SPEEDO STUCK

[Paul M]

Thanks Blacky,
On to it.
Regards, Paul

[MUNDIES]

Thanks all for your varied & interesting replies. After many attempts to fix it, I'll give it one more go trying your various thoughts (except taking the auto out). May have to have a serious look at 'howards' for a fix. I am getting used to looking at the speedo and seeing that I'm flying along at 90mph but only feels like 35mph.
Now tell me why you dont like Mondays (Mundies)
"The silicon chip inside my head has switched overload"

[fingers]

Thanks all for your varied & interesting replies. After many attempts to fix it, I'll give it one more go trying your various thoughts (except taking the auto out). May have to have a serious look at 'howards' for a fix. I am getting used to looking at the speedo and seeing that I'm flying along at 90mph but only feels like 35mph.
Now tell me why you dont like Mondays (Mundies)
"The silicon chip inside my head has switched overload"

.>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Use the KISS system mate ......Try another speed .......I will going to sydney some time soon (within the next week ) if you like, I will drop in an other speedo for you to try .....Let
me know if you can meet me on the highway somewhere ............Fingers

[Craig Allardyce]

I've had this problem before and found it to be a combination of a number of things, one being a loose nut that holds the speedo head in its casing, and the weight of the cable can force the drive unit to cock on an angle if the cable isn't kept reasonably straight out the back. This causes some misalignment insde the speedo between the spinning magnet and the cup that encases it. Also I found dirt and crap (very minor) stuck to the magnet inside the speedo unit. The magnet spins inside a pressed steel cup that drives the orange disc. There is very little clearance between both of them. If any stuff sticks to the magnet you'll find the disc will stick to the magnet when static or the disc will read erratic or way too fast.

[MUNDIES]

Thanks Fingers - your'e worth bottling. I have got another speedo on hand and will try this.Thanks very much for the offer.
Also Craig may have put me onto something with the 'miss alignment' of the cable also.
The plot thickens - will keep you all informed as to outcome.

[Devilrod]

The other thing to do is jack the car up and put on stands then disconnect the speedo and run the car upto 10 or 20mph and see if it turns. Likewise if you have a speedo cable spare cut the end off and place it in a drill and try that in the back of the speedo.

[Paul M]

Found Kynan's problem there was no speedo drive gear installed! The drill on the cable was a good idea to test that the rest was OK.
All fixed & working well. Thats everybody for your help.
Regards, Paul

[rosco]

Good work, Paul.... and the price of a driven gear vs what a speedo/auto elec/mech might have charged you....to find the issue and correct it..
I expect you appreciate that the appropriate driven gear should be used - determined by the diff ratio..?

Craig - great advice, have added your comments/suggestions loose-leaf to the "notes" section of my workshop manual...

Perhaps we should start another thread - "How accurate is your speedo?".. with GPS common amongst many of us, it would be interesting to note how different readings are shown. Tyres, modified drive-lines etc would amount to significant variants - but perhaps it might be of some interest to the forum if we stated them together with speed readings at perhaps 35, 50 and 60 mph...?

For example, I have 13" x 4.5" wheels, 185/70 tyres, 3:08 diff - 35 shown as 36, 50 as 54, 60 as 66.
Odometer shows 10.1 m @ 16.09 kms

I suggest a new thread be posted if this is to be persued..

frats,
Rosco

[Craig Allardyce]

Hey Rosco,
here's a spread sheet I did sometime ago that calculates out your speed versus different tyre profiles, gearbox and diff ratios, and engine rpm.
Might be good for the new thread and for those that are wondering what their real speed should be after doing the usual driveline mods.
All you have to do is change the figures in the three lower yellow highlighted cells to whatever your set up is and it will show you road speed versus engine RPM.
The top box details some gearbox ratios if you needed to know what revs/speed in each gear. Tyre profiles at the top right hand corner are relative to 13" wheels only.

Cheers

FB Gearbox-diff calcs.xls

[rosco]

Thanks Craig,
yours parallels one I did when deciding on the diff and box combination back in '83, but then was only in handwritten format - I didn't seize on the opportunity to commit and create a spreadsheet as you have, thanks for offering yours to the forum..

If members response suggests sufficient demand, I'll open a thread and include your attachment - again, thank you Craig..

frats,
Rosco

[MUNDIES]

Thanks for the thoughts folks. Disconnected the speedo - gave it a squirt with WD40 , put it back together again and no luck. So after the silicon chip inside my head switched to overload, I gave it a rest for a few days. After about a week I took the old girl for a spin - and yes you guessed it! my speedo now works. Cant figure it out. I can see no reason, for there is no reason, what reason do you need ? Tell me - why oops getting carried away here. Happy now the bloody thing works.

[Cal]

If it happens again you're better off putting some oil on it, as mine was doing the same and the WD40 worked but didn't last long

[mr bean]

Hi Mundies,
Just read the post, I had a similar problem the other month with the speedo going nuts and screaming it's head off. It wase't the cable but the little shaft that come out of the speedo which conects to a second shaft that turns the milage cogs.
I took the speedo out of my ute, used a socket and cordless drill and corrected the miles, used my original backing plate and glass and put it back together ( a lot of stuffing around ) but so far all good.

Andy