300E Premature Belt Wear... - PeachParts Mercedes-Benz Forum

JohnM. · #1 12-30-2010, 02:00 AM

A couple months ago I upgraded to a larger S-class alternator (120A), new belt, new belt tensioner, ALSO replaced cracked plastic idler pulley (on bearing bracket). The belt has already developed some small stress cracks on the TOP side of the belt, very odd. They are only in a few places and 2-3" long. No pulleys are bent. Belt does not seem too tight or too loose. The only thing that changed was the alternator, and idler pulley. I have a feeling the idler pulley may be the wrong one, only because I didn't get it from my usual parts dealer. When looking at the belt with the engine off, the belt "bulges" slightly on the idler pulley; as if its too large in diameter by a bit? It seems to be pretty slow wear, its been 3000 miles / 3 months. But I would like to take care of this. What causes the TOP of the belt to crack?

samiam44 · #2 12-30-2010, 09:03 AM

How did it compare to the one you took off?

JohnM. · #3 12-30-2010, 07:20 PM

Quote:

Originally Posted by samiam44

How did it compare to the one you took off?

The old belt was worn in a completely different way because of a bent power steering pulley. But the "cuts/cracks" on the top of the belt have NEVER been there before. After I replaced the PS pulley the other type of belt wear is gone. Now just the cracks on top of the belt after a few hundred miles?

pawoSD · #4 12-30-2010, 07:56 PM

What kind of belt? Cheapo China Belts, LTd? Or a good Conti-Tech belt?

JohnM. · #5 12-30-2010, 08:05 PM

Its a Conti.....

pawoSD · #6 12-30-2010, 09:58 PM

After driving around for 8-10 miles at decent speeds, stop and check the belt. Is it super hot or smelling like burning rubber? Heat could cause excessive drying out of the belt/cracking.....

#7 12-30-2010, 10:11 PM

Have you checked the underside of the belt well? Is there not any cracking or splines cut or missing?

JohnM. · #8 12-30-2010, 11:42 PM

Quote:

Originally Posted by Rebe

Have you checked the underside of the belt well? Is there not any cracking or splines cut or missing?

No funny wear on the underside. Just small portions that have a cut/slice/crack on the top side. It's almost as if someone took a razor blade to the top of my belt in a few places.

Quote:

Originally Posted by pawoSD

After driving around for 8-10 miles at decent speeds, stop and check the belt. Is it super hot or smelling like burning rubber? Heat could cause excessive drying out of the belt/cracking.....

Even after long highway drives, the belt does not seem excessively warm/hot. There's only an occasional crack and always on the same line, not multiple cracks on different lines....

Ferdman · #9 12-31-2010, 08:07 AM

John, how are you tensioning the belt? Are you observing the indicator on the belt tensioner before and after tensioning? It would seem that the belt is too tight causing it to fail prematurely. A Conti-Tech accessory drive belt should last for many years and tens of thousands of miles.

#10 12-31-2010, 09:46 AM

This is just a suggestion, but have you tried turning the engine over by hand. It might point to a spot that is tight or you might hear some kind of unusual sound in a certain location. The old rule was in checking belt tension pushing down with thumb should have approximately a half-inch of slack. It is not exacting as getting a tensioner from a parts house to verify the exact measurement. Lastly, it is possible you have a defective belt there, even though it is a high quality brand of belt??

JohnM. · #11 03-06-2011, 05:58 PM

Replaced the belt today and saw 2 potential problems causing the excessive tightness and premature wear. First, belt tensioner indicator was mis-indexed by 25%, showing partial tension, when the belt was fully slackened. Second, when I replaced the tensioner I had forgotten how the shock absorber system worked. The shock can rotate the tensioner assembly and moves the roller pulley up or down to effectively de-tension/tension the belt when abrupt RPM changes occur, downshifts/upshifts occuring at the wrong time. I had transferred over the shock absorber fully extended. I wondered why I had to 'lever' old the belt into place before I even started to tension the belt. So I compressed the shock which gave me plenty of slack to install the new belt without prying it on, and then with the indicator properly indexed the belt *seems* to be much happier.

#12 03-06-2011, 07:59 PM

I wanted to check if you installed the new poly v belt? It's has the re-designed ribs & it's supposed to be more supple. The cracking and abrading like the past ones in not supposed to occur as likely.

JohnM. · #13 03-06-2011, 08:16 PM

The new belt was a Continental 6PK2415 which is what I've always put on the car. It didn't look any different than the one I replaced, but I did purchase from a different supplier than before to make sure the problem wasn't due a bad batch of belts. I've never had issues, or heard of premature cracking until the last belt change.

JohnM. · #14 12-02-2012, 09:06 PM

Replaced the belt AGAIN a few thousand miles ago and finally its not wearing itself out anymore, nothing else has changed in the belt system.

I'm chalking it up to poor quality or counterfeit Contitech belts. I did notice the material and pattern on this latest belt is a bit different than the previous ones....