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Gt6 Over Reading Erratic Speedo


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Hi all

Been using the Gt6 a bit more of late but will need to do something with the Speedo accuracy. 30 mph is close to the correct speed but will then bounce to 35mph, sometimes to 40mph and then back. Don't think it is the cable, got a feeling it's the Speedo. Think the price to recon is probably similar to a new after market Speedo.

Anybody had any success with a DIY repair. Short term I may get a cheap eBay digital dash top Speedo to make sure I stay on the right side, speed/average speed camera heaven where I live, until I can rely on the cars Speedo.

Was thinking ahead as I have a 2.5 to fit to the car at some point, with the option to fit an OD saloon box, if and when the D type gt6 box gives up. Knowing the mods envolved maybe now is the time to fit an after market Speedo that runs off the prop.

What's your thoughts?

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5 hours ago, Mark said:

Anybody had any success with a DIY repair.

I've had mixed results after taking a few apart, either totally killed them or had partial success doing something trivial. Is yours an occasional bounce rather than the usual wobble behaviour? My rev clock started doing an occasional flick, which gradually deteriorated until it was doing it constantly so got disconnected and replaced. I presume something picked up between the spinning magnet and cup part, and maybe it would have been possible to intervene earlier and save it. Or maybe not...

Cheap ones do come up on Ebay but obviously a gamble. I ended up buying 4 or 5 clocks to get 2 that work correctly. Your mileage may vary, if you'll pardon the pun.

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Renewed Speedo cable, now a silky smooth reading, so you were all right. I can now determine it's over reading by almost exactly 10mph compared to GPS, throughout the range, tested up to 60mph actual speed. 

OD gearbox, 3.89 diff 13" wheels. Pretty sure it's the original OD Speedo, but need to check as I think they are different to the non OD Speedo. 

Forgot how tight it is under the dash to get to the Speedo cable on a gt6 compared to a Vitesse. Found it easier to remove the speedo clamps and pull the gauge out from thd front of the dash, to get to the cable.

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Mark--10 MPH off over the range is an offset error.  It can usually be corrected by resetting the pointer on its spindle. Its a fiddly job, though, and a little risky.  Might be best to just do the continuous mental correction.

Ed

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2 hours ago, ed_h said:

It can usually be corrected by resetting the pointer on its spindle.

Thats a good idea :yes: Forgot about that. May give that a try.

I had to do something similar changing a speedo dial face on a mazda Eunos import from kph to mph.

Thanks Ed.

 

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2 hours ago, ed_h said:

-10 MPH off over the range is an offset error.  It can usually be corrected by resetting the pointer on its spindle

+1, it is a bit fiddly but one of the 'trivial' fixes I managed on my speedo. If you take the gauge out and remove the bezel, glass and then rear housing it's not too tricky. Hold the drag cup part still with the pointer at some speed e.g. 20mph, then just push the pointer back to the desired position of 10mph

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3 hours ago, PeteStupps said:

+1, it is a bit fiddly but one of the 'trivial' fixes I managed on my speedo. If you take the gauge out and remove the bezel, glass and then rear housing it's not too tricky. Hold the drag cup part still with the pointer at some speed e.g. 20mph, then just push the pointer back to the desired position of 10mph

I think the first thing I'd try is to put the pointer back at the factory setting.  There is a tiny white dot on the instrument face just below the pointer stop.  Remove the pointer and let the spindle come to rest.  Push on the pointer so that it is pointing at the dot. Retract the stop and move the pointer past it.  Release the stop. and the pointer should bear lightly against the stop.  This sets the proper preload for the pointer spring.

Ed

[img]http://bullfire.net/TR6/TR6-40/SDC12005a.JPG[/img]

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3 hours ago, ed_h said:

I think the first thing I'd try is to put the pointer back at the factory setting.  There is a tiny white dot on the instrument face just below the pointer stop.  Remove the pointer and let the spindle come to rest.  Push on the pointer so that it is pointing at the dot. Retract the stop and move the pointer past it.  Release the stop. and the pointer should bear lightly against the stop.  This sets the proper preload for the pointer spring.

Ed

[img]http://bullfire.net/TR6/TR6-40/SDC12005a.JPG[/img]

Looking at your picture try Ed's method first as it looks like your pointer is not on the 'dots'.

As for editing your own posts. Click on the three dots top right of your post and it will give you a drop down menu with edit in there

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2 hours ago, Escadrille Ecosse said:

Looking at your picture try Ed's method first as it looks like your pointer is not on the 'dots'.

That's not my Speedo, that's Eds post.

Thanks for all the info, I'll give that a try today. 

Speedo has to come out again anyway, just discovered no indicators, thought I could see a spare green wire with no home hanging up there :ohmy:. Need some new glasses.

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4 hours ago, Mark said:

Speedo has to come out again anyway

:sad:

I hate fighting with GT6 dash items…. To much stuff in too small an area. Right place and right order both matter and no room for gorilla paws or even medium size hands!

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9 hours ago, Nick Jones said:

The ability to edit posts is a donors perk iirc…..

That appears to be the problem.  I subscribe to maybe half a dozen related forums, and am a paid member of the couple that I use the most, but not Sideways. Yet.

Ed

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  • 2 weeks later...

Managed to have a play with the speedo, but only just been able to get the car up to a range of speeds due a a misfire.

Speedo has been in and out three times, and as mentioned earlier, is a b*gger to get to. Gave up using my eyes, and can now remove and replace in under 10 mins by feel. Took a few hours to get sensation back to my fingers, and to be able to sit up straight again :biggrin:.

Got the Speedo operating consistently through a range of speeds now where the speedo is reading slightly higher than the actual speed, so no fear of inadvertently  speeding, getting caught on camera.

First pic show pointer turned back 10 mph. Second pic shows the white spot, pointer stop removed, pointer sitting close to factory setting as in Eds post.

Been tweaked a couple more times since, to get more accurate readings

 

 

20210829_141001.jpg

20210829_140856.jpg

Edited by Mark
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