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Ok, odometer play time.
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Trevor Jessie
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Drive shaft turns too fast, front wheels turn(pivot), so rear wheel seems logical to me.
Jim_Gruber
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Easier on the back wheels. I simply took a piece of straight bar stock and drilled hole for bottom of spring mount. It goes over to underneath brake drum where I fastened /glued magnetic reed switch, not the POS that comes with the Sigma Unit. Can be any standard Magnetic Reed switch, try local Electronic Surplus Supply Houses, packaging is usually better for mounting than the Sigma Unit and switch was something like $2.50. I simply adapted a piece of right angle bracket to position the reed switch fairly close to the magnet. I tried a button magnet but the flatter / wider magnet that came wit hthe reed switch again was a better package to mount to the brake drum.
Ragarding display, I mounted with a bracket I attached to the windshield support rod. About 2" over and right angle upwards, used rubber bands to go around the upright piece. Sonething as I recall came off a curtain rod I modified to fit.
One thing I am planning on adding is a little 12V lamp at night. Autozone has mini 12V directional lamps that are perfect to sit up on the dash and provide illumination at night. Something like $6.96 - $12.95 depending on packaging. Would fit up on dash and be unseen pointed directly at Sigma Unit.
I've got pics I can take if anyone is interested.
Ragarding display, I mounted with a bracket I attached to the windshield support rod. About 2" over and right angle upwards, used rubber bands to go around the upright piece. Sonething as I recall came off a curtain rod I modified to fit.
One thing I am planning on adding is a little 12V lamp at night. Autozone has mini 12V directional lamps that are perfect to sit up on the dash and provide illumination at night. Something like $6.96 - $12.95 depending on packaging. Would fit up on dash and be unseen pointed directly at Sigma Unit.
I've got pics I can take if anyone is interested.
Jim_Gruber
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Use JB Weld to mount the magnet. That rusty brake drum will not give you a good surface to mount to. I tried using the 5 minute epoxy and it let loose and it trashed my original installation.
Other advice, mount magnet to provide minimum contact. In otherword how you orient the magnet is important in getting accurate readings. I used a rectangular magnet mounted across the drum so as to provide a shorter magentic field for opening and closing the switch. Makes for more accurate speedo reading.
Again a reed switch from electronic surplus shop works better than the Sigma unit for mounting. Plus it had life expectancy of better than a million cycles.
Other advice, mount magnet to provide minimum contact. In otherword how you orient the magnet is important in getting accurate readings. I used a rectangular magnet mounted across the drum so as to provide a shorter magentic field for opening and closing the switch. Makes for more accurate speedo reading.
Again a reed switch from electronic surplus shop works better than the Sigma unit for mounting. Plus it had life expectancy of better than a million cycles.
Jim_Gruber
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Rick,
Tried to send you pics but your e-mail address bounced back, send me a correct e-mail to thistle_3619@yahoo.com and I'll resend.
Tried to send you pics but your e-mail address bounced back, send me a correct e-mail to thistle_3619@yahoo.com and I'll resend.
Glen_B
Jedi Trainee
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Mine didn't work all that well or long. I JB welded the magnet to the lip if the brake drum and the sensor to the brake backplate. It was intermittent at best.
Another major downside is that there isn't a single lighted cyclometer available and you won't see it at night.
Glen Byrns
Another major downside is that there isn't a single lighted cyclometer available and you won't see it at night.
Glen Byrns
OP
regularman
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I saw the brake drum pic :thumbsup:
Jim_Gruber
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Easy able to light the cyclometer. Little 12V Mini Directional Surface lamps available from the AutoZone, PepBoys of the world. $6.95 to $12.95. Real small, dime sized LEDs' that are directional.
Kim I think that picture of the brake drum was my original round button magnet. I used the 5 minute epoxy on that one and it did not hold. JB Weld is the ticket, I'm in favor of a rectangular, long magnet as the axles do move in and out around corners believe it or not. And round magnet depending on positioningcan go in and out of contact with sensor. Since changing to rectangular long contact manget not an issue with speedo losing reading when going around quick turns. Speedo corrects itself within a fraction of a second but sometimes can act a little screwy.
