Loose Screws, Bolts and Fuses Faking Contact - PeachParts Mercedes-Benz Forum

pschmidt · #1 08-10-2010, 02:36 PM

I've been working on an 81' 300TD for several months now. When I have a problem, like it suddenly won't start, I pull out my MB CD and try to figure out what needs to be fixed. When that fails, rather than pull out the little hair I have left, I read the forum. So far the forum has provided my with other things to look at but not the solution to my problem, other than relieving my frustration, which is a good thing.

Loose Screws. When my Benz refused to start the day before I was leaving on a business trip to Texas and Karolyn, my wife was going to use it around town, I was stumped. It would start if I sprayed WD40 into it and start again when I restarted it hot. (This is not about WD40 as starting fluid. Talk about that in another forum.) I knew it had something to do with the GPs since I didn't have time to investigate, I handed Karolyn the can of WD40 showed her where to spray it and left on my business trip.

When I got back I started to check the GP system. The GPs were fine, all worked. I then opened the GP timer relay. It looked fine. The 50A fuse was intact but when I started to stick the volt meter probes into it I noticed that one of the screws on the fuse was loose. I tightened it and! Viola! Problem solved.

Loose Bolts. The rear windshield wiper was similar. A bolt holding the wiper motor came loose and jammed the wiper mechanism. Good thing I didn't leave the wiper button on or I could have burned the motor and spent money on the problem.

Fuses Faking Contact. The climate control never worked properly since I bought it. The blower only worked on Hi and the A/C was mediocre at best. One day while I was investigating how remove the passenger side kick panel, the blower motor stopped all together. MB manual no was help other than to explain how to remove the motor.

The forum suggested a lot of possibilities, most costing money. I checked the voltage to the blower motor and at the blower regulator, none at the motor, 6-7 at the regulator. Where was the power? Fiddled with the fuses again with the blower on, spun it, took it out but when I put it back in it I pushed it in too far and the blower started working. The end of the fuse holder had melted and was forcing one end of the fuse not to make contact.

Cleaned the holder, chipped away the offending plastic and now the climate controls work fine.
Moral, Look for the simple stuff first and do some head scratching, the massage helps the hair grow.
Peter

Diesel911 · #2 08-10-2010, 05:00 PM

When first seen the Fuse looked good untill I pulled it out.
A quick look at the Glow Plug Strip Fuse and it looked OK; a closer loop proved otherwise.

Concerning answers on the Forums. Members with a lot of mechanical experience often forget to mention the simple things because they check those things as sort of a second nature or they keep those parts so well maintained they know they are not to cause an problem.

The others tend to comment on what the replaced that fixed the problem.

In between that there is a lot of self learning going on.

Yak · #3 08-10-2010, 07:50 PM

The blower motor fuse is a problem area. M-B provides an aux fuse kit for the fuse. You remove the fuse and it gets replaced by a matchbox-sized fuse holder. That reduces the likelihood of a full fuse-box meltdown and electrical fire.

When I bought my car I thought I was scammed: "hey - the A/C sort-of worked on the test drive, but now it's kaputt and there's no fuse but some melted plastic....oh, okay, extra holder...got it...."

pschmidt · #4 08-10-2010, 08:47 PM

Thanks, I'll look into it. It did seem like it might be a problem if the fuse gets so hot it melts the plastic.

Diesel911 · #5 08-10-2010, 09:08 PM

The Plastic Bodied Fuses have caused the same issue on other circuits besides the Blower Circuit; better just to get rid of them.

pschmidt · #6 08-10-2010, 09:23 PM

Are you talking about the fuse holder box, which is plastic with metal fuse holders as in your thumbnail or the fuses, which are ceramic?

vstech · #7 08-10-2010, 10:39 PM

official fuses are ceramic, and copper or brass, or tinned copper, but walmart/mcparts store "german" fuses, are plastic, and they cannot handle the heat and melt...
replace all the plastic aluminum/copper fuses, and put in real german ceramic fuses.

Diesel911 · #8 08-10-2010, 11:55 PM

Quote:

Originally Posted by pschmidt

Are you talking about the fuse holder box, which is plastic with metal fuse holders as in your thumbnail or the fuses, which are ceramic?

I am not speaking of the Fuse Box itself.

My Fuse Box did not melt;it just burned the Brass Contact area a little due to the high resistance created by the Corroded end of the Fuse.

pschmidt · #9 08-11-2010, 12:15 AM

The problem with my #8 fuse was that the fuse melted the box a little and filled the hole at the end of the fuse holder. One of several things are could be happening 1) the blower is pulling too much current, 2) it's normal for this fuse to get this hot without blowing or 3) the melting was caused a while ago and went unnoticed by whomever was trying to fix the A/C.

Yak · #10 08-11-2010, 07:46 PM

There's speculation that the blower bushings wear and increase resistance. Resistance draws more current. The steady increase in current over a long period of time at the high resistance point in the circuit causes the fuse to overheat, but there's not excessive current so it doesn't pop.

Then the fusebox melts.

pschmidt · #11 08-11-2010, 09:21 PM

I thought that might be the case and looked at the brushes in the blower motor. They are low but replacing them is not as easy it seems.
I would have to somehow open the back of the brush holder (pry with pliers), cut the wire holding the old brushes and re-solder wire of the new brushes onto the old wires.
The solder point of one of the brushes is inaccessible because the motor cannot be disassembled easily, i.e. with a few screws, it is pressure fitted together.
I'll be looking for a new blower motor in my travels.

whunter · #12 01-26-2014, 09:10 PM

for new members.

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