Adjusted my Speedo with success

[Neilnaz]

Hi all, I decided to start a new topic on this as some of the threads are a little old that I found. Background:

I have a 1971T Targa it has a 915 gearbox from a later car (I am imagining 1975 onwards). The car runs 205/60/R15 tyres. As a result of this possible mis-match the speedometer reads 8-10km/h fast. This mis-read is fairly consistent at all speeds so it isn't merely a gearing issue. I imagine that speedometers are not hugely accurate and an over-read is safer than an under-read.

Anyway, I just decided that I would have a go at changing things. The picture below shows what I did. I haven't taken pictures at every stage.

The result is that I have around a 3-5km/h over-read. I haven't been out and mapped each speed - I was on my own using a speedo app so it wasn't easy/safe to complete a proper check.

When moving the pointer roughly 5degress relative to the shaft, I did lift the pointer so that it sat to the left of the stop point. When I had adjusted the position the pointer still remained pointing at the same angle. The mechanism finds the balance between spring and magnetic polar force. Once adjusted I lifted the end of the pointer to sit just to the right of the stop point.

I am happy with end result though. I thought those with older speedometers might be interested. One thing to bear in mind is that it is easy to cause damage to the needle and/or the mechanism. So tread very carefully.

Cheers, Neil

[Discseven]

Neil... nice speedo work. Am interested in what was it like to get bezel off? Have attempted to remove mine and even with much force... no success.

[Neilnaz]

Hi Discseven, I turned the speedo face down on a cloth on my table and started at one point using a narrow flat-blade screwdriver easing the edge out. Picture explains the process. It took me 30 minutes of easing the metal.

Hope this helps.

Cheers, Neil

[Discseven]

Neil... tried to pry bezel slowly off. Started to scratch housing so stopped.




Put clamps on (one tight and one loose) to increase leverage. Seems like my bezel is frozen on.

[Neilnaz]

Hi Karl that is interesting. I was able to get a narrow flat-blade screwdriver between the bezel and the body. I turned the screwdriver through 90degrees and moved onwards a few mm. Do you have a very narrow blade screwdriver or could you run a knifeblade around first? It was very obvious once I had managed to get the screwdriver blade between the bezel and the body.

Best of luck, Neil

[Discseven]

Know exactly what you're speaking of Neil. That's the way I did it too but again... not working on my speedo. (EDIT: is my temp / pressure gauge--not speedo.) What I've not done yet is apply penetrating oil. So that's next move. Then will try again.

Does your case have the same "small" indent next to bezel?

[Neilnaz]

Hi Karl, my speedo looks very much like your top picture in post #4 but the bottom picture in the same post (with the clamps) shows the back of the case to be different. Mine is an all-in-one with no back-plate screwed on like yours.

I would have thought that you should be able to do the same as I have done. I followed previous advice about getting the bezel off. Maybe apply a little more force? There seems to be a gap between bezel edge and case that should enable the screwdriver to purchase?

Best of luck, Neil

[Discseven]

Yup... others have removed bezel as we're discussing with no problem. I've got stuck one. Mine does have screws in back... but want to access face plate & needle so must get in from face side. Will apply penetrating oil and see what happens. May be some time before I get to this as am in process of rebuilding my Targa top. Thanks for your input Neil.

[techweenie]

Back in the bad old days, we used to pull out the speedometer and feel the back edge of the bezel for disturbance if we thought the odo had been rolled back.

I think the bezel is some kind of brass alloy - it will tolerate removal and re-installation. The speedometer shop specialists use something like a can opener with a roller to reinstall.

[Hil911]

There are a few discussions about this with regard to changing the glass and removing the interior misting. I did all my gauges.

I don't see the bezel sticking on unless it was literally glued. It's held on only by the folded back edge with no real "sleeving". Mine was apparently aluminium or it might have been aluminum.

It's hard to get them off without scratching the back edge but it is hidden once installed and a black marker does wonders.

Oh - I had to lift the edge more than half the way around the gauge before the bezel would come off.