Inside the Rabbit gas tank/obscure parts source?

Tom A

Tom A

New member
I have the gas tank from my 83 GTI ITB car cut open, and need to replace the diaphram on the bottom of the surge box. It is the round black thing in the center of this picture:
pickupbottom3.jpg


It has the VW logo, Audi rings, and a part number:

171 201 740

I went to my local VW dealer, and the part number did not show up in the computer, and the inside of the tank wasn't in his catalog. Any idea where I could get a replacement?

Thanks,

Tom
 
Internal tank parts are not available from VW; you'll either have to repair yours or scour a junkyard...
 
We have bought used and brand new tanks before; not real expensive, and probably the better choice anyway.

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Lesley Albin
Over The Limit Racing
Blazen Golden Retrievers
 
<font face="Verdana, Arial" size="2">Internal tank parts are not available from VW; you'll either have to repair yours or scour a junkyard...</font>
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Tom, I couldn't find that P/N either on my EPC5 list. The P/N for the entire tank is 170 201 075 J
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Thanks for checking guys. It is really too bad, the factory surge tank is a neat design, and it works very well. When it was working, I could run the car until it sputtered, then add 2 full 5 gallon dump cans without spilling, to a 10 gallon tank. Whatever was left in the tank had to be less than what fits in the stock filler neck, probably less than a gallon. Too bad I have to scrap it for what should be a $3 part. If I could find one in a junk yard, it would be at least as old as the one I am replacing, and may have the same problem. No way to inspect it through the sender opening. The car isn't street legal, so I can't really test it without going to the track.

<font face="Verdana, Arial" size="2">We have bought used and brand new tanks before; not real expensive, and probably the better choice anyway.</font>
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I did some digging on the cheap replacement tanks, and from what I can tell reviews are mixed. Some work fine, others the hoses don't quite match up, and I have no idea what they use to prevent sloshing under side load. They certainly don't use the same thing the stock tank does, or they couldn't sell it for what they do. A factory tank is out of my price range, and a used tank could have the same problem in a few months. Right turn fuel starvation isn't exactly an isolated problem.

My tank is at a radiator shop, and they are going to make me a brass surge box with a filter to replace the factory plastic one. I am already into them for an hour labor to boil it out and cut it open, having them fix it would end up costing me the same as buying an aftermarket tank at this point, plus I know the tank is in good shape, and all the hoses will fit. He is estimating that it will end up ~$250, which isn't bad considering S.F. Bay area labor rates. If the new surge box works even close to as well as the stock one, I will be happy.

If anyone is interested, this is what the stock innards look like:

pickup3.jpg


The screen fits in the 4 rails sticking up from the bottom, the problematic diaphragm can be seen through the hole at the bottom. This picture the top is removed from the box. The 2 square things are little trap doors, that fit in the sides of the tank. They are hinged at the top, and keep the fuel in the surge pot under side loading. The notches at the right and left sides of the box are where the hinges fit, and they are held in place by the top of the housing. The white spot on the left side of the box is one of the holes for the doors.

The fuel flows in the little doors, through the filter and then down between the diaphragm and the housing. The pickup is on the bottom of the housing, is pulls the fuel up and then directs it to the left into the feed pipe for the fuel pump. You can see the back side of the pickup inside the box, running from the center top to the left corner. There is an "O" ring that keeps the pipe sealed to the housing.

If I can, I will post a picture of the new box.

Thanks again,

Tom
 
Tom:

You're right, the stock setup works great 'til that diaphragm goes. Mine disintegrated and got sucked up by the pump, ruining the pump. Killed a second pump before figuring it out and cleaning out the pieces. Then had a tank that starved at ~4 gallons. Put in a used tank w/ good diaphragm, ran dry, looked in through sender hole and the bottom of the tank was barely wet. Couldn't have been more than a couple of quarts in there.

I had never taken mine apart, just peered in through the sender hole. What I never could deduce by looking in the top - why the diaphragm? I'd have thought that the pickup could simply have come from the bottom of the surge tank. Any thoughts having looked closely at it?

Regards,

Al Seim
www.actdigital.com
 
Tom, thanks for the great info. Were you able to get a pic of the custom unit?

Al, did the tank without diaphram that starved with ~4 gal starve mainly during right-hand turns? If so, I suspect that the diaphram is there to keep the fuel from backing out of the pickup tube during right turns (note that Tom's picture is rotated 180 deg).

The diaphram seems to be bigger than the hole, but located under the hole. Thus, it must be designed to let fuel pass from top to bottom, but not from bottom to top (which is where fuel from the pickup tube would otherwise go to back out of the pickup tube during a right hand turn). Make sense?
 
I did get a few pictures of it while it was still under construction. Here is the one that came out the best:
brassbox.jpg


It is simply a brass box, with a few holes cut in the sides. The line you see in the photo is the return line, the pickup is in the bottom. There is a mesh sock-looking filter on it (an AC Delco part), which I didn't get a photo of.

The diaphragm allows the inlet to the pickup to be as low in the tank as possible, while forcing the fuel to travel through the screen on it's way to the pickup. I am not positive, but I think the right turn thing has less to do with the fuel running out of the pickup line, than simply sloshing it the left side of the tank, allowing the pickup (which is offset to the right) to suck air. Mine had just a pin hole, but on a mechanical fuel injection that uses fuel pressure to controll things, it must have been enough air to screw with the pressures and make the engine cut out.

The diaphragm seems to be a very poorly chosen component of an otherwise excellent design. I realy wish they were available. As it stands, I probably lost a gallon or so of effective fuel capacity, because the new pickup won't work as well as the old one.

Tom
 
With the diaphragm gone, as mine was, you effectively had no surge chamber at all, as the inside of the surge chamber "leaked" straight out the bottom. I discovered this by pouring liquid into the top of the surge chamber - it came out the bottom.

I suspect that Tom is correct, right starves fist as the pickup is closer to the right, but that left would have starved too with the fuel a bit lower.

In my case, the hiccups started with maybe 4 gallons remaining, then got worse, but you could run - albeit poorly - for several laps that way.

With the "good used" tank, it ran perfectly until it coughed a couple times then died - couldn't even get back to the pits. But the fuel was really all gone!

Al Seim
Action Digital Race Data Systems
www.actdigital.com
 
Follow up: Well that didn't work.

It still cuts out at just over 1/2 a tank. Unfortunately at this point I think the cost effective solution is to keep the tank full.

I can get about 40 minutes from a full tank.

Tom
 
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