w116 300sd Belt tension
- Thread starter Gito
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Mostly self adjustable nowadays.
There use to be a special tool for measuring the belt tension. It consisted of a small metal piece about 4 inches long with a yellow plastic piece in the center. You pressed it against the belt on a open span and it would read how tight the belt was. I think NAPA use to sell them. They were cheap and they worked.
JHZR2
Staff member
In order to properly adjust the tension on V-belts (the style most c ommonly found on 123s and 126s and other models), MB (as well as Volvo, Porsche et al.) recommend by name the "krikit" belt tensioning device. It is made exclusively by the Gates Rubber Company in Denver, the same Gates that make hoses and belts. To get one, call your local Gates retailer (NAPA etc.) and order tool # "91107", cost-about $18.
Start with the power steering pump and get a 13mm socket, and a 3" extension, also have a 13mm box end (a wratchet wrench preferably). Look on the face of the pump, you will see three 13mm bolts facing front. Hold them with the box end, and get the socket on the back side of each bolt and loosen. On the machined edge just below the cap for the pump you will see a single nut facing up - that is the tensioner bolt.
For the A/C compressor, you will need a 17 or 19mm, not sure exactly I used a box ratchet wrench and sockets. There are three bolts holding it, they face the back of the engine. On the back side of the compressor, you should also loosen the metal clamp holding the refrigerant lines to the frame of the car. That bolt should be 13mm. Once all four of those are loose, on the front of the compressor is a strap with a nut on the end, and you adjust the nut to gain or reduce slack.
For the alt/wp belts, you will need that 17mm box wrench again, and loosen from the back of the alt three 17mm bolts you find back there. Then on the bracket holding the alt to the block of the car, you will see a funky long nut on a threaded rod sticking out of the top bolt on the alt. You should immediatly soak it in PB Blaster rust penetrant or aero kroil. Let it soak for an hour or so, to help prevent damage - to replace it is like $50. Once you are sure it's free, loosen it, and adjust the belts. Keep in mind that random parts stores don't stock the correct belts... they stock "close" belts... they will slip. go to the dealer or an import parts store and get the correct metric belts! It's a matter of around half a cm!
Start with the power steering pump and get a 13mm socket, and a 3" extension, also have a 13mm box end (a wratchet wrench preferably). Look on the face of the pump, you will see three 13mm bolts facing front. Hold them with the box end, and get the socket on the back side of each bolt and loosen. On the machined edge just below the cap for the pump you will see a single nut facing up - that is the tensioner bolt.
For the A/C compressor, you will need a 17 or 19mm, not sure exactly I used a box ratchet wrench and sockets. There are three bolts holding it, they face the back of the engine. On the back side of the compressor, you should also loosen the metal clamp holding the refrigerant lines to the frame of the car. That bolt should be 13mm. Once all four of those are loose, on the front of the compressor is a strap with a nut on the end, and you adjust the nut to gain or reduce slack.
For the alt/wp belts, you will need that 17mm box wrench again, and loosen from the back of the alt three 17mm bolts you find back there. Then on the bracket holding the alt to the block of the car, you will see a funky long nut on a threaded rod sticking out of the top bolt on the alt. You should immediatly soak it in PB Blaster rust penetrant or aero kroil. Let it soak for an hour or so, to help prevent damage - to replace it is like $50. Once you are sure it's free, loosen it, and adjust the belts. Keep in mind that random parts stores don't stock the correct belts... they stock "close" belts... they will slip. go to the dealer or an import parts store and get the correct metric belts! It's a matter of around half a cm!
I also use a Krikit.
JHZR2, good pictures/diagrams.
Where were you 10 years ago...lol
Wish I had these images when I first replaced the belts 10 years ago on my other 1979 300sd. It took me forever to get the job done.
This 300sd had an AC belt and it took me a while to figure out how to loosen it.
I finally saw 19mm bolts behind the compressor and the vertical adjusting bolt on the side of the compressor. I'm leaving the AC belt out this time, since the compressor is not working
What I have never gotten around is how to properly adjust the tension of the belts.
