question: hub-mounted speed sensor?

[Jonathan]

I haven't had a functioning speedometer for years now. If I hook up an angle drive it dies within 5 miles. The cable turns fine until I hook it up to the angle drive, and then it becomes very difficult to turn. I have no idea why.

If someday you figure it out, please let me know, because this is EXACTLY what mine does.

[Bitsyncmaster]

Getting MPH is very easy if your going to build custom electronics. Any of your sensor ideas will work. You would want more resolution than 1 RPM of the wheel for slow speeds.

The big problem is getting a display that many people (with money) like.

[Nicholas R]

You know this is just a thought. Some of the transmissions in the Renault UN1/369 series have vehicle speed sensors in them. Ours just has a plug/plate blocking where the sensor goes. I'm sure ours could be swapped over to have the VSS installed. No idea about automatics though.

[DMCMW Dave]

You know this is just a thought. Some of the transmissions in the Renault UN1/369 series have vehicle speed sensors in them. Ours just has a plug/plate blocking where the sensor goes. I'm sure ours could be swapped over to have the VSS installed. No idea about automatics though.

I'm not so sure. Our trans is assembled backwards due to the rear-engine configuration and I'll bet that the speed sensor won't fit the differential in this configuration. I'd also love to see what that looks like.

[Ron]

I still don't know how those wheel hub-mounted sensors works, though -- how they get their pulse, I mean.

Basically, as the axle (or output shaft if transmission mounted) turns, teeth mounted on a disk about the axle/carrier/integrated into the rotor, etc. pass by the pickup coil causing a pulse/signal which is sent to the computer. The computer uses the pulse/signal to calculate how to drive the speedometer.
Similar to how the distributor drives the tachometer or common ABS setup:



K700129941SKF.JPG


A magnet and pickup coil is another way....

Food for thought- A D's Governor Computer has an unused wire connected to a generator driven by the output shaft. It is terminated in the "Black Block"......

[Farrar]

Thanks! That's simpler than I thought it was.

A magnet and pickup coil is another way....

This is what I was hoping was not involved...

[Dangermouse]

Thanks Ron, I never knew that about ABS sensors. We use that sort of thing in industry to detect motion/no-motion also.

[Nicholas R]

I'm not so sure. Our trans is assembled backwards due to the rear-engine configuration and I'll bet that the speed sensor won't fit the differential in this configuration. I'd also love to see what that looks like.

I think you're right. After looking into it more, it looks like the sensor is actually gear driven by a separate gear on the differential assembly that is opposite the differential ring gear.

The speedo drive gear is mounted onto the differential carrier and mates with a driven pinion located in the right hand side of the casing.

With our differential flipped, that drive gear would be on the other side. The sensor assembly only fits in one side of the casing though so it's clearly a front wheel drive only sensor.

[Farrar]

How about using a stepper motor where the angle drive used to be?

Confession: I've never removed my angle drive, so I don't know exactly how it works...

[TTait]

I looked into this about a year back... Took my instrument cluster to a local speedometer shop and they said it would be very easy. First we mount the speed sensor, this can happen at the front wheel, the transmission, or on the rear axle using various universal sensors that create a pulse.

Then they remove the speedo unit and use appropriate spacers etc. and shoot a digital photo of the existing speedo to use for reference. They can create a duplicate graphic, or set you up for a 140, 160 mph unit. If you want the DMC logo added, or if you high,low beam indicators that need to backlight, they can work that out too. In some cases they use the original speedo face if you are willing to have a remote trip counter reset.

The big problems are that it has an electronic readout odometer and that the location of the reset knob is fixed, so you would have to create a new lens and have it drilled out. The odometer starts from zero, so you cannot pre-set it to the current mileage on the car.

They then set a couple dip switches etc to tell the new electronic speedo unit what the indicated speed is for a given angle, and then you hook up the sensor wire, power and ground.

Final step is to take the car out on the road, and use the trip reset knob to put it into a calibrate mode, then drive the car for exactly 5280 feet (1 mile) and turn calibration off. The speedo then knows what the scale of its display is, and exactly how many clicks of whatever sensor you chose per mile, and it just works from there on out.

Its not cheap - we did not get into all the details, I decided to give the angle drive one more chance, as it was still under warranty - and to date the replacement has been fine.


As to those of you burning through angle drives, consider buying a single piece long speedo cable from Rob Grady - it eliminates the lambda counter and and should eliminate most any hidden problems. I suspect that the lambda counter spins well enough in your car when turning it by hand, but would catch, snag, or drag when it runs at speed.

I know Hervey sells a long cable too, but the one I got from him did not screw down onto the angle drive well enough and/or the cable inside the housing was a bit too short, and it could pop loose and spin, or partially jam and rip up the angle drive. Of course, that only ever happened to me, he "has sold thousands of those cables and no one has ever had any trouble with it whatsoever".