No worries and no rush. Just let me know when you've received payment. I'm Mike from California, in case that helps any.

 

Heh, not to wander into what is probably a controversial topic, but I'm with you on that one. I can live with slow tracking and quick delivery by the post office though

BTW, I've never bought so much stuff for a car I don't yet have possession of. I now have: wheels, self jacking dollies, this resistor, and the car has yet to arrive. Keeping my fingers crossed for a delivery tomorrow or the next day - and then I need to wait around for the title & bill of sale before I can drive it anywhere.

 

It may be that nobody needs this. But Sam has agreed to indulge my tendency to worry and include some notes on installation and testing with resistor kits. (If you already have the full paper, www.scorekeeper.com/jaguar/jaguar01.htm, you don't need this.) The final product will be close to what's below, but I wanted to get something posted here since guys have begun receiving their kits. Shorthand version: there two important considerations: heat and proper latch closure.


Installation:

1) Be sure the car’s ignition is off; remove the ignition key.

2) When opening the 2-pin connector (one black wire, one white) leading to the hydraulic pump ... this connector is retained by friction only, no clip, but it can be hard to open. A mix of pulling and rocking motions, with a little patience, will get the job done.

Testing:

1) The resistor will become warm, but not hot, in normal operation. It is possible to make the resistor hot by repeatedly raising/lowering the top in rapid succession. This will tend to make the solenoids on top of the pump and pump’s motor hot too. Repeated raise/lower cycles in rapid succession should be avoided.

2) Test the operation of the convertible top with the car’s engine off. It is normal for raising and lowering the top to take 3 to 5 seconds longer, and for latch closure to take 1 or 2 seconds longer, than before installing the resistor. Do not hold down the "raise/lower top" rocker switch for more than about 5 seconds at latch-closure time if the latch does not close, confirmed by the "bong" tone.

If the latch does not close, try a second test with the engine on. Use engine-on for testing, and for day-to-day operation, only if engine-off does not work properly. (engine-on produces more hydraulic pressure, which is not needed if engine-off works properly.)

If both of the tests in 2) fail, something is wrong. Remove the resistor kit from the circuit and please report the event here. If either of the tests in 2) succeeds, the Voltage Reduction System has been successfully installed.

 

So this SIMPLE device is all I need to do to reduce the pressure used to move my top up and down? What about the other procedure to do this? I am confused as this seems much more simple and does the same thing.

 

By "other" procedure I assume you are referring to the pressure relief valve? This has been debated a bunch but here is my (maybe biased) take. At the time my hoses failed at the latch, two guys here (Walt and Gus--especially Gus) were studying this problem to the extent that a PhD dissertation could have been written. In short, the pressure that the existing pump delivers was much more than is actually needed to operate the top. They came up with the pressure relief solution and the valve is sold by Walt's company (LSI). I bought this since nothing else was available at the time and the LSI valve solution is simple and direct. Pressure that goes into the system is absolutely predictable and it does not matter what condition the battery is in, if the engine is off or on, etc. The end result under ALL conditions is that the pressure is exactly limited to 900 psi (I believe that is what the valve is set at).

The resistor solution goes about limiting pressure by running the pump slower. This is less predictable (sensitive to battery condition and whether the engine is running or not). There was also spirited debate on what negative effects this might have on the pump since you are running it at some reduced efficiency. The other negative (in my opinion) is that the electronics in these cars are spooky enough without altering existing circuits.

Of course there is a big price difference (about $20 for the resistor versus $279 for the valve). I have to admit that if I was looking today for a solution for my car, I might seriously consider the resistor and try that first given the negligible cost. Still I would consider the valve the better solution.


Doug

 

Not to rehash a subject that's been beaten to death, but there are essentially two ways to reduce the hydraulic pressure. One is to add a pressure relief valve that opens when the pressure in the line exceeds a certain amount. The second it to reduce the power output of the motor that turns the hydraulic pump. A simple analogy would be an electric water heater. They all have pressure relief valves on them. If the pressure gets too high the valve opens and steam is released, lowering the pressure. However if you simply turn down the power to the water heater, the water can never get hot enough to turn to steam and cause the pressure which would burst the tank. The resistor reduces power to the pump by turning the extra, unneeded power into heat. When you install the resistor and then run the pump motor, the resistor absorbs some of that energy and releases it as heat. The motor has less electrical energy coming into it, therefore it can't put out as much mechanical energy as is did without the resistor. Less energy out = lower pressure.

The main difference between the electrical and hydraulic solutions (besides cost) is the way the two solutions affect the hydraulic pressure. The relief valve solution is only going to clip off the peak pressures. That's a good thing because the peak pressure is what causes the burst hoses. The top will pretty much work at the same speed it did prior to the installation of the relief valve. The electrical solution is going to cause the motor to pump fluid more slowly, therefore the top will take a few seconds longer to open and close. The pressure during most of the cycle will be the same whether you use the electrical or hydraulic solution because it takes X amount of pressure to move the top. With the resistor it will take slightly longer to generate X amount of pressure, but the amount of energy needed to raise the top doesn't change. If it takes 800 PSI to move the top over the "hump" without the resistor, it will still take 800 PSI to do it with the resistor. It will just take the pump slightly longer to generate that 800 PSI.

