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How to fit a wheel sensor


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I posted a query about sensors for Brantz meters some time ago and got some very helpful replies. On balance the wheel sensor looked the best option. Now I have to fit one it looks nearly impossible on the front hub of a TR6. The instructions tell me that I need to set it up within 1mm of 4 bolt heads and the only ones available are those holding the disk to the hub. There is barely room and the bolt heads vary in height making it very difficult to get a consistent gap without grinding the individual heads.

 

Am I doing something silly or should I opt for the speedo cable instead?

 

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I use a wheel sensor on my 4 and have it through the brake disc dust cover. It takes a little adjustment to get it to *just* clear the bolts, but it's not too hard. I then run the wire up the upright, along the upper wishbone and into the engine bay. I can send photos if that's helpful.

 

Others do something a bit more robust by drilling the brake caliper mounting and putting the wheel sensor through that. But I haven't found any issues with the dust cover and most of my rallies utilise a lot of gravel roads.

 

I'm assuming that your bold heads SHOULD be all the same height...

 

BTW, I also have a speedo cable sensor as a backup (and I have a sticky label on my Brantz with the speedo cable calibration number in case I need to switch. Note also that the colour coding of the wires is different for the wheel sensor vs. the speedo cable sensor, so make sure you have that clearly marked somewhere so that you get it right in an emergency).

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A lesser-known alternative is to make two small rectangular flat steel tags with a suitable hole to fasten on to the propshaft flange bolts at the back of the gearbox or overdrive. I file one end for a snug fit on the prop flange boss to avoid the tag rotating. Fitted opposite each other keeps it in balance; four would give slightly better trip accuracy but I've had excellent accuracy on regularities with two. A bracket for the sensor to 'view' these 'targets' needs to be fabricated - on my non-overdrive TR4 the original anti-vibration damper weight (discarded!) clamp is ideal although on my overdrive T2000 saloon two large hose clips work fine. This position is well-protected but subject to some trip inaccuracy from wheelspin the same as a speedo cable drive; the hub mounting is better for accuracy (on a RWD car!) but more vulnerable to stone damage. However, on most UK regularities wheelspin is minimal or non-existent, and you don't need the trip on a test!

 

I still cannot understand the common use of speedo cable trip drives. It may be an easier option to fit but when the speedo cable breaks, you've lost the lot and TR speedo cable can break regularly! A hub drive plus a prop drive with a changeover switch would be a good 'belt 'n braces' system, but use a top quality switch and soldered connections. Also, run the power and earth wires from the Brantz directly to the battery well away from the coil and HT leads, even the main loom if you can avoid it.

 

Nigel

Edited by Nigel 628
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You may be right, but I hadn't heard of that one. Weren't external front hub cable drives used in period anyway? I know some events ban electronic tripmeters in favour of mechanical ones, which immediately puts the onus on competitors to pay silly money for genuine Haldas (I have a 1973 CCC ad for Twinmasters at £33 brand new...) and the like which are a pain to calibrate. So then we get Brantz Retro Trips which are mechanical with electronic triggering which some events allow but others have to be fully mechanical, etc etc. What a load of tosh. My car had one fitted as bought, I believe to do the Monte Challenge (do the crew have to wear period clothing only in sub-zero temperatures too?), not easy to set up as the calibration buttons are underneath to make it look 'period' but is therefore physically difficult to calibrate, almost impossible in the tight confines of a TR4! I slung it out as the clacking sound drove me mad too! Most sensible UK regularity rallies allow a modern, easy to use electronic trip which is cheap enough if you can afford a classic car and to rally it; OK average speed readouts are banned but that's fair enough, got to give the navvy something to do!

 

When I see cars having modern safety items banned (rollover bars and seat belts!!) for so-called 'period authenticity' on rallies which involve any sort of fast driving I feel the world has gone mad. This is the 21st Century for heaven's sake, can't we have some common sense whilst still keeping classic cars reasonably authentic and yet everyone on a level playing field. My TR4 is used for in the historic class of modern stage rallies so is required to conform with MSA log book requirements the same as any other car. I don't hear the hair shirt types of period authenticity moaning about that, but you wouldn't believe how much a full roll cage stiffens a TR chassis up and improves the handling. Where do you draw the line? How many so-called historic rally cars built to accurate period standards can be found to using modern plastic zip ties which were not available back then, for example..........

 

Nigel, in a slightly tetchy mood today....

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  • 3 weeks later...

Would you have more room for the sensor if you got rid of the disc cover, rally cars should not be fitted with anything that obstructs airflow from brake components, they do very little in reality except to look authentic and running without them on all the rally cars I've built has never been problematic.

 

I have converted and fitted a sensor in the speedo cable but its all a bit of a bodge, unlike the way that a Halda drive is done.

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Way back when I was rallying my 1958 TR3A, I removed the hub cap of the nearside front wheel and modified the grease cap to hold a speedo cable securely in the center of the front hub, This must have been about 1962 or so. The speedo cable came out horizontally from the center of the wheel hub and curved back into the front wheel well where it ran my Halda and speed-pilots up on the dashboard. The problem with this is when I would be driving too close to bushes, shrubs, etc. on the RHS, the cable extending outward would get tangled and broken in the bushes.

 

Don Elliott, Original Owner, 1958 TR3A - now with 193,071 miles on the clock from new + a few more miles from rallying because the trip odometer on the dash was disconnected.

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