How to C-Notch a C10 Truck Frame
We’ve all been there. You’ve installed lowering springs or blocks and your truck’s stance is dialed in. On your first trip around the block, you notice that the rear axle is pounding on the bump stops or worse yet, the frame itself. “I can live with that,” you think. But a few weeks later, once the honeymoon period is over, you’ve grown tired of the terrible ride and realize that it’s time for a C-notch. When you get there, here are a few things to know.
Do you need a C-notch?
The answer to the question of whether your lowered truck needs and underbed notch is determined entirely by your application. However, we have found that getting a truck down in the weeds where it looks good will often require more rear suspension travel that the stock rails will allow. Mock your truck up at the ride height that you want and be realistic about how much suspension travel you need. An inch or two is not enough.
Since the above video shows the install of a C10 C-notch, here’s a case study from your author’s personal history. My ’69 C10 was dropped five inches in the rear. This is a fairly common drop for these trucks and it really makes a difference in the appearance. However, with that fairly mild amount of drop, the rear axle tubes ended up less than an inch off the bump stops. I can tell you from the experience of driving the truck around that way that an inch is not enough and the ride quality was miserable.
Step Notch vs. C-notch
There seems to be some confusion about these terms. Quite simply, a C-notch is a section removed from the bottom of the frame, while a step notch requires that the rails be completely cut out and replaced with new metal. A step notch is for radically lowered trucks and will be necessary if you want your truck to “lay frame” or air down to within inches of the ground. Keep in mind that this amount of lowering requires radical changes to the rest of the truck and is not for the faint of heart.
What is a Bolt-on C-notch
Many C-notch kits require welding. A bolt-on C-notch can be installed by drilling holes in your frame and installing with bolts. We used a bolt-on kit in the above video on our ’68 C10 project and found the install to be quite simple and many of the holes already existed in the chassis. Depending on your application, there may be a bolt-on kit available that will simplify things if you’re not a welder.
It’s also worth noting that just because a kit is a bolt-on, that doesn’t mean you can’t weld it. If you’re a good welder and would feel better about your install if it were welded solid, that’s also an option.
Does the C-notch weaken your frame?
The answer to this is also simple. If done right, your frame will not be weakened by notching it. It’s possible to do this the wrong way and create a dangerous situation. If you’re at all in doubt about your abilities, please check in with an experienced builder or a certified welder to make sure you’re not sacrificing the structural integrity of your frame. Remember that the original frame under your truck was designed by a team of engineers and put through rigorous testing. Just cutting out chunks of it willy-nilly will not result in a safe and square foundation for your project.
The bolt-on kit that we used in our C10 is made from ¼” steel and bolts in with 7/16” hardware. It picks up multiple mounting points over a large area and more than makes up for the small portion of frame that we removed.
C-Notch how-to guide
There are a million ways to do this. The important thing is to be sure to reinforce the frame to make it as strong or stronger than it was before being cut. Also be sure to allow enough travel. Mock everything up at the ride height that you want first. It would be a bummer to fully install a notch, only to realize that it still didn’t allow enough suspension travel.
Here’s how we did it. The above video shows the install of our Bolt On 1963-1972 Chevy C10 C-notch kit. There are other options available, but this kit is among the most straightforward. You’ll notice that we were working on a bare chassis. This obviously makes things way easier, but isn’t necessary. This process can be done with the truck assembled, it will just be a bit more awkward.
We started by removing the old bump stop tabs on the outside of the frame. Since we were installing this in conjunction with our C10 G-Comp Rear Suspension kit, we also removed the crossmember, but as you’ll see in the video, this isn’t necessary. Only the tabs on the spring plate will need to be trimmed to install this kit with the stock crossmember.
As you’ll see in the video, we were preparing to cut the framerails when we remembered that we would need to remove a few rivets. Those of you who have done this know that sometimes there’s some struggle involved, and we were concerned about hammering on at frame that was weakened with a section removed for the notch, so we chose to do this first. It’s also important to note that once the rivets were out, we were careful to support the frame with jack stands in multiple places before cutting to ensure the weakened frame did not get out of shape.
Rivets removed and chassis braced, the next step in our install was to mark the frame with our cut lines. Using the notch as a template, we aligned it as it will be installed (easy to see by referencing the holes in the notch relative to the rivets in the bottom of the rails). Mark around the outside of the notch portion, and cut conservatively. It’s always easier to take more metal away than it is to add it back. We drilled the corners to give us a nice radius and provide a place to turn our cutoff wheel. Don’t leave any sharp corners in your cut portion, because these are sure to turn into cracks down the road.
Once cut and dressed up, we were then ready to install the notch and the bolts in the bottom. This allowed us to drill the sides of the frame for the remaining bolts. With those holes drilled and bolts installed, we were ready to add the provided poly bump stops and complete our installation.
It’s also important to consider all the other things that will change by allowing the rear axle to travel higher. Be sure to check clearances around the driveshaft, above the rear axle housing to the bed floor, tire to fender, etc. Just because you’ve made room for the axle doesn’t mean the rest of the truck is going to cooperate.
With some careful consideration and a careful install, a C-notch will drastically improve the ride of your lowered truck. If you've been dragging your feet and suffering with a lack of rear axle travel in your truck, we highly recommend installing one of these. You won't regret it.
