24v Lightweight LR fuel tanks reading 1/8 when empty!

[ruxy]

30 minutes ago, osiford said:

I've just scanned this thread, and from what I can gather, the gauge in question reads OK, except at the critical empty end of the scale, so the basic system seems to be working OK. I've had to fit a number of new sender units and gauges on various vehicles, and none of them are exactly precision calibrated instruments. I have dealt with most as follows. Remove sender unit, and drain tank. Next put in a known quantity of fuel, say a gallon. This is, if you like, a "reserve", as it should have this amount available still, when the gauge reads empty.  If your gauge was reading too high a level when the tank ran out, bend the float arm slightly upwards. Reinstall and check reading on gauge. If still not showing empty, remove sender and re tweak. Some folk may not agree with this approach, but I can't see any problem, and I've always been happy with my fuel level readings on the road. Why make things complicated, if a simple solution is available? Just my thoughts, for what they are worth.

There is not much scope for frigging the float arm angle - bend it to improve a reading at low tank and you start to make the full tank reading more in error & it may have been correct in the first instance.

[ScarboroughSeadog]

1 hour ago, osiford said:

I've just scanned this thread, and from what I can gather, the gauge in question reads OK, except at the critical empty end of the scale, so the basic system seems to be working OK. I've had to fit a number of new sender units and gauges on various vehicles, and none of them are exactly precision calibrated instruments. I have dealt with most as follows. Remove sender unit, and drain tank. Next put in a known quantity of fuel, say a gallon. This is, if you like, a "reserve", as it should have this amount available still, when the gauge reads empty.  If your gauge was reading too high a level when the tank ran out, bend the float arm slightly upwards. Reinstall and check reading on gauge. If still not showing empty, remove sender and re tweak. Some folk may not agree with this approach, but I can't see any problem, and I've always been happy with my fuel level readings on the road. Why make things complicated, if a simple solution is available? Just my thoughts, for what they are worth.

Thought of that- but the 1/8 reading is at absolute minimum on the sender arm (bent or not), so doesn’t work.

[ScarboroughSeadog]

1 hour ago, ruxy said:

You know  ,  many bread& butter car manufacturers went off this style of sender unit because they are useless for accuracy.   Take  Fiat Group  ,  small cars  £ cheap   Uno Mk1  ,  Uno Mk. 2  Punto  - they had a plastic tube down the tank from the top (a little larger on dia. than a toilet roll tube )  inside is a tubular float (giving variable resistance)  about the size of said toilet roll card tube , this has a small coil spring at each end.  This design probably went back to the 500D of the 1960's  + earlier  ?     Land Rover could have introduced similar but didn't, you have to work around what you have if you want originality,  probably ndividuals would had done better operating modifications if it were not for fuel safety and insurance cover.

That said, I’ve owned mine for nearly 25 years and until recently the fuel gauge readings have been spot on. The problem I’ve got is resolvable- just need to figure out the fault. 

[ScarboroughSeadog]

On 3/7/2023 at 10:06 PM, ruxy said:

Both fuel tank sender units & dash level gauges for 24 volt are different to 12 volt.  You should have 560757 senders , No.. should be stampd on and  552616 gauges.  

Hhmm   -  tap in neutral position , somewhere in my office I have a tap/bracket with switches assembly but I can't find it.  IIRC the switches are N.C.  (normally closed).    Fuel tap lever in neutral - you would only do that as a gratis extra anti-theft (expect running for only 1/2 mile downhill - don't ask , I caught the wife out once).  The fused supply is fed white (Ignition control) & you don't leave Ign. on without engine running.  So - yes , I think you would have both switch contacts bridged  & point (cinch) between the control coil & deflecting coil feeding both tank units , not a normal situation - you are not supposed to do this & I would expect a spurious reading on the gauge.

 

Just double checking that the Lucas switches are NC? So the circuit is made when the nipple is NOT depressed/activated? If the nipple is depressed by the tap, that breaks the circuit and therefore stops any reading from the tank connected to that switch, correct? I'm thinking if one switch is faulty and remains closed (or partially closed) when activated, that would mean both switches (tanks) are closed (reading) at the same time, which might explain why the gauge reads 1/8 when the tank it should be reading is empty? Does that all make sense? Feels like a bit of a eureka moment, but not in the shed until Sunday eve.....

