WARNING...maybe, certainly an inspection point, 1985 300D Federal.
 

Squealing belts and rattling noise led me to the alternator on my newest used car, Silver Bullet. What I found folks might wish to put on their maintenance inspection lists:

1. Loose belts.
2. Adjustment nut device bending 5 degrees out of line.
(I decided to remove the unit, clean everything, check things out).
3. Lower (pivot) bolt sheared at threaded receiver (causing the rattling at idle).
4. Sheared situation caused the lower holes on the alternator "shroud" to oval. Will require replacement of the shroud bracket.
(Removed alternator).
5. Upper alternator adjustment stamped plate cracked or broken through in three places. Inspection caught this just in time for a MIG job quick fix.
6. Nub of the pivot bolt still stuck in the mount plate. Tight quarters above and below. Tried several techniques to remove, no luck.
7. Getting the alternator-to-engine mount plate out of the car is a big deal: four nuts on the plate face, one bolt behind the balancer (requires removal of fan, pulley, and fabricate of a tool from flat stock and a trimmed 17mm 3/8dr socket. This mount is aluminum, the inserts for the bolt threads a steel alloy.

Did everything I could think of to remove the nub of the threaded bolt end, to no avail. Taking it to a machine shop tomorrow.

While this is a pain, I have learned a lot. Buying that MIG welder and continuing to learn how to make specialty tools with it more than returned the $450 I paid for it. (Fixed the seat belt receiver guide on Sweetness with it in about 45 minutes).

Just suggesting therefore folks add this to their checklists for wonderful geezer diesels. Good luck on your projects.

Frank

PS. I'll be leaving 25 JAN, going to Pakistan to do some construction work for Uncle Sam. May or may not be able to access the forum, depends on INTERNET service in the places I'll be working.

You're not the only one to report this kind of thing. What do you think caused it?

I'm trying to picture what all of this looks like. Any photos?

Went through this ordeal on my '82 240D shortly after I bought the car in September 2006. The numerous underhood rattles I dealt with included loose and broken brackets where the tranny cooler lines were fastened to the oil pan, a broken weld at the radiator support, an engine oil-cooler detached from the bottom of the radiator, all bolts loose or missing from the electric radiator fan and it's brackets, rubber mounts and a chunk of aluminum broket off the air-filter housing, and a bottom alternator pivot bolt sheared off, allowing the alternator to rattle around until it's bottom bolt-hole was greatly enlarged. Fortunately the adjustment bracket wasn't yet ruined. First, I removed the aluminum bracket and alternator together. Because of the enlarged hole in the alternator, and enlarged fore & aft clearance between the alternator and bracket, I was able to tilt the alternator and separate it from the bracket. Then I removed the broken stub of the lower bolt from the bracket. I also fabricated a steel insert to fit the enlarged alternator pivot hole, and reinstalled the whole assembly, with a new bolt and assorted washers to reinforce the adjuster bracket and take up the fore & aft slack in the lower pivot. So far the whole mess has remained tight and rattle-free for over a year.

Happy Motoring, Mark

this is what was wrong with my SD, and the reason I got the car for free... it's good to have parts cars...

I second this scenario, its happened on both my 85 300D and my 83 240D. If the alternator isn't installed correctly, with the correct belt tension it will continue to work, possibly for thousands of miles. The oval-ing of the holes I think is a result of mis-installation, and/or from rebuilt altenator with slight variations in the locations of the holes. Eventually there is enough slop in the alternator for it to wedge itself at an angle other than 0 deg to the pulley and this is when the bottom bolt can snap.

Also I've snapped replacement bolts that were non OEM cheapo advance auto bolts on that lower hole. Probably because it has machined threads and a combination of overtorqueing and insufficient hardness on the bolt.

Yeah, it was late at night when I finished my alternator surgery, and there was no way to get a new or used OEM bolt, so I used a cheapo one I had from Home Depot. I generously lubed the threads so (hopefully) it won't corrode in the aluminum, and managed to get it tight without breaking. I guess if it snaps again, I'll bite the bullet and get a new alternator too.

Happy Motoring, Mark

harder bolts are more brittle. so maybe it was too hard of a bolt? but prolly just cheeep chineee crap.

Interesting thread. My 240d is a 85 euro spec. the altenator pulley seems out of alignment with the crank and water pump pulleys. the long pivot bolt was missing when I obtained the car. I replaced it with a 6" long or something like that weeks ago. The other day the belt, which seemed to be rubbing a bit on the engine side jumped off the pulleys. Not sure what that was about, but it happened the day after I had stiffened up the forked bracket that aids in tensioning the alt. When you ran the tube nut down to pull the alt. up, the bracket would bend. So I welded a piece of steel on top of the fork in the car. since the belt jumped, I thought it's time to straighten the threaded rod, fork, etc. Removed that and rewelded a newly fabricated, stronger fork to the bracket.
I was gonna ask if the pully on the front of the alt. can be be moved foward on the shaft. I'm guessing woodruff key, and maybe set screw?
any of you folks done this before?
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You did not say how far you wanted to move the pulley. Here is a pic I took I do not know if the 84 300D alternator is the same as Yours. You might be able to use some washers to move the pulley forward but it will depend on how many threads are left on the shaft to put the nut on. I do not think you could move forward more the 1/4 inch or so. The big washer goes between the fan and the pulley. There may not be enough meat on the pulley for the threading for a set screw.
http://i242.photobucket.com/albums/f...11/zPulley.jpg

I"ll take a measure with a straightedge today, but I'm guessing about 1/8"+. I see what appears to be a torque wrench. What is the correct spec on the alt pulley retaining nut?
Also, what's the best way to "trap" the motor shaft when torquing the nut? I've bent blades before doing it wrong.
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Don't know if there is a torque spec for the pulley nut. Many alternators have a hex hole in the shaft, for holding with an allen wrench while the nut is turned. I've also seen the nuts removed and installed with an impact gun. Otherwise, I'd suggest holding the pulley in a vise, with the jaws cushioned if possible.

Happy Motoring, Mark

That is not a torque wrench.
 

While torqueing the nut is a nice thought I have never done that on any alternator. This is what is over in the corner of the pic. It is a 12 volt DC impact wrench sold by Harbor Freight for changing tires. I just squeeze the trigger couple of times and the nut comes off. When I install the nut besides the lock washer I put on couple drops of Loctite on the shaft threads and squeeze the impact trigger it raps on the nut and the shaft spins; when it stops spinning I repeat the process one more time and it is done. I have used this impact wrench and the pneumatic ones to do similar things since around 1975 with no problems. Amazingly I used this 12 volt impact to remove a crankshaft damper bolt that was torqued to 250 foot pounds and I had no way to keep the crankshaft from moving. I just kept rapping on the bolt until it came loose. When on sale this impact wrench sells for around $20 from Harbor Freight. Might also be good for someone who lives in an apartment as no need for an air compressor or AC socket.
http://i242.photobucket.com/albums/f.../zDSC00658.jpghttp://i242.photobucket.com/albums/f...zzDSC00659.jpg

One word of caution. I recently put in a new alternator. When tightening the bolt to the fan (with an impact wrench), the nut/lockwasher would tighten on the shoulder of the shaft without pushing down on the pulley, leaving the assembly loose on the shaft. Happened with two different alternators. I had to get a washer that slid over the shaft so that the lockwasher did not hit the shoulder of the shaft but pressed on the washer which in turn pressed on the pulley.

I remember your post. When I read it I kept thinking that maybe the rebuilder did not use metric lock washers. In any event the alternator in my pic has been on the car for more than 2 weeks now and no problems after putting in new bearings.