Hey guys,
as the title says my speedo is way out. According to GPS around 30km/h at least.

My speedo is this style:



any ideas on how to fix it? is it hard to do?

thanks

speedscreen

i got a speedo correction box off them. you just measure how many rotations on your cable over 10m and the make a box. you screw it onto your gear box, and then the cable into it. corrects the speedo reading if measured correctly, and best of all you can have it altered if you gange diff ratios or rolling diameter of wheels.

The correction box will work if your speedo is off a percentage. For example: 30% off at 100 (30kph), 30% off at 50 (15kph). That is usually caused by fitting larger tires than the stock 12" tires. Or if you have changed the diff ratio.

It won't help if it is off a fixed 30 kph. For that you need to fix the gauge by resetting the needle or swap the speedometer with a good one.

Click Speedometer, see section Speedometer Calibration.

does anyone know what gear i need to run with a ute diff(4.11) and 60a 4 speed box ? when im going 80kms my speedo says im doing 60mph

60mph is 100km correct?

cheers

62 mph = 100 kph
60 mph = 97 kph

60-series Transmission was fitted to A14 & A15 engines. They have a machined speedometer drive gear which cannot be changed. The removable speedometer driven gear can be changed.

Which gear you need depends on the Diff ratio + Tyre diameter.

We can calculate what change you need by your readings:
97/80 = 1.21
So you need a gear that is 1.21 different from the gear you already have. 60 gearboxes came with different gears so we don't know which one you have.

That leaves two unknowns. We only need one of them to figure out which gear you need.
* Rear Tyre size you have
* Speedo driven gear you have

Most (and I haven't pulled apart a datsun one to be up front here) mech speedos are a simple enough gadget. There's a magnet attached to where the cable slots in. when the cable spins, so does the magnet. It is surrounded by a circular 'cage' that is connected to the speedo guage 'needle' or pointer. The magnet never touches the cage, but as it spins, it tries to pull the cage with it, and the needle/pointer swings around the guage. the pointer is spring loaded, so it will return to 0 when there's no movement of the cable/magnet, adn the faster the thing spins, the further it will manage to 'encourage' the pointer around the dial.

And that works pretty well. But the reason I bring it up is that over the years things will wear a little bit, and the magnet (it could also be reversed - the cage spins and the magnet is attached to the pointer, I suppose) - well anyway , the magnet no longer just spins, there's enough play in there (worsened by the cable itself wearing/getting old and trying to magnify this issue) for it to 'wobble' just a little whilst it is spinning. Then instead of just magnetically moving the cage/needle/pointer, it will actualy scrape against it, and it will pull it further than if it was prevented from actual contact with the cage. Then it wobbles back, lets go and it continues.

If it is just a mild wobble, it'll probably smooth out mostly and just give a high reading, but if it gets more severe, you'll experience it grabbing and springing back , and, at higher speeds especially, the speedo needle will jump forward and backward like one of those lie detector needle things..

If it is down to wear (and by this stage - being close to 40 years old, it's a strong possibility) then the speedo will tend to be somewhat accurate at lower speeds, but worsen as the cable rpm and 'wobble' get worse, and read higher and higher.

What this means is that the corrector box might 'fix' it for 100km/h but it would no longer be accurate at 60km/h (or whatever roadspeeds you choose, and for km/h or mph, whichever is being displayed).

To 'fix' this it's likely possible that an instrument maker/repairer (and there are a couple in Melbourne, or used to be, and they mostly do resto work for rarer musclecar era fords and various other old british cars and so forthe) could make/fit a plastic or bronze bush to have the magnet/cage spinning without any wobble (but still spinning freely without binding of course). The problem I suspect would be the price - even if you remove the speedo from the dash and give it to them, so there's no extra fitting charges, it still won't be cheap.

As to exactly how much - nfi, but if you happened to have a spare speedo, you could probably take it apart and see how it works, and if a diy re-bushing might be possible. If at all possible, find a completley broken speedo, and pull that apart, that way you won't lose any sleep if you break/damage it further whilst learning/finding out how they are taken apart 'properly' and what can be done to fix them.

After all that, the pointer/cage is spring loaded, and it will probably be a 'clock' type wound flat band of spring steel. For sure over the years it will have lost some tension, so even once you fixed the 'wobble' issue (if it _is_ in fact an issue, which isn't 100% certain) - well then you might also need to increase the spring preload just a little to bring the indicated speed back to where it should be. As to how easy that would be on this particular speedo, I don't know, but it _should_ be doable.

whoa awesome reply John. It does sit smoothly at speeds and has very little wobble if any. I think the error is different from lower speeds to higher speeds. Yea few people have said too hard dont worry about it but i find it really annoying

What i'm thinking about doing (pretty dodgy I know) is work out where each speed is on the dash then print out new numbers for it and stick it over the top of the old.

hehe I have done that to my sedan, printed out a new gauge face. The only problem with it is that the odometer still reads incorrectly by a lot.

The repair/adjustment/calibration is discussed in our club article: Speedometer Calibration

if you want dodgey, silicon a magnet onto the inside of your drivers side wheel and then hook up a bike Speedo. Works a treat as they are easily adjustable. Did it on two previous cars additional to the car Speedo. You can even get back lot ones.

I know one other member that had done it too. I did it originally on mini in the late 1990s to check the Speedo calibration. Left one as a permanent fixture in my old inre so I wouldn't get speeding fines as it was so accurate. Might do it again lol.

good idea unfamillia.
I wonder if you could do that and some home hook the output up the the factory speedo...