Speedo drive disintegration

I installed a new speedo drive on my 75 MK3 a few weeks ago... put it on with the spacer on the outside as per the exploded diagram in the manual. When I installed it the speedo worked briefly, then stop working completely. Just got around to looking at it and here's what I found:



The end cap is missing and the guts of the unit are gone. Is this something that could happen with incorrect installation or is this something only a defective unit would do??? I am pretty sure I installed the drive properly, although fitting the drive over the left axle was tough, the drive had to be lapped to slide on easily. That could have been due to paint decreasing the ID. I also got the ears of the drive in the slots, so I am at a loss... totaling about $140 if this is my fault!

I also noticed that the cable end that goes into the speedometer is too short and doesn't engage the internal gears:



The exposed end measures just under 7/16". I bought both the drive and cable at the same time from Old Brits... I guess I need to know if others have had drives disintegrate like this and if the cable end is too short. Thanks in advance.
-paul

I had the inner assembly drift out of my repro speedo drive just like yours, I think that the fit of the parts of these new drives is poor. i was lucky as I found the problem before I lost any parts and managed to araldite the parts back together again. You haven't done anything wrong, I would send the part back for a replacement.

Been there and done it.... twice . Third time i lockwired the front end to the back end so it is impossible for the ends to come off. Unfortunately i believe that this is what we get for parts any more. I would guess that they must offer a seasons warranty on this type of stuff so i'd be sending it back.

The inner cable length is correct and must NOT exceed 7/16 " at the speedometer end.

Thanks for the confirmation... I'll see about getting a replacement for the drive unit. This speedo issue has been dogging me for a year now. I am still uncertain about the cable. If the inner cable has to be 7/16" and STILL does not engage the speedo gears, what should I do? I just had the speedometer rebuilt and when I hooked the old cable (protruding length just over 9/16") to the unit and spun the thing with a drill, the gauge moved. I read earlier posts noting that lengths over 7/16" chew up the speedo internals (something the rebuilder noted was wrong with my gauge). It's a Veglia gauge, could this be the issue? Thanks in advance.

-paul

Hi there , just a two cents idea , may be idiot...is your inner cable could be upside down, so shorter towards the gauge , and longer towards the drive , thus pushing out the endless screw which is in the speedo drive and then popping out the cap.........I was trying to repair one yesterday ............

Just got an email from Old Britts and Andover has seen these drive units fall apart before, so it's being replaced free of charge (nice). As for the speedo cable, I think that I didn't have the cable properly tightened up. The other day I tightened it to a point where I felt some resistance... but the thread might have been gummed up because today I was able to tighten it up a bit more and spun the cable with a drill... viola... needle movement. Now if the rain would let up, I could enjoy the fruits of my labor...
-paul

My speedo stopped working on the trip down to Donnington. Full marks to the NOC as Neil had the parts available in the NOC van at Donnington. We also fixed a commando with a dead coil using parts bought from the van.

Investigating the failure we found the square drive end on the old cable was smaller than the square hole in the old drive gearbox, and the drive's square hole had worn just enough such that it didn't have enough grip to turn the cable. The new cable was a good snug fit and worked perfectly in the old drive. Now I have spare drive, but as they're made of chocolate its worth keeping.

Advise anybody with probs to check the cable fit.

t is nice to have a clean, smooth working speedo.

I took the speedo drive and cable off years ago and just go by the tach. Life is simpler,no lubing, erratic needle display, etc

but then, I also eliminated all the little warning lights on the headlamp, took turn signals off, very little can go wrong nowadays ......................