Alternator belt adjusting - Mercedes-Benz Forum
Reply
 
LinkBack Thread Tools Display Modes
#1 (permalink) Old 06-20-2009, 09:56 PM
BenzWorld Elite
 
Date registered: Feb 2007
Vehicle: 300SD
Location: Florida, USA
Posts: 10,958
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
(Thread Starter)
Alternator belt adjusting

Here are some tips on alternator belt tensioning on 123 and 126 chassis diesels using a special bolt with a rod welded to it at the 90 degree angle. The procedure described is for a 123 chassis (85 300DT in this case).

1. Because of limited access you are better off removing the air intake duct, the air cleaner, and the air cleaner to turbo plastic elbow. Also, removing the EGR valve corrugated stainless steel tube will make the job much easier.

2. Do not turn the tensioning bolt rod nut until you have loosened all bolts to permit the alternator to pivot freely!!!!!!!

3. Get under the car with a long 17 mm box end wrench and loosen the bottom pivot point bolt. Sometimes this may be rather difficult if the bolt is tight, hence a long wrench helps. Because of proximity of the A/C hose bracket, there does not appear to be enough room for a socket/breaker bar, unless you loosen the hose bracket and get it out o the way.

4. I made a special tool for holding the tensioning bolt head stationary while loosening the 17 mm nut on the other side of the bolt. I took a 1/2 inch drive 17 mm socket and cut a slot in it with a metal cutting circular saw, so it would clear the welded rod. I held the adjusting bolt head stationary while loosening the nut on the other side which was very tight. If the nut is tight and you do not use a special tool to hold the adjusting bolt head stationary, you will bend the adjusting bolt rod!!!! It is not very strong to withstand the torque.

5. There is one more 17 mm nut to loosen. It is the adjusting bracket mount bolt which must be loose to allow free pivoting of the alternator adjusting bolt int he bracket slot. Do not attempt to loosen the nut on the front of the bracket (closest to the radiator) because it is welded to the bracket!!!!!! Instead you must loosen the head of the bolt on the back side of the bracket. The access is rather frustrating - once again not enough room for a socket, so use a long 17 mm box end wrench.

6. After loosening all three, you can now turn the alternator tensioning bolt rod nut and the alternator should pivot freely.

Not a user friendly adjusting system, in fact it appears to be designed so you damage or break things unless you know exactly what you are doing. The price of a new adjusting bolt and bracket is astronomical - the cheapest price on a new bolt is about $ 50 and a new bracket from the dealer will run about $ 150. The bracket will bend also if you keep turning the adjuster bolt nut without loosening all of the bolts mentioned above.

I recommend you use good quality belts such as Continental or Gates to avoid having to tension them frequently. Cheap Auto Zone belts will require just that as they will stretch constantly.

Last edited by p100; 06-20-2009 at 10:17 PM.
p100 is offline  
Sponsored Links
Advertisement
 
#2 (permalink) Old 06-21-2009, 06:57 AM
BenzWorld Elite
 
::matthew's Avatar
 
Date registered: Jul 2008
Vehicle: 1985 300D W123 Cali
Location: Tallahassee, FL
Posts: 1,404
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
were you able to get it done without buying parts?

1985 300D cali 190K

::matthew is offline  
#3 (permalink) Old 06-21-2009, 08:30 AM
BenzWorld Elite
 
79Mercy's Avatar
 
Date registered: Oct 2006
Vehicle: 1979 280CE
Location: Jacksonville, Florida
Posts: 6,106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Matt, we didn't have any trouble changing your belts....

The early style alt bracket is what really sucks.

'79 280CE with 226,000 miles
'76 240D 4 speed with 190,000
'85 300D Turbo with 266,000 miles


GONE but not forgotten
'76 300D with 195,300 miles
"83 300D with 174,000 miles

79Mercy is offline  
#4 (permalink) Old 06-21-2009, 10:14 AM
BenzWorld Elite
 
::matthew's Avatar
 
Date registered: Jul 2008
Vehicle: 1985 300D W123 Cali
Location: Tallahassee, FL
Posts: 1,404
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by 79Mercy View Post
Matt, we didn't have any trouble changing your belts....

