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MG MGB Technical - Earthing (grounding) steering column
|Here's a weird one. On my '69 the horn works by the button shorting the horn contact to earth (ground) through the inner column. Mine isn't working so I investigated, and guess what? The inner column isn't grounded. There is no continuity using my multimeter between the inner column and a good earthing point. The rack housing is earthed (well it would be, seeing as it is bolted to the car), but the column is isolated electrically from the rack housing.|
I'm at a bit of a loss. It's true I have had the rack out and cleaned it up and replenished the oil. But given that the column shaft is mounted in the housing with ball races, and meshes with the rack that has a metal damper pressing on it, I fail to see how it can be isolated. But it is. Any suggestions?
|I know you can get a high-resistance path to ground on the later collapsible columns, but haven't heard of it with the earlier solid and collapsible type. It can either pass through the bearings/bushes between the inner and the outer, then through the outer bolts to the body, or through the inner, UJ, rack shaft, bushes and bearings to the rack casing, front cross-member to body, neither of which are particularly electrically friendly. It's difficult to see how *both* paths could be completely isolated.|
My V8 was HR, and so was the Moto-Lita horn button, which probably explains why the car came to me with a single moped horn on it! Rather than try and ground the inner properly and open up the flimsy horn button I opted to install a relay which has been fine, relays taking much less current than twin horns, so any resistance in circuit has a much smaller effect.
If yours is completely isolated a relay on its own won't help, you could try a second horn brush from the outer to the inner ... that is if you are absolutely sure it is the inner which is isolated, and not some other problem with the existing brushes and horn button.
|Paul Hunt 2010|
|Thanks Paul. Since I posted the question I've located the source of the problem. Because of the way I installed the V8, I split the lower column and put a second Flaming River UJ right at the bottom down by the rack & pinion. It is that UJ that is isolating the column. I don't know why, because before the winter it worked OK.|
As I already have a relay in the horn circuit, I have simply wrapped a piece of copper wire stripped out of mains cable round the end of the upper shaft where it exits through the bulkhead and attached that to ground. The tiny current needed to trigger the relay seems to be able to get through there fine, so it should pass its MOT. The steering shaft rotates round inside this copper wrap without hindrance and touches it at random places. Not sure how to effect a permanent solution.
|How about a small jumper lead between the fixing bolts on the second UJ joint ?. Barrie E|
|I don't think any of these columns have any ball races in them, rather the inner is supported on various kinds of bushes, mostly felt or plastic by my memory. Some cars have metal bushes mounted in rubber; don't recall the specifics of MGs, it not being a frequent repair issue. I think you will find on careful examination that there is always a means of grounding the inner column if it is used to operate the horn. It can be aggravating indeed when you do need to fix one and find out it's different from all the others you've already figured out! It's a sort of movable feast over time and model, but generally involves a little spring bronze finger somewhere in the T/S switch/steering hub area. Sometimes there is an actual brass slip ring on the column or bottom of the steering wheel hub; in other cases it just runs on steel, with a graphite grease lube. Something, like maybe a Triumph, has a ground brush about halfway down the column, going through a hole in the outer to contact the inner. Cars that do use the inner as ground, like Jaguar and some Triumph, always have jumpers across U joints/couplings and a ground lead on the steering box - which frequently gets left off.|
I like Mike's quickfix, add a little graphite grease and it'll no doubt work forever, or at least until 10 minutes before the next MOT!
|Fletcher R Millmore|
|Thought some more about this. Even if the inner isn't electrically contacting the outer it should be contacting the rack shaft through the UJ. If it's getting to the rack body from there, then connect an earth strap from under one of the rack mounting bolts direct to the body somewhere convenient. If it isn't getting to the rack body for any reason, and that does have a ball-bearing at the pinion, then there should be scope for mounting a brush to rub on the rack shaft.|
|Paul Hunt 2010|
All true, but any antifriction bearing "should" be well lubed, hence no direct metal to metal contact; there might actually be sufficient contact to make things work, but I doubt it is intended to depend on this. It is widely known in design circles that using AF bearings as electrical conductors is very bad practice, and any decent bearing catalog will list this as a cause of bearing failures.
|Fletcher R Millmore|
|I've studied it carefully and in standard configuration the inner column is designed to be grounded through the rack housing. There is no other possibility. I did put an earth strap on the rack housing bolt but that didn't make any difference. The problem is definitely the Flaming River UJ that I have right down adjacent to the rack (see picture). I don't know how these things are constructed but there is no electrical continuity through it. I could bridge the UJ by attaching a wire strap between the clamp bolts on either end, but as the car is now completed with the V8 in place, it's pretty hard to get at. I think I'll stick with my copper wire coiled round the upper shaft. It's working a treat for now.|
|My ZS schematics show a spiral cable for the horn buttons, of which there can be several on some models, i.e. a continuous cable that winds up when you turn the wheel in one direction and unwinds in the other. With only 3 or so turns lock to lock on the MGB there's probably some scope for that, if the sliding copper wire proves unreliable.|
|Paul Hunt 2010|
This thread was discussed between 19/03/2010 and 22/03/2010
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