44 replies to this topic

[rodomo]

There have been a few threads lately regarding speedo faults so I thought I'd put something together that might give a bit of an insight?

(to be honest, i've been nagged into this )

If you think your speedo is reading faster than your car is going, OR, if you think your speedo is reading slower than your going L@@K HERE:
http://codes.oldholden.com/Speedo/

This thread is more to do with other speedo faults/failures.

This pic identifys the difference between your speedo and your odometer.
This speedo is Commodore (no Torana speedo was harmed during the production of this thread)as sometimes people might say my speedo isn't working when in fact it is, but the odometer isn't.
Also shown is a trip meter.



So..............
Now that the glossery and terms are out of the way, we'll start at the source.
This is the output shaft of an Aussie 4 speed. You will see the hole in the shaft that drives the clip for the speedo gear. This shaft also drives your tail shaft.



The speedo drive gear clip is made from spring steel.



It fits into the hole in the output shaft.



And the clip drives the plastic speedo drive gear. The splines you can see in the gear are just to let the gear slide over the splines in the shaft, they do not drive the gear, only the clip does.



So here is the output shaft, driving the clip which drives the gear. These are all housed in the extension housing.



The drive gear drives the driven gear which drives the damn cable.
Driven gear is blue in this instance but there are other colours as well as different coloured drive gears.



Tomorrow, the damn cable, which is the most common reason for most speedo faults.

Edited by rodomo, 17 June 2010 - 01:09 AM.

[76lxhatch]

This speedo is Commodore as sometimes people might say my speedo isn't working when in fact it is, but the odometer isn't.

And we know that the odo and trip in almost every early Commodore ever made stopped around 200k because they stripped one side of the stupid worm gear...

[MRLXSS]

Very interesting! Thanks Mr Dammit!

[rodomo]

THE DAMN CABLE

I say that because as mentioned above, it is the cause of most speedo faults.
The plastic gears and the clip drive the cable so it stands to reason if any of those parts fail it is because there has been too much load on them driving the damn cable.

If ever you have to replace any of those parts, as part of the job, I would remove the cable from the car, inspect, clean, lubricate refit or replace it.

This cable was recently removed from a LC. The inner cable was broken at this kink near the speedo head.



Here is a recent thread which tells of this type of kink being common on LC/J if the cable isn't correctly routed.

http://www.gmh-torana.com.au/forums/index.php?showtopic=46456&st=0&p=513321&hl=speedo%20cable&fromsearch=1&#entry513321

Another common fault on old cables is eventually the outer sheathing might crack or chaff.
This can allow moisture to enter the cable which will eventually rust the inner cable and outer steel cable. This will also put undue load on the drive gears.



Undue load on the cable can also cause the cable to "whip" while rotating. This means the cable can slow or stop momentarily in a tight spot but then as the cable is still being driven, and therefore wound up, it will "whip" suddenly as it is released, much like a wind up spring would.

This will cause a flicking/jerky needle at the speedo head and you might also hear noises from the cable.

The cable also has a seal where it enters the driven gear. This is to stop gearbox oil from entering the cable. I'm not sure about Torana but I have seen cars leaking oil from the speedo head.

[rodomo]

And we know that the odo and trip in almost every early Commodore ever made stopped around 200k because they stripped one side of the stupid worm gear...

Yes, and the little gears running up the side also split and no longer grip the shaft.

SPEEDO HEAD.



This next pic shows the sacrificial Commodore speedo head apart. The spindle is magnetized and as it rotates, it starts to drag the drum in the same direction magnetically and the needle starts to lift against spring pressure.

The only mechanical link between the spindle and the drum is a tiny spigot that still allows the spindle and drum to move independantly of each other.



The diagram shows a side view. B shows what happens as the spindle and drum bearings wear.
The spindle and drum cock in the bearings and the gap between lessens to a point where the spindle and drum can actually touch. A give away to this initially could be a noise in the speedo head and the needle reading higher than it should or the needle will act very erratically, violently jumping backwards and forwards.



A bit hard to get a clear pic of the needle return spring but they look a bit like this and hide in behind the speedo face.



I've heard that 4cyl Toranas dont have a needle return spring as they struggle to find enough horsepower just to lift the needle?

A couple of fitting tips:
Make sure the square holes in the driven gear and speedo head are clear of any debris before you fit a new cable. If the holes have crap in them, it can compress the inner cable as you tighten the nut at the speedo head. This can put undue load on the inner cable as it will be pushing against the sides of the outer cable.




With a mirror and light, you should be able to see the condition of the drive gear and clip without pulling the extension housing off. Rotate the tailshaft to position the clip into view.



If you have to pull the extension housing off, take care when refitting it to align the reverse gear selector back into the groove on the gear.



Also, use the correct gasket or if you have to cut one, use the same thickness paper as original.
If the paper is too thick, the output shaft can move backwards enough to start synchro or jumping out of top gear issues.

[Statler]

I use Singer sewing machine oil.... just a couple of drops.

[Statler]

For a second there I thought 'speedos' meant the swimmers.....

Pics and stuff????



Good write up mate! Probably be useful to someone, someday...

Weren't you complaining about getting a speeding ticket last week, because [as you claimed] your speedo was reading wrong?

I would say that it's helpfull to you right now!

[Heath]

Oil is probably not actually ideal. I would be recommending a silicone-based lubricant, that is what I used on both my speedo and my clutch cable.

[lcgtr1970]

thanks for posting that info mate. very helpful!

[Collo]

When are you gonna show us how to wind the odo back?

[REDA9X]

Great work to put this together Rodomo, I have pinned it.

[rodomo]

"If ever you have to replace any of those parts, as part of the job, I would remove the cable from the car, inspect, clean, lubricate refit or replace it."


What would you suggest for lubrication?

I would just use engine oil. Wipe it on the inner with an oily rag, not too much.
Graphite powder sounds good too.

[S pack]

"If ever you have to replace any of those parts, as part of the job, I would remove the cable from the car, inspect, clean, lubricate refit or replace it."


What would you suggest for lubrication?

I would just use engine oil. Wipe it on the inner with an oily rag, not too much.
Graphite powder sounds good too.

Extract from GMH service bulletin.
All HOLDEN HQ AND LJ TORANA

At initial assembly of speedometer cable to casing, the lower end of the inner cable is lubricated with grease; usually grease is applied to the lower (transmission) end of the cable and extending approx 20" from the lower end. The upper end does not require initial lubrication and adding lubricant will produce speedo instrument seizure or erratic operation, because the grease will migrate from cable into the instrument.

At the same time, it is recognised that Servicemen investigating cable noise can attribute the condition to lack of lubricant. However, this is not a correct assumption as cable noise results drom routing errors, where the cable is kinked or bent. The act of removing and installing a cable to add lubricant has frequently overcome the noise condition, not because grease was added but simply because cable routing was altered and cable 'run' improved.

The purpose of this item is to caution Servicemen against over lubrication of speedo cables; the lower section of the cable only needs to be lubricated as lubricant applied at the upper sections will enter the head and result in a subsequent speedometer instrument failure.

When investigating speedometer instrument failures, check for the presence of of grease (or oil) at the cable connector. Grease at this area indicates overlubrication of the cable; alternatively the entry of transmission oil at the lower end has forced grease up the cable. Transmission oil at the instrument indicates seal failure at the transmission connection.

It is good practice then, to check for oil at the transmission end of the cable. Always remove grease from the upper two-thirds of the cable to prevent a re-occurance of instrument failure.

[Statler]

If it's bouncing, it is grabbing somewhere.

Check the cable routing.