Technical Service Bulletin
Bulletin No.: 001-26
Date: August 12, 2026
Public Release Date: August 13, 2026
Subject: Manual Axles Stops and Steering Gear Poppets
Applicability: All XOS Trucks
Service Category: Axle & Steering
Section: Axle & Steering Components
Market: USA and Canada
Introduction:
This procedure establishes the correct sequence for (a) setting and verifying the
front axle knuckle stop screws to achieve the specified 45° wheel cut on the
Hendrickson 10K front axle, and (b) setting the internal unloading (poppet) valves on
the TRW THP60 steering gear so that hydraulic pressure is relieved just before axle
stop contact in both directions.
The axle stops MUST be set and verified before the poppets are set. The poppets
self-position against the axle stops; if stops are moved after poppet setting, the
poppets must be reset. The THP60 is equipped with unloading (poppet) valves, one
at each end of the rack piston. When correctly set, a poppet trips just before the
steered wheels contact the axle stops in each direction, dropping hydraulic pressure
in the gear for the last fraction of travel. This is intentional and required behavior:
1. Heat and pump protection. Without poppet relief, steering to the lock puts
the pump at relief pressure (up to 2,685 psi / 185 bar max operating pressure
on the THP60), dumping energy into the fluid as heat. Sustained operation at
relief pressure degrades seals and damages the pump — this is also why fulllock holds are limited to 10 seconds during setting.
2. Steering linkage load reduction. Relieving pressure before stop contact
prevents the drag link, pitman arm, steering arm, kingpin stops, and axle
beam stop pads from reacting full hydraulic force every time the vehicle is
steered to the lock. On the 10,000 lb front axle this is a meaningful fatigue and
durability consideration for the linkage and knuckle stops.
3. Full wheel cut must be preserved. The poppet trip point must be just short of
stop contact — the wheels must still physically reach the stops to achieve the
specified 45° wheel cut and turning radius. Poppets that trip too early reduce
usable wheel cut; poppets that trip too late (or not at all) leave the system
steering against relief pressure at every lock.

Distinction — poppets vs. relief valve: The relief valve only limits maximum supply
pressure to protect the gear. It is not position-sensitive and does nothing as the
wheels approach the stops. Audible pump/relief squeal held at the locks is evidence
the poppets are NOT functioning or are set incorrectly.
Why axle stops come first: The poppets self-position against the axle stops during
the setting procedure. The stops therefore define the poppet trip points. Any change
to the stop screws, steering linkage, pitman arm timing, or transfer of the gear to a
different vehicle invalidates the poppet setting and requires it to be redone
Repair Procedure Overview:
1. Update to latest software.
2. Perform a functional check of the vehicle to confirm its current state so we
know if the repair process unexpectedly impacts other vehicle systems.
3. Pull all open cases for the vehicle, these should all be completed during this
repair process.
4. Determine if any batteries need to be replaced. If any batteries need to be
replaced, procure the new batteries, remove the respective batteries from the
vehicle, and leave them off the vehicle.
5. Perform the removal and installation of HV boxes and cables per repair
instructions
6. Record date and time of completion of repair to track Viriciti data post repair.
7. Drive 50 miles.
8. Perform an AC charge session to full charge.
9. Review telematics for approval of truck release.
Vehicle Applicability:
Model Year

Model

All

ALL

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Warranty Information:

Model

Operation
Code

Operation Description

Time
(Hours)

ALL

0204X

Steering and Axles

1-2

Impacted Part #
VN00-JB-A0027
VN00-KB-A0065

Tools and Parts Information:

Item

Spec

Turn plates (wheel cut gauges), L/R

Capable of reading ≥ 50°

Jack + jack stands

Rated for front axle load (10,000 lb axle)

Allen wrench

7/32" (THP60 poppet adjusting screw)

Open end wrench / socket

3/4" (THP60 poppet sealing nut), 5/8"
(fixed stop bolt, if equipped)

