DIY Mod for Easy Soft Top Drain Tube / Hose Cleaning

[Kimo]

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Earlier this summer, my hydraulic motor was replaced due to blockage of the (poorly designed) drain tubes.

For those who are not aware, when rain and wash water stops flowing down the "water outlet tubes" (see diagram item # 13) and out of the "water outlet valves" (see diagram item # 18 and pictures), it must accumulate in the well 'funnels' (see diagram item # 14). (Each of the well funnels has a small hole in the bottom that feeds the tubes - oddly, these holes are only about the diameter of a pea, much smaller than the drainage tubes they feed.) Accumulated water will corrode and eventually kill the motor, as the motor sits directly in the well on the driver's side (which means that this tube is the most important of the two).

The water outlet valves (shown in the picture directly above the key) complicate matters as they are designed such that they will not pass anything but water, meaning twigs and leaves will not pass through. Many owners simply remove these valves. Indeed, my valve was already (after less than 60 days) partially blocked with a piece of metal (see picture).

Having researched the matter, it now seems to me that the best way to periodically clean and clear these tubes of debris is to blow compressed air UP from the bottom of the tubes (after removal of the valves). While it is (barely) possible to see the hole in the passenger side well if you look down it with a flashlight (see pic), it is NOT possible to see or access the driver side well hole because it is blocked by the motor. Thus, blowing up (or, I suppose, sucking down) from below are the only viable options. Indeed, there is a good DIY on this forum that utilizes this method (see attached PDF below).

The main obstacle to routinely blowing/sucking from the bottom is that the valves and tube ends are a pain in the ass to get to. Yes, it is indeed possible, and many do it routinely, but it requires hand contortion and the sacrifice of several dermal layers each time it is done (see pics of my hand during, and then one day post-mod), plus it is almost certain that the car needs to be lifted at least 6-12 inches every time. These factors make it all too easy to simply blow off routine cleaning of the drains.

So why not do it once, insert an access tube for future cleaning, and be done with it?
That's what this mod does.

To do this, you will need to procure some suitable vinyl tubing (Lowe's / Home Depot?). I used some Tetra branded pond tubing - about 1/2" Outside diameter and 3/8" Inside diameter (see pic).

Jack the car on one side using the jacking pad and a suitable stand (be safe!!) and then reach into the square hole just forward of the front splash guard, bend your wrist and reach outwards toward the fender until you find the valve (I found the driver side valve easier to get to than the passenger side). It may help to take a good peek in there from under the car with a flashlight to locate the valve, but be sure it is safely raised! When you find the valve pull it out! Store it away.

Now, contort a bit more to feed the new hose up and into the existing tube hole far enough that it will stay (mine went almost a foot) -- and then cut the new hose about 8 inches below the access hole (this excess will be normally tucked back up into the access hole). Do the same on the other side. Important - When the new tubes are tucked back into the wells, make absolutely sure there are no kinks!! and then test flow with water as described below.

You now have easy access to the tubes, and can blow them from below every time you wash the car, check the tires, check the oil -- you get it.

Now, my only concern with this mod was that I was decreasing the inside diameter of the (approx.) 5/8" stock tube by another 1/4" by inserting the access tube, which might arguably cause a bigger problem than not doing anything at all. But the vinyl tube is actually about the same diameter as the barb fitting for the one-way valve, and I thoroughly tested the system by pouring water down each side and ensuring that there was good water flow. Some debris actually came out of the ends of the new tubes, so they do seem to work at least as well as the stock setup.

Of course, I'll also keep an eye on things by pouring water frequently to validate continued functionality. (Note that bottles of water are more effective - and easier to control - than a garden hose for this -- see pictures for pouring location.)
And by the way, if you are not inclined to go to the trouble of blowing your tubes periodically, you should at least do yourself a favor and routinely verify proper tube drainage by pouring water as described above and watching the amount and speed of discharge. If there is minimal flow, you've got a problem.

Some additional notes: When you blow compressed air up the tubes, ensure the top is DOWN, and you can definitely hear the air coming up the tubes and out of the holes in the bottom of the wells. You may even see debris blowing out!

This is obviously most effective for those with access to an air compressor, but I suppose you could also suck from below -- as it'd be better than NO cleaning.

So this is how I did it. Some may think it's overkill, some may question the insertion of another tube in the stock tube. Some may simply not care. But I'm a little more confident now than I was yesterday that I'm doing everything I can to keep these tubes clear. Another $1400 soft top motor replacement is just not worth it to me (luckily the first one was on BMW's tab).

Hope this helps someone.

Mike

[Nate4641]

Thanks for the write up!

[gas-can]

Nice idea Kimo.

Only worry I would have with this would be stuff getting caught in the transition from the z4 tube and the external tube.

Also, can you be sure that blowing stuff back towards the motor is such a good idea? What's to stop something from really blocking the passage? Perhaps attaching a vacuum attachment to your external pipe to suck would make more sense?

Blow vs suck...that's the question

-gc

[Kimo]

Originally Posted by gas-can

Nice idea Kimo.

Only worry I would have with this would be stuff getting caught in the transition from the z4 tube and the external tube.

Also, can you be sure that blowing stuff back towards the motor is such a good idea? What's to stop something from really blocking the passage? Perhaps attaching a vacuum attachment to your external pipe to suck would make more sense?

Blow vs suck...that's the question

-gc

Thanks.

I considered that, but am reasonably satisfied that this transition is less restrictive than the stock transition point at the bottom of the tubes caused by the valve barb and the one-way flapper. It is, though, a valid concern and this mod means that you definitely need to routinely blow to clear any debris that might tend to accumulate at this transition. (If an owner is not going to keep up with it, then a better approach (in my opinion) would be to simply pull the stock valves and verify good flow every so often by pouring water down the tubes.)

Re. suck v. blow, you can definitely hear the cleared tubes when you blow, which is instant feedback that the drains are clear - not sure if you can really tell with a vac approach. And the hydraulic motor, though located in the well above the drain hole, is pretty well shielded from flying debris. The ideal situation would be that all debris is blown all the way out of the funnel and out of the well. I suppose the worst it can do is settle back into the funnel and clog the tubes again - leaving you right where you started.

All that said, I believe I'm going to rig up something to also SUCK from the bottom through the extension tubes, as part of a belt and suspenders approach to a comprehensive cleaning routine. It can't hurt.
The important thing is to routinely verify good flow as often as you can, and -- if modded as above -- especially after tucking the tubes back up in the fender access holes.

[chazLuke]

I was thinking that we could use a tubing adapter in place of the plug and be able to use much larger diameter hoses. To do that I need to know what the threads and diameter are on the plug. Does any one know that or have a part number for the plug so I can buy one and measure it? Or at least know what the part is called by BMW?

[StickMon]

This bit?

[chazLuke]

I bought one from Ecs. Unfortunately these don’t have threads, only ribs so my idea won’t work unless we find a version that is press fit.

[Piper1]

I wanted to bump this up as theres so many still asking about ways to clear the drains. I’ve done this with a nylon braided hose from Home Depot to prevent it from kinking and it’s such a quick way to clear them. It takes more time to get the 2 gallon air compressor filled then it does blowing the drains out.

[jwolf]

For 5 years I have taken a garden hose, adjusted it for a tight stream, aimed in that hinge area up top and then let the water go full blast for a few seconds. I do this when it is very warm and the hinges can dry quickly. Has kept things clear.