A raised telehandler boom should stay where you put it. If yours creeps down while you hold a pallet at height, or the telescopic section slides back in under load, the hydraulic system is losing oil somewhere. JCB Loadall boom drifting is a common problem on older machines with many hours, and it is also a safety problem: a load that sinks by itself can hit a trailer, a racking beam or a person.
This guide explains where the oil can go, how to narrow the fault down and what to check first. It applies to JCB Loadall telehandlers in general, including the Side Engine Loadalls (526-56, 531-70, 535-95, 541-70, 550-80 and others) and the compact models. Circuit layouts, valve types and test figures change between models and serial numbers, so use the service manual for your machine for every value and procedure.
First: which movement is drifting?
A Loadall boom has several rams, and each one can drift on its own. Before you look for the cause, find out which movement it is:
- Lift (boom down) – the boom angle drops. The fault is in the lift ram circuit.
- Extension (boom in) – the telescopic section retracts by itself. The fault is in the extension ram circuit.
- Carriage tilt – the forks tip forward or back. On most Loadalls the tilt circuit works together with a compensation ram that keeps the forks level as the boom moves, so check both.
Mark the ram rods with tape or a paint pen and measure how far each one moves in a set time. That tells you exactly which circuit to test.
The three ways a raised boom loses oil
With the boom up, the weight is held by oil trapped in the full-bore side of the lift ram. The boom can only come down if that oil escapes:
- Past the piston seal, inside the ram. A worn or damaged piston seal lets oil pass from the full-bore side to the rod side. There is no external leak, so this is easy to miss. Scored ram tubes and contaminated oil speed up seal wear.
- Through the load holding valve. Lift and extension rams on telehandlers are normally fitted with a valve on or near the ram that locks the oil in when the control lever is in neutral. Dirt on the valve seat, a worn valve or a wrong setting lets oil leak back to the hose.
- Past the control valve spool. A worn spool or bore in the main control valve leaks oil to tank. If the holding valve is in good order it will normally stop most of this, so spool leakage on its own usually shows up as a slower drift.
External leaks from hoses, fittings or rod seals are the easy case: you can see the oil. If there is no visible leak, it is one of the internal paths above.
How to narrow it down
- Check the oil. Hydraulic oil level, grade and condition. Dirty oil is the most common reason holding valves leak.
- Do a drift test as the manual describes. The manual tells you the boom position, any test load, the oil temperature and the time. Measure the ram movement and compare with the allowed figure.
- Watch for heat drift. Settling only after hard work, when the oil cools, is often normal. Drift with the machine cold is a fault.
- Isolate the ram from the valve. The Hydraulics section of the manual explains how to check the ram seals separately from the holding valve and the control valve. Follow it step by step, because it depends on how the holding valve is fitted on your model.
- Check the holding valve. Clean and inspect, or replace, as the manual describes. Some valves are adjustable; set them only to the value and procedure in the manual.
Quick diagnosis table
| What you see | Likely leak path | Next step |
|---|---|---|
| Oil on the ram or hoses | External: rod seal, hose, fitting | Clean, find the leak, replace the seal or hose |
| Drift, no external leak, holding valve tests good | Ram piston seal | Ram seal test, then reseal the ram |
| Drift stops when the holding valve is replaced or cleaned | Load holding valve | Check oil cleanliness so it does not return |
| Slow drift in several movements | Control valve spools or oil contamination | Oil condition, valve inspection |
| Settles only after hard work | Oil cooling and contracting | Compare with the allowed drift in the manual |
Safety: never work under a raised boom
The load holding valve is what keeps a raised boom up. Never loosen a hose, a fitting or the valve itself while the boom is raised or carrying a load. Lower the boom fully or support it mechanically, put the forks on the ground, stop the engine and relieve the hydraulic pressure before you start. The care and safety section of the manual describes how to make the machine safe for your model.
Which JCB Loadall service manual covers your machine?
JCB has published many Loadall manuals, each for a group of models and serial numbers. Older manuals use lettered sections (hydraulics in Section E), newer ones use numbered sections (hydraulics in 30 Hydraulic System). The publication numbers and models below are taken from the title pages:
| Manual | Models (title page) | Hydraulics section |
|---|---|---|
| 9803/3600U, issue 16 | 500 Series from m/c no. 561001 (505-19, 505-22, 506-36, 508-40, 510-40, 506B) | Lettered sections |
| 9803/3630-14 | Side Engine Loadalls | E Hydraulics |
| 9803/3750-07 | Side Engine Loadalls | E Hydraulics |
| 9813/0900-3 | Side Engine Loadalls | E Hydraulics |
| 9803/3690-8 | Compact Loadalls | E Hydraulics |
| 9813/9050, issue 1, 01/2018 | 531-70, 535-95, 541-70 | 30 Hydraulic System |
| 9813/5600, issue 4, 05/2018 | 526-56, 531-70, 531-T70, 533-105, 535-95, 535-T95, 536-60, 536-70, 536-70LC, 536-T70, 536-T70LP, 541-70, 541-T70, 550-80 | 30 Hydraulic System |
| 9823/0550, issue 1, 03/2018 | 531-70, 535-95, 536-60, 536-70, 536-70LP, 541-70, 550-80, 560-80 | 30 Hydraulic System |
| 9813/8750, issue 1, 07/2017 | 533-105, 535-V125, 535-V140, 540-140, 540-170, 540-200, 540-V140, 540-V180, 550-140, 550-170 | 30 Hydraulic System |
Several manuals list the same model names for different build years and engines. Check the serial number range inside the manual (Machine Identification in the older books, 01-06-03 Model and Serial Number in the 9813 books), or send us your serial number and we will confirm the right one. You can also search all Loadall manuals in the store.
The manual used in this guide
PDF, instant download after payment, nothing is shipped. Searchable, printable, works on phone, tablet and PC.
Get the PDF – €50Why work from the manual
Holding valves look similar from the outside, but their settings, test procedures and fitting positions change between models. Replacing ram seals that were never the problem costs a day of work and a seal kit. The service manual shows the hydraulic circuit for your machine, the drift limits, the test procedure for each ram and the correct holding valve setting, so you fix the leak that is actually there.
Working on a backhoe loader as well? See our JCB 3CX sideshift troubleshooting guide.
Not sure which manual fits your machine?
Send us the model and the serial number from the identification plate. We check it against the manual title pages and reply with the right one before you pay.
Ask about my serial numberFrequently asked questions
Is some boom drift normal on a JCB Loadall?
A very small amount can be. When hot oil in a raised ram cools down it contracts, and the boom settles slightly. Drift you can see within minutes, or drift with a cold machine, is a leak. The service manual gives the allowed drift and how to measure it for your model.
How do I know if it is the ram seals or the holding valve?
Follow the test in the Hydraulics section of the manual for your machine. In general, a leaking piston seal lets oil pass inside the ram, while a leaking holding valve or control valve lets it escape back to the valve and tank. The manual explains how to isolate each part safely.
Can I remove the load holding valve with the boom raised?
No. The holding valve is what keeps the raised boom up. Lower the boom fully or support it mechanically, stop the engine and relieve the hydraulic pressure as the manual describes before you loosen any valve or hose on the ram.
Which JCB Loadall service manual do I need?
It depends on the model and serial number. Older Side Engine Loadalls use lettered-section manuals (9803/36xx and 9803/37xx), later machines use 9813 and 9823 manuals with numbered sections. Check the model list on the title page, or send us your serial number.
