speedo drive

CTV400B

CTV400B

New Member
I have an interesting little problem with my speedo drive. This fault only happens when the I have driven over 10mls or so. Every time lift or put my foot down on the throttle the speedo either jumps up or slows down .I know its not the speedo or cable as i have a calibrated Halda driven of the cable and have taken it along our measured 6.22Km and it used to accurate to 5mtrs now 500mts. It therefore is an issue in the box. I have taken out the spur gear and inspected it apart from 2 teeth which are slightly marked the rest show no sign of wear. to my way of thinking i believe it may down to the output shaft thrusting forward and back causing the 2 gears to come out of mesh. Has anyone had the same experience if so how was it remedied
 
Demetris that's what I'm hoping for it was just in case it might have been something else more serious thanks
 
Assuming it's the flange being loose, what is happening is the gear on the output shaft is slipping, as it has no key and is just clamped between the rear bearing and the output flange.

This could be bad news in an early series one car, as the original mainshaft had a thread and the flange was held on with a nut. The thread could (and would) break, leaving you to replace or repair the gearbox. They changed that to a bolt somewhere in 1968, eliminating that failure.

Yours
Vern
 
Vern Klukas said:
This could be bad news in an early series one car, as the original mainshaft had a thread and the flange was held on with a nut. The thread could (and would) break, leaving you to replace or repair the gearbox.
Click to expand...

When that happened you'd have difficulty engaging second gear as the whole mainshaft would move forward and you'd only get the gear with a "crunch" if you got it at all. When I worked at a non-franchised specialist we used to have the mainshafts machined to take a stud which seemed to work better than the original wth the threaded bit as part of the shaft. Mainshafts must have been in short supply to go to the bother.
 
harveyp6 said:
Vern Klukas said:
This could be bad news in an early series one car, as the original mainshaft had a thread and the flange was held on with a nut. The thread could (and would) break, leaving you to replace or repair the gearbox.
Click to expand...

When that happened you'd have difficulty engaging second gear as the whole mainshaft would move forward and you'd only get the gear with a "crunch" if you got it at all. When I worked at a non-franchised specialist we used to have the mainshafts machined to take a stud which seemed to work better than the original wth the threaded bit as part of the shaft. Mainshafts must have been in short supply to go to the bother.
Click to expand...

That's true, I had forgotten about that symptom. The slipping speedo was very common. The first one I saw with the thread snapped off was pretty funny. The car had the slipping speedo, and after telling the customer that all would be well in about 20 minutes when I went to tighten the nut it just twisted off along with the thread. "About that 20 minutes…"

Yours
Vern
 
Many thanks to all
I dropped the propshaft and tightend the nut on the flange the speedo now works a treat and so does the Halda and is accurate to +/- 5 mts superb
I should point out the gearbox is out of a 2.2 and the engine is now a 2000TC
 
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