603 diesel engine - acc belt tension adj or shock?
 

I have replaced the accessory belt shock annually on my 350 SDL ... it sounds like it is shot again.

Could it be that I should have replaced the accessory belt tension adjuster? It looks like it absorbs part of the vibration load and then allows some of it to go to the shock ... am I on the right track?

If I am, I should replace both at the same time, right?

Indications are a bit different this time ... usually, it just starts a low pitch rattle. This time it sounds more like a "tinging" noise that I have read is typical ... scary sounding (like chain rails coming loose).

It might be the bearing in the tensioner.

Unhook the spring and shock and see if you can move the tensioner smoothly up and down with no sideways movement or wiggle.

I got lucky and got my hands on just the bearing at the dealer, they told me they only sell the whole assembly normally.

The bearing alone is available through FastLane on this site.

The shock has to do with vibration. The tensioner assembly itself, if bad, prevents the belt from being tight enough. It is usually necessary to replace the tensioner but not necessarily the shock.

Good luck,

Thanks for quick responses, guys.

I took a look during cold startup this morning (30F) ... can push down on base of shock (or top of tensioner ... CD ROM calls the tensioner "tensioner adj.) and it stops the vibration - vibration is very high frequency and resulting sound is a "rattle" with "tinging" vice banging.

The tensioner is original ... the car, in 138K miles, has had at least (counting previous owner) 8 shocks installed ... the ones I have removed have been very "loose" - i.e. easily depressed and extended by hand (new ones going in were pretty tight in both directions).

If I go to the trouble of pulling the shock, and, I know the tensioner is the likely cause of the repetitive replacement of the shock (is this true?), would seem reasonable to simply replace the tensioner, too, right? (seems like price for tensioner was in the $60 range and shock was about $25 ...).

What do you guys think?

Thanks, again!

The tensioner should not be cocked or angled, it should be "straight" or parallel to its mounting point. Mine was original at 250,000 miles and while it still worked, it was gritty to turn (got my money out of that bearing!). The labor to keep checking/replacing what isn't the problem may cost more than replacing everything. Its obviously been a problem area on your car.

Brian

Thanks, again ...

Larry - is it your impression I need to replace the tensioner bearing, then? And, that this is at the heart of my repetitive replacement of the shock?

Is there a chance that "this engine just does this?" Trying to think it out ... seems reasonable that the lack of proper belt tension from the tensioner could force the shock to do all the work and at a higher frequency than the shock is designed for?