Char-Lynn Steering Unit Troubleshooting: Hard Steering, Wander, No Centering

Hard, slow, wandering or non-centering hydraulic steering is usually a supply or cylinder problem, not the Char-Lynn (Eaton) steering control unit: low pump flow, a relief or priority valve set too low, a leaking load-sensing line, a cylinder leaking past its piston, or worn linkage. Eaton's own repair manual says the steering unit is generally not the cause of most steering problems, so check pressure at the unit inlet, tank back pressure and cylinder leak-by before you open it, and save the teardown for binding, thermal shock damage, or a gerotor timed wrong on reassembly.

That last one is the classic rebuild mistake. A unit that steered fine before a reseal goes back together with the meter one tooth off, and now the steering wheel oscillates or turns by itself. Nothing is broken; it just needs retiming.

Know what thermal shock is before you blame the unit. Eaton defines it as running the hydraulics for a while without steering, so the oil is hot and the steering unit is cold, then turning the wheel quickly. With more than a 28°C [50°F] difference, the spool and sleeve can seize for a moment, cause internal damage, and then free-wheel. Eaton offers a neutral bleed option for closed center units that may exceed that limit.

Char-Lynn steering troubleshooting chart

This follows Eaton's troubleshooting chart from its repair manual for the 3, 4, 6 and 12 Series steering control units (Form 7-304), rewritten for the shop floor, with our checks added.

Symptom	Likely causes	The check	The fix
Hard steering, or loss of power assist	Worn pump, stuck flow divider, worn pump compensator or a relief letting pressure fall below spec, overloaded steer axle. On load sensing systems: a leaking or kinked LS signal line, or a sticking priority valve.	Gauge the steering unit inlet and steer against the stop. Compare with the machine maker's steering pressure.	Repair the pump, flow divider or relief. On the priority valve, check the spring, a sticking piston and the damping orifices at both ends of the main bore.
Slow steering	Same list as hard steering: not enough flow or pressure reaching the unit, or a priority valve not giving steering its share	Measure flow to the steering unit at the engine speed where it is slow, and compare with the rated flow for the unit.	Restore supply. If the inlet pressure is wrong on an LS system, Eaton points to the priority valve relief cartridge.
Wander or drift (will not hold a straight line, or veers slowly one way)	Air in the oil, worn linkage, a bent cylinder rod, a loose cylinder piston, a leaking crossover relief or anti-cavitation valve, severe wear in the unit. A single-rod cylinder that slowly extends on its own can be normal on closed center systems.	Check reservoir level and foam, then do a cylinder leak-by test. Look for slop in the linkage with the engine off.	Bleed the air, repair the linkage, cylinder or accessory valve. Replace the steering unit only after those check out.
Wheel turns but nothing steers (slip or free wheeling)	Leaking cylinder piston seals, a leaking accessory valve between the cylinder lines, a loose steering wheel nut or broken column splines, a meter short of oil after repair or a long sit, no flow (low oil, burst hose), thermal shock damage	Start the engine and try again: Eaton says a dry meter usually cures itself once the engine runs. Then check the column connection and cylinder leak-by.	Tighten or replace the column, replace cylinder seals or the accessory valve, add oil and fix leaks. Thermal shock damage means a new or rebuilt unit.
Steered wheels turn the wrong way	Lines connected to the wrong cylinder ports. That is the only cause Eaton's 7-304 chart gives; it is not a timing fault.	Trace each cylinder line from the steering unit to the cylinder and confirm it lands on the right cylinder port.	Reconnect the lines correctly.
Kick at the start of a turn (kickback)	No inlet check valve, so oil pushes back through the unit when cylinder pressure is higher than inlet pressure	Confirm the unit has an inlet check, or one is fitted in the inlet line.	Install a check valve.
Poor centering, or slow return to center	Binding or misalignment in the column or the splined input, high back pressure in the tank line, large particles binding the spool and sleeve	Gauge the tank port. Eaton says back pressure on these units should not exceed 300 PSI. Disconnect the column and see if the unit centers on its own.	Align the column pilot and spline, revise the return line, clean the unit and filter the oil.
Steering wheel oscillates or turns by itself (the unit "motors")	Parts assembled wrong or the steering unit improperly timed, then lines connected to the wrong steering unit ports. On a load reaction unit, some wheel return is normal.	If the unit was just resealed, suspect timing first. Confirm the hoses against the port markings on the steering unit, and confirm whether the unit is load reaction or non-load reaction.	Retime the gerotor (see below), or reconnect the lines correctly.
Binding or locking up	Large particles in the meter section or between spool and sleeve, insufficient hydraulic power (Eaton flags units over 15 cubic inches), severe wear or a broken pin, thermal shock	Look at the filter and the oil. If another component has failed, assume debris is everywhere. On a large unit, check supply flow and pressure.	Clean the unit. Eaton says to flush the system with the steering unit bypassed if another component shed debris. Severe wear, a broken pin or thermal shock damage means replacing the unit.
External leakage	Worn input dust seal or quad ring seal, hardened end cap or spacer plate seals, cap screws that have lost torque, high tank back pressure	Clean it and find where the oil starts. Wet at the input shaft is the input seals; a wet seam at the meter end is the meter section seals.	Reseal with the complete kit, torque the cap screws in sequence, and get the tank back pressure under the limit.
Shimmy, or free play at the steered wheels	Broken or worn linkage between cylinder and wheels, leaking cylinder seals, air trapped in the cylinders or lines (spongy steering)	Check every pivot and anchor point between cylinder and wheels. Bleed the cylinders.	Repair the linkage, replace cylinder seals, bleed the air. Eaton notes that cylinder ports on top help keep air from being trapped.

