Drive belt size - 1983 300TD - PeachParts Mercedes-Benz Forum

rstl99 · #1 07-08-2014, 11:29 AM

Hi all,

I called the MB dealer and he told me the belts needed for my 83 300TD are: two 9.5x1035 (alternator/water pump), one 12.5x925 (compressor) and one 12.5x1145 (power steering).

I have some new belts I had ordered previously, all CONTI-SF brand:

13x1145
13x925
10x1035

Questions:

1. Can a 13 belt be safely used when 12.5 is recommended by dealer? Or should I order the dealer belts (not much more expensive than the Conti ones)

2. It looks like the two alternator belts on my car were installed upside down, am I looking at this wrong?? You can see that they are quite worn, too.

vstech · #2 07-08-2014, 11:48 AM

for some reason, the dealer is quoting SAE size for the belts... (they compute down to 9.5 from 3/8" etc...) the conti belts are correct. those belts in your pic are installed correctly, just they have relief notches on the outside. v belts grip on the angle inside, not from cogs or anything.

rstl99 · #3 07-08-2014, 12:07 PM

Quote:

Originally Posted by vstech

for some reason, the dealer is quoting SAE size for the belts... (they compute down to 9.5 from 3/8" etc...) the conti belts are correct. those belts in your pic are installed correctly, just they have relief notches on the outside. v belts grip on the angle inside, not from cogs or anything.

Thanks for the quick reply! Glad to know the Conti belts are fine. In fact, the MB service manual also lists the belts as 12.5 and not 13. My replacement belt doesn't have those notches on the outside, which led me to think that maybe someone had put them on inside out, which made no sense because of the angle of belt edge, but strange things happen...

For some reason, I only ordered one for the alternator, so will need to get another one in order to replace the pair. I'm halfway through the process of replacing the rad and hoses, so it's the perfect time to do this (more room to access and slip belts over fan etc.).

Cheers.

vstech · #4 07-08-2014, 12:27 PM

the alternator belt pair is best ordered as a set... for some reason, no two belts are the same, and ordering from different boxes leads to insufficient tightening of the belts...

if you only ordered one, I'd order two more to be sure I got a matched set.

rstl99 · #5 07-08-2014, 01:00 PM

Quote:

Originally Posted by vstech

the alternator belt pair is best ordered as a set... for some reason, no two belts are the same, and ordering from different boxes leads to insufficient tightening of the belts...

if you only ordered one, I'd order two more to be sure I got a matched set.

Thanks, I indeed just ordered a pair from the MB dealer (not more expensive than aftermarket parts source as it turns out, up here in Canada anyway). Then, the fun of loosening all the necessary bolts and slipping off the old belts. I'll feel better driving the car with new belts, a new rad and hoses.

rstl99 · #6 07-09-2014, 08:39 PM

Damn, the MB belts are too snug to fit on the pulley, with the alternator belt tensioner all the way out. The single Conti belt I had ordered previously fits very loosely, so I've ordered another one to match, and will try to return the MB belts for a refund... (MB belts are 9.5-1035, the Conti belt is 10-1035).
At least I'm getting good practice removing and replacing these belts...

rstl99 · #7 07-10-2014, 10:41 AM

In a search, I found the nugget that for tight fitting belts, a resort is to remove the fan pulley, put the belts on, and reinstall the pulley. Worked great, and I was then easily able to adjust the tension.
So the MB-supplied belts were ok after all, and now all four new belts are on the car, one less thing to worry about for a hundred thousand miles or so...
Now onto my main job before I got side-tracked on this, radiator replacement!
Thanks again.