However, the hydraulic rams that move the top typically aren't the problem. The vast majority of the burst hoses are the ones that go to the latch right above the rear view mirror. When the latch closes the pump continues to run for a second or two. You've probably noticed this when you've raised the top. You can hear the motor straining as it tries to pump more and more fluid into the hydraulic lines. THAT is when the hose bursts. The relief valve solution vents that excess fluid back into the hydraulic fluid reservoir preventing the pressure from getting high enough to burst the hose (think relief valve on the water heater). The electrical solution limits the power of the pump so that it can't generate the high pressure that would burst the hose (think turning down the power on the water heater).

Both solutions work. It's just a matter of what you're comfortable with. My background is in electrical engineering, and I believe Dennis's is, too. Dennis did all of the research to determine what value resistor needed to be used to reduce the pressure as much as possible without reducing it so much that the top would no longer work. Since I'm an electrical guy I was comfortable with Dennis's solution. The hydraulic solution that Walt and Gus came up with is a fine solution, and I'll even admit that I think it's superior since it just clips the peak pressures and doesn't slow down the operation of the top. But I wasn't comfortable with the idea of disconnecting all of the hydraulic hoses, and then I read a post where someone had to take their pump to a machine shop to get a plug removed because it stripped out when trying to remove it. I found that a little bit scary, but that's just me. Some of you might think "no big deal" because you're comfortable with that kind of thing. But for me, personally, the resistor made the most sense. It's cheap, effective, and I don't care if the top takes an extra 5 seconds to close.

 

By the way, I'd also like to add that if you have a hydraulic hose that's already close to failure, both of the solutions are just going to delay the inevitable. A frayed, leaking hose is eventually going to burst, no matter what. It would be interesting to do a survey in a few years to compare the rate of failure between unmodified cars, those that have a relief valve installed, and those that have the resistor installed.

 

Edit: forgot the one about battery condition.

Just a few factual points:

* It is not correct that the pump operates at reduced efficiency when run at reduced voltage.

* Far as I know, there has been no debate about "negative effects" on the pump among people with the electrical background required to have an informed opinion. There is no basis in electrical engineering for this idea.

* Concerning effects on the overall electrical system ... There are none. Any electrical transients (noise) generated when running the pump at reduced voltage must be smaller than when running the pump at higher voltage. The resistor itself is what's called a passive element; it cannot generate any transients of its own.

* The pump prressure does not depend in any significant way on battery condition. The battery would have to be so weak as to be unable to start the car before a measureable pressure change would occur. Because pressure is controlled by voltage in this system, two pressure/voltage points are always available: one when operating engine-on (alternator voltage), one when operating engine-off (battery voltage).

 

If you would like to read my research about the hose failures and why you can go to my page Auto Repair I also have information about the pressure relief valve if you care to read about it. Be an informed consumer.

 

Sam,

I see this one a little differently. Seems to me we could have hoses which are in a condition where they could withstand, say, 1000 PSI pretty much indefinitely, but if hit with 1600 PSI ... splat!

Any system which reduces peak pressure could extend the life of such hoses ... maybe for the life of the car.

What do you think?

 

I'l put my 2-cents in on this one. I am not sure what you have observed on your hoses Dennis, but especially on cars that live or have lived in hot climates, the outer jacket of the hoses literally disintegrates, ultimately effecting the integrity of the crimped connector on the end of the hose, as well as exposing the inner 'pressure load bearing' tube to the environment and rapid deterioration.

IMHO, no pressure reduction solution will delay the inevitable in these cases. In cooler climates, this deterioration may well be much slower.

 

weeeeeell, being cheap, always short on cash maybe I will go the cheap route for now. If the hose is ganna go sooner or later what the heck.
I do have records of the system having an issue years back and it was flushed with new fluids, it's been in the shade most of the time, then all the time with us, and it appears I have the earlier hoses that were less prone to failure so maybe I will be safe for a few more years.

 

I've seen pictures of hoses that are decayed and fraying, probably the same pictures that WhiteXKR was talking about. I think hoses like that are going to pop eventually no matter what. There are probably other hoses that would burst if they are forced to endure 1600 PSI over and over, but those same hoses will last for the life of the car if the pressure is reduced to something they can handle.

In other words, I'm acting like a politician and riding the fence.

 

Not just pictures. I have a former sunbelt car. Just the slightest touch and the outer covering would peel away.

 

My own car started life in New England. There is nothing visible in the way of degradation of the hoses, which sort of fits with the idea that heat is a factor.

So, are we just buying time with pressure reduction, or is it a permanent fix? I'll jump on the fence with Sam and say there may be cases in both categories.

But since I don't know of any hose failures with pressure reduction in place, for a change I'm going to be an optimist and assume it's permanent until a case pops up to the contrary. Anyone know of one?

 

Sam,

I am new to the forum and it does not permit me to send you a PM. I am interested in one of these resistor kits .... nice job! I can be reached at ivan@thecarnut.com

Ivan

 

Well, it looks like all 10 of the next batch have already been spoken for. I'm going to go ahead and order enough parts to make another 20. I had no idea these things would be so popular.

 

Sam, I also would like one of these for my '03 XKR when get the next batch made. You can reach me at iswan@verizon.net. Thanks !

 

Please forgive my ignorance as a coupé owner, but what does this gizmo do exactly?

 

The hydraulic hose that controls the latch at the top of the windshield has a tendency to burst and spew green hydraulic fluid all over the dashboard, radio, climate control buttons, leather seats, etc. Once it happens it costs $1800+ to get it repaired at the dealer, or you can do it yourself for the cost of the hose plus one or two days of labor (the entire interior has to be removed).

This resistor reduces the pressure in the hydraulic lines, and prevents the hose from bursting in the first place.