Speedo under reading

Johnnybgood

Member
I've had the car for almost a year now and still can't work out why the speedo under reads by quite a large margin. At a true 30mph (Via satnav) the speedo reads 24. It's only vaguely accurate at about 60. The tyres are the standard 185 x 14.
Is it just a case of changing the speedo?
Thanks
John
 
Mine is similar. At 25mph on the speedo I am doing 30mph - so you have to be careful with speed cameras.
Don’t know the answer but would be interested if anyone else does.
I just adjust my speed accordingly. Usually I drive with the speedo showing about 5mph under the speed limit.
 
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Which flange nut? The speedo cable or a different one?
I'll crawl under sometime. I might find out why I have no reversing lights while I'm under there!
Cheers
 
You need to remove the four bolts that hold the front of the propshaft to the gearbox, when that comes away you can see the bolt (or nut depending on gearbox type). I would add that when the flange is loose as well as the speedo under reading it tends to waver as well.
 
You need to remove the four bolts that hold the front of the propshaft to the gearbox, when that comes away you can see the bolt (or nut depending on gearbox type). I would add that when the flange is loose as well as the speedo under reading it tends to waver as well.
Methinks you are having fun here. You seem to be suggesting that the propshaft is not rotating at output shaft speed due to a loose propflange nut. Hmmm. My speedo also under-reads but I sha'n't be checking there, I think. No wavering.
 
Methinks you are having fun here. You seem to be suggesting that the propshaft is not rotating at output shaft speed due to a loose propflange nut. Hmmm. My speedo also under-reads but I sha'n't be checking there, I think. No wavering.
If the drive flange is loose the speedo drive gear can slip on the output shaft as its only clamped between the flange and bearing
 
If the drive flange is loose the speedo drive gear can slip on the output shaft as its only clamped between the flange and bearing
Ooh I like that logic. I need to check this as mine doesn't read properly and wavers. The box has been reconditioned not long after I got it Anders never read correctly..
Could also explain part of my "clonk" noise.

Regarding the speedo I understand the magnets inside can loose their magnetism and cause errors. These need demagnetising to recalibrate the speedo..
 
If the drive flange is loose the speedo drive gear can slip on the output shaft as its only clamped between the flange and bearing
Ahh, perhaps I should have checked the workshop manual before being so sceptical. I may indeed check there although there is no wavering.
 
One of symptoms of the loose flange will be the speedo reads even slower when you are accelerating, and when you lift the throttle the speedo will leap up to the correct speed for a moment before reading under again.

Also, on early S1 cars, the output shaft has a threaded end and the flange is held with a nut. That thread can shear off, leving no way to fix except replace or rebuild the gearbox. Rover replaced it with a bolt for the needle bearing gearbox.

Yours
Vern
 
Also, on early S1 cars, the output shaft has a threaded end and the flange is held with a nut. That thread can shear off, leving no way to fix except replace or rebuild the gearbox. Rover replaced it with a bolt for the needle bearing gearbox.

When that breaks you get a crunch into second gear as the mainshaft moves forwards defeating the synchro. We used to get the shafts machined to take some studding and a new nut.
 
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