I called the Corvette museum and was able to order my original window sticker and build sheet and it arrived today. I'm a little confused on one item. The rear axle??? On the build sheet it calls for a HK1 which is a 2.87 axle but on the window sticker the norm is a 2.72 and now where in the option list does it say a 2.87??? Can anyone figure that one out??

 

Its helpful to list the year but I'm guessing you have got an 81-82 but the HK1 is the RPO (regular production option) code or ordering code. I think one of those years, 82, it was base equipment meaning no options so it would not have been on a window sticker but when the Corvette model box was checked, it would have called out HK1 as the axle code that translates to the 2.87 ratio on the buildsheet.

 

Differential code OA 2.72:1 for cars with standard rally wheels
Differential code OF 2.87:1 for cars with the optional aluminum wheels

Your build sheet will deal with exception control lists; your window sticker will show what the first owner was billed. Was your car ordered with aluminum wheels?

The aluminum wheels were lighter than the rallies, but I have never run across a source explaining why different gear ratios were required. Anyone know?

 

Tell me more about how you got the build sheet and original window sticker from the Corvette Museum.

 

 

https://store.corvettemuseum.com/ser...buildsheet.asp

Point and shoot. Be advised the NCM does not have 100% complete information, but they have most of the Bowling Green built cars.

 

I'm guessing, here....but the aluminum wheels also got a larger width tire. It was likely larger diameter, also. Perhaps the axle ratio change was to compensate for that larger diameter tire.

 

Yes it was ordered with the aluminum wheels with the optional tire sizes of 225/70/15s. I thought the optional tire size was the 255/60/15 but maybe that was for the Collectors Edition. If you don't have the build sheet and window stick invest in the $. It is very interesting!!

 

We really need to see both documents to suggest why this may have occurred...like do the VINS on both documents reconcile? And what year?

 

Ya I guess that would help. It's a 82 and the vins match, actually they break the vin it down. My car was # 2,147 built of 25, 407

 

For 1982, the 2.73 gear set came with the standard steel rally wheels and the 2.87 was supplied when the optional aluminum wheels were ordered. I've never found a good explanation for this, and it was the only year that GM did it.

If I had to guess, I'd say that it had something to do with GM's struggle to meet fuel economy standards, and avoid the "Gas Guzzler Tax". The reduced weight of the aluminum wheels, may have allowed the use of the slightly shorter axle ratio?

P225/70R15 was the standard tire size for 1982, in a black sidewall tire. If your build sheet and/or window sticker, show 225/70's as an option, it means that your car was ordered with them in the optional white lettered version. The P255/60R15 was also available as an option, on 82 Corvettes. The 255/60 only came in a white outline lettered tire.

Both the standard 70 series tire, and the optional 60, were made by Goodyear. The 70 series tire was a Goodyear "Polysteel Radial", while the the 60 was a Goodyear "Eagle GT" radial.

The P255/60R15 white outline lettered Eagle GT, was included as standard equipment on all 1982 Collector Editions.

 

Going back to your original question, because your car was ordered with aluminum wheels, the HK1 2.87 rear axle ratio was included with the wheels. This is why the build sheet shows the inclusion of HK1.

The 2.72 axle ratio, is probably listed at the top of the window sticker, in the box with the heading "The following items are standard on this model at no extra charge unless replaced by optional equipment:". The 2.72 was standard equipment, so it was listed as such, under the list of standard features on the car.

The HK1 2.87 rear axle ratio was not offered as a stand alone option, it could only be had with the optional aluminum wheels. When N90 aluminum wheels were ordered, the 2.87 automatically replaced the 2.72. The ratio wasn't listed, because it was part of RPO N90, Aluminum Wheels.

You had a similar situation when FE7 Gymkhana Suspension was ordered. Under standard equipment, the window sticker lists the fiberglass rear spring. Gymkhana Suspension replaced the fiberglass rear spring, with a steel 9 leaf spring, and added a rear sway bar, but the fiberglass spring was still listed at the top of the sticker and all that was listed next to the RPO FE7, was "Gymkhana Suspension". The additional features included with Gymkhana, were not individually listed.

I hope all of this makes sense to you, and answers your question.

 

Sure does thanks!

 

One item that I am disappointed about is my car has a power antenna but the window sticker list just a fixed mast. I could tell it's not factory just by the antenna nut, I like everything to be factory so I bought a NOS power antenna but now might be a pain in the butt to hook it up if the factory harness isn't there??? Maybe I'll try to incorporate the factory nut...

 

The antenna is a NOS Delco, it should be a direct bolt in.

Original GM service replacement power antennas came with a wiring harness, the power antenna relay, and instructions. The antennas were designed so that they could be retrofitted into cars originally equipped with a fixed mast antenna. I'm pretty sure that there is a terminal in the jack compartment, to connect the harness for the antenna into.

Check your antenna and see if it came with the relay, etc. If not, PM me as I know I have some NOS harnesses and relays. Whenever we were selling a power antenna to replace a bad one, we saved all of the extra parts. I may still have a copy of the installation instructions too, as I still have one NOS Delco power antenna sitting on the shelf. I've been saving it for 15 years, waiting for the original one in my 81 to stop working.

 

Aha!! A good example of an exception control. Noland Adams is a whiz with these, but I'm still learning. The N90 option had an exception control for the 2.87 ratio.

 

Ok...I'm on board. I have a stack of 82 buildsheets and browsing thru them I have several with FE7. I don't have the window stickers but on the build sheet when RPO FE7 is listed, the broadcast code NML in box 16 is called out. When FE7 is not listed in the RPO list, rear spring code 141 is called out which must be the mono spring. We also see the heavy-duty shocks ZA and ZE (front, rear) are called out for FE7.

So this is the application of exception control codes. Are you familiar with merchandising codes and how they were used?