Slippery SuperDork
8/15/19 6:13 a.m.

I need some help finding a v-belt. 

I currently have an AVX13X825 and it is too short, i probably need something 1.5-2” longer than this. 

This is for the AC on a 1987 BMW 325is. When I bought the car 10 years ago, the person I bought it from told me it was still running on R12. The AC was weak and I was able to find R12 and recharged it, it has lasted 10 years but the belt broke and I lost it somewhere on the way home. 

I bought two different sized belts that were called for it and neither works. Looking closely, the compressor is not even close to being factory and neither are the brackets holding it on, on top of that it says R134 only on the top surprise. I dont think the PO knew any of this, it was probably done by the first owner’s mechanic. 

Anyways, I cant figure out how the numbers on these belts work. I went to both Advance and Autozone and looked at all the belts and had no luck. 

This is what I have:

914Driver MegaDork
8/15/19 6:34 a.m.

I can't speak for Continental, but with NAPA belts the first digits are the width X length.  Run a rope (clothes line size) around the AC belt route then lay it out and measure its length.  Measure the width of the V pulleys.  That will get you closer than you are now.


Slippery SuperDork
8/15/19 6:51 a.m.

That’s exactly what I needed. I know the 13 on the Conti is the width in mm, but the length I cant figure out how it correlates to the 835. 

I will give Napa a shot. 

cdowd Dork
8/15/19 7:00 a.m.

Generally the 835 is mm also so a little over 2.5 feet. So an additional 1.5 inch would be 870 or 875 and 2 inches would be like 885.

Slippery SuperDork
8/15/19 9:29 a.m.
cdowd said:

Generally the 835 is mm also so a little over 2.5 feet. So an additional 1.5 inch would be 870 or 875 and 2 inches would be like 885.

That is what I always thought, at least on the serpentine belts its like that. It does not seem to be the case with these. 

Per the Continental specs the 835 is 14.25” long. 835mm = 32.875”

boulder_dweeb Reader
8/15/19 9:49 a.m.

I needed a new V-belt for the racecar, cause I move the Alternator.

Oreillys had a slew of 1/2" belts and sold me several to cover the size range. The Oreilly guys were very helpful and the belts were not expensive. No hassle when I returned the unused belts.


ShawnG PowerDork
8/15/19 10:49 a.m.

Go to your FLAPS

Tell them to go in the back and dust off the belt gauge.

Read the instructions on the belt gauge and measure the belt you have.

Use the belt gauge to figure out what the number will be on the longer belt.

Tell them to get you that one.

If they don't have a belt gauge, stop shopping there and find a real parts store.

According to my belt gauge, you need a 13A870

Slippery SuperDork
9/28/19 3:16 p.m.

One to update this thread as this has been solved. 

The Continental specs are incorrect on their website, the 835 is indeed 835mm which equals 32.875”. 

I went to Napa and bought an AX33 belt and it was HUGE. I went back to Napa and the guy that sold me the last one gave me a few belts and said to just return the ones that did not work. He was confident the number was the length in inches, but it did not matter as I had four different ones to try:

  • AX29
  • AX30
  • AX31
  • AX32

AX31 ended up working, at this point I did not care about the length as it worked and I had AC again. 

I went back returned the ones I did not use and bought two new ones for the power steering and alternator as they did not look good at all.

After installing them, I noticed the dimensions on the back of the cardboard. AX31 = 33”!! All their 1/2” wide belts are 2” longer than the number laugh

Streetwiseguy MegaDork
9/28/19 3:21 p.m.

Yeah.  They do that because people are evil, and they suck. 

ManhattanM (fka NY535iManual)
ManhattanM (fka NY535iManual) Reader
9/28/19 3:55 p.m.

I feel your pain, why can’t this stuff be simple?! I’ll spare everyone the details, but I had a similar experience late last night when the specced new belt didn’t fit. I always *thought* I knew how belt naming conventions work, but turns out NAPA is indeed the exception! 4 hours calling parts stores this morning...and I ended up putting the old belt back on and ordering what I hope works from Rockauto.

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