i recently installed a factory reman bosch alternator,wich has just turned defective is only putting out 12.65 with a load on it,this happened after i replaced a fuel pump and ran the battery dead after realizing the fuel tank was empty,i thought it was just the battery needing a charge but had alt tested,last time i replaced it i was not able to loosen the serp belt,i was able to loosen up the top rod/bolt that goes down to the tensioner,but no matter what socket or fitting i used up top to pivot the bolt and move the tensioner i couldnt get anything to fit,does anyone know what size bolt head it is,or if its a special type head? i had to replace the last alt with the belt still tensioned it took me 3 hours and was a real b if you know what i mean any pointers would be great thanks.marc

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enjoy life,take the coal that is handed to you and turn it into diamonds. { PHILLIPIANS 4:13}

Did you loosen the 19mm bolt that goes through the tensioner before loosening the adjusting rod? The adjusting rod is 13mm.

The tensioner adjusting rod is notorious for stripping out and snapping where it connects to the tensioner, so you will be turning the adjusting rod but its not actually turning the tensioner anymore. The tensioner assembly is also notorious for failing when the rubber core turns inside and it can no longer be re-tensioned. Also the belt adjuster shock can fail and in turn cause damage to the tensioner because the belt system can no longer absorb abrupt shocks like sudden RPM changes and ill-timed shifts.

I've done the tensioner 3 times on my car. The design sucks. And the quality of the replacement tensioners sucks even more.

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1991 300E - 212K and rising fast...

Did you charge the flat battery before installing the recon alternator?
Failure to charge it first can smoke a fresh alternator.....

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I choose to be happy, even when the Mercedes is being awkward, lol

Agree , Re-done it quite a few times on my 300se ,accumulated slipping tensioners which look new , tensioner shock and a tightning rod

When replacing the alternator it's worthwhile to recheck alignment of pulleys as it may be off due to a incorrect pulley spacer on the new unit.

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mark

i had a serpentine belt proffesionally installed about 3,000 miles ago,so i know the system is operating correctly,but i was not able to find the correct size socket for up top,did you mention that it is a 19mm?,the alternator was replaced just after i installed a brand new battery,so the car already had a brand new battery,then i put in the reman alt.im going to have to see if there is a warranty on the unit,then get a replacement,i will try a 19mm socket up top on the tensioner next time to pivot the tensioner,i dont understand how it works,do you have to loosen up the 13mm adjuster that goes down by the shock absorber first,then pivot the top 19mm bolt to move the tensioner to remove the serp belt,and then do you loosen or tighten the 13mm adjuster down below to tighten the belt,if the lower 13mm adjuster tightens and loosens the belt, what is the top 19mm bolt for? its confusing to me.thanks guys.marc

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enjoy life,take the coal that is handed to you and turn it into diamonds. { PHILLIPIANS 4:13}

You are going to possibly break your new tensioner if you do it the wrong way. Follow the factory manual. If it was installed professionally, you shouldn't be needing to tighten it. If the belt feels tight, it probably is.

If the belt is tight, I would return the alternator. You may have just gotten unlucky.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
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2003 Gray Mercedes ML350 - 122k

the 19 mm bolt goes through the front of the tensioner between the pulley, you have to loosen that up first before you louden the tensioning rod. only then can you remove the belt.

reliable source: went through 2 tensioners in 4 months and 1 tensioning rod

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1990 190E 3.0L

Yes. If you do not loosen the 19mm that goes through the middle first, your tensioner is good as toast.

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...