Irrational speedometer

R

Richard Thorley

Member
I have an unusual issue with my seepometer in that it generally under reads by quite a bit but if you stick to the same speed for a short bit then the creeps up to what seems more accurate. Strange part is that if you dip the clutch it drops again. If you blip the accelerator with the car in gear it rises back. I replaced the cable with a new one and I've tried another speedometer head/gauge all I can think of now is the angle drive on the back of the head or something in the gearbox any ideas much appreciated
 
The angle drives do go... there's one gearbox end and one speedo end... I dont have a manual though so i dont know from personal experience if that's the issue you're seeing.
 
I looked at my parts manual and i think there is only one angle drive on the back of the head on the manual box though Im happy to be corrected. I did wonder if they went but at £40 odd I didn't want to just buy one and waste my money if it was something else
 
Richard Thorley said:
I have an unusual issue with my seepometer in that it generally under reads by quite a bit but if you stick to the same speed for a short bit then the creeps up to what seems more accurate. Strange part is that if you dip the clutch it drops again. If you blip the accelerator with the car in gear it rises back. I replaced the cable with a new one and I've tried another speedometer head/gauge all I can think of now is the angle drive on the back of the head or something in the gearbox any ideas much appreciated
Click to expand...

Check that the rear flange isn't loose. This and your oil leak thread make me wonder if someone's been playing around with the box.
 
Hi. I had a similar experience some time ago on Rover, and it turned out to be the nut on the end of the gearbox main shaft not being tight, allowing the scroll which drives the speedo cable to slip thereby giving a faulty reading. tightening the nut solved the problem. John.
 
Thanks for the advice. I'm sorry to be so simple but any clues to identity the rear flange and the nut on the end shaft? I will try to have a look this weekend
 
Back of the gearbox is a round flange about 3" which bolts onto the propshaft. You can't see the nut as it's inside the joint, but you maybe able to pull it backwards and forwards to see if it's loose.

This is the LT77, but the flange is the same - this one hasn't got the nut on yet.

 
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