Hey guys,

I am planning to change my Serpentine Belt on my 88 300TE and I just want to confirm if the tensioner rod was reverse thread.

I've heard that the threads on those are rather soft so I thought I'd confirm before I put too much force trying to loosen it.

Thanks in advance!

Yes, they are "reversed" (aka "left hand") thread. They could have done it either way, but left hand gives a more normal "righty tighty-lefty loosey" action on the tensioner. The threads aren't any more or less durable than any other metal/thread combination, but there are a few things that make these susceptible to damage. First there is a central bolt on the tensioner itself, if this is tight, the threaded adjuster rod isn't going anyplace.
Second, when tightening, if the tensioner is worn out, as it often is, when you tighten the rod (turning it clockwise or "right") the small arm the threaded rod attaches to will go alot further than it was designed to and hit some protuberance such as a bolt head, or exceeds the geometrical limit, meaning the rod hits the tensioner itself, and breaks the rod or the tensioner "ear" that the rod attaches to.

Gilly

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Watch the pointer on the tensioner as you loosen it -- if it doesn't move at all, or only goes part way back to the beginning of the little "ramp" mark cast into the tensioner body, replace the tensioner. Otherwise, you will break the rod when you attempt to tighten the dead tensioner you have.

Bad design, although it works beautifully so long as the rubber holds up. The "spring" in the tensioner you "tighten" with the rod is rubber vulcanized between the tensioner parts, and it does a very nice job of keeping the belt tight and dampening vibration, but just like the rubber bushings in the rear suspension links, it dies of old age. Causes rapid belt wear, and broken tensioning rods if you don't notice it.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Great pointer guys, I'll keep a note on your advice!

Thanks