all speedo heads are not the same..

B-Hive · Post by **B-Hive** » Thu Dec 29, 2011 10:50 am

Set about replacing my speedo head in the GT today as it was both very noisy (tick,tick, tick) and the odometer didnt work either....at hand were several Mk2 speedo heads that presented identically to the one i was removing...

Made my choice and after a half day's work, the "new" speedo head was installed..

Result not good.. even though it was now quiet, new speed over read by 10-20%...

Upon closer examination of the heads i noticed that that spring on the MK2 head was lighter and 6 coils against the Mk1 slightly heavier copper and 7 coils ..(ie lighter spring on the mk2 head), although otherwise visually identical..

As there are so few mk1 owners here this post is prob not that important but thought I'd share the information never the less...

So tomorrow... pull the whole lot out and start again with the original speedo rebuilt with parts (other than spring) from the newer heads!!

Anyone know a good shrink??

Gibbo2286 · Post by **Gibbo2286** » Thu Dec 29, 2011 11:18 am

I'm not sure about this still being the case but the old Smiths and Jaeger speedos used to have a number in very small print on the face near the centre spindle which had to match on the replacement, it referred to the different gear ratios across the range.

B-Hive · Post by **B-Hive** » Fri Dec 30, 2011 6:56 am

Unfortunately my theory didnt hold up..

"Original" speedo put back today after installing a worm gear that is responsible for the odometre, as well as an alternative magnet that didn't scrape the chamber..(cause of the tick tick)..

but far from being accurate..it is now worse than ever...and now (as the odo is moving)... all the numbers are in line but dont line up properly within the speedo fascia . (They have kinda drifted 10% up into the fascia frame)

A classic sign of speedo tampering on two fronts, the worst being to me that the car may not have a MK1 GT speedo...As I'm imagining that they are almost impossible to get hold of.. Previous reply post (Gibbo2286) reminded me that the GT has a bespoke gear box. So all i can think is that when i had the speedo connected before I was more focussed on how things were running, and not getting a ticket for driving an unregistered car when in the process of giving her a test run

I'll check tonight to see if I can see any difference between the magnets

Well at least its accurate when its stopped!!!

Post by **Tim Leech** » Fri Dec 30, 2011 4:26 pm

I have a spare speedo/binnacle from a Mk1 GT with grey surround, I imagine that its no use being in MPH?

JayW · Post by **JayW** » Fri Dec 30, 2011 8:55 pm

It may also assist you to know there is more than 1 speedo drive type at the gearbox end (three i believe), it may just be a case of matching your head to the correct drive gear.

JayW · Post by **JayW** » Fri Dec 30, 2011 8:55 pm

It may also assist you to know there is more than 1 speedo drive type at the gearbox end (three i believe), it may just be a case of matching your head to the correct drive gear.

B-Hive · Post by **B-Hive** » Sat Dec 31, 2011 2:17 am

Roverman wrote:I have a spare speedo/binnacle from a Mk1 GT with grey surround, I imagine that its no use being in MPH?

Thanks but yeah would like to keep it in KM/h if i can!!

BTW.. I just noticed that your GT has been SORNED ,,how in the hell did that happen and when?

Happy New Year everyone!!! Cue "Auld Lang Syne"

B-Hive · Post by **B-Hive** » Sat Dec 31, 2011 5:36 am

Just "thinking out loud" now..

Fortunately, as i have now done it several times, removing the instrument panel is a doddle..

So, original speedo with swapped worm drive back in place,, the only other difference being an identical magnet/shaft. This one does not baulk in its chamber so nice and quiet...

Did an experiment and discovered that the odometer is spot on,,,but the speedo is between 15 and 20k's over reading.

I seriously dont recall it being out at all prior to removing it..

My interim solution is as crude as it is simple...I have simply repositioned the needle at about -15 (below the zero) This seems to work out quite nicely for anything up to 100km/h after that it starts being a little optimistic again.

My only other thought was that with the magnet skimming its chamber that it corrected an inherently very inaccurate speedo head.. So fix one problem and another one appears...how many times have i heard that.. not beyond reality...its the only thing that makes sense here..

And here i was thinking that it would be a simple swap out job

Post by **Tim Leech** » Sat Dec 31, 2011 9:29 am

My GT is sorned as I wont use it in the winter, no point, as I have another car to use, It will be out and about come spring.

Regarding the speedo, mine does have KMH on it, aswell as MPH, you may be able to swop the face off yours to the working of mine?

Mines a 150mph speedo for reference.