Changing the Speedo Sensor on a Turbo

[ChrisRidett]

Hi guys

I've had my dashboard apart and cleaned etc, got my INFO centre working but i'm pretty sure the sensor has failed for the speedo.
New one has been obtained, and I got under the motor and managed to locate where the sensor is ( after much faffing )

So, behind a plate held on with 3 x bolts , lies the inner driveshaft for the OSF. Above this would appear to be the sensor, but right in the way is a tube that goes between the Turbo and the Sump area.

Whats the pipe??......looks like I need to disconnect it to get to the speedo sensor bracket, but cant find anything on the forum or in the Haynes manual to refer to it specifically at that location.

From the positioning of it, it looks like the oil return pipe, but the presence of a Jubilee clip suggests otherwise......would have thought more Coolant/Breather pipe if a jubilee was being used.


Hence my confusion and I pass my question to all knowledgable 480 Forum !!!!

[Iroll480]

Did you check the resistance from the speedo sensor? You can pull the connector (brown and yellow wire) somewhere under the battery, resistance should be between 1,5-3,0ohm.

[ChrisRidett]

I havent yet, I could compare readings between the the old and new sensor.

But the way in which the speedo died on me , progressively, leads me to believe that either the sensor end has become so covered in crud it can no longer measure anything ( in which case the reading on the meter would read ok anyway ), or that part of the sensor has died , which may - or may not reflect on the measurement.

I reckon its the former, and that the end is filthy, but i dont want to go through the hassle of removing it, only to put it back in. Once its out, a new ones going in.

[glasgowjim]

i agree with you Chris especially as a new sensor is only £35 and given the awkwardness of working on a tyurbo engine I would definitely go for a new sensor.

[Iroll480]

What I mean to say is that you can measure the resistance of the old sensor while it's still in place. Just remove the connector under the battery tray and measure the resistance. No need to remove the sensor, that way you're sure you don't put a new one in while the old one is still doing it's job properly, can safe you an awkward fiddely job. Never heard of one that isn't functioning because of dirt built up. But offcourse as it's a 480 everything is possible!
The failing of the speedo like you described can also be caused by a bad soldering joint on the PCB from the infocentre, at least that was the case when mine speedo started working intermittently, gradually getting worse till it stopped functioning at all. Here are some pics of the formentioned soldering joints. I don't remember which one exactly, but it's one of these 18 points. I just heated them all with a soldering gun till melting point, et voila my speedo worked again and is still functioning after 3 years.

[ChrisRidett]

Thanks for that, I did take the dash out and clean up the contacts, I also checked the solder joints to see if any had cracked.

The only problems I could see with it were the oxidisation, which i tried to clean up as best i could. ( Time is always my enemy )

After cleaning it the Info Centre worked great, but not a jot from the speedo. This is a link to the full size pic of my pcb.

http://www.orpington-computer-repair.co ... 011137.jpg

When the speedo and Info centre were playing up, if I pressed the dash about, the info centre would display all manner of funny signs with each press but the speedo wouldnt normally be affected.

Noticed the other day in the snow, it came back to life for a while, then died again.
Previously the speedo would not work at all from first start, then it would twitch very periodically with road speed. Not so much like a dodgy contact, but like it was missing a regular section of its count. Then it would improve to the point that the twitch just caused the spear to vary around the indicated speed. Each 'twitch' being a regular identical pulse.

My gut says sensors gone. Oh for an oscilloscope, I could test off the sensor from the connector then!

[Captain Slow]

Now the info centres behaving, does it show the average speed/mpg/av mpg?

[ChrisRidett]

Average speed/ Avg mpg/ Inst mpg / Range ........Are All Showing .......... " - - - "

External temp / oil Temp / engine temp /Petrol level all showing ok.

The major Plus point ....the petrol gauge !!!! It was costing me a fortune when I planned a run as I couldnt tell how much was still in there, so would fill Poppy up just to be sure!!
Before the speedo failed if the gauge played up, I'd reset the trip when I filled up and judge it from that, but when both went it got harder!!!

[Captain Slow]

A long shot for you as youve had the dash off already-so far when my speedo has given up it has just been one of the multi-connectors from cable to the pcb that has worked loose and ive just pushed that in and its worked...think Ive just been fortunate!

[ChrisRidett]

Thanks for the feedback everyone.

Think I'm going to hold off on replacing the sensor for the moment, might try and do it same time as the water pump, if I can leave it till the weather gets a little better!!

In the meantime I may try and rig up some form of tester with the new sensor. Will take some readings, but I suspect the sensor is a Hall Effect one ( magnets and electricity) should be able to rig something up.

If I can test off the senor in situ - that would help.

I'll report back if i have any success!