What year did GM switch from the 7.5 to 7.65 in the 3rd gen cars?

I am building up a new rear end using GM / Motive 3.73's - 28spline for my CMC race car.

Can I use this mini-spool which is listed for a 7.5 rear in a later model 90-up 7.625 case? I think the guts are basically interchangeable as long as the spline counts match. Is that correct?

http://store.summitracing.com/partde...5&autoview=sku

thanks

 

Not quite....

At some point, maybe in around 86 or 87 I'm not sure the exact year, they changed the internal details of the carrier. Small gears from before won't interchange into the later carriers and vice-versa. Since those "mini-spools" take the place of the small gears, they have to match the year of the carrier.

On top of that, the hole in an originally 26-spline carrier where the axle comes in, isn't big enough to allow a 28-spline axle to fit through, even if you put the 28-spline side gears in it (which I'm not sure they will even fit).

Bottom line, you pretty much gotta know what you've got, and get the right mini-spool for it.

It doesn't have anything to do with 7.5" vs 7.625", as such; but the carrier change occurred at about the same time.

 

hmm. Well let me restate it this way:

I have 7.625" gears - 28 spline.
And I am looking at a '90 housing / carrier
will the 28 spline mini-spool shown above work with that combo of parts?

 

Looks like the right one...

AFAIK there's only one 28-spline variant; so that makes it easier.

 

cool..

One more thing I thought of - the gears in the 90 rear are 3.08's - is that considered a 3-series carrier so a 3.73 will bolt in? Or is 3.08 a 2 series carrier and shared with the 2.73?

 

I do believe that the 3.08 is a 2 series carrier.

Just looked it up on the Strange Engineering website for confirmation. 3.08 is a 2 series carrier.

Also, when the rear changed to the 28 spline axles is when it got the 7.625" title, but I believe gears and axles can be swapped all day long between any of them as long as the spline count matches up.

 

that is what I was thinking. Well - I guess I will pass on that rear end and look for one with 3.42's so I don't have to change the carrier.

 

X2 for the 3.08's being a series 2 carrier. Pontiac went to a 26 splined 7.625" rear in 1985. Chevy went to the 26 spline 7.625 rear in 1986. GM used 26 splined axles in 7.625 rear ends until 1988. GM switched to 28 splined axles in 1988(some 88' F-Bodies came with 26 splines and some came with 28 splines. 1988 was the crossover year.
----------
The GU5 3.23 gear ratio is also a 3 series carrier.

 

Gm changed to 28 spline in 1990 although there may be a few late production model 89's with 28 spline.

As mentioned above, you can't use a 26 spline carrier for 28 spline axles so putting a 28 spline mini spool into a pre 1990 carrier won't work.

A mini spool is designed for dirt track racing where a locked differential is required but maximum traction to the ground is never achieved.

Using a mini spool on the street or drag strip is asking for trouble.

The difference between a 7-1/2" and a 7-5/8" is nothing. It's only the overall size of the gear that changed. Everything else stayed the same. A gear set on an older 7-1/2" carrier will fit on a 7-5/8" carrier because the carriers are the same.

To do what you want to do you need
28 spline mini spool
1990+ 28 spline open carrier. Third, fourth gens, S10 etc.
28 spline axles either aftermarket or from a 1990-1992 third gen
Any 7-1/2" or 7-5/8" gear set in the series to fit the open carrier.

 

The application is a road race car, and the mini spool actually works rather well - that is what I am using now and I am fairly happy with the operation. Much cheaper than a locker rear and seems cleaner and longer lasting than welding the carrier which is what many guys running this class end up doing.

 

You do have another option for the gear set change.

If your car is currently equipped with 3.08 gears which is a 2 series carrier and you want to change the gears to say 3.73s but are not willing to change the carrier as well, than get yourself a 'thick' gear.

For example, the company 'Yukon Gear & Axle' make 'thick' gear sets. Meaning a 3.73 ring & pinion for a 2-series carrier. It would be like adding a spacer onto the ring gear except its actually incorporated into the ring gear.

CLICK HERE TO SEE FOR YOURSELF

Not to mention, Yukon gears are probably one of the best/strongest gear sets you can buy for the money.