Also a test point so you can measure open/close will aid in positioning magnet from reed swith. I built bracket that holds the reed switch( a piece of and old curtain rod that I had in the garage this is so scientific )so I could position the reed switch closer or farther away to adjust sensitivity. Gap is almost up to 1/2" as I recall before it cuts out depending on the power of the magnet you use.
Grind the rust off of the back of the brake drum on a spot before you try to JB-Weld.
Play with it and have some fun. This is a creative engineering exercise.
Kim I think that picture of the brake drum was my original round button magnet. I used the 5 minute epoxy on that one and it did not hold. JB Weld is the ticket, I'm in favor of a rectangular, long magnet as the axles do move in and out around corners believe it or not. And round magnet depending on positioningcan go in and out of contact with sensor. Since changing to rectangular long contact manget not an issue with speedo losing reading when going around quick turns. Speedo corrects itself within a fraction of a second but sometimes can act a little screwy.
Also a test point so you can measure open/close will aid in positioning magnet from reed swith. I built bracket that holds the reed switch( a piece of and old curtain rod that I had in the garage this is so scientific )so I could position the reed switch closer or farther away to adjust sensitivity. Gap is almost up to 1/2" as I recall before it cuts out depending on the power of the magnet you use.
Grind the rust off of the back of the brake drum on a spot before you try to JB-Weld.
Play with it and have some fun. This is a creative engineering exercise.
dklawson
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Jim, out of curiosity (and forgive me... it's been years since I've looked at the rear hub of a Spridget or MGB), could you clean off the hub flange inside the rear brake assembly and bond (and safety wire) the bar magnet there? I assume the springs for the shoes are probably in the way, but I was thinking this would be a little lower in temperature and protected from rain.
OP
regularman
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I got an old brake drum to play with. I wonder about spot welding a small nut or something onto the drum. I don't trust epoxies on metal that gets hot like a brake drum. Not that I would eve get it that hot, but most will lose adhesion at around 300 degrees.
OP
regularman
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No, Rick. Its not that complicated. You measure the runout of the tread and then each time the magnet goes by it puts in that amount for distance. The diameter of where the magnet is does not matter when doen this way. The magent is only counting revolutions and each rev pulse is the destance you put in for runout.RickB said:
dklawson
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Yep, that's what he's saying.
To fine tune that number/scale, program the wheel size variable and then drive the car through a known measured distance of several miles. Divide the Sigma trip odometer change by the actual mileage driven and you'll come up with a correction to a multiply (or divide) your wheel size variable by. You can easily get the accuracy of the Sigma down around 1% without hard work.
Kim, what are you planning to do with a nut welded onto the drum? I guess you could buy a ring magnet and put a bolt through it so you could screw it onto the nut. The nut itself won't be magnetic... especially once it's been heated by welding.
To fine tune that number/scale, program the wheel size variable and then drive the car through a known measured distance of several miles. Divide the Sigma trip odometer change by the actual mileage driven and you'll come up with a correction to a multiply (or divide) your wheel size variable by. You can easily get the accuracy of the Sigma down around 1% without hard work.
Kim, what are you planning to do with a nut welded onto the drum? I guess you could buy a ring magnet and put a bolt through it so you could screw it onto the nut. The nut itself won't be magnetic... especially once it's been heated by welding.
Jim_Gruber
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Just use some JB Weld, that stuff is used to mend cracks in cylinder heads. This isn't rocket science here. JB Weld, simple solution, works fines lasts a long time. Try the simple method first. It's worked on Bugsy for last year and David Lieb has used on hisa autocrossing Midget for 3+ years and he gets brakes far hotter autocrossing than we ever will.
Jim_Gruber
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Takes 4 hours or so to cure up maybe overnight. Put a large clamp on it the hold in place while it dries. You needed an excuse to buy a larger C-Clamp anyway, Take grinder to spot on brake drum and get some shiny metal there. Don't go crazy just get the bog lumps off. The textured rusty surface even gives it something to grip to.
Did the pics I sent over show how I did the mounting bracket to the bottom of one of the rear axle bolts. Didn't remove the axle bolt just snugged another bolt onto the same stud already hanging down. A little bend and it fits right in place across the brake drum.
Did the pics I sent over show how I did the mounting bracket to the bottom of one of the rear axle bolts. Didn't remove the axle bolt just snugged another bolt onto the same stud already hanging down. A little bend and it fits right in place across the brake drum.