As above, I know there isn't a direct drive these days, but while one or both (not sure which) wheels spin the rev's obviously climb but the speedo reading doesnt change.
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Where is the speedo drive taken from
As above, I know there isn't a direct drive these days, but while one or both (not sure which) wheels spin the rev's obviously climb but the speedo reading doesnt change.
Sure it's not the clutch?
The speedo at a guess would have to be fed via a sensor connected to a drive shaft.
It could also be fed from the ABS sensor, of which there will be one on each side just behind the brake disc's.
If it was the clutch it would rise with the rev's but it doesnt, I suppose it could be off a drive shaft that wasnt spinning.?
Originally Posted by Birchy63
Only one the front ones though. That also explains why the speedo didn't rise if it was the wrong wheel spinning.
The speed referance is given from the rear wheel bearings inbuilt encoder.
It is taken from the differential I believe. Can't be the rear wheels because if you pull away abruptly - ie wheel spin the speedo will tell you your doing 10mph when you are bearly moving.
It could be a clutch problem if the revs are rising/fluctuating and the speedo isn't changing accoridingly.
Gazza4
Rear wheel sensor would be in line with what I am getting, the speed wont be taken by the flywheel as every time you change up it would register as going slower due to the revs dropping, I can sit there with the wheels spinning in 4th with no speed registering and to me that wouldnt indicate a problem as I am not moving, The speedo is spot on when driving thus it is working correct. just puzzled as to where the speed info comes from?? must be the rear as Grimy says.
There are speed sensors is in the front wheel hubs, that are a part of the hub. If the revs rise and the wheels spin as you say, then the clutch is not slipping cos the wheels are turning. I assume it is driving fine, in which case the fault may lay with the dash board, which is fed by the CAN; or it could be a control module but I doubt both wheel speed sensors would fail at the same time.
The rear wheel speed is also monitored for ABS function but if the rear wheels fed the speed indication, you would not get a speed reading on a rolling road, which you do.
Interesting thread, it wouldn't have been from the clutch anyway, as how would the auto's register?
Ok, maybe I gave an over simplified answer, the speed is actually determined by the ABS module which looks at all the wheel encoders but afaik it uses only the rear two for a speed referance. It then sends a canbus signal to the insrument panel.
nutron, are you sure you get a speed reading on the RR? I've not seen this before? Only the RR's own speed reference.
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