Is there an gear ratio listed in most RPO glove box door lists?

[57rookie]

Short of pulling my diff cover off (which I don't want to do since the tranny shop just resealed it a filled with fresh oil), is there a list of RPO codes that someone could list with the corresponding rear axle ratio? I was hoping I could look up the code on my glove box door sticker to determine rear axle ratio...............
Thanks in advance.

[motornut]

here's one to try
http://www.73-87.com/chevy_ids/rpo-eg.htm#rpo-g

[Keith Seymore]

The link Motornut provided is a good one.

However, there are two caveats:

1) Base axle ratio (GQ1) is usually not called out by ratio, because it varies based on driveline options. Hopefully you've got one shown like GU6, GT4, etc, which are known by the specific RPO.

2) That's assuming the rear axle has never been changed, which might be a bit optimistic since the vehicle is 25 years old (or older). Would have been a good time to count teeth while the tranny shop was changing the fluid (which was a good thing to do, by the way).

K

[57rookie]

Perfect, thanks guys. I will (l check when I go back to my truck (which is in the body shop currently). It is definitely the original axle (only has 70K original miles on it). I will be hooking up a tach but I am hoping for a 2.73 or in that area as I want to be able to drive on highway without turning 3k, and I just had the TH350 rebuilt so I don't want to have to change to an overdrive unit.

[hatzie]

Originally Posted by 57rookie

Perfect, thanks guys. I will (l check when I go back to my truck (which is in the body shop currently). It is definitely the original axle (only has 70K original miles on it). I will be hooking up a tach but I am hoping for a 2.73 or in that area as I want to be able to drive on highway without turning 3k, and I just had the TH350 rebuilt so I don't want to have to change to an overdrive unit.

You might be happier with 3.08 or 3.55. Lower RPMs are not always better. You want to run the engine in the middle of its' sweet spot while you're cruising for good mileage.

[Keith Seymore]

2.73 (or GU2) is base for many, many combinations in our trucks.

What year is your truck?

K

[57rookie]

Keith, it is a 1986 GMC. I like you work for a truck OEM presently as a factory District Service Manager, but we build class 8 heavy trucks in a few brand names - largest global truck manufacturer but I love GMC/Chevy when it comes to my projects!. I appreciate the RPO info and will check my list when I visit my truck next week - in its final block sanding /paint stage! I will install a tach along with other final touches and was hoping to find a small enough tach to fit where the clock would go in the bezel. Do you happen to know the gauge size of the little ones in the bezel?

[Keith Seymore]

Here's the info packet from the GM Heritage Center archive for an '86 Chevy pickup:

http://www.gmheritagecenter.com/docs...olet-Truck.pdf

Powertrain charts showing axle availability start on page 20 (of the pdf; page 18 as shown on the page)

I don't know offhand the diameter of the openings in the bezel but could measure very quickly.

K