GM vs Ford Alternators

Scope

Before we get started let's preface this article by saying that there are a ton of different variations of alternators especially as you get into the 80s and 90s. For the basis of this article we are going to concentrate on the applications that would equate to CVF pulleys and brackets.

GM Alternators

To begin with there are three main GM alternators that we deal with: 10DN, 10SI and 12SI.

The 10DN was an externally regulated alternator typically found from the early 60s through the early 70s.

The 10SI, where the "SI" stands for "System Integrated", is an internally regulated alternator that replaced the 10DN external regulated alternators beginning in the late 60s on into the early 80s.

As vehicles began to use more electronic features, the need for more power brought about the 12SI which was usually a higher amperage and used from the early 80s on through the end of the decade when alternators started to get different mounting bosses, clocking points and hole spacing.

Ford Alternators

Ford alternators are commonly referred to in the industry by generation level as in 1G, 2G, 3G. What we typically deal with as it relates to our product is 1G and 2G which is what our brackets and pulleys were designed around. But we also get a lot of questions about 3G as well.

The 1G was popular for a long time and was used not only by Ford but also by AMC and Jeep. Pretty much everything from 1964-1985 used the 1G alternators which were externally regulated 4 wire alternators and ranged in amperage from 35A to 90A.

In the early 80s Ford started to transition to the 2G alternator which has roughly the same case size but had higher amperage offerings and internal regulation.

The 3G replaced the 2G and brought with it some case design changes that made it larger and also went to internal cooling fans. The inherent problem when it comes to 3G alternators is that there is a lot of variance in the aftermarket with where hole placement is, casting housing thickness, depth of case around the alternator shaft, and so on. So a lot of our brackets will work with a 3G alternator but in some cases modification may be necessary.

The CVF Difference

So the biggest difference between the two alternators as it pertains to our bracketry centers around the mounting ear. A GM alternator is typically around 2" and a Ford alternator is around 3". The through hole between the two is different as well. Typically the GM is a 3/8" through hole and the Ford is a 7/16".

The other main difference is going to be in the center to center distance between the top and bottom hole. A Ford will be 6.8" and GM will be 6.6".

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