Correct belts for ALT/WP 1985 300CD- 10x1035 look too thin! - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 04-05-2023, 09:38 AM

I am working on a friends '85 300CD, and he wanted the alternator/water pump belts replaced (among other things). I could see why, as the belts looked way too thin, and were riding way down in the pulleys. Looking at other cars in my collection, the belts are wider. I trusted several online Euro parts sites that called for a 10X1035 belt (set of two) for the water pump/alternator. When they arrived, I realized they were the same skinny belts that were on the car. For some reason they don't seem right. I am sure every other 617 turbo I have seen (and I have seen MANY) has wider belts. I am not going to put these thin belts on, so does anyone know if just a wider belt with the same length will work?

vstech · #2 04-05-2023, 11:51 AM

Set them in the groove, if they sit high they are fine, but several belt brands list the 10×1035 but ship a 9.5mm which is imperial unit 3/8" and they call it close enough...

ROLLGUY · #3 04-05-2023, 08:03 PM

Quote:

Originally Posted by vstech

Set them in the groove, if they sit high they are fine, but several belt brands list the 10×1035 but ship a 9.5mm which is imperial unit 3/8" and they call it close enough...

The belts I got are Genuine Continental 10X1035. It is hard to imagine that this is the size (width) that was on these engines when new.

shadetreemechan · #4 04-06-2023, 08:08 AM

There were two different options with different pulleys. Some take a 10x?? and others a 13x??. I have had the same concern with the 10mm width belts, but when I moved up to a 13 it worked fine for a while but after 10k miles or so the wear on the sides of the belt ate into the actual fibers of the belt and it gave way (on the side of the interstate 300 miles from home) . I would stick with the 10x belt if that was what it had and it appears to have been working.

ROLLGUY · #5 04-08-2023, 09:45 PM

Attached are photos of four 617 turbo engines with wide belts (either parts cars or drivers) in my yard. I don't have a photo of the thin belts in my friend's car, but the belts are much thinner than any I have seen. They are just like the new belts I ordered (10X1035). Is anyone out there running the thin belts on their 617 turbo?

vstech · #6 04-09-2023, 08:45 AM

Yes

ROLLGUY · #7 04-09-2023, 09:43 AM

Quote:

Originally Posted by vstech

Yes

Can I get a photo please?

vstech · #8 04-10-2023, 04:25 PM

Sorry, I didn’t check in yesterday.
I will snap one in my 84

ROLLGUY · #9 04-10-2023, 08:10 PM

These thin belts are riding way deep in the pulleys, but are the size (10X1035) called out for a 617 turbo on every Euro parts website I looked at. It is hard for me to believe this is the correct size, when every one I have seen up till now had the wider belts (photos in post #5).

shadetreemechan · #10 04-10-2023, 09:43 PM

The water pump pulley is designed to take either belt. It is the alternator pulley that varies. I will try to take a picture tomorrow.

shadetreemechan · #11 04-10-2023, 10:27 PM

Sorry I just went out to verify and was wrong in the previous post. The water pump pulley is also width specific. What I found by looking at the 4 cars in my driveway is:
both 617s used 10mm pulleys. Both 616s had 13 mm water pump pulleys, one 240 had a 13mm alternator pulley, while one had a pulley for 10mm.
Looking at my sons 115, both his water pump pulley and his alternator pulley are designed for a 10mm belt. So my yard survey (1976 240, 1982 240, 1983 240, 1984 300TD, 1985 300TD) it would appear that 617s came with 10mm, early 616s had a 10mm, and at some point they switched to the 13mm on the 616. Somewhere in my alternator swapping I inadvertently put a 10mm pulley on my 1982 240 which explained why it trashed the 13mm belt it had on it last year.
Pics are of a 10mm 617 pulley with both a 10 and a 13 mm belt, a 10mm belt in a 13mm water pump pulley, 10mm belts in a 10mm water pump pulley, and a 10mm belt in a 13 mm alternator pulley. My 1983 240 has a 10mm belt but seems like it should have a 13. That 10mm belt has been on it for years so it must not be an issue to downsize like it is to upsize.

ROLLGUY · #12 04-11-2023, 09:53 AM

Quote:

Originally Posted by shadetreemechan

Sorry I just went out to verify and was wrong in the previous post. The water pump pulley is also width specific. What I found by looking at the 4 cars in my driveway is:
both 617s used 10mm pulleys. Both 616s had 13 mm water pump pulleys, one 240 had a 13mm alternator pulley, while one had a pulley for 10mm.
Looking at my sons 115, both his water pump pulley and his alternator pulley are designed for a 10mm belt. So my yard survey (1976 240, 1982 240, 1983 240, 1984 300TD, 1985 300TD) it would appear that 617s came with 10mm, early 616s had a 10mm, and at some point they switched to the 13mm on the 616. Somewhere in my alternator swapping I inadvertently put a 10mm pulley on my 1982 240 which explained why it trashed the 13mm belt it had on it last year.
Pics are of a 10mm 617 pulley with both a 10 and a 13 mm belt, a 10mm belt in a 13mm water pump pulley, 10mm belts in a 10mm water pump pulley, and a 10mm belt in a 13 mm alternator pulley. My 1983 240 has a 10mm belt but seems like it should have a 13. That 10mm belt has been on it for years so it must not be an issue to downsize like it is to upsize.

Great information, thanks! It appears that N/A engines had or could use either size, but from what I have seen so far, Turbo engines with two belts have the wider belts. I will look at the two N/A cars I have in my yard, and see what they have.

The reason I am researching this, is my friend's car had slipping alternator belts. I saw the thin belts, and immediately thought that was the problem. Trusting the two online Euro parts catalogs I saw (they agree), I ordered the 10mm belts. Later realizing that they were the same size that were on the car, I looked at some of the other cars in my yard- all the turbo cars had the wide belts.

I have a theory: I suspect that ALL the belts on the cars in my yard are Aftermarket, and that none are Continental brand (metric). That would make sense, as they are 15XXX (15/32 wide). The power steering belt is 17/32 wide (vs 13mm). It could be that when the 13mm belts I ordered arrive, they will sit higher in the pulleys than an aftermarket belt will, as they are 1/32 wider (1/2 vs 15/32). Either way I will use them in the car. The thin belts may be what is called for, but they just don't look right!

vstech · #13 04-11-2023, 05:21 PM

Pics of the belts installed

ROLLGUY · #14 04-11-2023, 05:43 PM

Quote:

Originally Posted by vstech

Pics of the belts installed

Well then, I am now dumbfounded. Those look normal, and not riding down in the pulleys. Could it be that 10mm is not the top (outside surface) width of the belt? If it was, then they would look like the attached photo in post #9.

vstech · #15 04-13-2023, 11:57 AM

Quote:

Originally Posted by ROLLGUY

Well then, I am now dumbfounded. Those look normal, and not riding down in the pulleys. Could it be that 10mm is not the top (outside surface) width of the belt? If it was, then they would look like the attached photo in post #9.

Are those belts new? They certainly look waaaaay too thin.

Mine are O.E. true 10x1005 continental belts as shown in the picture.
They have a LOT of miles on them, but as you can see, they fit properly.