Wet Kit Installation on a Peterbilt — Ames Hydraulics

Wet Kit Installation On A Peterbilt — What’s Actually Involved

If you’re pricing a wet kit installation on a Peterbilt, the answer is not one number — it depends on the model, the trailer you’re pulling, and how the PTO is going to be driven off the transmission. We install wet kit systems on Peterbilt 379, 389, 567, 579, and the 389 Legacy Class trucks. Every install is different because the drop-in space behind the cab, the transmission spline, and the trailer’s pump requirements all change what parts you need.

Our shop is in Ames, Iowa. We do wet kit installation on Peterbilt trucks every month for owner-operators, small fleets, and independent haulers who don’t want to pay dealer rates and don’t want a shop that “sorta knows” the hydraulics side. We build the whole system in-house — PTO, pump, tank, plumbing — sized to the actual trailer that truck is going to pull.

The Four Pieces Of A Wet Kit On A Peterbilt

Every wet kit installation on a Peterbilt breaks down into four parts. First is the PTO, which mounts to the transmission and gives you a rotating output shaft. Chelsea, Muncie, and Parker are the common choices; the exact model depends on which transmission is in your Peterbilt (Eaton Fuller, Allison, or the newer PACCAR TX-12/TX-18). Second is the pump — gear pumps for lighter-duty single-line dump work, piston pumps for high-flow walking-floor and live-bottom applications. Third is the tank, usually 30 to 60 gallons, mounted behind the cab, side of the frame, or under the sleeper. Fourth is the plumbing: pressure line, return line, and case drain if you’re running three-line.

The Peterbilt cab-to-fifth-wheel space is generous on the long-hood models (379, 389, 389 Legacy), so tank placement is straightforward. On the shorter 567 and 579 you have less real estate and we often end up going with a lower-profile tank or side-mounting.

Single-Line, Two-Line, Or Three-Line — Which Fits Your Peterbilt

The most common wet kit installation on a Peterbilt is a two-line system, because most drivers who add a wet kit are running walking floor or live-bottom trailers, and those need pressure + return. A single-line install is enough if you only run a simple end-dump trailer. Three-line adds a case drain and is required when you’re driving a piston pump on the trailer or running larger hydraulic motors — grain-hauling live-bottom trailers and some blower trailers fall into this category.

If the plan is to potentially haul side-dump trailers or switch between trailer types, we usually recommend the two-line install with a pump and tank sized for the largest expected demand. Undersized pumps are the single most common mistake we retrofit on a Peterbilt — the driver picked a cheap gear pump for a dump trailer and now can’t unload a live-bottom because there isn’t enough flow.

PTO Selection On A Peterbilt Transmission

The PTO drives the pump, and PTO selection is where a bad install shows up. On Eaton Fuller manuals (the 10-speed and 13-speed common in the 379 and 389), Chelsea 442-series or 852-series PTOs are the standard. On Allison automatics that appear in some 567 and 579 configurations, Muncie hot-shift PTOs work well because the driver can engage them from the cab. The PACCAR TX-12/TX-18 automated manuals in newer 579s use different PTO housings — the aftermarket has caught up on these but a shop that isn’t paying attention will mis-order a PTO and burn a week waiting on the right one.

We spec the PTO after we confirm the transmission and after we know the pump’s required RPM. A pump running at wrong PTO ratio will overheat and destroy itself. Getting this right is the single biggest reason wet kit installations on Peterbilt trucks fail early.

Tank Sizing And Placement On A Peterbilt

Tank size depends on cycle time and how hot the fluid gets. A single-line dump trailer that lifts once every 15 minutes can run a 30-gallon tank. A walking-floor unloading continuously for 4 minutes needs closer to 50 gallons of fluid so the return oil has time to cool before it’s pushed back through the pump. On a Peterbilt 379 or 389 we typically frame-mount a 50-gallon steel tank between the cab and the fifth wheel. On the shorter 567 we’ve done side-mounted saddle-tank installs to preserve the space.

We build steel tanks in-house when we need a specific size or shape that doesn’t come off the shelf. That includes baffled internal walls, sight gauge, filler-breather cap, and suction and return ports oriented so the plumbing runs clean.

Cost Ranges For A Wet Kit Installation On A Peterbilt

Basic single-line wet kit installation on a Peterbilt runs $2,800 to $4,500 depending on PTO and pump choice. Two-line and three-line installs are $4,500 to $8,000. Three-line piston-pump installs for heavy live-bottom or large-motor applications push $7,000 to $9,000. That range covers the PTO, pump, tank, plumbing, and labor. It does not cover fixing whatever the previous shop did wrong if we’re doing a retrofit — that gets quoted separately.

Every job gets a written quote before we start turning wrenches. We do not surprise-invoice.

Independent Scope And Referral

We are not a Peterbilt dealer. We do not do PACCAR MX-13 engine work, we do not chase electronic dash faults, and we do not do warranty work. What we do is the hydraulic side — wet kit installation, dump hoist rebuild, PTO service, and system troubleshooting. If your Peterbilt is under warranty, Housby in Des Moines is the right stop for warranty work and we’ll tell you that. Out-of-warranty hydraulic and structural work is what we do every week.

Turnaround On A Wet Kit Installation

Wet kit installation on a Peterbilt is typically a one-to-two-week job depending on parts availability and how loaded our shop is. If you can drop the truck for a full week we can usually turn it faster than that. For urgent installs we can quote priority scheduling — call us and we’ll be honest about the timeline.

Get A Quote

Call or text 515-292-2599. Tell us the Peterbilt model, transmission, and what kind of trailer you plan to pull. We’ll ballpark the install in 10 minutes over the phone and quote it firm once we see the truck.