How to Lower a C10: Drop Spindles, Springs and Flip Kits

To lower a C10, most builders swap in drop spindles and lowering springs up front and flip the rear axle on top of the leaf springs with a frame C-notch out back. A typical bolt-on combo drops a 1973-87 truck about 4.5 inches in front and 6 inches in the rear while keeping usable suspension travel. Everything else (cut coils, blocks, shackles, air ride) is a variation on how far you want to go and how much you want to spend.

We build in our driveways here in Orange Park, and Rob drives a 1966 ratted C-10, so C10 talk never really stops around here. Here's a plain-spoken look at the options, what each one actually does, and where people get themselves in trouble.

Start with a plan: how low, and for what?

Before you buy anything, decide what the truck is for. A daily driver that still hauls mulch needs a different setup than a show truck that gets trailered to the cruise-in. Ask yourself:

• How low? Mild drops are mostly bolt-on. Big drops bring C-notches, shocks, bump stops and wheel fitment questions along for the ride.
• Do you still haul or tow? Some rear lowering parts reduce load capacity. Others keep it.
• What year is it? Kits are year-specific. The parts for a 1963-70 truck are not the parts for a 1973-87 truck, so buy for your exact year.
• What brakes are you running? According to Speedway Motors, GM added front disc brakes to C10s in 1971, so earlier trucks came with drums. A drop spindle swap is a natural time to fix that.

Front end: how to lower the front of a C10

Drop spindles (the best first move)

Drop spindles move the spindle pin higher on the spindle body, so the wheel sits higher relative to the truck and the truck sits lower. In Speedway Motors' 1963-70 C10 front-end write-up, the drop spindles alone accounted for 2.5 inches. Speedway's lowering guide notes that drop spindles don't change suspension geometry or ride quality and work with stock-length shocks, which is why most builders start here.

The catch: some applications have minimum wheel size or backspacing requirements because of tie rod end clearance. Check that before you fall in love with a set of wheels. On early trucks, the disc brake spindle kits in that same write-up also switched the truck to a 5-lug, 5-inch bolt pattern, which opens up a lot more wheel choices.

Lowering coil springs

Drop coil springs are shorter springs with rates matched to the truck. The Speedway C10 build used 2-inch drop springs, and stacked with the 2.5-inch spindles that made a 4.5-inch total drop up front. They're cheap and simple, but ride height isn't adjustable, and big drops can bring bump steer and the need for shorter shocks and modified bump stops.

Cutting coils (do it right or don't do it)

Cutting the stock springs is the budget-rat-rod classic, and it does work for small adjustments. Speedway's guide is blunt about the rules:

1. Never use a torch to heat or cut a spring you're keeping. Heat weakens the spring.
2. Don't take more than about half a coil, and use a cold cut method.
3. Expect a stiffer ride, especially once you cut a full coil or more.

And stock springs carry a lot of preload. Control them when you pull them out, keep your fingers clear, and use a floor jack to lower the arm slowly.

Drop control arms

Dropped (often tubular) control arms bolt on, usually come with new ball joints and bushings, and keep stock ride quality. They cost more, but if your original arms are worn out anyway, they can make more sense than a rebuild. The builder in the Speedway C10 story found exactly that: worn stock arms, so tubular arms won out.

Rear end: flip kits and the C-notch

The rear of a 1973-87 C10 rides on leaf springs with the axle mounted below them. An axle flip kit relocates the axle from the bottom of the leaf spring to the top. One supplier lists 4 to 7 inches of drop depending on the truck, and Speedway puts the typical range at 5 to 7 inches, based on axle diameter plus spring pack thickness.

Here's what a flip kit needs to work right:

• A C-notch. With the axle sitting that much closer to the frame, it runs out of room. A C-notch is a notch in the frame rail over the axle that gives it clearance, so the truck keeps suspension travel instead of slamming the axle into steel.
• Bump stop work. Plan on removing or relocating the stock bump stops.
• Shocks for a lowered truck. Shorter shocks or relocation brackets are usually required.

The good news: a flip keeps stock load capacity, so the bed still works like a bed.

Other rear options

• Drop shackles: the easiest leaf-spring part to install, usually about 2 inches of drop, with a slight change to pinion angle.
• Drop hangers: typically 2 to 4 inches, but installation often means drilling or cutting rivets.
• Lowering blocks: cheap and easy, but they only work with underslung axles, need longer U-bolts, and tall blocks (2 inches and up) can cause wheel hop.
• Lowering leaf springs: simple, but they may reduce load capacity on a truck.

Air ride: low when parked, drivable when moving

Air suspension lets you change ride height on the fly, lay it down at the show and air up to clear a driveway lip. It also costs the most and takes the most work: brackets, hoses, fittings, a tank and controls, and leaf-spring trucks may need a full kit such as a 4-link. If you want that parked-on-the-ground look without dragging the exhaust home, this is the route.

A common C10 lowering combo

If you want a starting point, a lot of complete 1973-87 kits package the same recipe:

• 2.5-inch drop spindles
• 2-inch front lowering springs
• 6-inch rear axle flip kit
• Frame C-notch, plus hardware and bump stops

That's the 4.5-inch front, 6-inch rear drop you see on a lot of street trucks. Add shocks built for a lowered truck and get an alignment when you're done.

Driveway lessons before you start

• Inspect ball joints, cross shafts and bushings while it's apart. Lowering a truck on worn parts just makes worn parts lower.
• Set wheel bearing preload carefully, don't overtighten the spindle nut, and put cotter pins in every ball joint and rod end.
• Watch the springs as you lower the jack. Short drop springs can shift and miss the crossmember pocket.
• Budget for the stuff nobody puts on the box: shocks, alignment, maybe wheels.

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Frequently asked questions

How much does a flip kit lower a C10?

An axle flip kit typically lowers the rear of a 1973-87 C10 about 5 to 7 inches, depending on axle diameter and spring pack thickness. Many kits are sold as a 6-inch drop and require a C-notch.

Do you need a C-notch to lower a C10?

For an axle flip, yes. Flip kits call for a C-notch so the axle has room to travel without hitting the frame. For other rear parts, follow that kit's instructions.

Do drop spindles ruin the ride?

No. Drop spindles don't change suspension geometry or ride quality and work with stock-length shocks. Check wheel size and backspacing requirements, since tie rod ends can limit clearance.

Can I just cut my C10's coil springs?

For small adjustments, yes. Use a cold cutting method, take no more than about half a coil, and never heat or torch a spring you plan to keep, because heat weakens it.

Sources: Speedway Motors lowering options guide, Speedway Motors C10 front suspension write-up, Switch Suspension flip kit listing, CJ Pony Parts C10 lowering kit listing.

Photo: Damian Kamp on Unsplash