9 Costly Peterbilt 379 Exhaust Stack Replacement Mistakes to Avoid

Although replacing exhaust stacks on a Peterbilt 379 is a bit easier than some other models, it can still be a time-consuming and tedious experience that can easily take up entire weekend.

The difference between a DIY semi-truck exhaust installation taking a few hours and a few weeks is just one piece of faulty hardware.

So, be prepared.  

Here are the top mistakes to avoid when replacing exhaust parts on your Peterbilt 379.

#1. Buy Extra Exhaust Hardware Before Starting a Peterbilt 379 Exhaust Installation

While exhaust kits are fairly comprehensive, they don’t account for everything needed to secure the entire exhaust system.

You’ll need to buy additional exhaust components separately.

Start with 2 extra pre-formed band clamps and a piece of flex pipe (at the bare minimum).

Realistically, you’ll probably need more. Double check your setup beforehand just to be safe.

Remember to order enough flex pipe material and flex clamps at both ends, securing it to the rigid exhaust pipe tubing.

#2. Buy a Complete 379 Exhaust Kit Assembly Before You Start Installation

There’s nothing worse than chasing down individual pipes, clamps, and elbows because you forgot you needed a spare/replacement.

Make sure you have everything you need.

At 4 State Trucks, we sell complete 379 exhaust system replacements so that you’re not stuck in the garage Saturday with a disassembled exhaust system waiting for more parts before you start work on Monday!

Choose From: 

• Unibilt vs Non-Unibilt Sleeper Styles 
• 96", 102", 108", 114", and 120" height options
• Standard (factory-style) vs Quiet spools 
• Exhaust stack lengths of 52" (2003 and earlier) and 55" (2005 - 2007)

Quick Tip on the 379 Exhaust Kit Setup: Silicone vs Foil

The kits come with silicone to hold the pipes together. Once silicone heats up and dries, it's permanent. The pipes won’t come apart in one piece. Imagine it. If your 379 chrome stack tops happen to be pointed in different directions, you'll have to restart the installation.

This is partly why some drivers prefer using heavy-duty aluminum foil (a temporary adhesive). The foil is folded over a joint and acts like a leak-free gasket between the two joints. The foil disintegrates in the heat over time. When you need to swipe out pipes, they're easily removed without breaking apart.

Here's what's included in an exhaust kit:

Our Peterbilt 379 exhaust kits come with new lower brackets, and even the bolts to secure them, and the grommets to go from the bracket to the clamp, and the hardware to complete the entire exhaust up until the bottom of the elbows or the front of the y-pipe.

But it depends on what kit you buy.  

Once you get to the front of the y-pipe and onward, there’s nothing in the exhaust kits to hold that stuff in place.

#3. Don’t Forget to Buy Y-Pipe Hangers

Thankfully, we don’t leave you (or your exhaust) hanging!

We sell complete y-pipe hanger kits. The y-pipe is what holds up the entire bottom of your exhaust. For drivers who install long-drop elbows or custom Pickett style exhaust kits with deep drops, y-pipe hangers are essential. You can custom make your own y-pipe hangers, but a pre-made set is far more convenient.

Peterbilt owners who forget to order y-pipe hangers are bound to see bottom exhaust components falling out while driving down the highway.

#4. Remove Everything and Start Fresh to Avoid Stress

Reusing old hardware is risky.

Granted, is removing all of your exhaust components more expensive? Technically, yes.

But if you just have a weekend to finish your brand-new exhaust installation and get back on the road by Monday, this is, by far, the easier option.

Use a grinder with a cut off tool to just remove everything. Cut it all off and swap it with new components. This alone will save you enormous time and stress.

#5. Do Not Reuse Old Flex Pipe Tubing (Here’s Why)

While you’re driving down the road, the Peterbilt 379 cab bounces up and down. The exhaust pipes are bolt-mounted directly to the cab itself.

The Peterbilt 379’s PACAAR engine, on the other hand, is hard mounted to the frame of the truck, so it doesn’t budge. But the exhaust stacks keep moving right alongside the cab.

Something must give, right? That’s the job of the flex pipe.

