Project: 1939 Jaguar SS100 Replica Classic Roadsters, LTD. "Duke"

[Cadillac Jim]

If you send me a schematic of your gas gauge and any information that you have on the sending and receiving units, including wire colors in the harness, I will take a look at it and, if possible, send you back a schematic of a circuit that you can build in a few minutes that will make them work together. You can use PM if you like.

[Cadillac Jim]

I think that the lettering is fine but that Texas Jim is right - it detracts from the elegant beauty of the car.

Old Ford gas gauges used a bi-metallic strip, like old mechanical thermostats, in a U-shape. Resistance wire was wound around one leg of the U. When the tank is empty, the sending unit has high resistance and the two legs of the U are about the same temperature, and this makes the gauge read Empty. When the tank is full, the resistance wire heats one leg of the U which moves the gas gauge needle to Full. This has the advantages of the needle moving slowly so sloshing doesn't move the needle around, it reads Empty when the key is off, and it is quite reliable and inexpensive. I suspect that this is the way that the "Industry standard, many popular cars" also work.

Most modern gauges are galvanometers, with the exception of mechanical pressure gauges where a curled tube straightens a bit when the fluid inside has higher pressure and moves the needle. A galvanometer simply measures the current. If you have a PCM, you can use PWM with a regulated voltage and very precisely control where the needle points, which is the way that most modern "analog" gauges work.

An analog galvanometer gas gauge uses the galvanometer movement as a voltmeter, which works if the resistance in the galvanometer movement is far higher than in the circuit under test. This is easy with a gas gauge, because an inexpensive galvanometer will have a field coil resistance of about 1000 Ohms, possibly more. So, a simple resistance to battery voltage connected to the galvanometer, then hooked to the gas gauge sending unit, makes a voltage divider, so it is easy to set the gas gauge to read Empty and Full when the sending unit resistances are at minimum and maximum.

My circuit will use an inexpensive op-amp, and it will use a voltage divider on the input, and output the reverse of the input. Scaling and offset are TBD, depending on the sending unit specs and the gauge specs.

Barring documentation on the sending and receiving unit, you can use a DVM to make measurements when the tank is near Empty and when it is Full. First, read the voltage on the gas gauge terminals (all of them if there is more than an input and a ground). Then, disconnect the gas gauge and see if there is voltage coming from the sending unit so you can tell whether the other side of the sending unit is grounded or connected to ignition voltage, then turn the key off and measure the resistance.

You might measure the resistance across the gauge input terminals, but be sure and use a DVM and not a cheap analog ohmmeter.

Something like this will host your gas gauge interface:

http://www.circuitspecialists.com/64-8931.html

Size of this example is 1.5" by 1.75" but I will look for something smaller if everything will fit. Wires will be ignition voltage, ground, tank sending unit in, and gas gauge out.

[thedukejag]

Hello, My name is Rick and my wife and I bought Duke SS Jag late last year and due to weather we have only 20 miles on it.We were aware of a few glitches in it but expect no big issues as was driven by the previous owner(we will see on that,right).Really like your progress so far,nice methodical work.Thanks for for the photostream link,just a ton of info from those pics I will try to upload a couple pics later. Rick

[Bruce Nunnally]

Hi Rick - welcome; I am interested to hear more about your Duke.

[Bruce Nunnally]

Jim- once the Duke SS-100 is back from the shop I will measure the resistences across the sender.

[Cadillac Jim]

Anything you can get on the gauge is important too. Ideally I would like the resistance of the gauge, but the most important things are the voltage on it when it reads Empty and when it reads Full.

I'm trying to decide if I want the simplest possible circuit, with one op-amp, or a robust circuit, with a quad op-amp. Op-amps with automotive temperature range are not cheap but with only one it should not be a significant expense relative to a new sendiing unit or complete gauge package that might not match your other gauges.

I wonder if this mismatch is because someone changed the gas tank?

[thedukejag]

In my garage

[thedukejag]

http://i720.photobucket.com/albums/ww205/78aldo/JAG/1939Jaguar.jpg?t=1396830194 Craigslist ad

[Bruce Nunnally]

Oh nice - you have the hardtop as well. I was just wishing I had purchased one of those when it was posted for sale. How do the side windows work with hardtop?

