What 14-Bolt Do I Have? GMC or Chevy 14-Bolt Rear Axle Identification

This is why GMC or Chevy 14-bolt rear axle identification is a challenge. For decades, Chevy and GMC trucks, vans and SUVs came equipped with a 14-bolt axle. Between 1973 and 2000, a few 14-bolt axle variations were produced. If you’re wondering what kind of 14-bolt axle you have – and you’re working with a 14-bolt axle from the year 2000 or older – this guide is for you.

NOTE: If you’re more of a visual learner, check out our 14 bolt axle identification chart for a quick and easy guide.

First, To Identify Your 14-Bolt Rear Axle, You Can’t Go By Year, Make and Model

Before we get too far into this guide, we need to explain something. You can’t really figure out what kind of 14-bolt axle you have by looking up your vehicle year, make and model. There are two main reasons for this:

  1. GM offered more than one axle on multiple models. Chevy and GMC trucks, vans, and SUVs could be ordered with axle upgrades, and many vehicles were. There’s such a thing as a “heavy half-ton,” for example. A heavy half-ton may have a semi-float 14-bolt instead of a standard 10 bolt. There are also some 1-ton trucks that have semi-float axles instead of the full-float axle you might expect to find. It’s all about how your specific vehicle was ordered.
  2. You never know what the previous owner did to your vehicle. Unless you’ve owned your Chevy or GMC since it was new, you can’t be certain about what the last owner did to your truck, van, or SUV.

So, rather than looking up what kind of 14-bolt axle your vehicle is “supposed” to have, just use our guide to figure it out.

The Main 14-Bolt Axle Options

When most people talk about 14-bolt axles, they tend to focus on three attributes/options:

  1. Full-float or semi-float style
  2. Stud mounted drums or slide-on drums (full-float axles only)
  3. Single rear wheel, dual rear wheel, or cab-and-chassis (full-float axles only)

If you’re going to upgrade or otherwise modify a 14-bolt axle, you need to know what type of axle you have.

Full-Float vs. Semi-Float

“Float” refers to whether or not the weight of the vehicle is placed on the axle shaft (aka half-shaft) or the axle housing. If an axle is a “full-float,” it’s designed for use in a heavy-duty application. Because full-float axles use a wheel hub that mounts to a spindle, it’s possible to remove the axle shaft without removing the wheels. This is a big advantage for off-road use. This is because broken axle shaft repair is much simpler with a full-float axle. Additionally, the full-float 14-bolt axle uses a 10.5″ ring gear.

You can spot a full-float rear axle by looking at the wheels. Full-float axles have a tell-tale “axle end” that sticks out from the wheel surface. This is because the wheel hub on a full-float 14-bolt axle will stick out beyond the wheel mounting surface anywhere from about two to four inches. The full-float axle bolts to the end of the hub. On a full-float axle you can see a set of bolts at the axle end in addition to the 8 lugs you see on the wheel.

14-Bolt Axles as Upgrades to a 10-Bolt Axle

Semi-float 14-bolt axles are not quite as rugged as full-float 14 bolt axles. Compared to the 14-bolt full-float axle, the 14 bolt semi-float has a smaller ring gear (9.5″), and the axle shaft can not be removed without also removing the wheels. Still, the 14-bolt semi-float is a solid axle for a lot of applications. Compared to a GM 10-bolt axle (for example), a semi-float 14-bolt is a nice upgrade.

You can spot a semi-float 14-bolt axle by counting the lugs (if it’s a six lug wheel, it’s a semi-float), or by looking at the wheel surface. On a semi-float axle, the axle shaft terminates at the wheel mounting surface. So, there will not be a visible axle end.

NOTE: Some semi-float axles have 8-lug nuts. So, if you have 8 lugs but no visible axle end, you have a 14-bolt semi-float axle.

Dual Rear Wheel vs. Single Rear Wheel vs. Cab and Chassis

If you have a full-float axle, you’ll want to determine the width of the axle from wheel mounting surface to wheel mounting surface (WMS). This is important because it may help you buy the right upgrades (like one of our disc brake conversion kits), but also because it will help you figure out how you’re going to mount your 14-bolt if you’re doing a swap.

From wheel mounting surface to wheel mounting surface, there are three widths:

  • Single rear wheel (SRW) has a wheel mounting surface to wheel mounting surface distance of 67.5 inches.
  • Dual rear wheel (DRW) has a WMS to WMS distance of 72 inches.
  • Cab and Chassis has a WMS to WMS distance of 63.5 inches.

Stud Mount vs. Slide On Brake Drum Axles

Last but not least, if you have a full-float 14-bolt axle you’ll want to figure out what kind of brake drum mount you have. The slide-on style of brake drum is found on newer 14-bolt axles (1988 onward), while the stud-mounted drum can be found on any 14-bolt produced between 1973 and 2000.

To figure out which kind of drum you have, you should remove a wheel. If the wheel mounting surface is also the face of the brake drum, you have a ‘slide-on’ style drum. It’s called a ‘slide-on’ because it slides on over the wheel studs.

If the wheel mounting surface is the hub, than you have a stud mounted drum. This means the drum is “held on” by the heads of the wheel studs. Removing a stud-mounted drum requires…persuasion. This video is a good reference (skip ahead to about 4:55 to see the stud removal).

Additional Rear Axle Identification References

While Lugnut4x4 is an authority on all things 14-bolt, there are inevitably questions that will come up that aren’t answered here. So, in addition to this blog post, if you have a 14-bolt axle question, be sure to checkout the following:

Of course, when it’s time to upgrade your 14-bolt axle from drum brakes to disc brakes, be sure to check out our 14-bolt disc brake conversion kits here!