Is it the steering unit or the system?

Do these in order. Most of them take a gauge and a few minutes.

Check oil level and condition. Low oil and air explain wander, spongy steering and erratic steering on Eaton's chart.
Gauge the steering unit inlet while steering against the stop. Low pressure here is a pump, relief, compensator or priority valve problem, not the steering unit.
Gauge the tank port. Compare with the maximum back pressure for your series in the table below.
Do a cylinder leak-by test. Turn to full lock, hold it, and check whether oil passes the piston. A cylinder leaking internally lets the wheel turn without steering.
Check the load sensing line on LS systems for leaks, kinks and the right fittings, and make sure the priority valve matches the steering unit. Eaton says a dynamic signal steering unit must be used with a dynamic signal priority valve.
Disconnect the column and turn the input by hand. If the binding goes away, the column or its alignment is the problem.
Check the linkage with the engine off for free play at every joint.

Eaton steering unit operating limits by series

From Eaton's 2006 Char-Lynn steering catalog, plus the 7-304 repair manual for the 3, 4, 6 and 12 Series.

Series	Max system pressure	Max back pressure
Series 5	140 bar [2030 PSI]	21 bar [300 PSI]
Series 10	275 bar [4000 PSI]	21 bar [305 PSI]
Series 20	241 bar [3500 PSI]	10 bar [145 PSI]
Series 25	241 bar [3500 PSI]	21 bar [300 PSI]
Series 40	241 bar [3500 PSI]	21 bar [300 PSI]
3, 4, 6 and 12 Series	See your unit's spec	300 PSI (tank line, per 7-304)

For the catalog series, Eaton also lists a maximum 28°C [50°F] difference between the steering unit and the system, a maximum system operating temperature of 93°C [200°F], and ISO 18/13 recommended filtration. Note how low the Series 20 back pressure limit is. A return line that is fine for a Series 10 can be too much for a Series 20.

Why does my steering wheel turn by itself? Load reaction vs non-load reaction

Before you condemn a unit for "self-steering," find out which type it is. A non-load reaction unit blocks the cylinder ports in neutral, so the axle holds where you left it. A load reaction unit connects the cylinder ports to the meter in neutral, so road forces turn the steering wheel back, much like a car. Ease off mid turn on a load reaction unit and the wheel spins back as the machine straightens. That is the design, not a fault.

Eaton adds a rule here that catches people: a load reaction unit needs equal oil volume both directions, so a parallel pair of cylinders or one double rod end cylinder. Do not run one with a single unequal area cylinder.

Steering valve timing: the classic rebuild mistake

The steering unit's meter is a gerotor, and it has to be timed to the spool and sleeve through the drive. Eaton's 7-304 manual for the 3, 4, 6 and 12 Series lays it out like this:

With the spacer plate on, rotate the spool and sleeve until the cross pin is parallel with the port face.
Install the drive so its slot engages the pin, and mark the drive spline so you can see how the slotted end lines up with the splined end.
Set the meter on with its seal side toward the spacer plate and align the star valleys with the mark on the drive. Eaton's drawing shows the pin, the drive mark, the star valley and the port face all parallel.
Line up the bolt holes without lifting the meter off the drive, then fit the drive spacers, end cap seal and end cap.

Eaton's Series 10 repair information says the same thing in one line: the pin slot in the drive must line up with a valley (the minor diameter) of the gerotor star. On the Series 5, Eaton's Series 5 repair information (PDF) shows timing grooves on the wear plate, gerotor and end cap that must all be in line, and Eaton warns the unit will not function if they are not.

Get it wrong and the steering wheel turns by itself. Eaton's 7-304 chart lists parts assembled wrong or the steering unit improperly timed as the first cause when the steering wheel oscillates or turns by itself, ahead of lines on the wrong steering unit ports. If a freshly resealed unit does that and the hoses are right, take the end cap back off and retime it. Steered wheels that go the opposite way to the wheel are a plumbing fault, not timing: Eaton gives lines connected to the wrong cylinder ports.

