Rattling / 300SD Alternator Tensioner Adjustment? - PeachParts Mercedes-Benz Forum

chetwesley · #1 08-03-2007, 03:44 PM

Can anyone give me good advice on how to properly adjust the belt tension on the alternator on a '83 300SD?

It seems that my inner belt is a little loose, while the outer one is fine. It seems there are two aspects to the tension - the bolt that fits between that little fork (which does very little as far as I can tell), and then the sliding adjustment in the mounting bracket, which seems to be adjusted by the bolt in the bracket.

The reason I ask is that I am getting a loud rattling from the area of the alternator which comes and goes. Visually, I can not see anything causing the noise, but the inner belt does seem loose as I mentioned, so I am wondering if the alternator being a little cockeyed is causing the fan on the alternator to rub on something. The noise sounds similar to when I once had a loose alternator pulley and fan and the fan was bouncing around on the shaft.

Any other ideas of what the noise could be? Loud tinny rattling from the area where the alternator is.

Thanks as always.

#2 08-03-2007, 04:01 PM

if you have a loose belt you may need to replace both as a matched set. most likely the rattle is the adjustment bolt...i have never seen one that was not broken where the bolt is welded to the ajustment threads. when i replaced my alt i had found that the spacer behind the upper bolt was missing, a local boneyard had the proper spacer and without it the alt was cocked to one side.

Uncle Possum · #3 08-03-2007, 09:13 PM

I am getting ready to change out my alternator on 82 300SD. Does anyone have a picture or a drawing of how this is supposed to go together?

Quote:

Originally Posted by Diesel Head

if you have a loose belt you may need to replace both as a matched set. most likely the rattle is the adjustment bolt...i have never seen one that was not broken where the bolt is welded to the ajustment threads. when i replaced my alt i had found that the spacer behind the upper bolt was missing, a local boneyard had the proper spacer and without it the alt was cocked to one side.

chetwesley · #4 08-04-2007, 12:47 AM

If it is still in there, just look at it -- it isn't that complicated. There is the alternator itself and then it is on a tension bracket. There is one bolt that goes through the tension bracket and the alternator, one bolt that mounts straight from the alternator onto an actual mounting bracket to the engine, and another that I believe mounts the tension bracket to the mounting bracket. The bracket that mounts to the engine can stay put, and just the alternator and tension bracket come out.

When I originally took my alternator off, I took it out of the tension bracket which I left attached under the hood. However, I discovered that when putting it back on, you really need to put the tension bracket on the alternator before you put the whole thing back on the car because there is a big spacer which is pretty much impossible to put in the right place given the space to work in the engine compartment.

By the way, I figured out what was making the noise. It was actually one of the little bolts that hold the alternator itself together. The nut to one of those bolts fell off the back of the alternator and the bolt was just rattling around in there. That is strike two against NAPA. I am never buying anything from them again.

#5 08-04-2007, 01:10 AM

Quote:

Originally Posted by Uncle Possum

I am getting ready to change out my alternator on 82 300SD. Does anyone have a picture or a drawing of how this is supposed to go together?

This is a copy of the photo from the manual (crappy quality photo).

toomany MBZ · #6 08-04-2007, 06:57 AM

See if you can recognize anything in this pic. Change 'em both out. I used 1015mm on my car, B.C. went with 1000's. It says to use the 1035's. Best bet is to remove and measure. The local AdvanceAutoZone type stores have a device for this purpose. I changed out the alt on my '82 300D, same bracket... it's been a while, but I did not mount bracket to alt first, the spacer looks difficult to install, it's not really. My biggest problem was remembering the bottom most bolt screws into the bracket, no nut. Oh, and I bent a ratchet in the process, probably a thread around here somewhere. That was belts on the SD, but same routine. Loosen all bolts, and be careful with that adjusting bolt, $$$ to replace.

chetwesley · #7 08-05-2007, 01:39 AM

I tried to get that spacer in there with the mounting bracket still on, and after about 15-20 frustrating minutes of trying to fit it in there and get the bolt through lined up correctly, I realized the 2 min it would take me to take off the adjusting bracket and mount the alt to the bracket outside the engine compartment was probably worth it...

Personally, I wouldn't bother with trying to lay on your back under the car and play twister with your fingers to get that spacer on, when you could just take the 2 min to take the bracket off and have the spacer in place in 30sec sitting comfortably... just my .02

Uncle Possum · #8 08-05-2007, 11:23 AM

I swapped out the alternator this weekend before I saw this Picture. I couldn't figure out why the adjustment bolt had about a 1/2" long bolt welded to the back side of it. With the tensioner bolt broken, there is nothing to keep the larger adjustment bolt from turning, plus the little piece of remaining tensioner bolt , made it nearly impossible to put a back up wrench on it. This also makes it very difficult to properly adjust tension.