Peterbilt 378

PeterbiltClass 8

Peterbilt 378

The set-back-axle workhorse for heavy vocational duty.

The 378 was the 'little brother' of the 379, using a fiberglass hood and a shorter 119-inch BBC that made it a favorite for dump, mixer, and heavy vocational fleets through 2007.

Maker

PACCAR

Years

1986–2007

Body

Vocational

Rating

Up to 80,000 lb GCWR

Power

350–550 hp

Applications

Construction, Dump, Regional-haul

Engines

Caterpillar C15Cummins ISXDetroit Series 60

Trouble with your 378?

Describe the symptom and Mike — the free AI truck consultant — will help you figure out what's wrong, which part is involved, and whether it's safe to drive. Free, no account.

Common replacement parts

Real products from the PartsNow catalog. Confirm fitment with Mike before ordering.

3030HNTRX - 3030 SPEC LONG SHAFT HNTRX BRAKE CHAMBER

3030HNTRX

3030HNTRX - 3030 SPEC LONG SHAFT HNTRX BRAKE CHAMBER

OTR10143 - AUTO SLACK ADJUSTER, 11/2-10DRIVE 5.5,6.5

OTR10143

OTR10143 - AUTO SLACK ADJUSTER, 11/2-10DRIVE 5.5,6.5

5-808330 - BRAKE KIT FOR 4709DEN SHOES

5-808330

5-808330 - BRAKE KIT FOR 4709DEN SHOES

370036A - OIL BATH SEAL

370036A

370036A - OIL BATH SEAL

348-4195 - HUB CAP (SENTINAL LARGE DIAM)

348-4195

348-4195 - HUB CAP (SENTINAL LARGE DIAM)

5008414PGBXW - AIR DRYER CARTRIDGE, PURAGUARD

5008414PGBXW

5008414PGBXW - AIR DRYER CARTRIDGE, PURAGUARD

11444 - GLADHAND BRACKET MOUNT

11444

11444 - GLADHAND BRACKET MOUNT

15W40 OIL - 15W40 OIL (ROTELLA) GAL JUG

15W40 OIL

15W40 OIL - 15W40 OIL (ROTELLA) GAL JUG

Brakes & Wheel End Air System Filtration Electrical & Lighting Suspension & Steering Cooling System Drivetrain Body & Cab Exhaust

Find parts at PartsNow.ai Call or text (865) 290-5485

Guides from the shop

Trailer & Coupling

Fifth Wheel Not Locking? Diagnosis & Fix Before It Fails

Fifth wheel not locking or slipping under load? Step-by-step diagnosis, lube checks, jaw inspection, and rebuild-vs-replace guidance.

Electrical & Lighting

Trailer ABS Light Won't Go Off? Sensor & Wiring Guide

Trailer ABS light staying on? Step-by-step diagnosis for wheel speed sensors, harness corrosion, and ECU faults before you swap parts.

Aftertreatment & Emissions

DEF Lines Freezing? Winter Prevention & Fixes for Fleets

Stop DEF freezing from parking your trucks. Learn heated-line checks, tank insulation, and SCR fault codes before derates hit.

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