Similar to a Chinese finger trap, the harder you pull on the flex pipe, the more it tightens and clamps down. It’s nearly impossible to remove it once it is put together.

At 4 State Trucks, we sell pre-cut flex tubing in various lengths which can be easily sliced with a grinder cutoff tool for appropriate sizing.

Let’s say you want 3 feet of flex tubing. You buy 36-inch flex pipe with 2 pre-formed band clamps. This will reach all the way from the frame pipe to the y-pipe.

Expensive? Sure.

But it is less expensive than the downtime of dealing with stubborn, old flex tubing over the weekend.  

#6. Don’t Forget to Use Anti-Seize on All Stainless-Steel Exhaust Hardware

Use anti-seize lubricant on all your stainless-steel exhaust hardware.

“Why? Isn’t stainless material corrosion-resistant?” You ask.

If you thread a nut onto a bolt, it has a tendency to cross thread itself and seize up.

The anti-seize solution will lubricate the hardware and prevent it from getting stuck. This saves you tremendous headache in the future. This can be found at nearly any big-box hardware store or auto parts shop. 

#7. Never Use an Impact Tool on Stainless Steel Exhaust Parts

Hand tools offer a gentler approach when dealing with stainless steel material.

The impact driver tool loves to walk a thread and then cross that thread. Now you’re stuck. You’ll need to go to Lowe's to find matching hardware for your exhaust kit.

It’s a completely avoidable stress point.  

Use hand tools only!

#8. Visually Inspect the Truck's Exhaust System Before You Place an Order

Crawl under the truck and do a visual inspection. Sometimes the exhaust looks okay, but, in reality, it’s a rusty mess.

It's likely that the hardware and band clamp connectors need to be replaced entirely. The hardware sees extremely hot temperatures and will wear down, becoming brittle, whether it's a grommet that won't budget, or bolt that snaps off when you turn it.

It's unpredictable.  

Here's a potential scenario: It’s a Sunday afternoon and the parts shop is closed, and you’re going to work on Monday. Now you're stuck waiting on new parts.

It's easy to avoid this. Always inspect the exhaust system before placing an order!  

Tip: Start the inspection at the turbo and move upwards through the exhaust system.

Here’s are two critical things to watch for:

• Rusting at the joints
• Black soot at the joints (indicates a leaking system that’s rusted from within)

#9. Verify the Exhaust Parts Before Disassembling Your Truck’s Exhaust

Here’s a frustrating scenario:

You’ve laid out all your shiny chrome, you’re ready to install those sleek-looking chrome stacks, but you’re MISSING exhaust components! And you’ve already cut off the old exhaust on your truck…

So much for that weekend project. Now you’re stuck waiting on new parts to arrive.

That’s life. Stuff happens. The truck parts company might have mispackaged or mislabeled the item before shipping it.

Be proactive.

So many drivers forget to verify the quantity and condition of the exhaust parts before disassembling their existing exhaust setup, opening the packaging, and beginning the installation.

In fact, one Peterbilt 379 owner received one Aussie turn-out chrome stack and a flat top stack. Short on time, he had to drive with mismatched stacks for two weeks until the new, replacement exhaust parts arrived.

In other words, you do not want to be short parts in the middle of an installation.

ALWAYS inspect the shipment first.

Side Note: For Peterbilt 379 models made in 2004 (and a lot of Peterbilt Glider models), the exhaust brackets at the top are flipped upside down. Why? No particular reason. 2004 was a bridge year for the 379 model. 

It's the exact same bracket, just reversed, making the center section a few inches higher than normal. This trips up Peterbilt 379 owners who think they've ordered the right hardware and overall stack height on paper, but quickly discover that it won't actually fit the truck! 

Shop for Peterbilt 379 Exhaust Parts at 4 State Trucks

Give your Peterbilt 379 exhaust a facelift. Find everything you need to complete a seamless exhaust system overhaul on your truck, including replacement exhaust pipes, mufflers, brackets, grab handles, hardware, and more.

Shop online, drop by the 4 State parts shop in Joplin, Missouri, or order your next part on the 4 State Mobile App today!