Alternator fitment issue

[Drewsk]

Replacing the alternator on my 85 GW because the old had failed. Ordered the alternator off rock auto, opted for a higher output version. Got it on today and the lower bracket won’t line up. I loosened it but the bracket is bottoming out against the oil filter attachment. Is there an adapter or anything I can do the get this to fit, or am I out of luck and need a different alternator?

[Drewsk]

After doing a little digging it appears I may have bought a 15si alternator, would that be what’s causing the misalignment? It was listed under rock auto for this year, so I assumed it would fit. It’s and 85ah unit

[akguy09]

15si is physically larger than 10/12si with no actual improvement a good 12si can from a Chevy pickup application can get a 94amp alt

[candymancan]

Easy unbolt the bolt to that lower bracket slightly. It swivels up and down for adjustment for other alternators. I put a 94amp 12si on my 76 J10 from its original 37 amp.. and only had to make slight alterations to mount it.

That lower brackets swivels easy. Use washers to make up the gap if there is one where you bolt it.

[Stuka]

The 15si shares a housing with the 11si, which has a 6.83" bolt spacing. These are intended for higher outputs, so the case is physically larger to have a larger winding.

The 10si and 12si have a 6.6" bolt spacing. These are what most people swap in.

I would suggest returning the 15si and getting a 12si.

There is more data here: http://www.billavista.com/tech/Articles ... -Guide.pdf

[candymancan]

stuka that lower bracket swivels it can swivel down to accomidate that bolt, the bolt hole is behind the lower arm of that bracket.. onnce you swivel it down itll be fine

[Stuka]

stuka that lower bracket swivels it can swivel down to accomidate that bolt, the bolt hole is behind the lower arm of that bracket.. onnce you swivel it down itll be fine

It depends which bracket he has. There is more than one style used. The photo is too close to see for sure. One is a single piece of stamped steel that is C-shaped. Both top and bottom holes are in this single piece. So there is no room to move either one.

I am unsure as to what years the different style mounts were used.

Single Piece:

single-piece.jpg

Two Piece:

two-piece.jpg

[akguy09]

" I loosened it but the bracket is bottoming out against the oil filter attachment"


Quote from the OP...so I doubt he can move the lower bracket anymore....probably best to just get a 12si

[Drewsk]

Thanks everyone for the feedback. It does appear to be a two piece bracket, but there is no more room for it to move. Getting a 12SI alternator, Napa had one in hand but it’s only 63amp, but came with the double pulley so it’ll at least be a direct swap. The original alternator came from rock auto, and they won’t take the return since it has been installed. There’s some pretty good rub marks on the case at this point too. Anyone in Colorado need a 15si 85amp alternator?

[candymancan]

The other thing i had to do with the 12si over my 37amp was i had to widen the top hole on the alternator itself. Thr long bolt for my 37amp was thicker than the 12si hole. So i had to shave it larger with a drill bit for it to fit.

I was worried a little as its already thinmer aluminum than the 37amp. And i made it even thinner. I also had to add shims. The 37amp top mounting was 3 inchs. The 12si was 2 incha. So i had to buy thick washer ring like shims. Here is my video how i did it

https://youtu.be/igtPRNxQ99I?si=1wiIiNKlFDWwZO7g

And this video goes more in depth on how i wired the 3 wire 12si from the older 2 wire 37amp with the external regulator

https://youtu.be/FcgjJ0rSYMw?si=KWII8l6XCYbvwBxy

[will e]

A while back a guy on this or the other forum sold lower brackets that would accommodate a CS140. I was prescient enough to pick one up years before I converted. There is still limited adjustment space but it is workable.

[candymancan]

I mean my 150amp fit just fine on my 90 gw ? Cs144 power master. But i dunno this seems confusing now to me

[tgreese]

To the OP, your Napa store can order in anything you want within a day. You needn't settle for what they have in the store. Mad Electrical has a page describing what to order to get the part you want. http://madelectrical.com/electricaltech/delcoremy.shtml Also discusses the pulley issue - I'd expect any application with AC to come in with a double pulley. Also, clocking of the alternator is trivial - you can set it to any clocking angle you want - ask if you need more coaching.

[Drewsk]

Tgreese thanks for that link, it explained quite a few things for me. I was able to get the new alternator successfully installed last night, tested it and it showed 14.49 while idling after start up. I’ll test it under load with lights and radio etc later today. At least I have a working charging system now. Might take a stab at rebuilding the old alternator that came off the GW to have on hand as a backup.

[tgreese]

NP! These "systems integrated" SI alternators are modular and easy to work on. BTDT. If the old alternator is broken in the electronics (the regulator or the diodes), IMO it may be worthwhile to rebuild it. Then again, it may be better to part it out and put the diodes and regulator in your spares bag. The parts are available if you search. The only consumables are the bearings and the brushes - I presume these are available too. If there is a problem (short or open) in the field or stator windings, it's toast and destined for the parts bag or the trash. The TSM has quite a lot about these alternators; worth reading IMO.

[Drewsk]

It’s an Delco 12SI unit, the autozone test said it was a bad voltage regulator. It was measuring 12.05 across the battery before I pulled it. It certainly needs a good cleaning, and I believe the voltage regulator is a readily available piece

[tgreese]

A bad (open) diode can make low voltage too. The alternator makes 3-phase AC which is rectified by 6 diodes - the diode bridge. You can test the diode bridge with a multimeter. Test the diode trio too. I expect a bad regulator is more likely - the older alternators (sp. the Motorolas) popped diodes occasionally, but I think the SI diodes are more rugged.

I believe there is no easy way to test the regulator by itself on the bench. If you repair, you kinda have to test all the other stuff first and what's left is the regulator.

Regulator: https://www.rockauto.com/en/moreinfo.ph ... 84&jsn=589