Does angone have any pictures of the back of the speedo which shows the calibration pots and which one does what - I need to adjust mine but I'm not touching it unless I know which one does what!

 

Thanks in advance.

IIRC there is only one.

If there is only the one pot will it let me calibrate a speedo that consistently shows 5mph too low on the dial? IE when showing 25 I'm actually doing 30.

no, recalibrating using the pot will adjust the characteristic.

if the speedo shows a speed that is consistently a few ml/km off (as in you case) it's just a matter of adjusting the needle.

 

-Eric

If there is only the one pot will it let me calibrate a speedo that consistently shows 5mph too low on the dial? IE when showing 25 I'm actually doing 30.

 

I think the question is: is your speed always out by 5mph, or is it out by 5mph @ 30 and 10mph @ 60?

 

Moving the needle will resolve the former, and I imagine tweaking the pot will do the latter.

 

I'll be sorting my speedo out in the next day or 2, and I'll let you know what I find, with pictures where appropriate!

Its deffo 5 miles out all over the range.

The U.K. speedo that I looked at has two pots, one for adjusting the needle position (i.e. if it's out by say 5MPH over the range) and one for adjusting the deflection(i.e. if it's O.K. at 30MPH but 5MPH out at 100).

So - to clear up the confusion - can anyone supply a picture?

(I'm sure someone must have pics and know all this for sure, but nothing's been posted so far so I'll have a go...)

 

Not yet, but I took the rest of my dash apart at lunchtime and took some pics with my phone. Not great but they'll do the job and I'll post them this evening, unless anyone beats me to it.

 

Point of (non :) ) interest- It looks like my speedo module has been replaced at some point- the PCB is shiny and green, whereas the revs module looks old and brown.

 

If you imagine the speedo facing directly away from you, there are 2 pots on top of the speedo PCB which face upwards. The one on the left is marked "20k" and by inspection of the PCB is wired in series with R10, so it should be this one which alters the scale. The one on the right is marked "2k", and I imagine this alters the offset.

 

Tomorrow I'll mostly be borrowing my mate's GPS widget to check it out.

Sounds good Mark - post up how you get on.

Point of (non :) ) interest- It looks like my speedo module has been replaced at some point- the PCB is shiny and green, whereas the revs module looks old and brown.

 

Old story (must be true, it happened to a friend of a friend):

 

Back in the 70s a car nut buys a Cortina 2000E as a cheap classic. He lavishes care and attention on it, best oil, regularly changed, top class maintenance, drives carefully - as I said, a real car nut who turns up at club events and enters concours!

 

After 10 years of the best TLC he decides to sell it on BUT having looked after it so well, he thinks it'll never get what it's worth thanks to the mileage. So he wrestles with his conscience and decides to knock a few thou off the mileage with a little judicious clocking. (only a few thou, honest mate)

 

So he gets the speedo out, turns it round and on the back there is a sticker.....

 

 

 

 

"Oh no, not again"

 

hehe

Gio- :rofl: Is there a joke board on this forum? Dont think there is yet...

 

Alrighty then- these are the pics of my speedo module. They're taken looking straight down, with the speedo facing away (or up on the picture... oh you'll work it out... :slap: )

 

A small philips screwdriver will turn the pots, and if you look closely you'll see there are 2 dots on the bit you turn so you know where it's actually pointing.

 

I'll be drilling a hole or two in the speedo housing so I can drive along with a screwdriver in the pot so I can tweak-on-the-move. Cunning huh? :D

 

To be continued...

Tell you what... this time I'll remember to attach the pics... :xxx:

When you have drilled the holes post a pic so I can see where you did them - that swould be ideal so I dont have to dismantle the whole housing!!!! Which pot does what in the picture?

Also - just to be cheeky - If I wanted to change the speedo to UK speeds by using the resistor method, where and how is that accomplished? Pictures speak a thousand words as they say, and not being an electrician, I love pictures!

If I were you I'd take the whole thing to bits- otherwise, to drill through the clock housing you'd need to take the windscreen out (bit excessive don't you think?! :rofl: ) Secondly if you leave the speedo module in situ there's the risk of damaging components when the bit pops through.

 

Steve-o posted some good instructions on how to dismantle the binnacle. :bow: (and if you want to change the resistor you'll need to do this anyway) http://www.300zx.co.uk/forums/showpost.php?p=297744&postcount=3

 

I'd add a point:

 

Step 5.5- it helps if you remove the panel under the steering wheel before step 6, as I hate unclipping things when you can't see what the state the clip's in!

 

I'll go into the resistor change when I've taken some more pics...

Ok. Rested a screwdriver in the scale pot and had a quick dash up and down the local A-road. My mate in the passenger seat read out GPS speed while I drove to the speedo and gave the screwdriver a twist as necessary.

 

After 5 mins I had it so at 70mph the GPS speed would fluctuate between 69.0 and 69.5mph, so I'm happy with that. :dance:

 

I didn't touch the other pot as I didn't need to, so I don't know for sure that it does the offset...

I've had the binnacle and the clister out before so I'm OK with that - which pot did you adjust for the scale?

 

All good info so far and we've managed to make this post quite long now!

LOL probably boring the pants of anyone else reading it all! :tongue:

 

Ok, with reference to my earlier photo it's the one on the left that does the scale and the one on the right that (allegedly) does the offset. Attached are the 1000 words, with the scale pot circled.

Hmmm, I'm certain that my speedo only had one pot., now I'm going to have to take it apart to be certain. I do know that it's a UK speedo, but not sure whether it's Series I or II ....

Ok, the last bits...

 

5 attached pics showing:

 

1 The dial-side of the speedo PCB. The small area in the middle where it says "R10" next to a squiggle is where the old resistor was. Note the artistic new curve incorporated into the speedo dial on the right... :(

 

2 The rear of the speedo PCB. Near the top, in the middle, you can see the new light-blue resistor which I found was much easier to mount on the rear, but then I'm no soldering expert (which explains the modification to the dial :x: ).

 

3 The location of the holes in the clock mounting. The scale pot is the one on the left as you look at it.

 

4 Ditto with the clock assembly in situ.

 

5 How it looked like from the dial side, with the screwdriver in tweaking position (NB scale pot is now the one on the right as you look at it).

 

All tickety-boo :dance: