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PostPosted: Sat Jan 26, 2019 6:49 pm 
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Location: Portsmouth
Car Model: 96 V4 & 9-3 Turbo-X
I'm putting together the drawings for a replacement fuel tank in stainless steel, in case Fliptops group buy doesn't work out, but i'm struggling with fuel level sender options. My own was removed from the tank as a big blob of rust, with no continuity and no movement on the arm, so i'm needing a new one.

Scandix do one that is supposed to be a replacement for 1976 onwards. Mine is a 1975. Anyone know what changed that would make it incompatible?

Also the Scandix one doesn't use the brown wire on the sender. They say in the instructions that it is only an earth, but on the wiring diagrams it goes to the instrument, and there is a separate earth marked, which i'm assuming is the little black tank earthing wire that goes straight to the body.
Is the brown wire actually for the low-level warning lamp? And would this mean that the low-level light doesn't work with the Scandix sender, or is the low-level light worked out internally to the gauge based on resistance of the sender?

Does anyone know what the resistances should be for a functioning sender for full and empty in case I need to find an aftermarket sender and use a resistances converter to get the gauge to read right.

Aftermarket senders are a whole extra can o worms, as most need a deeper tank than the one we have.

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PostPosted: Sat Jan 26, 2019 9:48 pm 
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I don't know if it is the only difference but looking at the diagrams in the parts book the early tank looks much, much shallower than the later one, although I've never looked closely at one in real life. Therefore I would expect the later sender to have a greater range than the earlier one.
The shallow depth might not be a problem if you can get a generic sender to fit (or if the later one will screw on) and use a range converter. You should be able to programme the range converter without knowing precisely the resistance range of the original sender. I can't remember where I saw a range converter recently but I'm fairly sure the one I saw had a programmable output to drive a "low fuel" lamp.
If you use a lever-arm type like the original then even if the range of movement is far to deep you could just let it hit the bottom when empty and convert the range appropriately. Of course you could shorten the arm to cover the full resistance range with less float movement.

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PostPosted: Sun Jan 27, 2019 5:30 pm 
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Location: Fliptop Towers, North Yorks...the flat bit.
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76 on would be the 96L with the rear seat mounted further back and less space for the tank. I don't know the details of the difference though.

When we were looking at a manufacturer last year (or was it the year before) the suggestion was to use a standard VDO sender and boss in the tank to replace the original, but this may require some calibration. Can't be a big job to make an adaptor to allow fitting of both...that would llow a common tank to suit those wishing to retain the original sender or those wishing to switch to a modern type.

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PostPosted: Sun Jan 27, 2019 6:40 pm 
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That is my plan, but i need to find a sender that will work with the gauge if possible, as the "translator units" have a reputation for being tricky to set up, and i need to work out how to do the holes before i get quotes for tanks and gaskets.


Ive got some other points to discuss with you all below. Need input from people with more 96 experience than me.

At the moment I've got the tank modelled up using straight folds instead of the rolled bends, forming large chamfers. This will be much cheaper to fabricate than the rolled corners. Doesnt change capacity by much. Will be a bit easier to fit in the slot.

Currently missing on my model is the "dent" for the spare wheel. This was pressed-in to the originals before folding and welding. We dont have tooling for that, so it would have to be a separate piece folded up and welded in. This adds a lot of welding, cost and scope for leaks. Its also a bugger to measure. Do we really need it? Or could we change the shape of the tank to extend the "dent" across the whole width of the tank? We'd loose a bit of capacity, but save a lot of money.

After a bit of experimentation i think that having the filler neck coming out at 90deg to the tank nearer the rear will be no more difficult to fit and remove than it is at the moment, and much cheaper to fabricate. The other alternative would be to have just a stub on the tank, and a separate 90deg section of hose or solid pipe to go between the original filler hose and the tank. However this will have an extra joint over original, and will put more joints inside the cabin giving more possibility for leaks and fuel fumes in the cabin.

The inside will have two baffles rather than the 1 originally, and will have a 38mm section of tube instead of the folded box over the outlet pipe to act as a local baffle to the outlet. Should be sufficient for both carb engines, and anyone who has or wants to convert to injection.

The outlet pipe will be in 1/4in stainless. We have 3 options on how to get it out of the tank.

1. Most like original: pipe goes to a boss welded on the tank with a BSPT female thread outside for a new stainless 1/4in hose barb.
2. Pipe goes to a boss threaded for an M10 Banjo bolt with 1/4in barb. Cheaper to machine than BSPT, but that would leave the outlet at 90deg to the current direction of the tank outlet barb, or need a 90deg banjo. Works out about the same cost as 1
3. just run the outlet pipe through the wall of the tank and connect the flexible pipe directly to it with a hose clip, but that may make removal and fitting of the tank tricky as the hose would need to be pulled off the barb. Would be about £30-£45 cheaper though.

Anyone wanting to do an injection upgrade will have to have the return line from the fuel rail teeing into the pipe from the tank before the fuel pump, possibly with a small swirl pot too, unless enough people wanted a second connection into the tank to make it worth it. I suspect I'm the only one thinking currently about doing an injection conversion though.

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PostPosted: Sun Jan 27, 2019 9:07 pm 
- You can fit a C900 space saver tyre to a 96 wheel, I don't think you need the "dent" this way.
- The original fitting is NPT, not BSP.


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PostPosted: Sun Jan 27, 2019 9:44 pm 
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The saab fitting is custom with a male taper seat inside a female thread. Its more like an inverted brake pipe union in that regard although brake pipes don't go to barb hose fittings.
It is also mild steel, so not compatible with the stainless tanks.

As it will need to be replaced, its better to replace with a standard fitting, and the most common i could find were BSPT. That thread has the advantage of sealing well just through tightening, especially if a bit of ptfe tape is used on the threads.

The brake pipe idea does open up another option though, flare the end of the 1/4in pipe coming though the wall of the tank and the other end of the solid fuel pipe on the floor of the car, and get a fuel hose made to match to go between them. People can choose whether they want to just fit the flexible fuel host onto the tank, or have a screwfitting pipe made up.

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Last edited by beardydave on Sun Jan 27, 2019 10:42 pm, edited 1 time in total.

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PostPosted: Sun Jan 27, 2019 10:15 pm 
Aaargh, you're right about the fitting. Last one I took apart was a month ago when I installed an electric fuel pump; my memory is not what it used to be... I guess the thread is 3/8 UNF then? (Almost) all other fittings on the V4 are American, so I'd choose NPTF over BSPT for uniformity.


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PostPosted: Sat Feb 02, 2019 2:35 pm 
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Fuel filler pipe is 1 3/8in (roughly 35mm). No body makes stainless tubes in that size. I can find 32mm, or i can find 38mm.
Same for filler hose (mine has perished and needs replacing). Can't seem to find it this side of the Atlantic.

Best I can suggest is to use 32mm and clamp it down tight, and stretch any replacement rubber hose over the filler neck.
d

EDIT:
Ive found one supplier of 1 3/8 45deg tubes. They're intended for exhausts and they are ~£22 each.
http://www.everyexhaustpart.com/cart/tu ... -bend.html

Malbrad have fuel filler hoses in stock, and in the absence of any other information I have to assume that they are 1 3/8 inch too. That solves that problem.


On other notes, i've found a hose tail like the original for the supply line. Uses a 1/4in BSPP thread and a 60deg conical seat. Should be easy enough to get bosses machined up and welded to the tank to suit this.
https://www.hoses.co.uk/adaptors-and-fi ... t1ugp2ca73

Advantage is that the nut is loose, so should be easy to tighten up without twisting the hose.

May possibly need new fuel hoses, I think the original is 5/16in, and i can only find that in NPTP thread like this one
https://www.hoses.co.uk/adaptors-and-fi ... t1ugp2ca73

This one will twist the hose whilst tightening, which won't do it any good. Alternatively if you replace the hose, fit the tank end, then fit the body end. Still a problem if the tank has to come back out again at any point.


I would appreciate someone with a car in better condition than mine doing a bit of research to confirm what sizes things are / need to be. Nothing is listed in the manual as to fuel hose size, and it's not as easy as it used to be to get replacement fuel hose now that Halfords don't stock it.

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PostPosted: Wed Feb 06, 2019 10:36 pm 
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Car Model: 96 V4 & 9-3 Turbo-X
I've finished modelling up the fuel tank. Just got to finish the drawings and send them off for quotes.

Final specification as follows:

Main panels - 0.8mm Thick 304 Grade stainless. This may increase to 1.2mm thick if the sheet metal shop recommends it for ease of welding. The main body of the tank is made in two parts. A roughly U-shaped bit for the front and back, and then a top panel with sides folded down. This is the easiest way to make it using folded sheet, and lets the welder do all the internal welding with good access.
Inlet pipe - 1 3/8in pre-bent tube. I've found one supplier of this. It's not cheap but we don't really have a choice. It's hard enough finding 1 3/8in stainless tube, but if the shop can find it, then it may be a welded bend.
Breather - 1/2in tube, hand formed.
Filler vent - 1/4in tube. This is much shorter than the original, exiting from the side of the tank next to the fill/breather pipes. It's only for allowing air back into the tank as fuel is removed, so doesn't need to be as long as Saab's original.
Baffle Plate - Slightly different design to Saab's original. Same thickness as main panels.
Outlet connection - 1/4 BSP. I found a thread gauge, and this is the same thread as the original and uses a 60deg female cone for sealing, same as the original. I've linked to adapters a post or two ago that will fit, or the steel original can be used at risk of corroding the stainless tank.
Internal Outlet pipe - 1/4in stainless or copper tube, bent to shape. If it's stainless it will be welded to the outlet connector, if copper it will be braised.
Outlet Pipe Baffle - to replace the piece of folded steel around the outlet pipe. Theoretically it will work slightly better, according to a random racing fuel tank designer on the internet I asked, but i can't confirm that.
Drain - M10 nut welded to outside with caphead screw and copper washer.
Gauge Sender - Welded pocket 4 1/2in diameter, 20mm deep. Hole pattern to match original senders. Aftermarket sender which *should* be compatible found on ebay here. Others are available, but they need to use a 5-hole SAE 1810 bolt pattern. Aftermarket senders may need signal converter such as this. Screws have been changed to M4.
Spare wheel pocket has been extended across the width of the tank. We loose a bit of capacity, but it makes the tank much much cheaper to make than keeping the pocket.
The tank earth will be fine just using one of the sender bolt holes.

There's probably £110 of sheet stainless here at 0.8 THK, and £140 if it ends up being 1.2 THK. There's another £40 of pipes, and the outlet connector which will have to be turned specially. The big cost will be the welding. There's several meters of welding, and it has to be good quality TIG or it will leak. I reckon it will take most of a day to weld up a tank, and that will be several hundred pounds. The tanks will have to be leak tested with water too. Once I have a price i'll post it on the Group Buy thread.

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PostPosted: Thu Feb 07, 2019 11:56 pm 
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Great work, Dave. Have you discussed with Steve at Malbrad? If not, let's have a chat at the weekend. Will be good to get a many buyers add possible, obviously.

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