OT - car speedo sensor

[Dave Plowman]

I've got a problem with the speedo sensor on my old SD1 Rover - it's intermittent and no longer available new. It's a fairly rare SD1 - an EFI auto which has a different axle ratio from all the rest, so a less common sender - others for the range can still be bought.

It's a sealed unit of course, and the fault would appear to be internal - I've re-made the plug connections. And not only does it stop the speedo and mileometer working but the OBC as well. So I'd like to have a go at making a new one. Obviously, one which fits inside the box and is gear driven as the original is a bit too complicated, but a toothed disc on a wheel or the propshaft would be an easier thing to make. Any suggestions? The technology Rover used is 20 years plus old, so what would be the modern way of supplying the pulses? The alternative would be to purchase a standard unit and do some form of pulse multiplication, but that's a bit beyond me.

[Gary Cavie]

No doubt a silly question, but I guess you've phoned Rimmers?

[Old Fart at Play]

Nothing changes. My 827 is the same. It's sealed but can be opened with a couple of slices from a Dremel. Inside is a disc with 8 magnets. If I wanted to fix it I could get a hall-effect transistor from Maplin.

Anyway, isn't it more likely that the senders are independent of the axle ratio and the speedo is different for each model?

Roger.

[Richard Faulkner]

In article , Dave Plowman writes

Same problem on my Citroen XM

[Dave Plowman]

I must admit I've not wanted to hack it apart, although I might get a spare of the wrong sort and try this before starting on mine.

One would hope so, but the speedo heads are all the same, and only the sensor changes. There are about half a dozen ones across the range including manuals which are of a different design too.

The snag, of course, is that you can't simply change for a different one and fiddle something - the drive gear is different too and requires a strip down of the box to change.

[Andy Dingley]

I'm breaking an XM in a week or two. Can I help ?

[Matt]

My XM was a '90 with the mechanical speedo drive, the plastic gear had broken inside the gearcase. I replaced it and was really chuffed to have a speedo till 40 miles later it stopped working. Never bothered to see why it had failed again especially as I could never get the suspension computer to work for more than about a mile. It's been sitting in my workshop for a couple of years, anyone want it coz I really need the space?

Matt

[Richard Faulkner]

In article , Andy Dingley writes

I dont know - is the instrument panel easy enough to replace? (by my mechanics, not me ). How much would you want for it? Does it work OK?

[Tony Williams]

In article , Dave Plowman wrote: [snip]

Dave, do you have figures of the pulses per mile (or whatever) for the various sensors.... for the present dud one and for a mechanically interchangeable replacement?

PS: Look up the RCA CD4089B binary rate multiplier.

[Dave Plowman]

I haven't, but I do have information on the number of teeth on each sensor gears, and a spare speedo which I can drive off an oscillator.

The snag with this approach is it means at least partial stripping of the box to change the drive gear as well as the sensor, so it would be a last ditch attempt. The sensors which are still available are not cheap either new. I was thinking more of perhaps fitting an ABS sensor and disc to one wheel, and then converting this pulse output.

Thanks - I'll bookmark this.

[Tony Williams]

Sorry. I was under the impression (from a previous post) that you could get another sensor assembly that fitted straight in, but which gave the wrong number of pulses/mile. Electronic conversion of the pulses/mile could have been the simplest thing to do.

[usenet]

It's easier on Series I XMs than Series II (I have one of each).

For more XM info and help come and join the XM-L list at Yahoo groups (if you aren't already a member).

[Andy Dingley]

Only if I saw the rest of the car away from around it. You do _not_ want to mess with the dashboard on an XM. Horrible job.

If there's a useful gearbox sender I can extract with moderate effort, then I can probably strip it before it goes to the scrappie. But I'm not going near that dashboard !

[usenet]

It's actually not too difficult on a Series I XM when you know which way it comes out.

[Richard Faulkner]

In article , Andy Dingley writes

I am completely lost as to how these things work, so dont know if it would be useful or not.

It's going in to the garage in a few weeks for lots of niggling jobs, so I am hoping that the mechanics can identify the problem and sort it. If we get to that point, and it is a gearbox sender problem, I'll let you know and - if its gone, its gone

[Richard Faulkner]

Mine's a 1995 XM Executive Estate - presumably series II?

[Dave Plowman]

Yes - I didn't make it clear. It would certainly be the sanitary way to do it. I'll have a look at the w/s manual to see just how much of the box has to be stripped to change the gear - it might just be the rear extension. I'm not taking the box out, though, it weighs a ton. ;-)

[geoff]

In message , Dave Plowman writes

Wimp - I drove my old SD1 around for several months with an engine/gearbox in the boot until I got around to changing the engine in my other one

[Dave Plowman]

Heh heh. Wonder how many modern non estates you could do this with? Or need to, come to that. ;-)

By folding the front passenger's seat down as well as the rear, I got a Vicorian front door in with the hatch closed.

[TimM]

I don't know much about the technology, but is the right axle gearing one available in kilometres/hour?

There are convertors on the motorbike scene which scale km/h down to mph.