Torque wrench, ft·lb

Calibrated

Combination wrenches for knuckle stop
screw & jam nut

Per axle hardware

Approved hydraulic fluid

Per TRW approved fluid list / vehicle
spec

Feeler stock or machinist scale

For stop screw gap checks

New poppet adjusting screw & nut kit

TRW kit 021407-X1 (THP/PCF60) IF
RESETTING Poppets

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Procedure:
Table of Contents
A. Preconditions
B. Part A — Axle Stop Setting & Verification (45° Wheel Cut)
a. Position vehicle
b. Measure existing wheel cut
c. Adjust stop screws
C. Part B — THP60 Poppet Setting
a. Determine which case applies
b. Initial Poppet Setting — new or internally reset gear (per TRW manual)
c. Poppet Readjustment — single gear (per TRW manual, THP60 values)
d. Verification (all cases)
D. Records

A. Preconditions
1. Vehicle unloaded, on level floor, tires at specified cold pressure.
2. Steering linkage complete: drag link connected, pitman arm installed with
timing marks aligned, tie rod set to specified toe.
3. No leaks; reservoir at FULL; system air-bled per TRW manual p.16 if the gear
was recently serviced.
4. Wheel cut spec is 45° .

B. Part A — Axle Stop Setting & Verification (45° Wheel Cut)
a. Position vehicle
1. Center the front tires on the turn plates. Zero the turn plates with wheels
straight ahead (steering gear on its timing-mark center).
2. Start the Vehicle; idle 5–10 minutes to warm the hydraulic fluid.
b. Measure existing wheel cut
3. With the Vehicle on, steer slowly to full LEFT until the knuckle stop contacts
the axle beam stop pad. Do not exceed 40 lb rim pull.
4. Record inside-wheel angle (LH wheel on a left turn) and outside-wheel angle.
5. Repeat to full RIGHT and record.
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c. Adjust stop screws
6. If the measured inside-wheel angle is not 45° (+0° / −0.5°, or per Xos vehiclelevel spec if tighter) in either direction: a) Loosen the stop screw jam nut on
the affected knuckle. b) Turn the stop screw IN to reduce wheel cut, OUT to
increase, in small increments. c) Re-steer to full lock and re-measure. Iterate
until 45° is achieved at the inside wheel on each side. d) Hold the screw and
torque the jam nut to the Hendrickson/Xos fastener spec. This should
typically be 1 in between the nut and the top of the axle’s stop.

7. Clearance check (mandatory): At both full locks, verify minimum clearance
between tire/wheel and all chassis, suspension, brake hose, harness, and body
structures per Xos vehicle spec. Hydraulic disc brake hoses (15.0" disc,
hydraulic per dwg 080920-000) must have no tension or contact at full lock
through full jounce/rebound where accessible.

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8. Verify LH and RH wheel cut are symmetric within 1° unless the vehicle spec
states otherwise.

C. Part B — THP60 Poppet Setting
a.

Determine which case applies

Condition

Action

Case 1: New gear from TRW/OEM, or
poppet seats replaced/reset internally
during overhaul (poppets ready for
automatic positioning)

Use Initial Poppet Setting, Section 7.2

Case 2: Gear previously in service on this
vehicle and axle stops were just moved,
OR gear transferred from a different
vehicle, OR poppets may have been
disturbed

Use Poppet Readjustment, Section 7.3

Case 3: Gear removed/reinstalled on the
same vehicle, stops and linkage
unchanged

Verify only (Section 7.4). Reset per 7.3 if
poppets do not relieve correctly

CAUTION (Case 1 gears): With the drag link disconnected or before poppet setting,
never rotate the input shaft more than 1.5 turns from center — this can disrupt the
automatic poppet feature and require gear disassembly to reposition the poppet
seats.
b.

Initial Poppet Setting — New or internally reset gear (per TRW manual).

Prerequisites: axle stops set per Part A; pitman arm correctly timed; a fixed stop
screw installed in the housing, or a poppet adjusting screw installed so it duplicates
the fixed stop screw length.
1. Vehicle on, vehicle unloaded.
2. Turn the steering wheel to full travel in one direction until axle stop contact is
made. Maximum input: 40 lb rim pull on a 20" wheel. If excess effort is
encountered, allow the vehicle to roll forward or jack the front axle.
3. Turn the steering wheel to full travel in the opposite direction the same way.

