Richardtr3a Posted October 4, 2014 Report Share Posted October 4, 2014 My fuel gauge will only register half full and then down to empty. Today I took out the sender which is the original unit. Without the earth at the tank the gauge leaps to full. If I earth it out properly it will only register 1/2 full if you move the float to the maximum position. Is it possible to open it up for a clean up or shall I buy a new one. I read that they have to be matched to the panel instrument. How do you do this? Maybe I should send it away for overhaul. Any advice would be very useful Thanks, Richard Quote Link to post Share on other sites
RobH Posted October 4, 2014 Report Share Posted October 4, 2014 Richard - see the links in the slightly earler topic 'TR2 Fuel gauge' Rob Quote Link to post Share on other sites
Lebro Posted October 4, 2014 Report Share Posted October 4, 2014 If the gauge follow the movement of the sender smoothly from empty to half full then the sender is probably OK, but the gauge may need setting up. This is done by moving the position of the two coils inside. A bit trial & error, but it can be done (& I have) Bob. Quote Link to post Share on other sites
Richardtr3a Posted October 5, 2014 Author Report Share Posted October 5, 2014 Thanks for the link. I have found a really useful set of instructions on the MG experience site. It shows photographs and an explanation of how to check the ohms on the sender and make adjustments. This may well be my problem. However i have two electrical questions. My car is positive earth. I am not sure that the MGA is also positive earth. So will I need to connect the multimeter the other way to the two terminals. Do I leave the sender connected and the ignition off while I take the measurement. I am sure that there are other pitfalls but it may be simple adjustment. Thanks Richard Quote Link to post Share on other sites
RobH Posted October 5, 2014 Report Share Posted October 5, 2014 If you are just making resistance measurements, pos or neg earth will make no difference and there's no need to swap the leads. Make resistance readings with the power off otherwise you may wreck the meter. Best with the connections off too so there is nothing else in-circuit which might affect the reading. Rob Quote Link to post Share on other sites
Richardtr3a Posted October 5, 2014 Author Report Share Posted October 5, 2014 Thanks. I will have a go this afternoon. I need to understand electricity more. Richard Quote Link to post Share on other sites
Ian Vincent Posted October 7, 2014 Report Share Posted October 7, 2014 My understanding of the fuel gauge on aside screen is that it is a Wheatstone bridge and polarity doesn't matter. Rgds Ian Quote Link to post Share on other sites
Lebro Posted October 8, 2014 Report Share Posted October 8, 2014 (edited) Fuel gauge on a sidescreen consists of two coils - one connected between ign & earth - this pulls the needle to full. The other is between ign & earth via the tank sender (variable resistance). this (when tank empty - ie zero ohms) pulls needle down to empty. from this one can deduce that the 2nd coil is "stronger" than the first. Adjustment is a case of moving the coils nearer, or further away from the pivot point of the needle. A fiddly excersise, but not that difficult. Polarity not important. Bob. Edited October 8, 2014 by Lebro Quote Link to post Share on other sites
Richardtr3a Posted October 9, 2014 Author Report Share Posted October 9, 2014 Thanks for the help. The reference to the MGA site is misleading in that the OHMS quoted are not the same as the TR3. My sender is producing readings of 0 and 79 ohms when off the car. This is satisfactory for a TR3. The next stage is to adjust the gauge to suit the sender. So I am sending the unit away to a repair man who can adjust it for me. Are there any suggestions? Thanks Quote Link to post Share on other sites
stuart Posted October 9, 2014 Report Share Posted October 9, 2014 You could try talking to Clarkes who did your control box. Stuart. Quote Link to post Share on other sites
Richardtr3a Posted October 9, 2014 Author Report Share Posted October 9, 2014 Thanks Stuart, Cox Automotive were the control box experts and I have some in stock. They are calling back soon. Richard Quote Link to post Share on other sites
AlanT Posted October 9, 2014 Report Share Posted October 9, 2014 Oh thats why they don't need a regulator. They should have stuck with this method! Quote Link to post Share on other sites
Richardtr3a Posted October 9, 2014 Author Report Share Posted October 9, 2014 Sorry Alan there may be some confusion here. My TR3A needs a control box that works and I have had old ones rebuilt by Cox and my troubles with new stock have now ceased. My current problem is the fuel gauge sender which seems to be working and I am having the gauge adjusted to suit. At present it only reads 1/2 full even if the tank is near the top. I am using a dip stick until it all works properly. Thanks Richard Quote Link to post Share on other sites
RobH Posted October 9, 2014 Report Share Posted October 9, 2014 Richard - I think Alan was commenting on the earlier post by Bob. The opposing-coils design of the gauge automatically compensates for voltage variation, so a sidescreen car doesn't need a voltage regulator for the dashboard instruments like later models have. Rob Quote Link to post Share on other sites
Richardtr3a Posted October 9, 2014 Author Report Share Posted October 9, 2014 Thanks I thought that I had missed something. Quote Link to post Share on other sites
Lebro Posted October 10, 2014 Report Share Posted October 10, 2014 Richard. I can setup your gauge to your sender (assuming either is not terminaly damaged) just send me a PM if you would like me to. I have done the gauges in both my TR, & my 1935 AeroMinx. (no charge - just postage) Bob. Quote Link to post Share on other sites
Ian Vincent Posted October 10, 2014 Report Share Posted October 10, 2014 (edited) Richard, It really is dead easy to adjust the gauge using the two screws on the back and your own sender. Don't worry about the 79 Ohms, all you are doing is varying position of the coils inside the gauge to show full scale deflection when the tank is full and zero when it is empty. Rgds Ian Edited October 10, 2014 by Ian Vincent Quote Link to post Share on other sites
Richardtr3a Posted October 11, 2014 Author Report Share Posted October 11, 2014 Richard. I can setup your gauge to your sender (assuming either is not terminaly damaged) just send me a PM if you would like me to. I have done the gauges in both my TR, & my 1935 AeroMinx. (no charge - just postage) Bob. Thanks for the offer. I will bring the two parts to Leatherhead if you send me a PM over the weekend. This is very helpful. Quote Link to post Share on other sites
Lebro Posted October 11, 2014 Report Share Posted October 11, 2014 PM sent Quote Link to post Share on other sites
Lebro Posted October 18, 2014 Report Share Posted October 18, 2014 Richard. Fuel gauges done, you have a PM re the Speedo Cheers Bob Quote Link to post Share on other sites
Richardtr3a Posted October 19, 2014 Author Report Share Posted October 19, 2014 thanks for all the help and advice. The garage is very impressive and the vintage collection looks like even more fun. One day I will have a decent garage. Thanks Richard & H Quote Link to post Share on other sites
Richardtr3a Posted October 23, 2014 Author Report Share Posted October 23, 2014 I am now trying to connect the overhauled fuel gauge up to the original wiring. I have two terminals one marked B and one marked T. I need to know which takes the the power from A3 with a green cable and which takes the other cable to the sender unit. I also have an earth cable which was connected to the bracket to get a good earth. It is amazing what an overhauled speedo can do. My needle is now steady and the trip works. It is very satisfying, Thanks Please help. Richard & H. Quote Link to post Share on other sites
RobH Posted October 23, 2014 Report Share Posted October 23, 2014 B- battery, T- tank Quote Link to post Share on other sites
Lebro Posted October 24, 2014 Report Share Posted October 24, 2014 +1 & very important to get a good earth on both the sender, & the gauge. Bob. Quote Link to post Share on other sites
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