The early style alt bracket is what really sucks.
we had three people taking turns on that pivot bolt...and at least one broken wrench

1985 300D cali 190K

::matthew is offline  
#5 (permalink) Old 06-21-2009, 10:26 AM
BenzWorld Elite
 
79Mercy's Avatar
 
Date registered: Oct 2006
Vehicle: 1979 280CE
Location: Jacksonville, Florida
Posts: 6,106
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by ::matthew View Post
we had three people taking turns on that pivot bolt...
True... I didn't think we were going to tell anyone.

'79 280CE with 226,000 miles
'76 240D 4 speed with 190,000
'85 300D Turbo with 266,000 miles


GONE but not forgotten
'76 300D with 195,300 miles
"83 300D with 174,000 miles

79Mercy is offline  
#6 (permalink) Old 06-21-2009, 10:51 AM
BenzWorld Elite
 
Date registered: Feb 2007
Vehicle: 300SD
Location: Florida, USA
Posts: 10,958
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
(Thread Starter)
Quote:
Originally Posted by ::matthew View Post
were you able to get it done without buying parts?
I actually bent the rod on the adjusting bolt trying to loosen the nut, but I was able to straighten it out. After that I made a special slotted socket to hold the bolt head in place and this worked fine. After I found out what the prices for the replacement bolt and bracket were, it was an easy alternative.

The problems one runs into are overtightened fasteners on these done by former owners or their mechanics. In my case it was the adjusting bolt, in your case it was the bottom pivot bolt.

If you make a slotted socket like I did, the slot must be cut in a certain location, otherwise the socket will not fit. Mark the location of the slot before you cut it. I used a foot long 1/2 drive extension to hold the socket during cutting.

Last edited by p100; 06-21-2009 at 11:01 AM.
p100 is offline  
#7 (permalink) Old 05-07-2012, 11:27 PM
BenzWorld Junior Member
 
Date registered: May 2010
Posts: 14
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Do not attempt to loosen the nut on the front of the bracket (closest to the radiator) because it is welded to the bracket!!!!!!
aaand THAT is why no amount of PB blaster seems to be doing the trick, apparently. This point cannot be emphasized enough!
nkrumm is offline  
#8 (permalink) Old 05-08-2012, 04:12 AM
BenzWorld Elite
 
Stretch's Avatar
 
Date registered: Jul 2011
Vehicle: 1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
Location: The Netherlands
Posts: 4,048
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Here are some pictures of the alternator bracket






1981 300D (non turbo) 123.130 => Project car - stripped to the bone

1992 190E 1.8 <=>2.0 201.018 => This car shouldn't be in bits too
Stretch is offline  
#9 (permalink) Old 05-08-2012, 08:51 AM
BenzWorld Elite
 
Date registered: Mar 2008
Vehicle: 1984 300D
Posts: 4,581
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
If some one snaps off the skinny threaded Rod and does not want to pay the $40 something for a New Stock type Bolt:
Using an Eye Bolt to repair a broken alternator tensioner bolt eyebolt on Alternator
Stuck on V-Belts: ALternator bolts frozen and tension bolt broken - Page 2 - PeachParts Mercedes ShopForum
300Dman is offline  
#10 (permalink) Old 05-08-2012, 08:53 AM
BenzWorld Elite
 
Date registered: Mar 2008
Vehicle: 1984 300D
Posts: 4,581
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Note: there is more then one type of Alternator Bracket and Adjuster out there so it is possible that the one on you Vehicle might not be the same as the one in this thread.
300Dman is offline  
Reply

  Mercedes-Benz Forum > Mercedes-Benz Sedan Forums > W123 E,CE,D,CD,TD,TE Class


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Topic Author Forum Replies Last Post
Cannot get Alternator Belt tight enough - Alternator Bracket jonbobshinigin W123 E,CE,D,CD,TD,TE Class 9 04-15-2009 01:35 PM
Serp belt snapped. Alternator seized. New alternator ... doesn't fit??? Qualm W124 E,CE,D,TD Class 0 03-30-2009 07:05 PM
alternator belt sie617 V-Class 6 10-07-2008 01:16 AM
adjusting belt tension einspritzung W124 E,CE,D,TD Class 6 09-27-2008 09:30 AM
Adjusting Belt Tensioner jef_1_f R129 SL Class 5 08-27-2007 04:59 PM

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome