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Old 03-27-2005, 11:49 AM
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Join Date: Mar 2005
Posts: 9
350sdl belt tensioner

I have a 1991 350 sdl ( no rod jokes Please The belt tensioner is making noise, It is cocked at an angle . When you push down on the shock it gets quiet. What parts do I need to Replace?.....
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Old 03-27-2005, 02:49 PM
Posts: n/a
Funny, I just got done an hour ago replacing mine!

To replace it, you will need to remove the radiator then remove the fan and fan clutch then pulley wheel behind it, then lift the spring off the belt tensioner, ( I used a large pair of vise grips and pull like hell upward) un-bolt (center hex bolt) the tensioner, also unbolt the shock absorber from the head and pull it out.

I re-used the roller wheel, and shock, just swapped it over to the new tensioner. You probably should buy those two items new along with the tensioner, they are all separate, I just wanted to save a little money because there was nothing wrong with wheel and shock!

I did also put a new ribbed belt on as well as a new fan clutch.

You can order a new tensioner from just about any supplier, but Fastlane has them too. ...............BB
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Old 03-27-2005, 11:27 PM
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smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,154
If tesnioner is cocked then you need a new tensioner. If the shock quiets when you put pressure on it then the bushings are shot and you need a new shock. After all that, you might as well put on a new belt as well.

To add to what BusyBenz said, put a tire iron or long rod in the ~12cm hole of the pastic pivot that holds the top end of the spring. Remove the nut that takes a 13mm wrench at the end of the bolt that points forward from near the fuel filter. Tip the rod slightly CCW to release tension on the bolt and pull the bolt back so it clears the plastic pivot. Now tip the the rod CW to release tension on the spring so you can unhook it from the pivot. It's an alternative to "pulling like hell" like BusyBenz did

FWIW, I'm able to replace the tensioner in my SDL without pulling the radiator or fan.

Don't wait too long to do this job. Search the archives for DaveM/gsxr's adventures in replacing a timing chain cover after a bad tensioner tore loose. AFAIK, the engine is out of his car and he's still not done.

95 S420
87 300SDL
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Old 03-27-2005, 11:35 PM
Benster Tom
Posts: n/a
While your at it..

While your at it make sure you replace the "belt" and make sure your water pump is fine.....Now I think the Vacuum Pump is okay on this particular model. The vacuum pump on the earlier SDL's were known to be defective. Hatterasguy is very familiar with the Vacuum pump. His alertness made me aware of mine on my 300 SDL and I changed it out quickly.
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Old 03-28-2005, 09:51 AM
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Join Date: Feb 2004
Location: Ontario, Canada
Posts: 453
On my SDL the main tensioner assembly locating bolt had unscrewed itself from the block causing the tensioner to tilt. Be sure to use some 'Loctite' on the threads of both the main bolt and the pulley bolt when reassembling.

By the way, you can undo the Allen Bolt holding the Fan without removing the Radiator if you have patience and don't mind a few scraped knuckles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
1993 BMW 525iT White/Tan
1987 Porsche 924S Black/Linen
1972 Porsche 911 Viper Green/Black
1989 Porsche 944-S2 Red/Linen
Hoping one of my daughters marries a German Mechanic!!
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