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  #1  
Old 06-11-2015, 07:33 PM
Hit Man X's Avatar
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Question M103 belt tensioner lifespan

I am thinking mine is dying here as the compressor will slip a bit on higher RPM upshifts, belt has less than 10k on it. Tensioner was replaced Dec '03 at 210k, I am now at 306k.

It is tensioned properly and I have that little plastic pointer on it too. Shifts are not banging or anything like that. They are quick and smooth thanks to that Superior-Transmission kit installed.

Now this is on the 300SEL W126, so with a 3.46:1 rear diff it turns about 3500rpm at 70mph so most accessories wear faster than most vehicles. Pulleys sound found, just thinking about the strength of the tensioner itself.

Thoughts? Opinions? Jeers?
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'85 300SD 244k
'87 300SDL 251k
'90 300SEL 325k
'91 560SEL 189k

Eight others from IH, BMW, GM, Ford, and Volvo.

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  #2  
Old 06-11-2015, 08:20 PM
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100k on a tensioner is ahead of the game. They tend to fail after being loosened and re-tightened more often than outright failure out of the blue.
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90 300TE 4-Matic

Turbo 103 4-Matic, 3 cam advance
11-18 PSI, A2W I/C, 40 LB/HR
MS II Extra, 60-2 Direct Coil Control
3" Exhaust, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Brake Discs, .034 Booster.
3.07 Front and Rear Diff, 1st Gear Start

91 300CE parting

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197 intake cam w/20 advancer
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PCS TCM2000 running 722.6 trans, 600W PWM fan, water injection
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  #3  
Old 06-11-2015, 08:35 PM
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Are my symptoms common to the M103 tensioner failure?
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I'm not a doctor, but I'll have a look.

'85 300SD 244k
'87 300SDL 251k
'90 300SEL 325k
'91 560SEL 189k

Eight others from IH, BMW, GM, Ford, and Volvo.

Liberty will not descend to a people; a people must raise themselves to liberty.
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  #4  
Old 06-12-2015, 11:44 PM
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Location: SoCal
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When mine failed it just made it impossible to tighten. Alternator would squeel like crazy and I just couldnt get any tension after doing the whole procedure with the threaded rod and bolt in the center. For what its worth mine gave up after about 160k.
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  #5  
Old 06-13-2015, 02:04 AM
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If your tensioner is already bad, try doing this: Belt tensioner shock upgrade (w201 and possibly others)
As far as I can tell, this strut like rod adds great tension to the belt. Get a spring that you can wind around the rod like a coil over. It just so happens that I used a spring from an umbrella that was the perfect fit and had the perfect compression: not too soft and firm enough to add proper tension on the belt without being extremely tight.
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  #6  
Old 06-20-2015, 04:29 PM
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Well, I ordered a new one with a new shock last week. Old tensioner was bad, hell, it even allowed the belt to slip on a cold start some. Once the belt was off the tensioner pulley was easy to move with even mild pressure.

In any event, about three hours start to finish including taking the tools out. Belt is significantly tighter now. It was difficult to remove the power steering and water pump pulleys as they spun easily, with the belt on still.

Pretty sure just the shock was keeping tension.



Thanks to all that replied, here and via PM. I may just replace this thing every 50k for PM.
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I'm not a doctor, but I'll have a look.

'85 300SD 244k
'87 300SDL 251k
'90 300SEL 325k
'91 560SEL 189k

Eight others from IH, BMW, GM, Ford, and Volvo.

Liberty will not descend to a people; a people must raise themselves to liberty.
[/IMG]
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  #7  
Old 06-22-2015, 12:10 PM
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Wise decision HitMan. Mine let loose 90 miles east of Wenantchee in the middle of no where! Talk about limping 90 miles on a "wing and a prayer".
Anziani
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  #8  
Old 06-23-2015, 07:37 PM
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Driving updates, so far so good. A/C has not kicked off due to belt slip, even when I forced the trans to upshift hard.

I am a happy camper and would have paid more even.
__________________
I'm not a doctor, but I'll have a look.

'85 300SD 244k
'87 300SDL 251k
'90 300SEL 325k
'91 560SEL 189k

Eight others from IH, BMW, GM, Ford, and Volvo.

Liberty will not descend to a people; a people must raise themselves to liberty.
[/IMG]
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