help!

Maybe I'm just tired and am missing something here, but if you put it on a yr. ago and all was well until you tightened the rod w/o first loosening the 19mm center bolt, then you didn't install anything incorrectly to begin with.....right?

You simply forgot to first loosen the big bolt.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Basically, I need to know how to put the tensioner adjuster on the tensioner.

I just had to do this, so I'll try to replay if memory serves.
I probably did more than I needed to, but I pulled the fan, fan pulley, tensioner pulley, and power steering pulley. Then I loosened the power steering pump and slid it out of the way. That may not be necessary, you might try getting the tensioner off without moving the power steering pump first and see if that works. You will need to remove the stamped steel bracket that attaches to the front of the tensioner, belt idler, power steering pump, and another part that escapes memory right now. You will also need to remove the big bolt (19mm) that runs through the center of the tensioner.
I've probably done a fair job of making this sound pretty awful, but it really isn't that bad. Once you get the fan out of the way, the rest is pretty easy, just takes a little time.
Make sure you make notes on how the serpentine belt runs around the pulleys before you pull it off. Same with the various bolts that you will pull off.
Once you get the tensioner off you will see pretty easily how the adjuster goes on. Those break all the time, so getting a replacement shouldn't be tough.
You should check the tensioner once you have it off. Put the round part that the adjuster fits onto, the round part with the two flats on it, in a vise and move the tensioner in the direction it would go in when it's installed. If it doesn't spring back to the default position, it's bad and should be replaced.
When reassembling make sure the little plastic pointer is at the furthest mark to the right. The pointer can fall off when you have everything apart, so it's a good idea to get it back to the correct "0" position before going back together.
I think that's most of it.
Oh yeah, you'll need a special tool to remove the fan. Got any friends who are Benz techs? Perhaps you can get one through the tool service on this site.

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Fourings

84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)

Thanks for the insight. I'll try that.

Thanks for the help. Got the job done in 1 1/2 hours. It was cake. No more squealing.
For those of you who do this job, the adjustment rod (that slips on the back of the tensioner) has a little "c" clip that fastens the rod with the bracket connected to it. Make sure that clip is facing you, not the engine, when you put it on the back of the tensioner. If you put it on the other way, when you tighten the rod, it will bend it and make it useless.

Thanks to all the good info here, I just replaced my belt tensioner in my 1990 300te. Well, almost done.

Can somebody please tell me ASAP the proper setup for the long nut that goes on the end of the adjustment rod?

DOES THE LARGE FLANGE COLLAR AT THE BOTTOM OF THE NUT GO ABOVE THE BRACKET OR BELOW IT?

The old was below the bracket (I think) but I want to get it right before I reassemble the rest of the engine.

Mark

What symptoms did you have before replacing the tensioner?

glenmore
1991 300CE

1990 300te

My 2 hr job has turned into an all day affair. My original intention was just to replace the V-belt. I was following steps from the MB Manual that instructed to turn the main bolt on the tensionor 1/4-1/2 turn before turning the adjustment rod. I inadvertly turned the bolt on the pully and then attempted to turn the adj rod. Of course it stripped it. I was able to get replacement rod from my local dealer (way too expensive). I cleaned up all parts and reassembled onto car.

My original question was in regard to the long nut on the adj rod and whether the flange at the bottom of the nut goes on top or underneath the bracket that holds it. I asked this question because when I took it apart originally, the flange was underneath the bracket. I was hoping someone has done this repair or that someone could look at the tension adjusting nut (located just next to the power steering pump reservoir) and tell me if the flange is above or below the bracket.

Logically, it seems like it should be located above the bracket. So, that's the way I just put it in. All seemed OK. When I turned the nut counterclockwise the dial moves towards the drivers side fender.

I installed the 3 pulleys and now I am unable to get the belt on because the pully for the water pump almost touches the tensioner wheel. Not enough clearance to even get the belt on. I have tried turning the adjusting nut, and although it moves the pointer, the wheel does not seem to want to adjust.

I tested the tensionor in a vise before install and it seemed fine.

What am I missing here? I am now officially at the point of frustration. Each try at a fix means disallembling a bunch of stuff. (My hands are getting sore and the wife is giving me the evil eye).

My understanding of the tensionor is that at rest, out of the car, the pointer should be on the left hand mark. This is the tensioned position in the car. When you turn the tensioning nut counterclockwise, the rod is pulled up into the nut and the tensioner moves into the slackened position.

Off to in-law's for Father's day now. I won't be back till Sunday night but I will check messages from there if anybody has suggestions or questions. Then Monday morning, it's back to the greasy hands to get this thing running again.

Happy Father's day to all you dads out there.

Mark

The flange on the nut you are referring to goes under the bracket. The idea is that it pushes the tensioner pulley into position after the belt is installed. If I remember correctly you should have no tension on the adjuster when installing the belt. Once the belt is in place, turn the nut clockwise, which will "unscrew" it off the threaded rod because it's left hand thread, and that will push the tensioner wheel into position and tighten up the belt. Watch the pointer on the tensioner to determine when to stop turning the nut. Then make sure you tighten down the 19mm bolt that runs through the center of the tensioner.

__________________
Fourings

84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)

I didn't have any problems with the tensioner. The car was running hot and I was replacing the fan clutch. I wanted to loosen the belt so I could turn the fan pulley to the correct position to use the special tool to remove the fan. That's when I broke the tensioner adjuster. I have a friend who is a Benz tech who told me how to check the tensioner, since I had it off anyway.

__________________
Fourings

84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)

Fourings,

Ahhh, pushes. So I had it backward.
What should be the start position of the pointer?
I can't tell from the manual.
Should it be at the very end (right) of the adjustment range and then move to the left as you unscrew the nut?

Mark

Yes, the pointer should be at the far right (minimum tension) before you put the belt on, then (with the center bolt that runs through the tensioner still loose) put your belt on. Still with the center bolt loose, tighten the tensioner adjustment rod to where the pointer is at about 1/2 or 3/4 of the way to the left (maximum tension). After that's done, THEN tighten the center BOLT - This is always the last step! If the belt is too tight or not tight enough, remember to loosen the center bolt, then adjust the tensioner adjustment rod accordingly.
Hope this helps!

Guys - can't believe I spotted this - I just spent 3 nights doing thing.

Started of with e Timing Chain tensioner replacement - came out fine, but couldn't push against the new one enough to engage the threads without moving the air pump, so off came the belt...

Everything back together, I then tried to tension it. I didn't realize that the tensioner itself was worn out, and no amount of rod tightening would make it stop squealing, to the point of bending the rod. OK, apart again...

Still not realizing the tensioner was bad, I put a new rod in, and again, I bent it trying to overtighten it. Then the light went on and I went and got a second new rod and a tensioner. (also the top idler pulley...)

Third time being the charm, all is now well, other than the fact the the A/C compressor and Air Pump are a little noisy...but at 220K, we are talking band-aids here.

M. Gregorio
91 300E 2.6 220K
02 Explorer V8 130K
98 Jetta VR6 (Son's car...jury still out on whether this was a mistake...not the car, the driver's right foot......)
83 Fiat (Pinin.) Spider 46K

The part I need to understand about the tensioner and it's locking bolt is how to get a visual on it. Are you guys approaching the tensioner from above or below? I can't see much of anything as there is so much in that area around the power steering reservoir. Where is that 19mm bolt anyways and from what direction are you getting a wrench on it? Thanks.

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1987 300E
1967 Jaguar E-type Series I, 2+2