Get the load on the ground
Lower whatever is in the air, all the way down, and move it off the forks if you can do that safely. Never leave a load parked at height on a machine that drifts.
Safety Critical
Forklift Mast Drifts Down On Its Own
This is the one to stop for.
If the forks sink when the machine is sitting still, the forklift has lost the ability to hold a load in the air. Set the load down, keep everyone out from under the mast, and stop using the machine until it has been repaired.
Mobile forklift repair across South Carolina · 24/7 for emergencies.
Read This First
Drift is not an inconvenience. It is a load coming down by itself.
Most forklift faults cost you time. This one can cost somebody a limb. A mast that drifts is a mast that has stopped reliably holding what you put in the air, and the failure gets worse rather than settling at a level you can work around.
Owners often live with it for a while because it starts small. An inch over a few minutes gets noticed and then tolerated. The trouble is that internal leakage grows as the surfaces wearing against each other keep wearing, and the rate at which the forks come down is not fixed. A machine dropping an inch a minute this month is not guaranteed to still be doing that next month.
It also breaks a rule everybody already knows: nobody works under raised forks. A drifting mast means that even a load parked briefly at height is moving without anyone touching the controls.
Right Now
Do these in order, then park it.
This is not a troubleshooting list. It is a make it safe list. The diagnosis is a tech job because the fault is in parts you cannot inspect from outside.
Keep people out from under it
No one reaches under raised forks, adjusts a load from below, or steps through the mast. This applies even when the forks look like they are staying put.
Park it out of the way and take the key
Somewhere flat, out of the traffic route, forks flat on the floor. Take the key so nobody borrows it for one quick job.
Tag it so nobody uses it
A note on the seat is enough if that is what you have. The next person along has no idea the machine is faulty, and the fault is invisible until a load is in the air.
Note how fast it drops
Roughly how far, over roughly how long, and whether it is worse loaded than empty. That is genuinely useful diagnostic information and it takes a minute to observe safely with the forks low.
Check for external leaks while you are there
Fluid on the cylinder rods, down the mast, or on the floor. An external leak is a different and easier fault than internal leakage, so it is worth knowing which you have.
Why a mast drifts
A raised mast is held up by hydraulic fluid trapped under the lift cylinder pistons. Nothing mechanical is holding it. If that fluid can escape anywhere, the forks come down, and the speed depends on how big the escape route has become.
There are two places it usually goes. Past the cylinder piston seals, which lets fluid bypass inside the cylinder itself, or back through the control valve, which lets fluid return to the tank when the spool should be holding it shut. Both are internal, which is why you can walk around the machine and see nothing wrong.
Some machines also have a load holding or velocity fuse arrangement in the circuit. When those fail or get contaminated they can produce drift too. Working out which of these it is means gauges and isolating parts of the circuit, and it is not something to determine by guessing.
Tilt drift is the same problem
If the mast tilts forward on its own while parked, that is the tilt cylinders or the tilt section of the valve doing the same thing the lift circuit is doing. Treat it with the same seriousness, because a mast tilting forward under load is how a pallet ends up on the floor or on a person.
A machine that drifts in lift and tilt together points more towards the valve than the cylinders, since it is unlikely both sets of cylinder seals failed at the same time. That is a useful thing to mention when you call.
What the repair usually involves
If it is cylinder seals, the cylinder comes apart and gets resealed, provided the rod and bore are still in good condition. If the rod is pitted or scored, new seals will not last and the honest answer is that the cylinder needs replacing rather than resealing.
If it is the valve, it is usually a matter of the spool and bore having worn, or contamination holding something off its seat. Fluid condition matters here, because dirty fluid is often what caused the wear in the first place.
Either way, expect the fluid and filter to come into the conversation. Repairing the leak and leaving contaminated fluid in the system is how the same fault comes back in a year.
A Few Straight Answers
Drift questions
If the forks are coming down on their own, call before the machine goes back to work.
Call 843-920-6959How much drift is acceptable?
Treat any drift you can see as a fault. Manufacturers publish tolerances for their own machines, but the practical answer for an owner is that a mast which visibly sinks needs looking at, because the rate does not stay where it is.
It only drops an inch or two. Is that really a problem?
Yes, for two reasons. It is going to get worse, and it means the machine can no longer be trusted to hold a load in the air. The amount matters less than the fact that it is happening at all.
Can I keep using it if I never lift anything high?
That is not a fix, it is a habit that lasts until the day someone forgets. And the same internal leakage that causes drift usually shows up as weak or slow lifting too, so the machine is not really working properly anyway.
Is this the cylinders or the valve?
It takes a gauge and isolating parts of the circuit to say for certain. Drift in both lift and tilt together points more at the valve. Drift in lift only points more at the lift cylinders. Either way it is a tech job.
Can a cylinder be resealed rather than replaced?
Often yes, and it usually costs less. It depends on whether the rod and bore are still good. A pitted rod will destroy new seals, and we would rather tell you that before the work than after.
Would new hydraulic fluid fix it?
No. Fresh fluid does not repair worn seals or a worn valve. Fluid condition matters for stopping it happening again, but it is not the repair.
The mast is drifting and we are mid shift. What now?
Get the load down, park the machine, take the key, and call 843-920-6959. Emergency calls are answered 24/7. This is the sort of fault worth stopping for.
Do Not Work Around It
Forks coming down on their own?
Call 843-920-6959. Park the machine first, then tell us what it is doing.