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Trouble at the top
Classic American issue 183


For those of us lucky enough to own a convertible, we do not have to preach the virtues of, fun and frolics to be had with such great cars, well at least not to each other, just the uninitiated. Convertibles are meant to be driven and enjoyed, although this would happen mainly during our all too short but intense summer. Intense because we seem to cram so much into so few hot months as possible. How many times have you driven along a country lane with the top down, your favourite band oozing from multiple speakers, day dreaming about being a film star on sunset boulevard with a car full of beautiful women and………….sorry, must remember, don’t type everything your thinking.
This month we will mostly be covering maintenance, trouble shooting, use and care for your precious ragtop. There are two basic forms of convertible top, firstly the manual and secondly the electric. Let us, first, look at the more complex of the two, the electrically operated top. The basic principle of the convertible top mechanical operation is an electric motor and pump connected to a hydraulic fluid reservoir. This reservoir is in turn connected to the power rams by hydraulic hoses. The power rams are usually found either side of the rear seat area, attached to the convertible top mechanism. The pump motor will be powered in one direction for the convertible top to go down and in the other direction for the top to go up. This is normally achieved via a three-position toggle switch on the dashboard that activates the motor. The central position is usually neutral, pushing the toggle switch up activates the motor to raise the top, pushing the toggle switch down activates the motor in the opposite direction and the top goes down. It should be remembered that it is not the actual motor that is raising and lowering your roof. The motor merely drives the hydraulic pump, which does the work. With the pump being driven this action causes hydraulic fluid to be pumped along two hydraulic hoses. These hoses feed the fluid to one end of each of the hydraulic rams, as the pump moves the fluid into the ram it pushes the piston up extending the ram length, this in turn allows the top to be raised. With the motor running in the opposite direction the fluid is pumped into the rams from the opposite end and the rams will be retracted, allowing the top to be lowered. If this does not happen then read on and hopefully we shall diagnose the problem.

Lets take these individual components and look at the possible maintenance, failure and cure for most of the convertible top problems. Firstly the electrical system. As we have said a three-way switch mounted in the dashboard or centre console see fig 1, operates the tops motor, this three-way switch will mean a three-wire connection at the motor assembly see fig 2.

Fig 1.

Fig 2.
If you believe your switch is at fault a simple continuity check, in this part of the loom, may reveal a failure in the wiring or switch that could be easily remedied. Breaks in the wiring are easily fixed with bullet connectors, but for a professional job you should consider replacing the complete switch to motor wire especially if the wiring is old or brittle. As we have said before, a little more time spent now, could save you from having problems in the future. If you possess a multi-meter the test is very easy using a simple resistance check, if not a twelve-volt bulb in a holder with two wires will suffice. The test is a simple one and is carried out as follows. Assuming you have a meter, find the three-wire connection at the convertible top motor. One wire will be common (earth wire) and is usually black. Do ensure this is grounded properly, so many electrical failures are caused by a poor earth. The other two wires will be from the two positions of the toggle. Probe the connector with your multi-meter set at around twenty volts fig 3, one probe on the common the other probe to one of the other wires, fig 4.

Fig 3.

Fig 4.
Now have someone operate the toggle with the ignition on. Try the toggle in both positions, one position should give a reading of around twelve volts positive, if you are using the bulb and wire method you bulb should light up. Now move the probe to the other wire leaving the common in place. Now with the toggle in the opposite position you should have a similar reading, this will, however, more than likely be a negative voltage. The positive voltage driving the motor in one direction and the negative voltage driving it in the other. If you do not have a reading at one or both positions you need to check the fuse and as mentioned earlier the wiring and toggle switch. If you find a blown fuse it would be prudent to investigate why it has blown. Simply replacing the fuse without knowing the reason behind its failure can lead to more expensive problems later on. If you do get a good reading at both positions between the switch and motor, and you have power to the motor, it would be safe to say that the fault is elsewhere. As with most electric pumps used on convertible tops, see fig 5, the most common cause of failure is age. Because the motor does not get used often enough to actually wear out, the internal parts usually just physically break down. Because of the changes in design over the years, it is most unusual for modern electric motors on American cars to simply fail. The most age related problems we see are with vehicles dating from the mid seventies and earlier. Thinking about it this isn’t too bad and says a lot about the design of the American electric motor, and is a pretty good track record as we are talking about thirty plus year old electric motors only just starting to fail. The problem of motor failure can be rectified in two ways, the most obvious is replacement of the motor, the second option is refurbishment of the old motor. This service is available in most parts of the country, a quick scan through the Yellow Pages and you should find a number of companies offering a rebuild service for your electric motor. Obviously the replacement of the electric motor may be advisable if the hydraulic pump also has a problem. This would be the most cost-effective way of curing two problems in one go.
Moving to the hydraulic hoses, any suspected problems in this area can be checked with a simple visual inspection. The most obvious problem here is leakage. Secondly poor operation can be caused by crushed or kinked hoses fig 6. As always if you find any damage here replace the hoses as necessary.

