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Mrbarry

Speedo sensor

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So I am having issues with my Speedo sensor. Main issue, I have smashed 6 in as many months. It’s getting silly now. I set the gap from the prop to the max and all is well, but one hard gear change later it goes with a rattle, few of these and it grabs and rips it to pieces. Obviously a little float in the prop at the diff end then. 

Sooooo. I have a Mazda based kit and I’m told there is a stock sensor option in the rear of the box?? I am told I can run a smiths Speedo from it. Has anyone got experience of this?? Tia

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Just give up on it and get a GPS speedo - I'm in the process of doing that (although it seems to be my gauge that's died, sensor is fine).

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I suspect your diff is moving,  it will continue to take out sensors, and possibly do damage to the chassis and or diff unless you secure it. changing to GPS or gearbox sensor will stop the speedo issue, but you have the makings of a greater problem.

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Do you use the Mazda diff mounts? If so it could be the rubber mounts gone soft, replacing with new would reduce movements or polybush would reduce movement to very little

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I have no idea what mounts are used I didn’t do the build. I was under the illusion the diff was solid mounted? 

I beieve the issue to be the engine and gear box mounts allowing float, this would create articulation of the prop so that it can hit the sensor. As the sensor bracket is mounted to the body the two meet in a sticky end. More investigation needed when I have time  

I have machined polly engine mounts for other cars, I am new to the zero (well it sat for 18 months idle after I purchased it), I have had it mapped at Aldon automotive and it drives well. Just need a speedo :? 

 

So so far I have made a set up that reduces the throw of the accelerator, mainly to hold it 3 inches lower at rest so I can heal and toe during down shifts, I have done a bit of cosmetic work and changed the wheels. I have Carbotech brakes on order, I have fitted a new clutch master cylinder, and I’ve burned lots of fuel. 🤣

The list now is Speedo, colour change, new seats, vents to get air out of the engine bay, cut a hole for the TBs to get cold air, find out if the radiator fan is switched from a sensor or the ecu and lower it’s threshold, burn more fuel. Oh, and mount the fuel filter cap inside the boot pointing skywards, sick of fuel pouring on my feet as I get to fuel up!!! (I have more of a plan then it sounds)

 

if if I can’t do anything else I’ll mount the speedo pick up on an upright and pick up on a hub. Bloody cars haha. 

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The Mazda diff is a solid position mount without rubber if done correctly. Engine and gearbox are rubber mounted and if they have given up the ghost some you may get movement.

The early MX-5 transmissions has a cable speedo. Later ones put out an electrical pulse but that needs to be matched to the clock head or ECU if digital.  GPS speedo eliminates a lot of the headaches. 

I used marine vents for the bonnet. Will not pass IVA but will grated cheese nicely.

smDSCN4651.jpg.4e9825f512b42966098ebc6644ca97d1.jpg

I also just made up a new fuel filler neck out of an old mustang neck. Untested but should be an improvement. Tray sides probably need to be taller and a drain hose from tray leading to underside of car.

 1376236729_neckbottom.jpg.202ce51f4f42038ae646905f4ce6f86e.jpg1550214969_neckside.jpg.68d6514829c4fbae952cae811715d71d.jpg826700414_necktop.jpg.3679699ea9f37f82742d9d5e53262e8e.jpg

Mustang cap is vented but not locking.

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That’s a solid and helpful post indeed. 

I had the same idea for the filler, sit it in a tray with a drain to road, was going to use a locking cap tho. Then fit alloy covers over the ‘boot’ that fit flush under the leatherette cover, that set up will look ‘factory standard’ but be secure. A bonnet catch to lock and use the old filler cap as the pull for opening it. 

 

I am am under the impression the gear box and engine mounts are weak, will look closer. I am going to pick up off a road wheel for now I don’t have a lot of love for GPS speedos. Yes they work well but do have some foibles, me being a fussy bugger with a bit of OCD.......  

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55 minutes ago, Mrbarry said:

fussy bugger with a bit of OCD.......

That is a good way to be. Most other people on this site are probably of the same opinion. Makes for a better car.😁

I think the engine and gearbox mounts are pretty stout. But a broken bolt or loose nut can be a real headache.🤔

A tone ring off an ABS hub would be an interesting way to pick up a signal. Or did you have something else in mind?

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I did think that but the number of pulses at 120mph (if I ever for close I know) would be massive, I’m unsure what would be the limit for the gauges but that’s a lot of pulses per minute  

Just had a look and the back of the wheel studs are around 5mm proud of the main hub including a casting that they sit on, so it’s a sensible option to mount a proximity switch in a hole thru the crap shield looking at those. Then calibrate and it should be reliable. 

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your speedo sensor should be mounted above the diff/prop flange, if it isn't that's your problem, if it is the diff is moving.

You can use the pulse from the gearbox pickup if it is electronic, you just need to know the number of pulses per revolution to program the speedo head

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Yeah that’s where is mounted. Just going to shift it for now. 

Had a look under the car to find my speedo sensor is cable driven so no good. Not unless I do something to adapt it but sod that.  

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Kit car solutions do an adaptor for £33 that plugs in to the mx5 cable drive and gives a 5 pulses per revolution square wave out. Might just get that. It’s 5v feedback tho so need to check if the flight gauges need 12v or will pick up 5v. I assume it’s Hall effect so will be a nice ride and fall not a sine wave too. 

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That should sort the speedo, but If the diff is moving, other problems will develop.

The diff hangs on bolts from the cross member under the boot floor, but a lot acceleration and overrun forces are taken by the two bolts to the right of the diff front casing.

On the donor vehicle these bolt held the diff to the torque beam that ran from a mount at the back of the gearbox, making the diff and gearbox one unit.

The zero uses a plate on the chassis, to hold the nose of the diff, but it must be fitted with two HT bolts through the original torque beam bolt holes. the diff should fit flush with the chassis bracket, some have dowels that can stop the diff fitting flush, these need removing, bolts should be fitted with body washers. If this is not done the chassis bracket can flex allowing the diff drive flange to lift on acceleration and drop on deceleration.

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Sounds very much like that may be my issue. I’ll look tonight more closely, already have the diff cover out of the boot. 

Any one for any pictures?? 

Just joined up for the year too, worth a few quid for the help 👍

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