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4. The poppets are now automatically positioned to trip and relieve pressure as
the wheels approach the stops in both directions. Proceed to Section 7.4
verification.
c. Poppet Readjustment — Single gear (per TRW manual, THP60 values).
This procedure works in most cases with at least 1¾ hand-wheel turns each side of
center. For a large wheel-cut reduction where this fails, poppets must be
replaced/internally reset per the TRW Poppet Component section.
1. Warm-up: Axle stops already set (Part A). Idle 5–10
min to warm fluid. Shut the vehicle off.
2. Prepare adjusting screw: Using a new screw/nut
kit (021407-X1), thread the screw into the nonsealing end of the jam nut until the drive end of
the screw is flush with the nut. If the gear already
has an adjusting screw, back the nut off until flush
with the screw end.

3. Remove fixed stop bolt: Vehicle off, wheels
straight ahead. Remove and discard the poppet
fixed stop bolt and washer (5/8" wrench) from the
lower end of the housing, if equipped. If replacing
an existing damaged screw/nut, remove and
discard them.

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4. Install adjusting screw assembly: Turn the screwand-nut assembly (without rotating the nut on the
screw) into the housing using the 7/32" Allen until
the nut is firmly against the housing (3/4" wrench).
Tighten the sealing nut against the housing.
CAUTION: If the drive end of the screw sits below
the nut face, the poppet seat flange will break
during step 7.

5. Refill reservoir with approved fluid. Jack the front
axle so the steer tires are off the ground; support
on stands.

6. Push the upper poppet out: a) Start vehicle, idle;
b) Note which output shaft timing mark is nearest
the housing piston bore. c) Steer in the direction
that moves this timing mark toward the adjusting
screw until axle stop contact. d) Pull hard (up to 40
lb rim pull) after stop contact.

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7. Set the upper poppet: a) Steer the opposite
direction until the other axle stop is contacted. b)
Pull hard (up to 40 lb rim pull). c) Release; shut the
vehicle off.

8. Back out the screw: Loosen the sealing nut and
back the adjusting screw out until 1" is past the
nut. Tighten the sealing nut.

9. Set the lower poppet: a) Start vehicle, idle. b) Steer
in the original direction (timing mark toward
screw) to axle stop contact. c) Hold at full turn (≤ 40
lb rim pull) max 10 seconds at a time, release, and
repeat as needed while performing step 10.

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10. Position the adjusting screw: a) With the wheel
held at full turn, loosen the jam nut and hold it
with the 3/4" wrench. b) Turn the adjusting screw
in (CW) with the 7/32" Allen using finger pressure
only — no ratchet — until it stops. Do not force
further. Pause whenever the driver releases the
wheel; turn only while held at full lock. c) Back the
screw off 3¼ turns and tighten the sealing nut.
Torque sealing nut 35 ft·lb (48 N·m).

11. Lower the vehicle. Check and top off the reservoir.
WARNING: The adjusting screw must protrude no
more than 1-1/16" beyond the nut for proper thread
engagement. (Protrusion length varies by vehicle;
that is normal.)
d. Verification (all cases)
1. Vehicle on, vehicle on the ground, unloaded.
2. Steer slowly toward each lock. Confirm a distinct pressure/effort drop (poppet
trip) just before axle stop contact in both directions. Steering must still reach
the stops (full 45° cut confirmed on turn plates).
3. Confirm no relief-valve squeal held at the stops and no more than momentary
high-pressure dwell.
4. Re-verify reservoir level; check for leaks at the adjusting screw sealing nut and
all fittings.
5. If poppets do not relieve before stop contact in either direction, repeat Section
7.3.

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Records
Data

Value

VIN / vehicle no.
Axle P/N & serial (from tag)

080920-00__

Gear spec no. & date code (stamped
opposite input shaft)
LH wheel cut, inside wheel (deg)
RH wheel cut, inside wheel (deg)
Poppet procedure used (7.2 / 7.3 / 7.4 only)
Sealing nut torque verified (35 ft·lb)

Y/N

Poppet relief confirmed both directions

Y/N

Technician / date
QA sign-off

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