Speedo failure

[rswaffie]

Hi
During the restoration of my 3.8, I fitted a new gearbox angle drive and cable. All was well for 230 miles but then during a blast down the dual carriageway, the speedo and odo stopped working. I stripped out the interior to get to the angle drive (assuming it was either this or a broken cable). Removing the cable from the speedo and the drive from the gbox I found that the angle drive seems ok as the cable turned freely at the speedo end. However, after replacing the cable into the speedo, I found that I could no longer turn the drive spigot. Using a square ended peg, I found that the speedo end drive was quite stiff, although it did operate. I’m guessing it would have been too stiff for the cable to operate.
I’m going to send the speedo to Speedograph to fix, but is there likely to be damage to the angle drive internals given the possible extra strain put on the cable due to the stiff speedo drive?

[christopher storey]

Richard :it's fairly easy to remove the angle drive and check it for wear/looseness/stiffness etc by turning it by hand or in a variable speed drill/lathe . You may need to pry the gearbox to one side a little - I use a piece of 1" X 2" wood - to get withdrawal clearance

[mgcjag]

Hi Richard when you tried to turn the drive in the speedo which way did you turn it.....it operates by turning anticlockwise when viewed from the rear.....Steve

[rswaffie]

Thanks Christopher.
When I took the interior out to get to the angle drive, it turned freely, but only once I’d unscrewed the speedo end. So I’d assumed it was ok and the speedo was the issue.

Thanks Steve
It was anti clockwise.

I just thought that when the car was being driven with the failed speedo, the angle drive would still be trying to turn the inner cable, which would not be able to turn due to stiff operation of the speedo. As the inner cable doesn’t appear twisted or snapped, where would all that torque go? Could it strip the squared ends, the squared connections in the drives?

[MarkRado]

Hi Richard,
now that the speedodrive ist out, I'd take the opportunity to dismantle and check or have it rebuilt or get a new one (C17087=BG2402-02 for the moss box). The short shaft/ cable may be damadged where it is crimped to the gear.
Also see viewtopic.php?t=1601

[rswaffie]

Hi Mark
I do have another new drive from Caerbont but as the other seemed to be ok, I replaced it. If there is still a problem when I get the speedo back from Speedograph, I’ll have to swap it out.

[rswaffie]

So, I have reinstalled the newly refurbished speedo and connected the cable.
Took it out for a test and the speedo worked very smoothly for about 200 yards and then stopped.

Am I correct in thinking that from either end of the cable, I can pull the inner cable out, as it is the outer cable that is held in place at both the g/box drive and speed end? Is the inner cable held in position purely by the fact it is longer that the outer and so is held by ‘force’

I’m guessing I’m going to have to take another look at the g/box drive end (interior out again ) and possibly change the cable in case the ends have become damaged. I’ve got a new drive so may just swap it out as well.

Good news is that I’ve managed to bleed the brakes single handed, using a £12 bleed cable with a non-return valve from Halfords - took half an hour to do rears (fosseway remote bleeds) and fronts and didn’t need to Jack it up or remove wheels. Not done brake bleeding before (done the clutch) so feeling a bit better after the speedo disappointment!

[christopher storey]

No, you can't pull the cable out downwards as there is a plastic lug at the upper end which locates the cable within the outer and prevents it slipping out downwards . I shouldn't take it out at the moment - the first suspect has to be the angle drive, so I would get that off first

[JerryL770]

If you know that the speedo was stiff and is now free, I would suspect the most likely reason for failure now would be a sheared cable. Possibly it knotted enough to drive the mended speedo for a few yards, then parted again.

Can you disconnect both ends and see if one end turns but the other not.

Also, if your inner is too long, it can push up on the rotating part in the speedo and cause that to seize, I believe.

[rswaffie]

Thanks chaps. I’m going to wait for some dry weather and put the car on the drive, get the interior out so I can get to the gbox drive. I can then go through the tests and replace the drive and/or the cable. The cable is the 60” version which I believe is correct for a rhd car with a moss box.

[JerryL770]

The cable is the 60” version which I believe is correct for a rhd car with a moss box.

I don't mean the external length of the whole cable but more specifically the length of the square end which goes into the speedo. If this is too long it can push up the rotating magnet etc., but I think 1st indication of this would probably be a twitching needle.

The plastic stopper at the top of the inner may affect this length, without there being one, the o/a length of the inner cable may affect this. Too long and it's hard up against speedo and drive gear. Too short and speedo may not work at all.

[rswaffie]

Hi,
The speedo end protrudes c3/8”, the other end c6/8”.
This seems to tally with other threads relating to these cables. But with aftermarket items, you never really know until you try it!

[rswaffie]

By way of an update, I now have a working speedo.

Not being able to face removing all the interior to get at the angle drive, I went for the ‘cut a new access hole’ option.

This allowed me enough access through it and the existing rear access hole to get enough purchase to unscrew the drive and run through the tests suggested in an earlier post.

The angle drive had failed so I swapped it for a new one from Caerbont and all now ok.

The new hole was 76mm and a new plug from sng fitted nicely.

[MarkRado]