How do you identify a faulty hydraulic pump or cylinder?

If the roof is no longer working correctly and oil and hoses have been ruled out, two suspects remain: the pump and the cylinders. The distinction is important, because the price difference is significant. A reconditioned pump, depending on the model, costs many times more than a single used cylinder, and a complete new cylinder set can run up to over a thousand euros. It is therefore worthwhile to first accurately determine what is wrong.

 

What does what?

The pump builds pressure and moves the oil. There is one, and it operates the entire system. The cylinders convert that pressure into movement. There are several: for the roof latch, for the roof itself, and for the trunk lid or tonneau cover.

This difference immediately provides the most important diagnostic rule: if everything works poorly, check the pump. If one movement works poorly and the rest normally, check the cylinder for that movement.

 

Symptoms of a defective pump

• The pump makes no sound. If you press the button and hear nothing, the pump is not receiving power or the motor is broken. First, check the fuse and the relay; these are inexpensive parts that give exactly this symptom.
• The pump runs, but nothing happens. You hear it clearly, but the roof moves little or not at all. The pump is no longer building pressure. This indicates internal wear.
• The pump makes a different sound than before. Gurgling usually indicates air or too little oil; check that first. A whining or squealing pump that has sufficient oil is usually worn out.
• The roof becomes slower the more often you operate it. A pump that heats up and then performs less is a pump at the end of its life.
• The pump shuts off during movement. Thermal protection. The pump is working too hard, due to wear or because the mechanism is stiff.
• All movements are slow. If the latch, roof, and lid all move slower than before, the common factor is the pump.

 

Symptoms of a defective cylinder

• Visible oil at one cylinder. The clearest indication. External leakage means a worn seal.
• One movement is slow, the rest is normal. If the roof moves normally but the trunk lid comes up slowly, the problem is with that cylinder and not with the pump.
• The roof pulls crookedly. Two cylinders that should do the same no longer do so equally. One delivers less force than the other.
• The roof slowly retracts. If you stop the roof halfway and it then retracts by itself, a cylinder is leaking internally. The oil escapes past the piston inside. This is the most difficult malfunction to find, because nothing comes out.
• The roof doesn't complete the last few centimeters. A cylinder that no longer makes the full stroke falls just short. Often the roof almost closes, but the latch doesn't engage.

 

First rule out the inexpensive things

Before ordering a pump or cylinder, go through this list. These causes give the same symptoms and cost a fraction:

• Oil level. Too little oil gives exactly the picture of a worn pump: slow, gurgling, and a roof that just doesn't quite make it. In our article on refilling, flushing, and bleeding, you can read how to check this.
• Battery voltage. A convertible roof requires a lot of power. A weak battery leads to a slow pump motor. Measure the voltage during movement, not just at rest.
• Fuse and relay. A pump that makes no sound at all is often a pump that is not receiving power. Relays are inexpensive parts that often turn out to be the problem.
• Ground connections. Corrosion on a ground point in the trunk causes voltage loss and thus a slow pump.
• Stiff mechanism. A roof that moves stiffly due to dirt or dry guides forces the pump to work harder. This resembles pump wear, but isn't.
• Leaking hose. Pressure loss due to a leaking line gives the same picture as a weak pump. Check the lines for damp spots.

We regularly see customers order a pump when a relay or a hose repair kit was needed. Hence this paragraph.

 

New, used, or reconditioned?

For pumps and cylinders, you usually have three options.

• New original is the most expensive route and not always available for every model. For newer cars, it is sometimes the only option.
• Reconditioned offers the best value for most customers. A reconditioned pump is inspected, fitted with new seals where necessary, and tested before it leaves the facility. Considerably cheaper than new, with a significantly lower risk than used.
• Used is the cheapest route and the most variable. We test what we sell, but a used part remains a used part. For older models for which nothing else is available, it is often the only way.

We supply all three, depending on the model. View our range of hydraulic pumps.

 

After replacement: don't forget

A new pump or cylinder in a system with old, contaminated oil is a waste of your money. Replacement requires:

• flushing the system and filling it with fresh, correct oil
• complete bleeding by cycling the roof multiple times
• rechecking the oil level after bleeding
• inspecting the hoses: if the pump has worked extra hard for years, the lines have also noticed

 

Are you unsure about the diagnosis? Describe three things to us: where the roof stops, what sound you hear, and whether it improves with the engine running. We can usually get a long way with that. Contact us.