[ruxy]

5 days later ,  you have not returned  ?   I TRIED.   - another dawn another day.

You came here to HMVF  following the same query on a Facebook LR Group.   You told me I was wrong - but all the time I knew I was right.  You showed a photograph on Facebook of your panel - you did not show it here.  The fact is - that panel showing the new fuel gauge you fitted is cluster top RH corner ,  you have a manual brake TEST switch - no doubt whatsoever , only used on S3  early FFR's + 12 volt .  You said your gauge was LATE  (you listened to duff info. not to self).  However a late fuel level gauge is mounted on the group cluster at 6 o'clock. 

btw  -   The Lightweight wiring diagrams on the web site  for Land Rover Lightweight , coloured for the benefit by all by the web site owner Dave McCarthy ,  IIRC an accountant but good with IT.   I set him off with some diagrams for 12 volt/FFR  Rover 1 + S3  LWT  that I did for myself  circa.  1975   .   I spent 3 years as a ED with  34N Sig. Reg. (V)  , in fact I was among the first uncrating Larkspur & fitting to the URS. So have worked on LWT for 50+ years  (although I am  'mechanical'  I did do electrical to ONC  .   I can tell you that all (many) who have problems with accuracy of LWT fuel gauge / RH & LH tap change switches / tank sender units - that it is all about Ohms LAW.  

Many muppets will not listen ,   Dave McCarthy ploughed ahead quick (he owns the website)  , using the templates I had given , he did not ask me to proof read them, there are minor errors (that I am aware of) - I only use them to get to the area needed from time to time.

Early FFR circuit - EARLY  !    after fuse 7 to 8  ,  (Speedo head & Instrument cluster illumination is on a different area)  ,  you have only  THREE  (3 qy.)  resistance(s)   two sender units (variable) and the Instrument (which is moving iron , so voltage is not important)  .   Late FFR circuit  - LATE  !   (take it as all progressions to transistorized regulator)  after fuse 7 to 8  - that area is different because you have 4 qty. extra resistances    Moving Iron Water & Oil temperature gauges - water & oil Transmitters  (these are thermister (semi-conductor)  variable resistances.    The extra resistances are because the EARLY Water & Oil gaiges were Bourdon operation (mechanical)  .

In the case of the  VERY  LATE  12 volt LWT  -  the oil cooler was no longer fitted ,  the cluster only has two instruments - Fuel level and water temp.  The fuel level gauge is no longer at top RH , it is same as FFR - at 6 o'clock,  the Water temp gauge is no longer Bourdon from the oil cooler line  brass pocket.  The gauge position for oil is redundant (it is black blanked) , you only get a oil temp warning lamp - this now from a TT  (temperature transmitter) thermister that is sump mounted.  The 12 Volt  LWT  now uses the same tank Fuel Level 'senders' as the FFR (late)  and same moving Iron gauge as the FFR (late) cluster instrument.  The 12 volt original  gauge (bi-metal) with it's primitive vibrating type  10 volt output  bi-metal voltage stabilizer  - was tere-on deleted.

 

[ScarboroughSeadog]

Thanks Ruxy- will try and decipher all this when back in civilisation (away working in the north of Scotland at the moment). My fuel gauge is mounted at 6 o’clock- as you say, as per a late model fitting. Also have the late model oil and temp gauges and transmitters you describe.

Haven’t had much time to look at the lightweight, but have now replaced both Lucas switches and have one tank reading perfectly. One tank still not registering empty but suspect that is it’s sender- will replace and see. Expecting that will solve the problem, but will see! Will post a conclusion and findings as soon as I can- but don’t expect that that will be in the next few days.