Fig 5.
Fig 6.
Unfortunately, the rams are not so easily diagnosed for problems, but sometimes a visual inspection of the hoses can reveal a problem within the ram. If you are fortunate enough to have transparent hoses you may be able to see air bubbles in the hydraulic fluid when the pump is operated. If this is the case there is a good chance the ram piston or pump has a problem. If the seals around the piston are worn they will pass air as well as fluid. This causes the fluid to become aerated and in turn causes the top to operate poorly or in extreme cases not at all. Most hydraulic rams, fig 7, on cars are by the nature of their design not serviceable, and therefore must be replaced. If your top is working but possibly not as well as you would like it. It is always worth changing the fluid, especially on older systems where the fluid will have become discoloured and contaminated with age. Most convertible top pumps use automatic transmission fluid, however, some do use brake fluid. So it is always worth checking your handbook to find out which fluid your system requires. Using the incorrect fluid or mixing fluids can lead to hydraulic pump failure. After replacing the fluid always operate the top a few times, this will bleed the system. Once you have done this recheck the fluid level at the reservoir and top up as required.

Fig 7.
Fig 8.
Having checked out what we would consider the most obvious problem areas we move on to what may be thought of regular serviceable parts. It is always worth checking out the pivot points on the tops mechanism and lubricating these as necessary fig 8. You should find on most convertibles, you will be able to make adjustments at these pivot points fig 9. Making minor adjustments will allow for smoother operation and put less stress on the whole convertible top system. Whilst checking the pivot points remember to check the rest of the frame structure for any bent or damaged components.

Fig 9.

Fig 10.
We are now entering the final series of checks and with a convertible these are amongst the more important. It is always worth making a close inspection of the rubbers that seal the top to the side glass fig 10. and header rail (front screen) fig 11. These sealing rubbers are important in not only stopping wind noise and rain from entering the interior (yes we have all been caught out in the Great British summer), but also stopping those annoying squeaks and chirps that can add up an unpleasant drive.

Fig 11.
Fig 12.
Okay so we have lubed, adjusted, fixed and possibly replaced components, now let us turn our attention to caring for the convertible top itself. There are several do’s and don’ts, most of which are common sense, you will only ever drop your convertible top and break the glass rear window once, you will only put the top up or down while driving and turn it into a parachute once! So as you see common sense goes a long way to help caring for your top. As we have mentioned earlier, unless you are a die-hard enthusiast the chances are you will only use your convertible during our summer months. The all important point here is storage. If you are going to lay your car up for any length of time, it is worth considering the following. If it is stored inside always remember to unlatch the top to take the strain off of the convertible top material. Try to clean and treat the top before storage. Probably the most important thing to remember is never store your car with the top down. This will be detrimental to the material and if you have a soft rear window the damage caused to this may be irreparable. With the top folded there is a good chance of having moisture trapped for long periods, this will lead to mildew and possible staining of the fabric. The crease marks caused from ‘top down’ storage can be permanent and in time may turn into splits. With tops that have a removable headliner, it’s always worth removing and cleaning this as required. Most removable headliners are simply held in place with Velcro strips, see fig 12, and or pop fasteners. Be careful, as there may be some stitching holding it to the hoops. If the Velcro is not doing it’s job, it is easily replaceable and will make for a much better fit, this will help you to lose that ‘sagging bag’ look and it will transform your interior. Do take the time to inspect the attachment of the top material to the top mechanism and hoops. If the material is starting to part company with the metal hoops it must be reattached. Now whilst it may be possible to do this yourself, your local friendly car trimmer will soon have you and your convertible top reunited in next to no time. A well fitted top will go a long way to making the roof mechanism operate smoothly.

The convertible top material must be cared for, regular washing with shampoo and soft sponge is a good move, and regularly using a special convertible top cleaner will go a long way to help prolong the life of your top, and restore the more vibrant original colour fig 13. Once cleaned properly you should periodically treat the material with a good quality convertible top proofer, this will not only care for and protect the material, but will also help to keep the material supple and prevent the stitching from rotting. If your plastic rear window makes you feel like you are looking through nicotine stained pub curtains, there are products available to ‘polish’ some of the discoloration off.

Fig 13.
If you have a manually operated top, you can ignore some of what you have read. Many of you may be thinking that manual tops will be in the domain of older cars. This couldn’t be more wrong, take for example, the Corvette, no electric pumps or hydraulic rams to be seen here. The raising and lowering of the roof is all dealt with using brut force. This does of course mean that special care and attention should be paid to the condition of your convertible tops frame structure. As mentioned earlier damage to this can seriously hamper the tops operation and obviously even more so with a manually operated roof. Of course a manually operated top does not change the do’s and don'ts of storage and the care of the tops material. All this should remain relevant regardless of how your top is operated.

With the top held in place correctly and adjusted your car will take on a whole new appearance. You will find you have a new found pride in your beloved convertible, and driving it will make you feel that much better. Well, what are you waitin’ for, times a wastin’. Get your ragtop out and make the most of what we like to call……… summer.