Part number correction for *better* fitting belts

These belt part #'s are listed elsewhere on SS but I would discourage using them. Both alternator belts will be on the far/long side of adjustment. The 15455 P/S pump belt is too long IMO and cannot be properly tightened if it's stretched or worn even the slightest bit. These are the sizes that were installed (now removed) on my 1031.
Not reccomended P/N's:
· Driver side alt- Gates# 7575; Dayco# 15580
· Passenger side alt- Gates# 7483; Dayco# 15490
· Power Steering- Gates# 7448; Dayco#15455

EDIT on 3/11: Gates/Napa 7575 for driver's side alt is a good p/n and fits well, only 15580 is not recommended
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The following part numbers are from Autozone's computer for an '86 K30 with 6.2

Alternator (pass side) Dayco 15480
P/S pump Dayco 15445

Notice a pattern? Autozone's P/N's are for shorter belts

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Tested and Recommended P/N's
Pass side alt: 15480 (same AZ's P/N for a civvy 6.2)
Driver's side alt: 15573 (It fits)
P/S pump 15445 (Same as AZ's P/N for a civvy 6.2)

The belts that I listed as preferred are pretty much the bare minimum length. All three will all have to be "rolled on" by turning the crank with a long handled 1/2" ratchet or breaker bar even with the brackets fully loosened. You will also *need* a Lisle 12400 belt tensioning tool because with the shorter belts there's no room for the field-expedient prybar method of tightening. The shorter belts are more involved and difficult to install, but on the positive side - you'll never run out of adjustment and run much quieter than the longer p/n belts.


Auto Belt Cross Reference. Gates Napa Dayco Auto Belt Cross Reference
Note: Autozone's "Valucraft" line use Dayco P/N's

I had this same problem about 4months ago my mechanic figured it out. the belts would last for about 6months for me until it was resovled

you can add these to the wiki if you want to help so it does not get lost in the forum.

Info requires several notes on fitment/installation though, and I'm not sure how to add that to the wiki without making it confusing as heck. Maybe admin could make a note? The sizes currently on the wiki are approximately the longest belts that will fit and still work (any longer and you'd have no adjustment). The sizes that I listed are pretty much the shortest belts that will fit. See alternator pic below and note position of bolt head in the adjusment slot - it's only about 1/2'" away from minimum.

left to right...
Pic 1 is of what my pass side alt now looks like w/belt fully tightened for comparison
Pic 2 is of the special tool you'll need to do the job right.
Pic 3 is of belts actually used, so I can personally confirm they fit. Nothing special - $20 for all three.
Pic 4 is the "trick" for tightening the P/S pump bracket without denting up the reservoir with a prybar (put a 3/4" or 19mm wrench on the square lug on bottom to pull belt tight, and snug up the lower bolt with 15mm wrench to hold tension while you tighten the other hardware)

I used the napa part numbers and i had no issues with my truck though.

I thought I read the Dayco belts aren't the best quality?

I think I've figured out partially where the discrepancy comes from...

Out of curiosity I looked up the p/n for a fan/alt belt on Napa'a website for an '84 K30 with 6.2 diesel.
Napa'a site says p/n is 5725.
Napa 5725 crosses to Dayco 15480 (same as what I used)
So Autozone and Napa both agree on same P/N for pass side alt. 1984 or '86 - doesn't matter.
(strangely, the CUCV Wiki lists 15490 which doesn't jive with either)

P/S belt is where it gets interesting
on all the parts sites I checked for a 1984 6.2 they indeed list 15455
But...for a 1986 6.2 they list 15445 (notice only a one digit change)

The 15445 definitely fits my 1031 better, so I'll assume that my particular truck has the 1986 style brackets and/or power steering pump pulley? Makes sense that the pump's probably been changed out in the last 25 years.

Mystery solved

45FMJoe said:

I thought I read the Dayco belts aren't the best quality?

Click to expand...

I like the Dayco better than the Gates. I will not use the Gates again.



Ive used the part numbers in the wiki and they work. But my passenger side one is tight and the Driver side one is a little too long.

I plan on using the GATORBACKS in the WIKI I hope there better any info on this is appreciated.

when you change out a PS pump you usually use the same pulley. They dont come with a new one.

One thing to remember, the stock alternators came with a 77mm pulley. Sometimes during rebuild they where replaced with a different size. (usually 68mm). I have personal seen this.

http://www.steelsoldiers.com/cucv/47479-correct-alternator-pulley.html

Also pulleys do wear. Belts fit differently on worn pulleys.

