The Hidden Profit in Your Parts Department. A Diesel Stories Recap

Summary:

• Parts can drive half a shop’s revenue, but weak pricing, tracking, and inventory habits can drain margin fast.
• Skilled parts people protect bays, estimates, techs, and customers because they know how to find answers under pressure.
• Cheap parts stop looking cheap when downtime, air freight, spoiled loads, and angry fleet customers hit the work order.

A shop can sell millions in parts and still treat the parts department like somebody’s side chore.

Yep. That one should make a few shop owners shift in their chairs.

On this episode of Diesel Stories, host Peter Cooper, owner of Ascend Consulting, sits down with Jamie Irvine, who brings nearly 30 years of heavy-duty parts experience and hosts his own industry show, The Heavy Duty Parts Report. Together, they get into the real economics of a parts department.

This was not a neat little chat about filters and brake drums. It covered tariffs, inventory, counter people, margins, right to repair, downtime, and Saturday air freight.

The big idea is simple. Parts are not just boxes on a shelf. They are money, workflow, trust, and truck uptime. When that system breaks, the tech waits, the bay stalls, the estimate drags, and the fleet customer starts asking why that unit is still down.

That sounds familiar, right?

Parts Are Not a Side Hustle in the Shop

Peter made a point that a lot of general repair shops need to hear. In his experience, parts often drive about half of a shop’s total revenue. That means a $5 million shop might have around $2.5 million running through parts.

Now compare that to labor.

Peter pointed out that a shop may need six or seven diesel techs to sell that much labor. But on the parts side, one good parts person may touch a huge chunk of that revenue. That should change how owners look at the parts counter, the stockroom, and every stock order.

Jamie agreed that people often make the parts business sound too easy. Buy it, stock it, sell it. Done.

Not quite.

Inventory ties up cash. Price matrices matter. Internal parts sales differ from out-the-door sales. Rebates change the math. Delivery costs eat margin. And when parts move from distributor to bay to work order, someone has to track the cost.

Jamie put it bluntly when talking about delivered out-the-door parts: “If I’m not making 20% margin on that sale, I’m losing money.”

That matters because a busy parts department can still bleed cash. A shop can sell plenty of parts and still miss the profit hiding inside that work. Or worse, it can lose money while everyone feels busy.

Look. If the parts process is loose, the whole shop feels it. The tech waits with a wheel end apart. The service manager chases updates. The estimate sits. And the customer just knows their truck is not ready.

Your Best Parts Person Is Not Replaceable by a Catalog

Every good shop owner knows this person.

It might be Kenny. It might be Hank. It might be the older guy at the counter who can look at a brake shoe and know what you need before you finish your sentence.

Peter had that guy. His name was Kenny. Peter said he would wait in line for him because his time mattered. Kenny knew parts, and he made life easier for the shop.

That kind of parts person does not happen by accident.

Jamie said it takes a minimum of two years to train a parts person until they become useful. That may sound harsh, but anyone who has worked around heavy-duty parts knows he has a point. This is not just clicking through a catalog and hoping the VIN behaves.

It takes judgment.

Jamie talked about having mentors early in his career. One mentor would ask him, “Do you want me to tell you the part number, or do you want me to show you how to look it up?”

That is how craft gets passed down.

Peter also remembered flipping through paper catalogs and matching switches by sight. He joked about parts stores struggling to identify an O-ring by size, or tell the difference between similar valves.

That is not just nostalgia. It affects real shop flow.

If a tech gives an incomplete parts list, a sharp parts person catches what else may fail. If a DPF keeps coming back, a good parts person may ask about an upstream issue. Maybe the turbo needs a leak test. Maybe there is blow-by. Maybe the part is not the real problem.

That kind of thinking saves bays, labor hours, and customer patience. It also keeps service managers from rebuilding estimates because someone forgot the gasket, clamp, seal, kit, sensor, or hardware.

Cheap Parts Do Not Help When Spinach Is Dying in a Trailer

Price matters. Nobody is pretending it does not.

But in heavy-duty repair, price is not always the biggest cost. Downtime usually gets a vote, and downtime is loud.

Peter told a story about a fleet hauling spinach from Sacramento to Toronto. The trailer blew a hub. It was a Canadian trailer with air disc brakes, back when those parts were harder to find in the United States.

Everybody said no. Nobody had the hub. Nobody could get it.

Then one supplier said yes, but there was a catch. The part needed $1,400 in Saturday air freight.

Peter did not blink. He paid it.

Why? Because that spinach had a clock on it. From the minute it left the ground, it had only so many days to reach the store shelf as fresh produce. Saving a few bucks on parts would not matter if the load died on the trailer.

That is the thing fleets understand quickly. A cheaper part next week does not help a truck that needs to roll today. It does not help the driver, the dispatcher, or the customer whose freight is turning into compost.

Jamie summed up the real skill of a great parts person this way: “Being a great parts person is all about being able to find the answer, not knowing the answer.”

That line matters because heavy-duty customers do not just need parts. They need options. They need answers. They need someone who can say what is available, when it can arrive, what it costs, and what the tradeoff is.

A reliable vendor can beat a cheaper vendor when the truck is down, the driver is waiting, and the load has a deadline. Not every job needs Saturday air freight. But when it does, the shop needs someone who knows who to call before the approval turns cold.

The Conversation Kept Going

This episode covered a lot more than parts margins and counter people. Peter and Jamie also got into several issues that deserve their own shop meeting.

• Tariffs have made parts pricing more complex, especially when shops quote big engine jobs, retrofits, or upfitting work. Jamie said tariffs shifted some buying decisions toward local suppliers, especially when domestic options exist.
• Right to repair came up as a real issue for independent shops, not just a policy debate. When you can’t buy a single part for a transmission, a routine clutch job can become a $22,000 bill. Peter and Jamie talk through what parts access restrictions actually mean for independent shops.
• Turnover has a price tag most shops never see. The real cost of losing a parts person doesn’t show up as a line item on a P&L. Peter and Jamie talk about hiring, technician pay, shop culture, and why good people leave when shops treat them like line items.
• Bad technology and weak price matrices bleed margin on every sale. Most shops know when their systems are behind. Jamie argues that waiting to fix it is already costing more than the fix itself. 

So yeah, there is plenty more in the full Diesel Stories episode. If parts delays, margin leaks, downtime, and workflow hit close to home, this one is worth watching all the way through.

Watch or listen to the full Diesel Stories episode.