1987 300d serpentine belt adjustment - PeachParts Mercedes-Benz Forum

gravy train · #1 10-06-2009, 03:23 PM

Is there any other adjustment on the serpentine belt besides the tension pulley ? I have replaced the reg. and had the battery tested so I am down to the belt slipping or the alt..

babymog · #2 10-06-2009, 03:24 PM

No adjustment, just the spring to compensate for wear.

CANDIDE · #3 10-06-2009, 04:48 PM

Quote:

Originally Posted by gravy train

Is there any other adjustment on the serpentine belt besides the tension pulley ? I have replaced the reg. and had the battery tested so I am down to the belt slipping or the alt..

What is the voltage measured across the battery at idle and at 1500 rpm or so? At idle I'd be happy with 12.8V and at 1500rpm 13.2V.

If the belt is slipping the power steering pump would probably give you an indication.

ah-kay · #4 10-06-2009, 05:04 PM

OP: what actually is the problem? A slipping belt causing the alternator not to charge or just a general question on serpentine belt adjustment?

As other have mentioned, the serpentine belt is self adjust by the tensioner. Do you have cold A/C? The compressor is a more heavy load to turn. If compressor, power steering work then I would discount the belt slipping theory and look at the alternator proper.

gravy train · #5 10-08-2009, 02:19 PM

the issue the I am having is the battery light is blinking or will stay on. The higher the rpm or the more load it has the brighter the light gets. Before I replaced the reg. I was getting 16.75 volts at the battery @ 2000 rpm. Now its at 14.75 but when I turn everything on its 12.5. I guess I'll replace the alt. cause I figure thats my next step. Had to go out of town so I guess I'll get started tomorrow. Thanks for the help.

babymog · #6 10-08-2009, 04:11 PM

You are cooking the battery. The old one was cooked, the new one will be soon at 14.75v.

You probably only need a new regulator but driving it that way will cost you.

gravy train · #7 10-08-2009, 04:59 PM

I did replace the regulator. Before I did the volts were 16.75. I'm curious as to what the other item on the back of the alt. is. Its some electrical part that looks like it might be a resistor of some sort. It has one screw that holds it on and one wire that plugs into the back of the alt.

gravy train · #8 10-08-2009, 05:10 PM

Was curious babymog. Which do you think would be better to buy a rebuilt one from a parts store or have this one rebuilt ?

a2t · #9 10-08-2009, 07:29 PM

dump the wimpy 70 amp and go for 120 amp bosch or valeo (you might need to keep your pulley though). The 120amp is cheaper (go figure). If you really wanna overkill go for 143 amp or 150 amp

You will also need the wiring harness.

I think 143 amp is on 98-99 models. Theres a great thread on here (I think from GSXR, I will try to find it).

Or you can call call at The Benz Store in Atlanta, he will set you up with all you need. The 120 amp he sold me fit fine, no need to swap pulleys and its running perfect.

You want 14-14.5v at idle and w/all acces on. Any less will less/more reduce battery life.

babymog · #10 10-08-2009, 10:48 PM

Paul is spot-on with the logic behind the upgrade, and it is worth the investment.

If your original alt is working properly at this point, I'd finish troubleshooting before making any changes though.

gravy train · #11 10-09-2009, 02:42 PM

Taking the alt off today to have it checked. If its good I guess I'll keep trouble shooting. If its bad I''ll check with Benz in Alanta on the 120 amp. Thats a good idea I hadn't thought of.

a2t · #12 10-10-2009, 06:15 PM

the 120 amp is cheaper, this is a no brainer if its the alt.

but they will want your core because for some odd reason the 70 amp is a rare bird and the recyclers want it. my 120 amp actually makes headlamps brighter and the interior fan spins faster too. Win win.