I have always used the "feel" method which has worked somewhat.
This time around I want to properly adjust the belts using the correct method.
In the past, If the belt slipped when turning the power steering pulley with a wrench, I would adjust and snug it up some more.
I use to turn the engine using the power steering pulley but I finally stopped doing that for fear of damaging the pulley. Not recommended.
I now turn the engine using a breaker bar and a socket carefully positioned on the crank shaft pulley. No need to remove the fan shroud.
And you know that these cars require constant valve adjustments so we are always turning the engine.
Anyways, recently I had been experiencing over heating on hot days but also noticed that my lights were dimming and getting brighter during night driving.
I came to the conclusion that it could be my belts.
So many years had gone by since I last replaced the belts on my w116 that I forgot exactly where to first start...
I purchased this 300sd over the summer.
This car sure keeps me busy but its a keeper.
Good interior with no tears, no cracks on the dash, excellent exterior paint.
Anyways, since the car was over heating, I decided to replace the thermostat.
This was my first time replacing a thermostat on a w116 so I had to read up on it.
These thermostats have an arrow that needs to point up when installing.
Don't ask me why the arrow is supposed to point up, thats the orientation thats indicated on most manuals. Maybe you can chime in on the orientation of the thermostat and why the arrow must point towards the sky.
I see you know these cars pretty good so Im glad that I can turn to you and others on this site for help when needed.
Currently also trying to eliminate steering drifting when going over bumps or uneven surfaces.
I have replaced the steering damper but will also be replacing the front shocks and the tires, which have excess wear on the inside. Maybe I have a tire balancing issue of some sort.
I did not want to purchase new tires because I want to get 15 inch bundt rims so I will be removing my 14 inch bundts and tires off of my other 300sd and transferring them to this 300sd.
I hope that by replacing the shocks and changing the tires, I solve the drifting/shaking issue. The tire rods are tight.
Your instructions are clear.
Again, thanks for the diagrams, they are much more clear than the w116.org manual pictures.
Any advice is greatly appreciated
Where were you 10 years ago...lol
Wish I had these images when I first replaced the belts 10 years ago on my other 1979 300sd. It took me forever to get the job done.
This 300sd had an AC belt and it took me a while to figure out how to loosen it.
I finally saw 19mm bolts behind the compressor and the vertical adjusting bolt on the side of the compressor. I'm leaving the AC belt out this time, since the compressor is not working
What I have never gotten around is how to properly adjust the tension of the belts.
I have always used the "feel" method which has worked somewhat.
This time around I want to properly adjust the belts using the correct method.
In the past, If the belt slipped when turning the power steering pulley with a wrench, I would adjust and snug it up some more.
I use to turn the engine using the power steering pulley but I finally stopped doing that for fear of damaging the pulley. Not recommended.
I now turn the engine using a breaker bar and a socket carefully positioned on the crank shaft pulley. No need to remove the fan shroud.
And you know that these cars require constant valve adjustments so we are always turning the engine.
Anyways, recently I had been experiencing over heating on hot days but also noticed that my lights were dimming and getting brighter during night driving.
I came to the conclusion that it could be my belts.
So many years had gone by since I last replaced the belts on my w116 that I forgot exactly where to first start...
I purchased this 300sd over the summer.
This car sure keeps me busy but its a keeper.
Good interior with no tears, no cracks on the dash, excellent exterior paint.
Anyways, since the car was over heating, I decided to replace the thermostat.
This was my first time replacing a thermostat on a w116 so I had to read up on it.
These thermostats have an arrow that needs to point up when installing.
Don't ask me why the arrow is supposed to point up, thats the orientation thats indicated on most manuals. Maybe you can chime in on the orientation of the thermostat and why the arrow must point towards the sky.
I see you know these cars pretty good so Im glad that I can turn to you and others on this site for help when needed.
Currently also trying to eliminate steering drifting when going over bumps or uneven surfaces.
