320991271 Auto Crane Hydraulic Pump Motor - 12V DC - NexStar 3203EH / 4004EH - Slotted Shaft - Replaces 320991271

320991271 Hydraulic Pump Motor for Auto Crane NexStar 3203EH / 4004EH

Your Auto Crane NexStar hydraulic system is down — the pump motor has failed, it's running slow, drawing excessive current, or the brushes are burnt out. The dealer wants $1,052+ for a replacement motor. That's over a thousand dollars for a standard wound field DC motor. Your service truck is sitting on a job site with a fully functional crane that has no hydraulic power. Every hour it sits is money lost.

We sell the direct replacement hydraulic pump motor for $489 — saving you over $500 vs the dealer. This is the same specification motor: 12 Volt DC, 4.5-inch wound field, slotted (tang) shaft, CCW rotation. It bolts directly onto the hydraulic power unit on your Auto Crane NexStar 3203EH or 4004EH. Replaces Auto Crane part number 320991271.

⚠️ Critical: Verify Your Terminal Configuration Before Ordering

Auto Crane NexStar power units come in two electrical configurations:

• 1-Terminal (Case Ground): The most common configuration. The motor has one power post on the end cap, and the motor housing itself is the ground path. This listing is the 1-terminal version.
• 2-Terminal (Isolated Ground): Some NexStar units — particularly those with advanced computer controls — use a 2-terminal motor where the ground is isolated from the motor housing to protect the electronic controller. If your motor has two posts on the end cap, you need the isolated ground version — contact us before ordering.

How to check: Look at the end cap (rear) of your existing pump motor. Count the terminals (posts). If there is one post, this is the correct motor. If there are two posts, contact us — you need the isolated ground version.

The Problem

The hydraulic pump motor on the NexStar power unit is the heart of the entire crane system. When it fails, you lose all hydraulic functions — boom, outriggers, rotation, everything. The motor runs hot, the brushes wear out, and eventually the armature burns up or the field windings short. The dealer replacement is $1,052 — an absurd price for a standard wound field DC motor. And the lead time from the dealer can stretch to weeks, leaving your truck and crane completely out of service.

The Solution

This is the same specification wound field DC motor sized for the Auto Crane NexStar hydraulic power unit. Same 4.5-inch frame, same slotted (tang) shaft that interfaces directly with the hydraulic pump gear, same CCW rotation, same 2-bolt thru-bolt flange mounting pattern. It is a direct bolt-on replacement — remove the old motor, bolt on the new one, reconnect the power cable, and you're back in service.

Specifications

• Auto Crane OEM Part Number: 320991271
• Type: Hydraulic Pump Motor (Wound Field DC)
• Voltage: 12 Volt DC
• Motor Frame: 4.5-inch Diameter
• Shaft: Slotted (Tang) Drive — interfaces with hydraulic pump gear
• Rotation: CCW (Counter-Clockwise, viewing drive end)
• Terminals: 1-Terminal (Case Ground) — verify before ordering
• Mounting: 2-Bolt Thru-Bolt Flange
• Application: Hydraulic Power Unit Pump Motor
• Condition: Brand New, Heavy Duty

Compatible Equipment

The 320991271 hydraulic pump motor fits the following Auto Crane NexStar models:

• Auto Crane 3203EH (NexStar Hydraulic)
• Auto Crane 4004EH (NexStar Hydraulic)

⚠️ Verify your terminal configuration (1-post vs 2-post) before ordering. Also verify Auto Crane part number 320991271 in your service manual or on the data plate of your existing motor. Some older NexStar units may use a different motor specification — contact us with your crane model, serial number, and terminal count to confirm fitment.

Installation Notes

• Disconnect the battery before starting — this is a high-amperage DC motor
• Identify and label the power cable(s) connected to the motor terminals
• Remove the two thru-bolt flange bolts securing the motor to the hydraulic power unit
• Slide the old motor straight out — the slotted (tang) shaft will disengage from the pump gear
• Inspect the pump gear teeth for wear or damage before installing the new motor
• Align the new motor's slotted shaft with the pump gear and slide it into position
• Install and torque the two thru-bolt flange bolts
• Reconnect the power cable(s) to the motor terminal(s) — match original polarity
• Reconnect the battery
• Test all hydraulic functions: boom up/down, outriggers extend/retract, rotation left/right
• Check for hydraulic leaks at the motor-to-pump interface
• Verify the motor is not running excessively hot under normal operation

Symptoms of a Failing Hydraulic Pump Motor

• Hydraulic functions are slow or weak — crane moves sluggishly
• Motor won't start — clicks, buzzes, or draws excessive amperage
• Motor runs excessively hot — too hot to touch
• Burning smell from the motor area (burnt brushes or field windings)
• Motor runs but hydraulic pressure is low (worn brushes = reduced RPM = low pressure)
• Intermittent hydraulic function — works sometimes, fails other times
• Complete loss of all hydraulic functions (motor has seized or burned out)
• Excessive current draw blowing fuses or tripping the main power relay
• Visible brush dust or debris around the motor housing
• Motor chatters, grinds, or makes unusual noise under load

Frequently Asked Questions

How do I know if I need the 1-terminal or 2-terminal version?
Look at the rear end cap of your existing motor. If there is one power post (stud), you have the standard case ground motor — this listing is the correct one. If there are two power posts, you have the isolated ground version and need a different motor. Contact us with your crane model and serial number if you're unsure — we'll confirm which version you need.

Why is this so much cheaper than the dealer?
The dealer price of $1,052 includes significant markup on a standard wound field DC motor. This motor is built to the same specification — same voltage, same frame size, same shaft type, same rotation, same mounting pattern. We source it at a fraction of the dealer cost and pass the savings to you.

Is this motor as good as the one the dealer sells?
Yes. This is the same specification heavy-duty wound field motor. Same 4.5-inch frame, same slotted shaft, same CCW rotation. It is built for continuous-duty hydraulic pump applications and uses heavy-duty brushes designed for extended service life.

Will this work with my NexStar computer controls?
Yes, as long as you have the correct terminal configuration. The 1-terminal (case ground) version is compatible with standard NexStar systems. If your NexStar has advanced electronic controls that require an isolated ground motor (2-terminal), contact us for the correct version. Using a case ground motor on an isolated ground system can damage the electronic controller.

How long does installation take?
About 30–45 minutes for a qualified mechanic. The motor is secured by two thru-bolt flange bolts and one or two power cables. It slides straight out and the new one slides straight in. No special tools required — standard wrenches and sockets.