1985 300D- Alternator belt replacement- What am I missing?? - PeachParts Mercedes-Benz Forum

MongooseGA · #1 04-05-2017, 09:16 PM

Hey all,

In the process of replacing my alternator belts tonight. Some may remember that I've done this recently but a sudden engine mount collapse resulted in chewed up belts.

Following the guide from Pelican, I loosened the tensioner bolt first (holding the bracket to the alternator) then the bolt holding the alternator snug in place. I noticed that there's a 3rd bolt missing at the very bottom of the unit which would hold the alternator pretty low in the engine bay. I did not remove a bolt here, and there wasn't one there when I started tonight.

The problem I have is that even when I lift the alternator up to make the belts taught, it's NOWHERE near a proper fit; there's a ton of slack in the belts. In fact, they won't even seat in the pulleys, they're so loose.

What am I missing here? I remember having a tricky time when I did this a few months back, but at least then I was in the range of workable. I'm lost.

Link to A/V https://youtu.be/LEWVfRi0Smg

I guess while I wait to figure this out, I'm on to the turbo oil return gaskets and rings.

Alec300SD · #2 04-05-2017, 09:31 PM

You haven't fully loosened the alternator.
There is one nut and two bolts that you must loosen before you tighten the long adjusting nut on the tensioning screw.
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/617/13-340.pdf

MongooseGA · #3 04-05-2017, 11:04 PM

Quote:

Originally Posted by Alec300SD

You haven't fully loosened the alternator.
There is one nut and two bolts that you must loosen before you tighten the long adjusting nut on the tensioning screw.
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/617/13-340.pdf

Well, I feel like an idiot. Notice that shiny new water pump in the video?

...I forgot to put the cover back over the pump that these belts run over.

MongooseGA · #4 04-07-2017, 10:34 PM

For some reason I'm having brain fart after brain fart with this car. I got the car all buttoned back up after a bunch of maintenance work over the last few weeks and went to start it up. Ran fine for a bit, then I heard a clunk and the engine shut off.

I'd completely forgotten the 3rd bolt missing at the bottom of the alternator. The belts were snug and it tweaked the alternator toward the crank pulley. I scurried out to my local parts store and grabbed a bolt and nut, installed. Took a little motivation with a pry bar to get it into position but it worked. Then I had horrible squealing and burnt rubber smoke all over the engine bay. The belts were melting on...something? I could not find anything other than the pulleys making contact, so my thought is that the tensioner bracket is bent and not allowing the alternator to sit in line with the crank pulley.

I really needed this car for the weekend but I think that's out of the question. I'm thinking I can remove the alternator and replace the tensioner bracket to remedy. Maybe I can remove the existing bracket and love it into shape with a hammer? Any thoughts?

Seriously, I'll buy anyone local a case of beer to just come lay eyes on it and lend a hand. Luckily I have another pair of already, and by now I'm pretty much a pro and replacing all of the drive belts.

*Having done some more reading it looks like the bracket should come off with the entire alternator, which appears to be pretty easy to remove. Fortunately my tensioning bolt works just fine, I think its the actual bracket that's bent. Can anyone confirm my thoughts?

Alec300SD · #5 04-08-2017, 02:51 AM

Sorry I gave incorrect advice earlier, I misread your first post and didn't watch the video until after you posted that the water pump pulley wasn't installed.

In your video, I did notice that the two alternator belts were not parallel.
The front belt was actually in the air conditioner groove position on the main crank pulley.
If you didn't move the front belt back one groove on the main crank pulley, this would keep the alternator belts non-parallel and that could account for your recent symptoms.

MongooseGA · #6 04-08-2017, 03:50 AM

Quote:

Originally Posted by Alec300SD

Sorry I gave incorrect advice earlier, I misread your first post and didn't watch the video until after you posted that the water pump pulley wasn't installed.

In your video, I did notice that the two alternator belts were not parallel.
The front belt was actually in the air conditioner groove position on the main crank pulley.
If you didn't move the front belt back one groove on the main crank pulley, this would keep the alternator belts non-parallel and that could account for your recent symptoms.

Good catch, and you're correct. They weren't really in any groove in the video as there was so much slack before the water pump cover light went on in my head.

I just finished testing my theory. I pulled the alt and its bracket, found the bracket to be a little warped. Using some hand tools and a little simple physics I managed to get it back to being level on a flat floor at all four corners. I also made sure the sides where the bolts go through were square to each other and fit properly around the spacer underneath.