So just because a belt will fit your truck, it may not fit someone else's.

And as always, YMMV.

Warthog said:

One thing to remember, the stock alternators came with a 71mm pulley. Sometimes during rebuild they where replaced with a different size. (usually 68mm).

So just because a belt will fit your truck, it may not fit someone else's.

Click to expand...

That is true out of the four alts I own three have the same size pully and the fourth one has a smaller one.

Good points Warthog.

I have all the "not recommended" belts at the top of this thread and they are long. They do work, but I will probably try the shorter ones next time.

Warthog said:

One thing to remember, the stock alternators came with a 77mm pulley. Sometimes during rebuild they where replaced with a different size. (usually 68mm). I have personal seen this.

http://www.steelsoldiers.com/cucv/47479-correct-alternator-pulley.html

Also pulleys do wear. Belts fit differently on worn pulleys.

So just because a belt will fit your truck, it may not fit someone else's.

And as always, YMMV.

Click to expand...

Measured my alternator pulleys
Driver's side averages about 78 mm at far outside edge
Pass side is slightly bigger at about 79mm.
You'll have to trust me on measurements because it's hard as heck to focus on a dial caliper with one hand using a cell phone cam. But I'd say give or take a millimeter, they both qualify as "stock". Nowhere near the smaller 68mm figure.


Castle Bravo-
see before and after of Passenger side "Daycog" style with notches on outside on far left is before - wasn't a bad belt, just the wrong size. Don't have a "before" of driver's side but you can see what it looks like now with the new belt in 3rd pic from left.- much better fit with shorter belt.

Speaking of your "Daycog" style with notches on outside" I tried a set of that style..they were garbage. After 3 years, the upper cogged layer started delaminating, looked like they were 30 years old. The lower section still looked like they it would hold but replaced them as I couldn't stand looking at them.. Guy at store tells me they no longer carry that type as they weren't very good quality. Go figure.

GEEEZ thanks alot.!!! Now I gotta go back to Napa and figure out what I really need for belts!! I confuised now!!!

Here's what I learned today. After putting new shoes on my M1009 I felt comfortable taking longer rides. So 40 miles from home I blew both alternator belts off! Of course, it's 25 degrees and a 30 mph crosswind. Bad language followed. Got to a Napa and was told we can't find anything for that. I got on the internet with my phone (see dear I DO need internet on my phone) and gave him the Autozone numbers to try and cross to. Still no joy. He sent me to the local GM dealer. I went to the counter and he motioned outside and said I just sold one like that. Now we're in business!! He looked it up in the manual and called the SAME NAPA that had sent me here with numbers to cross. Magic happened, he had them!! So here are the NAPA numbers crossed from the GM manual. For the drivers side 25-7575 and passenger side, 25-7480. The alternators/pullys are the same as what were on it when I got it. The drivers side is midpoint for adjustment and the passenger side is just barely started for tightness. Hope this helps someone out there!

I like the idea of shorter belts. Shorter means less potential for belt deviation during operation. Need to go get lisle tool and shorter belts today! Tired of adjusting out slop every three months. Thanks for valuable information SS.

cucv1833 said:

I like the Dayco better than the Gates. I will not use the Gates again.



Ive used the part numbers in the wiki and they work. But my passenger side one is tight and the Driver side one is a little too long.

I plan on using the GATORBACKS in the WIKI I hope there better any info on this is appreciated.

Click to expand...

I went with the gatorbacks.
One thing I would recommend is get them asap.
It looks like no one is carrying them any more and the only way I could find them was ordering online .. (I think from rockauto) and thier stock was noted as basically 'untill what we have is gone'.
I followed the advice to go one size smaller on one of the belts and they all fit just fine.
PS belt was a little difficult to get tight, and I still plan to re-tighten it at some point.

Hi guys,

Matt1031 out of Atlanta here, came out to assist me with my alternator belts.
Since my drivers side had snapped and gone.
With his assistance, we found out that the proper size for at least my M1009 is
Napa part #: 25-7575 for the drivers side
And Napa part #: 25-7480 for the passenger side..

And both belts are long enough to put both alternators in the middle of there brackets,
when they are properly tightened, so there is room for future adjustment.

Hope this helps.. Thank you again Matt1031.. I appreciate your assistance..

Good day,

CJ