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Speedometer - Issues And Questions


Guest ali2992

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Guest ali2992

I'm looking to convert my digital speedometer to receive its signal from the gearbox instead of a magnetic pickup on the driveshaft. I've gone through about 3 sensors so far where they have come into contact with the driveshaft while driving. Currently the magnetic pickup is mounted to a bracket that is fixed to each side of the tunnel, i have the sensor secured in position and it is a perfect distance to clear all rotating objects and still sense the magnets. However, when the car experiences a bit of torque or a sudden change in momentum, i.e starting off from a standstill, putting my foot down, engaging and relasing the clutch etc, I hear a brief clunking where the sensor is obviously coming into contact with the driveshaft. Is it possible that the frame is warping under load and causing the sensor to be pushed towards the driveshaft? Because it's a fixed point coming into contact with another fixed point and I can't understand why.

 

I've had enough of replacing sensors though and I'm looking to convert to mechanical originating signal. I've spoken to speedy cables and they can easily put something together for me, I just want to double check that my logic is correct with the signal - my gauge requires a number in pulses per distance, I think it's pulses per mile. The transducer on the converter speedy cables supplies outputs 8 pulses per revolution. Is the number of revolutions of a mechanical speedo cable affected by the gear you are in? I.e if you are doing 60mph in 5th gear, does the cable spin slower than if you were doing 60mph in 4th gear? It sounds like a silly question typing it out but I want to check before I spend a fair amount of money on a converter that won't work with my gauges

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Guest ali2992

yeah that sounds like a better set up, one of my previous solutions involved aralditing some magnets to the prop further down and taking the reading from there in the hopes that there was more room to work with but they only lasted a few days before flying off, I don't know if the bond didn't take or what

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Guest 2b cruising

You can use your diff to prop bolts.

Make a bracket to fit to your diff mounts and position the sensor to either the prop or drive shafts bolts.

This way the sensor will again be moving along with the both parts.

If you have the mt 75 fitted they already have the sensors fitted for electronic speedo's as well as the mechanical type. That's how mine is done.

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Guest ali2992

Speedo drive is directly proportional to road speed, not related to the gear at all, otherwise you'd see the speedo change whenever you changed gear!

Yeah that makes more sense than what I was thinking! So I should be ok then

 

 

You can use your diff to prop bolts.

Make a bracket to fit to your diff mounts and position the sensor to either the prop or drive shafts bolts.

This way the sensor will again be moving along with the both parts.

If you have the mt 75 fitted they already have the sensors fitted for electronic speedo's as well as the mechanical type. That's how mine is done.

 

I have MX5 based, so mx5 diff, there are no suitable mounting points for me to fix a bracket to the diff, that would be my first choice. And then the driveshafts are push in so no bolts or anything to read off at all

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Guest 2b cruising

A loop bracket with a t piece coming off it to fit the sensor in the right place.

Make the loop a tight fit to the diff nose cone, drill and tap for a coupl of grub screws to lock it on the nose.

Easy Peasey lemon squeezy.

Use 5mm flat bar about 20 MM wide.

Wrap around the cone and cut to size.

Weld ends together.

Use same stuff for t piece then drill and tap that to fit the sensor threads.

Edited by 2b cruising
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I used a transducer on the end of a speedo cable for my telemetrix speedo. Output is 4 pulses per revolution of speedo cable, speedo needed pulses per mile. Standard ford cable turns 1000 per mile so 4000 per mile for calibration. Set it, passed sva never touched it since 7 years on the road.

I went this way because it was accessible where the prop isnt, didnt fancy dismantling car to glue a magnet back on.

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Guest peter2b2002

I used a transducer on the end of a speedo cable for my telemetrix speedo. Output is 4 pulses per revolution of speedo cable, speedo needed pulses per mile. Standard ford cable turns 1000 per mile so 4000 per mile for calibration. Set it, passed sva never touched it since 7 years on the road.

I went this way because it was accessible where the prop isnt, didnt fancy dismantling car to glue a magnet back on.

I did the same untill the drive gear in the gear box failed so now I stuck magnets onto the 1/2 shaft near the dif bracket bolted onto the difference been ok for 4 years( I still have the hall transducer that goes onto the speedo cable if you need one(I will put it in for sale list)

peter2b

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Guest ali2992

I did the same untill the drive gear in the gear box failed so now I stuck magnets onto the 1/2 shaft near the dif bracket bolted onto the difference been ok for 4 years( I still have the hall transducer that goes onto the speedo cable if you need one(I will put it in for sale list)

peter2b

Is the transducer just a standard 12v feed, earth and signal? I don't have a cable at the moment so I'd have to get a replacement speedo cable. Would the transducer fit any speedo cable?

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Guest peter2b2002

Is the transducer just a standard 12v feed, earth and signal? I don't have a cable at the moment so I'd have to get a replacement speedo cable. Would the transducer fit any speedo cable?

yes it just fits onto the end of the speedo cable where the speedo head was I have a cut down cable that I was going to use when I found out there was no drive out of the gear box

peter2b

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Guest ali2992

obv. not seen detail so ignore if I'm missing the point.

 

Diff cannot move in relation to the frame & tunnel sides.

If you take your speedo input from the diff input flange bolts, or magnets attached to the flange - you should be good.

 

The input flange should not be moving in relation to the rest of the diff; acceleration or not.

 

I jacked the car up last night and checked the diff mountings. The two bolts underneath are correct bolt sizes however there is probably about 1-2mm of wiggle room/play in them (I mean between the bolt and the edge of the shaft, considering that the tolerance for the speedo sensor is also 2-3mm, could this be why the sensor is coming into contact under load? As the gap will be taken up as the diff tries to rip itself away

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