differential mounting question

[TomMull]

I decided to clean the corroded earthing strap that connects to the frame through the final drive mount and connects to the tank strap bracket and the radio aerial. It connects to one of the bolts on the brackets that hold the rubber mounts for the final drive.
The task looked simple enough but the nut underneath began to spin. I am unable to get a socket or anything else under there to hold the nut. The nut appears to have a large OD and sockets will not fit between that nut and the washer on the bottom mounting.
So my questions: Is that nut supposed to be fixed to the chassis? Is it advisable to remove the mount on one side leaving all else intact?
Above is a picture of the bolt from the boot.
Tom

[wotsisname]

On a Spyder chassis and probably the original type, these mounts are held by two setscrews into captive nuts.
If you lower the diff or block it in place you should be able to take the middle bolt out and lift the mounting .. possibly have to drill the bolt or cut the head off. You might have to trim the shell to allow the mounting to be lifted.. hopefully you can sort it then

[TomMull]

On a Spyder chassis and probably the original type, these mounts are held by two setscrews into captive nuts.
If you lower the diff or block it in place you should be able to take the middle bolt out and lift the mounting .. possibly have to drill the bolt or cut the head off. You might have to trim the shell to allow the mounting to be lifted.. hopefully you can sort it then

Thanks wotsisname, makes perfect sense. Once I cut the bolt out I'll simply put a standard OD nut underneath, which I'll be able to get a socket onto, albeit with some difficulty. When I address my other chassis issues I'll put a new captive (welded) nut underneath.
Tom

[TomMull]

Here is the nut. The bad news is there is little that I can see that "stakes" the nut in place; the good news is that it fell right out after I drilled the head off the bolt (from the top thankfully).
It would be interesting to know how it was supposed ti be attached to the chassis.
For now I think I'll drill through it and use it as a stepped washer, which will fill the hole in the chassis, with a new standard nut underneath. That means it will be a two person project to install and remove it but no more drilling and cutting.

Tom

[Hawksfield]

Hi
The nuts are spot welded on my chassis on the underside.they have never been a problem when changing diff mounts.
I you dropped the diff you could get in to weld the nut in place.

Good luck

[TomMull]

Thanks John, I don't know if it is evident from the photo but mine has a "step" on it where it fits into the 1/2 inch hole in the chassis. The bolt is only 1/4 (edit: make that 5/16). I see no evidence of any type of weld or fixing of any type. Your suggestion is a good one but I've more serious chassis issues to address soon, so I'll wait until then to repair this properly.
By the way, is your chassis original?
Tom

[Bigbaldybloke]

This photo shows the nuts on a Spyder chassis but I believe the standard one is similar. I would also comment that I don't think that is the normal place for the battery earth to be connected to, it usually connects to the rearmost body securing bolt that come through the boot floor near the battery. No reason why it shouldnt connect where you have it but its not an easy place to access if you need to.

[TomMull]

Yes, Those appear to be "nutserts" or similar, very common now but quite different from mine. I might even be able to get one in from the top but I think a plain nut will work for now.
The earth cable, which does appear to be original to me, connects the radio antenna and the fuel tank bracket and nothing else. The battery earth is as you describe.
Of course it could be have been added at some point but it was under one of the tank brackets and under all the felt insulation so I it would seems an unlikely add-on.
Mine is a Federal car and I wonder if that earth might have been a US import requirement. Only a guess, I have no knowledge.
Thanks for the reply and the picture.
Tom

[Hawksfield]

Tom
My chassis is original s130 1971. I had have one diff mounting nut and a torsion bolt rewelded when I restored it in1986
As pointed out by bigbaldybloke the earth is at ached to a bolt in the boot that is through to the chassis rear.
Good luck on fiddly job

[TomMull]

Thanks for the info, John. Curious though, did your car have an earth on the fuel tank?
Tom

[Bigbaldybloke]

Only earth on my tank is by the cable to the tank level sender. Sounds like a good idea to have one though

[wotsisname]

The braided earth at that location is to earth the aerial. I believe it helps provide a ground plane - others with more knowledge of CB-radio/ ICE etc would know if this is correct. I've seen others post on this forum with it located in that position. The bigger the sheet of metal the better the radio reception.... or the further your CB signal will go.
The battery earth is as said to the chassis rear bolts, although the Wmanual says it was moved to the strut brace (behind the rear seat) at some point (separate hole required).
The fuel sender should have an earth at that point of the loom. I'm not sure about earthing the tank itself (chemical engineers, please pitch in).. a potential risk during refueling would be a static discharge, to offset this you would have to run an earth to ground (as in The ground). I'm not sure that earthing the tank to the battery would achieve anything.

[TomMull]

Yes Wotsisname, exactly as I found on my car. I would only add that my braided cable makes a stop at the fuel tank strap and bracket on the way to the aerial.
I don't know why they used the diff mount rather than the bolt for the battery earth, or the one beside it, but it really makes no difference although the bolt in the boot floor might have been slightly tidier.
The earth for the sender earth is as you describe also.
As for that fuel tank earth, I can only say that it has become common practice.
Thanks.
Tom

[The Veg]

Wotsisname is correct about RF ground-plane. Earthing the aerial base helps for reception, but a good plane is better and if transmitting is important, the more ground-plane the better. The boundaries of the plane have a directional effect on the aerial's performance as well: the direction in which the ground-plane extends farther from the aerial is direction from which reception will be best and towards which transmission will be best.

I did mobile RF-systems in both military and civilian applications for a few years; installed and tuned more aerials than I care to remember. There was one that went on top of a lorry with a fibreglass cab-roof, and I did in fact put a piece of sheet metal inside the roof for ground-plane. Only about 12x12" but it worked well enough.

[TomMull]

Just noticed this interesting discussion on the other Elan forum:
http://www.lotuselan.net/forums/viewtopic.php?f=19&t=45064
Tom