Convertible top opens slowly or stops halfway: a list of possible causes

A convertible roof that no longer moves at all is annoying, but clear. A roof that moves slowly, gets stuck halfway, or just doesn't quite make it, is trickier. There's no hard fault, and the problem appears one day but not the next. This very unpredictability is the most important clue. Below are the six causes we see most often, in the order in which you should best rule them out.

 

First, pay attention to when it goes wrong

Before you unscrew anything, it's worth noting two things:

• Does the roof always stop in the same place? If so, the problem is probably at that point in the movement: a sensor, a lock, or a mechanical blockage. If it stops somewhere different each time, that points more towards pressure, oil, or voltage.
• Does it work better when the car is warm, or worse? Poor when cold and good when warm points towards oil that is too thick or seals that only close properly at temperature. Worse when warm points more towards a pump that is overheating.

These two answers will cut the search work in half.

 

Cause 1: too little hydraulic oil

This is by far the most common cause of a slow roof. A hydraulic system needs a certain amount of oil to build pressure. If the level drops, the pump draws in air. Air can be compressed, oil cannot, and so the movement becomes spongy, slow, and uneven. Often the roof just doesn't make the last few centimeters.

Recognizable by: a gurgling or whining sound from the pump, a roof that moves jerkily, and a movement that becomes slower the more often you operate the roof.

What you can do: check the level in the reservoir near the pump and top up with the correct hydraulic oil if necessary. In our article on topping up, flushing and bleeding, you can read how to do this correctly. Important: a closed system does not lose oil without reason. If the level is too low, find the leak.

 

Cause 2: a leaking hydraulic hose

The lines bend with every roof movement. After ten to fifteen years, the rubber hardens and tears, almost always at exactly these bending points. A small leak doesn't immediately cause an oil puddle. It first causes pressure loss: the roof moves slower, and the cylinder supplied by that line lags behind the rest.

Recognizable by: a roof that pulls crooked or where one side lags, damp spots along the lines, an oily smell in the trunk.

What you can do: follow the lines from the pump to the cylinders and look for dark, damp spots. If you find damage in one place, you don't need to replace the entire line. With a repair kit, you only replace the broken section. If the line is affected in multiple places or the damage is too close to a fitting, a custom hose is the better solution.

 

Cause 3: a weak battery or poor ground connection

A convertible roof demands a lot of power. If the voltage drops too much during movement, the pump motor delivers less power, and the roof moves slower. With a really weak battery, the roof stops halfway and cannot continue. This is why the problem often starts after a period of inactivity, or only occurs in the morning.

Recognizable by: the roof works better with the engine running than with just the ignition on, the problem is worse after a cold night or after a few days of standing still, and other electrical functions also react somewhat slowly.

What you can do: measure the battery voltage, and also measure the voltage while the roof is moving. If it drops sharply, the battery or a ground connection is the culprit, not the roof. Also check the ground points in the trunk; corrosion there produces exactly this symptom.

 

Cause 4: dirt, dry guides and heavy mechanics

The roof mechanism is an assembly of hinges, guides, and rods. If anything moves heavily there, the hydraulic system has to work harder, and the movement becomes slow. Leaves and dirt accumulate in the roof compartment. Grease and lubricant dry out after years. Dried-out rubber seals stick and hold the roof back.

Recognizable by: squeaking or creaking noises during movement, a roof that becomes heavy at one specific point in its movement, visible dirt in the guides.

What you can do: thoroughly clean the roof compartment and guides and lubricate the moving parts with a suitable lubricant. Treat the rubber seals separately with a rubber maintenance product; dried-out rubbers stick and that takes more force than you might think. This is maintenance you should do annually, and it prevents a large part of the malfunctions later in this list.

 

Cause 5: a sensor or microswitch that switches too late

Modern convertible roofs check the position of everything during every movement. Hall sensors, microswitches, and position sensors report whether a lock is open, whether the trunk lid is clear, and whether the roof is in the expected position. If one of these reports is not given or is given too late, the system stops as a precaution. Often at exactly the same point in the movement.

Recognizable by: the roof always stops at the same spot, a message appears on the dashboard, or the roof sometimes works after trying a few times.

What you can do: reading an error code often directly points to the component. Hall sensors are available per model and are often easy to replace. A dirty or slightly bent microswitch can sometimes be fixed by cleaning and adjusting.

 

Cause 6: a worn pump or cylinder

If the problem persists after all of the above, the pump itself has weakened or a cylinder is leaking internally. An internal cylinder leak is difficult to see: no oil comes out, but the oil leaks internally past the piston. The result is a cylinder that no longer delivers full power, and a roof that just doesn't quite make it.

Recognizable by: the pump runs audibly but the roof barely moves, one specific part of the movement is slow while the rest is normal, or the roof slowly sags back if you leave it.

What you can do: this is the point where DIY rarely pays off. We supply refurbished pumps and new cylinders for most models, and are happy to help you figure out what is most likely in your case.

 

Quick diagnosis

• Gurgling pump, jerky movement: insufficient oil or air in the system.
• One side lags, roof pulls crooked: leaking hose or cylinder.
• Works better with engine running: battery or ground connection.
• Squeaks and creaks, heavy at one point: dirt or dry mechanics.
• Always stops at precisely the same spot: sensor or microswitch.
• Pump runs, roof barely moves: worn pump or internal cylinder leak.
• Slower the more often you operate it: oil or an overheating pump.

 

What you should definitely not do

• Don't keep trying. The temptation to press the button again is great. But a pump that works against resistance or pumps air will get damaged. A pump is one of the most expensive parts of the entire system.
• Do not manually push the roof through. This will force the mechanism, and in a pressurized system, this can damage cylinders or guides.
• Do not ignore a slow roof. Slow is the precursor to broken. A hose that has a small leak now will completely fail in a few months, often at the worst possible time.

 

Do it yourself or have it done?

Easy enough to do yourself: checking and topping up oil level, measuring battery, cleaning and lubricating, and repairing a hose with a repair kit.

Better to outsource: internal cylinder leaks, pump replacement, sensor faults requiring diagnosis, and anything that requires roof disassembly.

 

Is your roof not working at all anymore? Then also read what to do if your convertible roof no longer opens or closes. Can't figure it out? Contact us. Often, from the description of the sound and the stopping point, we already know where to look.