Symptoms persist. Wtf. This is incredibly defeating. I just roasted through a BRAND NEW set of belts tonight already trying to figure it out, I'm not about to do it again to this spare pair. The squeak I'm hearing sounds like more than a simple belt squeak, it's LOUD and has a sort of 'hollow' sound to it. I'm wondering if it might be something to do with the bearings? On to more research. I guess I won't be driving it tomorrow...

MongooseGA · #7 04-08-2017, 04:18 AM

Did some more reading, found others with similar symptoms that ended up being seized bearings. The alt belts had spun at some point tonight, but I'm pretty sure they were only burning on on the alt pully. Would bad bearings be intermittent or would it be completely seized up?

I found this in my searching:

Quote:

Originally Posted by newtodiesel

I was having a problem w/ the alternator (I think) a few weeks back But thought I fixed it.
the lights on the dash were all lit up even the fuel lite
the belts seemed tight enough.. I replaced the regulator.. Seemed to solve the problem..That was few weeks ago.

The lites went out,after replacing the regulator....

from time to time I would hear a noise under the hood I guess it sounded like kinda metallic sound I dont know if it was the pully or the bearings...but it sounded like it was coming from the alternator....I guess my fault for not investigating further I dont know how to check anyway......other more pressing problems right now...since I live in florida, you can imagine whats going on....

I think it is overheating because the belts are not there anymore.
I was driving it yesterday and had it sitting idle w/ no signs of overheating the extra fan in the front came on too. That was the first time I ever heard the extra front fan come on
so how hard will this be to replace the alt??? Will I just be cussing the whole time?

This is verbatim what I have experienced minus the cooling issues. Voltage regulator replaced, no alt lights for a while, then BAM, first incident of belt smoking.

Diseasel300 · #8 04-08-2017, 11:04 AM

Pull your belts and spin the pulleys by hand. They should be smooth and quiet. If you get one that's rough, makes noise, or doesn't rotate easily, you've probably found your problem.

Depending on how the bearing is failing, it is possible for it to work briefly then get so hot it starts to seize up. Especially if it is a ball bearing and the ball "cages" fall apart internally.

Mark DiSilvestro · #9 04-08-2017, 01:34 PM

It's also possible, while messing with the alternator and bracket, that something got bent and the alternator fan is jammed against something.

Happy Motoring, Mark

MongooseGA · #10 04-08-2017, 02:48 PM

It was the alternator. Totally seized. I threw in a new one this morning and the car is running like a top again.

Running so well in fact... that now it won't turn off. Normally something gets knocked off during oil changes in that big mess of lines by the filter. The only thing I could find today was this guy, but I couldn't find where he goes. Anyone able to identify? If I can't find the other end, am I able to cap this side off for the time being?

Mark DiSilvestro · #11 04-09-2017, 05:30 AM

On your first photo, resting near the end of that broken connection you're holding, I see a black line with a rubber elbow on the end that looks like it's just resting against another rubber hose. I don't see a splice connector on that rubber hose. So maybe it's the missing connection to the one you're holding.

Happy Motoring, Mark

MongooseGA · #12 04-09-2017, 10:49 AM

Hm, I'm not seeing it. You wouldn't happen to be looking at the end of the black zip tie would you?

Alec300SD · #13 04-09-2017, 11:01 AM

Maybe there is a cracked nipple hidden under the foam wrapped on the brake booster line?

Mark DiSilvestro · #14 04-09-2017, 11:59 AM

Quote:

Originally Posted by MongooseGA

Hm, I'm not seeing it. You wouldn't happen to be looking at the end of the black zip tie would you?

It could be an optical illusion in the first photo. That 'loose elbow' I saw in the first photo looks more like a leg of one of those rubber 'spider' connectors in the second photo.
The broken line you're holding could have snapped off your main vacuum supply to the brake booster.
Is all your vacuum equipment now inoperative?

Happy Motoring, Mark

BillGrissom · #15 04-09-2017, 02:37 PM

Ditto. That looks like a main vacuum feed. There should be 2 plastic nipples on the main vacuum tubing at the plastic check valve. It is common for them to snap off when hands move too carelessly around them. On one of my 300D's, I drilled out the broken nipple and epoxied a thin copper tube to form a new stub. You can buy that main vacuum tube new, but ~$60. I grabbed a spare from the junkyard. Anyway, even when no longer available, it wouldn't be hard to fab the whole system, since just a plumbing job. Just hang onto the metal fittings at both ends.