Hi Cairan

just do a search for "HUD GPS" - this one's the same unit, just a different label...

http://cgi.ebay.co.uk/HUD-51-CHANNEL-BLUET...7QQcmdZViewItem

regards
Dave

Interesting! I'm going to have a look at the Speedo situation this weekend, and there's a set of clocks for my AX on eBay for £12, which is cheaper of course, but I'm quite taken by the idea of this thing. Is it permanently mounted, or is it easy to move from car to car? My thinking is that if I can fix the dash speedo, I want to, but that one of these would be quite fun to move from car to car, because it's useful, but also to learn how accurate speedos are in general! I need to check whether the AX even has a ciggy lighter socket!

Also, help me out here. If the speedo on an XM underreads by 20%, that means that at an indicated 80, you're actually doing around 62 mph. Today, at an indicated 80, I was overtaking lots of people. I wonder how slow they were actually going? It could be a very interesting thing to learn.....

Legal position on speedometers is that they may overread by up to 10%, they must not underread

On the A9 as you enter Golspie there is a 'speed check' indicator at the side of the road which I use to test the accuracy of my speedo, a reading of 34 mph in the car shows exactly 30 mph on the indicator - a difference in excess of 10%. They have now installed one in Brora, up the road and that gives the same reading, so either the mph are different in Scotland or my spedo is very 'safe'

Peter.N.

Compared to my GPS my speedo is over reading by 3mph across the board. So at 70 that is reasonably accurate compared to many cars I think, but at 30 it is the 10% allowed.

Hi

Interesting discussion this one. Up around the M25 from here, near Heathrow, the overhead gantry cameras have just gone digital. Apparently now that they are digital the camera will be set to 79mph rather than the 90mph they were previously set at. Given that most speedos seem to over-read by 10%, you would have to be doing an indicated 99mph!!! to get nabbed with the old cameras. I guess this was done to nab the very fast drivers and be selective for them. Now the limit is going to be 87mph indicated, which is still fast but may catch a few more. To my mind it's not a problem - if you are going too fast you are going too fast but I do wonder whether the same limits will be put when the limits come down to 40 or 50mph. I can't imagine it will, but imagine how many people they will catch if the signs go to 50mph, they nab drivers at 55mph or an indicated 60mph. Most people are going through the signs at an indicated 60mph.

Cheers

Tony

hi Sam

you can move it easily enough, it's got a magnetic base and you stuck a metal plate to the dash to hold it in place - use velcro to fix it and it'd be easier. Only thing is the reflection off plain glass is poor as you get a double image off the 2 surfaces, so there's a polarising filter that you fit where the image is and that tends to stay put. It'd soon lose it's stick if you kept shifting that, but I expect it'd be easy to get more. Comes with 2 of these.

On the motorway, my V6 tends to be showing 100 on the speedo for an actual 80-ish, so as you say I'd be going way too slow. Must get round to changing the gearbox sender one day and see if that sorts it, as I've tried 3 speedo heads already, same result. Of course this throws the odo and trip readings out too, so my 105K miles is probably more like 85, depending on when this started to happen (I've owned it since 50K).

My other 2.0SEi's were within 5mph of actual, so I've always wondered what was done to the V6 in PO to cause this. sender unit or gearbox....

regards
Dave

Hi Dave

There is also tyre size and diameter variation with wear to take into account as well as the gear wheel in the sender. In the manufacturer's spec there are at least 8 different tyre sizes associated with XM's each with a different wheel diameter when new. Total permitted tread wear is of the order of 12mm on the wheel diameter. There is also some variation in new tread depth between manufacturers with the same tyre size. When I tried my dealer for a new sender and gear wheel they could not determine which of the 17 different listed ones fitted. Suggested I took it out and brought it in to them or counted the teeth and told them the colour.

Regards

XMexc

Hi Tony

The limits for the film cameras were simply to make the film last a reasonable amount of time in recognition of the limited storage space on a finite length of film. With the modern digital cameras storage capacity ceases to be a limit. They can be used in pairs as average speed cameras as well. Any statements made now about enforcement speed limits cannot be relied on as they can probably be changed from a central controlling computer at political whim. It is in the same league as the new 1 mile range mobile radar that can be set up where there is a good sighting distance to pick off speeders long before they see the need to slow down.

Regards

XMexc

While reading the input on this topic, I note that no-one seems to have asked whether the digital readout on the 2.5Td (and others) is reading the true speed in relation to the road wheel rotation, as it it not a mechanical device like the speedo head?

Its a pulse counting system so I would have thought it would have been pretty accurate, assuming it has the correct gear wheel as with the mechanical type.

Peter.N.

Hi All

Both types are based on the original mechanical drive fitted to the first XM's. There was even one variant that had both wire drive and electrical output. The electrical signals are generated by a Hall effect device which senses the rotation of the plastic drive rod. Typically they seem to suffer water ingress to the electronics. There may also be slippage due to wear of the plastic drive rod. In my opinion these are the causes of electronic speedo drop out. I remain to be convinced that intermittant speedo problems come from dash wiring faults.

Regards

XMexc

Hi XMexc

I can now confirm that a wiring fault was actually the problem with my red one. I drove down the track with the panel off and moved the wiring to the red plug as I was going and I could make the speedo go on and off. I soldered a couple of the leads that I thought were causing the problem and it worked fine until my daughter in law pressd the pressed the mileage reset button when it promptly stopped working again. The only thing that this would move other than the wiring is the instrument panel itself, and I have changed this twice. I will solder all the leads on next time and let you know what happens.

I also changed the sensor twice, the original one is now in my car working perfectly.

Peter.N.