95 e300d, belt, tensioner, and water pump questions
 

Today I removed my old & probably original tensioner assembly. ( less than 70,000 miles, 2nd owner ) I thought it needed replacing since it was bouncing quite a bit. I cleaned the old parts to check for wear. Big bolt shows no real wear, just a slight polish where the pivot bushings rub. Bolt is fairly tight when inserted into pivot hole.

New shock and old shock appear to be equivalent. Old shock top and bottom bushings are tight and shock compresses with about the same difficulty as the new shock. Both shocks elongate with a lot less force than required to compress them.

Old belt pulley shows to be tight and smooth.

From reading about the 'one way pulley' action I saw a few comments that the other belt driven components - power steering pump, ac compressor, water pump could cause some belt noise/problems and tensioner problems. The water pump turns but is not smooth through a revolution. Just doesn't feel right.

(1st ?) Does the water pump vanes cause any resistance if turned by hand?
(2nd ?) If vanes don't cause resistance, shouldn't turning a revolution be fairly smooth?

I had no noise or leaks in the past few thousand miles. Just the bouncing tensioner assembly.

(3rd ?) It seems the pivot assembly is built fairly well, has anyone ever drilled & tapped a small hole to insert a 1/8" grease zert?

Seems to be easy to do and should reduce wear of the pivot bushings and big bolt.

(4th ? ) Do Gates belts and hoses have a date stamp or code to show how old they might be?

(5th ? ) How often should belts and hoses be replaced? All mine look newish but I guess that can be deceiving.

1: The water pump should have some very slight resistance caused by the shaft seal.
2: The revolution of the water pump should be smooth. If it feels rough or "cogging" the bearings are on their way out.
3: Grease isn't the problem, water ingress due to missing caps and heat/age kill the bearing. Everything has a finite life, they seem to last around 100K.
4: Age isn't as important as condition. Hardened rubber or micro-cracking indicate replacement time.
5: When they need it. Seriously. If the hoses aren't swollen, hardened, cracked, or excessively soft, leave them be. Belt replacement is when it starts showing longitudinal lines (indicating it is worn down), or begins having cracks in the ribs.

The life of the parts in question will depend on how the car is driven, whether it is garage-kept or parked outside, the climate it is driven in, how well it is maintained, etc. Hoses can last for decades if they were quality to begin with and the cooling system is maintained.

Bouncing is not the criteria, excessive noise and tension device pulley out of alignment are the criteria for servicing the "system".

I am going to try the clutched alternator pulley from INA on my '87 wagon to see if that reduces the bouncing. The pulley was installed on the OM606 engines in the 210 series, so it is backward compatible to your car if you are interested. Looks like Peach Parts sells the pulley for about $30, but you also need special tools to install or pay a shop to install it for you.

Purchased a non MB part which came with grease nipple, seems okay quality wise but then again not much tot go wrong.

Tried to post a pic but photo wottsit images look to to be encrypted, google OM606 belt tensioner, image is viewable.

I recently installed the clutched INA pulley on my SDL, and even with the stock 70A alternator it makes a difference. Perhaps the most noticeable is the lack of the belt making a "wooooooooo" noise when the A/C is running. A certain website named after a South-American rainforest has the tool for ~$20-25. Most of the tools come with a T50 Torx or 10mm XZN bit. Be aware that the really old alternators have an 8mm Allen shaft instead of the above mentioned Torx or XZN.

Found a reasonably priced tensioner pivot arm supposedly INA
 

Mercedes wanted about $150 for their pivot arm.

This one INA W0133-2040882 Belt Tensioner Adjuster about $80 with shipping.
is available from a couple of suppliers. For now I trust this manufacturer.

Hopefully it is not a Chinese knockoff. Good quality and available parts are becoming extinct.

A few pics of new INA tensioner arm
 

Ordered the INA belt tensioner pivot adjuster INA W0133-2040882 yesterday. Received it about an hour ago. Unreal how fast delivery can be.

It actually looks a smidgen stronger than the original. Looks like a legit part. Marked made in Germany and comes in what looks like a valid INA box.

Now to figure out a good choice for grease.

A couple of pictures shows new next to old original.