[thedukejag]

Hi Bruce.Didn't come with the side windows,so I have no idea how they work.It did come with the framework for the convertible top ,but no material for it.I have the hardtop off and will probably leave it off.We have the Ford 2.8 V-6 and automatic and I'm guessing Pinto rear axle..Gas gauge doesn't work(VDO gauges).Headlights do not work on high beam,not sure why yet.I bought and modified the hood hinges ,so the hood can removed easier.Made new vent windows and making new hinges for those.Car still needs a lot of detailing .It's a work in progress ,for sure.

[Bruce Nunnally]

This one at Bob's Classics had the top and side windows with the top:

Mine has the leather-like top and zip-in side windows. I think i lost the zipper on one side on the road, so I'll have to work on that.

The headlight beams feed through different relays between high and low beam. The relays are on the driver side attached to the engine side of the firewall.

You may have a relay out, or a wiring issue. Do your high beams switch using a floor switch like mine?

Pictured example also has wood slats on the rear & truck which was very nice.

[thedukejag]

I would like to find a set of those windows and an assembly manual.That car looks good in white with the real wire wheels.Mine has a tilt column with the dimmer combined with the turn signal switch.Need to be a detective to gather information on what came from where.For instance had never heard of the Cologne family of Ford V-6's,but that's what mine has with Duraspark Ignition.I live in the Buffalo area of New York and it's been a brutal winter and really limited any garage time

[Bruce Nunnally]

There is an assembly manual on ebay now, so if I can get my hands on it there will be a pdf version available the next day! I emailed the poster to see if they would also offer a paper copy in case I don't win but no response.

Classic Roadsters, Ltd rated the V6 at 98 hp while the 4 was marketed at 88 hp. The largest engine I have seen in any of the Dukes was a 302 V8, which must be quite free-revving in that light a vehicle.

Even here in Texas I limit outings in the Duke Roadster to 62F+ days.

[Bruce Nunnally]

Rick -- possibly good news for you -- one of the pages in the ebay Duke Assembly manual auction is the sample page showing the headlight wiring:

[thedukejag]

The very little I've driven the car ,it seems to have enough power,just needs a tune up and I'm rebuilding a Holley 2 BBL to replace the Ford 2 BBL.Thanks for the schematic.Like they .."worth a thousand words".

[Cadillac Jim]

If the high beam doesn't work, look for a headlight relay, or the absence of one where it should be. I don't see one in the photo of the wiring diagram but that doesn't mean that there isn't one.

[thedukejag]

Thanks.....Will do

[Bruce Nunnally]

Nice I won the heavily worn assembly manual auction

http://www.ebay.com/itm/Duke-Assembly-Manual-Classic-Roadsters-1939-Jaguar-/201066915532?nma=true&si=rbDNjdAkJN2cj4edpd5bN1MkOIE%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

So soon we will have more info on several build topics

[Cadillac Jim]

If all the pages are legible, perhaps you can scan it all to PDF and put it online somewhere. I did that with a bunch of old Canon manuals on obsolete products that are no longer supported by Canon, with the permission of Canon:

http://jameskbeard.com/Photography/LegacyCanonManuals.html

About once a month or so, I get an e-mail from someone asking for a rare or non-existent manual, which of course I don't have.

[Bruce Nunnally]

Nicely done, Jim. Yes, exactly my plan.

[thedukejag]

Nice score.Nice day here yesterday,took some new pics and I will post them soon.Won't be home rest of today,try tomorrow.

[Martin Monaco]

that's fantastic news about the build manual Bruce. ;-)

[thedukejag]

cyberfooks: Thanks for the link to your pics.It is a great deal of information showing these cars stripped down.Getting excited to get our car back together and out to a couple cruise nights when they start,This is a big cruise night and car show area as there is usually at least three cruise spots any night of the week.we usually only did one or two per week when we had the Corvette as it was more a driver and not really up to show car standards.

[Bruce Nunnally]

Linear emailed that parts due Monday, so stay tuned. Slow parts.

[thedukejag]