I have replaced the steering damper but will also be replacing the front shocks and the tires, which have excess wear on the inside. Maybe I have a tire balancing issue of some sort.
I did not want to purchase new tires because I want to get 15 inch bundt rims so I will be removing my 14 inch bundts and tires off of my other 300sd and transferring them to this 300sd.
I hope that by replacing the shocks and changing the tires, I solve the drifting/shaking issue. The tire rods are tight.
Your instructions are clear.
Again, thanks for the diagrams, they are much more clear than the w116.org manual pictures.
Any advice is greatly appreciated
Originally Posted By: Gito
Your instructions are clear.
Again, thanks for the diagrams, they are much more clear than the w116.org manual pictures.
Wait a minute, these are the same diagrams that are in the w116.org manual. For some reason they looked different. I better start paying attention to detail
Your instructions are clear.
Again, thanks for the diagrams, they are much more clear than the w116.org manual pictures.
Wait a minute, these are the same diagrams that are in the w116.org manual. For some reason they looked different. I better start paying attention to detail
Originally Posted By: Astro14
Originally Posted By: Pontual
Mostly self adjustable nowadays.
And that comment applies to a 36 year old Mercedes
No, the comment applies to the question ^these days^.
Originally Posted By: Pontual
Mostly self adjustable nowadays.
And that comment applies to a 36 year old Mercedes
No, the comment applies to the question ^these days^.
Originally Posted By: Pontual
Originally Posted By: Astro14
Originally Posted By: Pontual
Mostly self adjustable nowadays.
And that comment applies to a 36 year old Mercedes
No, the comment applies to the question ^these days^.
Exactly.
The guy asks for advice on his 36 year old Mercedes.
You post something irrelevant about cars these days. Talk about off topic....
Originally Posted By: Astro14
Originally Posted By: Pontual
Mostly self adjustable nowadays.
And that comment applies to a 36 year old Mercedes
No, the comment applies to the question ^these days^.
Exactly.
The guy asks for advice on his 36 year old Mercedes.
You post something irrelevant about cars these days. Talk about off topic....
If you have any content why dont you help him, instead of grabbing my foot?
I had planned on helping him, once I got off my iPad and back on my PC.
But JHZR2s post covered more than I would have been able to provide. My 1981 240D had the same challenges, and John's pictures were perfect.
You clearly don't have content however, that's why I was grabbing your foot.
But JHZR2s post covered more than I would have been able to provide. My 1981 240D had the same challenges, and John's pictures were perfect.
You clearly don't have content however, that's why I was grabbing your foot.
Why not? He can still have an auto-adjustable system installed to avoid such hassle depicted in the photos. That would be a greater contribution to the op, much major than your mini police job.
Originally Posted By: Pontual
Why not? He can still have an auto-adjustable system installed to avoid such hassle depicted in the photos. That would be a greater contribution to the op, much major than your mini police job.
That's not a realistic or helpful suggestion, Pontual. Show me one example of an OM 617 engine with a modern belt system. The pulleys are not in the same plane, so how do you propose he convert it? Ever converted one yourself? Much easier to use a belt tension gauge. Or simply develop a feel for the belts, as I did on the OM 616 in my Mercedes. I ran that car for over 100,000 miles without a single belt problem. They were replaced when needed and properly adjusted.
Why not? He can still have an auto-adjustable system installed to avoid such hassle depicted in the photos. That would be a greater contribution to the op, much major than your mini police job.
That's not a realistic or helpful suggestion, Pontual. Show me one example of an OM 617 engine with a modern belt system. The pulleys are not in the same plane, so how do you propose he convert it? Ever converted one yourself? Much easier to use a belt tension gauge. Or simply develop a feel for the belts, as I did on the OM 616 in my Mercedes. I ran that car for over 100,000 miles without a single belt problem. They were replaced when needed and properly adjusted.
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Maybe isnt easy as you like. Im sure it is easy enoght to tighten the freaking belts in the first place, but you dont have good enough mechanic skills, though. Or are trying to get and exercise admin privileges here, over me with such minor police job? Find another to pick up.
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