Torque matters too. The 7-304 manual has the seven end cap screws pretightened to 150 lb-in, then torqued to 275 lb-in in sequence. Eaton's Series 10 manual calls for 11-17 Nm [100-150 lb-in] evenly, then 31-37 Nm [275-325 lb-in] in sequence. Use the manual for your series, and do not reuse an old spacer with a new gerotor: Eaton's 6-317 parts list says the spacer from the old unit will not work with a new gerotor, so it comes in the gerotor service kit.

Which seal kit does my steering unit take?

For the 3, 4, 6 and 12 Series (211-, 212-, 213-, 241-, 243-), Eaton's 6-317 parts list (PDF) gives three kits:

64466-000, the standard seal kit
64470-000, the same kit with a one-piece low input torque seal in place of the quad ring
64425-000, the Viton kit, which Eaton lists for synthetic fluids. Tell us the exact fluid before ordering.

Eaton's 64466 installation guide also covers the 110, 230 and 450 Series. For the other series, start at the parts catalog for your unit: 3, 4, 6 and 12 Series, Series 5, Series 20, Series 25 and Series 40. The factory parts bulletins are on the 3, 4, 6 and 12, Series 5, Series 20, Series 25 and Series 40 pages, and every steering part we list is in Char-Lynn steering parts.

No kit fits every unit. Steering units built for equipment makers can carry product numbers outside Eaton's catalog charts, and some use a different seal set. Kits fit the standard Eaton unit for the product number. If yours came off OEM equipment, compare the old seals with the kit before you install, and the equipment maker is the source for its own special kit.

Frequently asked questions

Why is my hydraulic steering hard to turn?

Usually not enough pressure or flow is reaching the steering unit: a worn pump, a stuck flow divider, a relief or compensator letting pressure fall below spec, or on load sensing systems a leaking LS line or sticking priority valve. Gauge the steering unit inlet before replacing anything. Temporary hard steering after a long idle can be thermal shock.

Why does my steering wander or drift?

Eaton's chart lists air in the oil, worn linkage, a bent cylinder rod, a loose cylinder piston, a leaking crossover relief or anti-cavitation valve, and severe wear in the steering unit. Check oil level, linkage and cylinder leak-by first. A single-rod cylinder that slowly extends can be normal on a closed center system.

Why won't my steering return to center?

Binding or misalignment in the column or splined input, high back pressure in the tank line, or debris binding the spool and sleeve. Eaton says tank back pressure on the 3, 4, 6 and 12 Series should not exceed 300 PSI; the Series 20 limit is 10 bar [145 PSI]. Disconnect the column to see if the unit centers on its own.

What happens if a Char-Lynn steering unit is timed wrong?

The steering wheel oscillates or turns by itself. Eaton's 7-304 chart lists parts assembled wrong or improper timing as the first cause of that symptom, then lines on the wrong steering unit ports. Steered wheels that turn the opposite way to the steering wheel are a different fault: Eaton gives lines connected to the wrong cylinder ports. The gerotor star valleys must line up with the marked drive and the cross pin, parallel to the port face. Retime it and the steering works normally.

Why does my steering wheel turn by itself?

On a load reaction unit some return is designed in, because the cylinder ports are connected to the meter in neutral. Otherwise Eaton's 7-304 chart gives two causes, in this order: parts assembled wrong or the steering unit improperly timed, then lines connected to the wrong steering unit ports. If it started right after a reseal, check the timing.

What is thermal shock in a steering unit?

Running the hydraulics without steering until the oil is much hotter than the steering unit, then steering quickly. Eaton puts the limit at 28°C [50°F] of difference. The spool and sleeve can seize for a moment and be damaged, sometimes followed by free wheeling.

Which seal kit fits a 211 or 212 Char-Lynn steering unit?

Eaton's 6-317 parts list gives 64466-000 as the standard kit, 64470-000 with the low input torque seal, and 64425-000 in Viton. Special units built for equipment makers can differ, so compare the old seals with the kit.

About the technical information on this page. Figures, procedures and part numbers here come from manufacturer service literature and are provided for reference only. They are only as accurate as the factory data, and the revision we have on file may not be the latest for your unit. Always confirm against the current manufacturer documentation for your exact model and follow safe work practices. RestoPower is not responsible for damage, injury or loss resulting from the use or misuse of this information, or from incorrect assembly, adjustment, installation or operation of any unit.

Send us the product number and the symptom

Give us the number off the steering unit tag, what the steering is doing, and your inlet and tank pressure readings if you have them. We will tell you whether it is the unit, a seal kit, or something upstream. In-stock parts ship within 24-72 hours and in-stock parts carry a 2-year warranty. If the unit needs a rebuild, the teardown evaluation is free and you get a firm, itemized quote before any billable work; repairs are done in our shop or through the RestoPower repair network, we arrange getting the unit to the shop doing the work, and work done in our shop carries a 1-year repair warranty.

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