Edited March 15, 2023 by ScarboroughSeadog

[ScarboroughSeadog]

Always good to finish these things off with a conclusion: replaced a faulty fuel gauge, replaced a faulty Lucas switch. All now working perfectly but there is an interesting issue with the senders. I have 3 senders marked TB1114-001W. This is the correct part number. One is brand new, one is say 10 years old, one is say 40 years old. Only the 40 year old one reads correctly (ie empty at empty). The other two newer ones read 1/8th at empty. I can only think the more modern parts have a different resistance scale? Fortunately with a repair made to a snapped spade connection I was able to use the original 40 year old part and all is working perfectly. Bit of a mystery though.

[john1950]

Perhaps the newer ones read to reserve on the gauge in red.

[ScarboroughSeadog]

2 minutes ago, john1950 said:

Perhaps the newer ones read to reserve on the gauge in red.

I have to say…..I think you’ve nailed it! These senders cover a few different set ups, and hence supply to different gauge decals etc. My particular (dated, less common) set up is an anomaly as far as these senders go. I suspect your explanation will save a fair bit of head scratching for many with this issue- I bet you’re right!

[ruxy]

On 3/20/2023 at 3:27 PM, john1950 said:

Perhaps the newer ones read to reserve on the gauge in red.

On LR military vehicles  - the fuel gauge indicated readings show   E  1/2  & F   with a strike mark at 1/4  & 3/4  full.  - there is not a red mark to show low/reserve.   The only difference on the early or late gauges is the position they are mounted within the instrument cluster.  This position is a good indicator on 24 volt FFR vehicles - exactly what tank level indicator you need to be matched .  The starting point is to establish that you have the correct parts for the age of the vehicle and to confirm you are using the correct wiring diagram.

[ScarboroughSeadog]

1 hour ago, ruxy said:

On LR military vehicles  - the fuel gauge indicated readings show   E  1/2  & F   with a strike mark at 1/4  & 3/4  full.  - there is not a red mark to show low/reserve.   The only difference on the early or late gauges is the position they are mounted within the instrument cluster.  This position is a good indicator on 24 volt FFR vehicles - exactly what tank level indicator you need to be matched .  The starting point is to establish that you have the correct parts for the age of the vehicle and to confirm you are using the correct wiring diagram.

Ruxy-  The TB1114-001W senders as now produced are a multi-fit part, which (correctly) span a variety of vehicle set ups from mine (older, less common, military specific) to a range of other classic civvy landrovers (which do have the red mark on the gauge). It would make sense if they are calibrated to by far the most common application (ie the latter). Fortunately I had a repairable 40 year old TB1114-001W which works perfectly- problem solved. Thanks for your help and advice.

[ruxy]

5 hours ago, ScarboroughSeadog said:

Ruxy-  The TB1114-001W senders as now produced are a multi-fit part, which (correctly) span a variety of vehicle set ups from mine (older, less common, military specific) to a range of other classic civvy landrovers (which do have the red mark on the gauge). It would make sense if they are calibrated to by far the most common application (ie the latter). Fortunately I had a repairable 40 year old TB1114-001W which works perfectly- problem solved. Thanks for your help and advice.

A multifit part - that sounds like Britpart or Unipart. The only way is to take the part to a franchise dealer , he should be able to check the computer and if a supercession to another Part No. then he should be able to advise if it is  due to a design change or change of sub-contractor( warranty traceability).  Many / most  Series parts have gone  NLA ,  some taken up for manufacture by such as Britpart , County Parts etc. Imported by Autopost Ltd  (often from Italy)  much of it made in PRC.

Jaeger were part of Smiths Industries ,  I think you will find that Caerbont Intruments took over the Smiths ranges & Jaeger , there always had been a bit of a cartel with Joseph Lucas  but Lucas did take over instrument manufacture from Smiths.  IIRC  the instrument manufacturing factory at Caebont, Wales was then a management 'carve-out' .  They are still there and understand still manufacture for S2 to S3 & you will find boxed by a few firms but genuine if sourced from Caebont.  Obviously at wide  £ asking, nothing £ cheap but some bulk purchase for retail is top $.    In the last two years or so by popular request & demand they started up production of specific Series ONE panel parts ISTR inc. the speedo head.