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Dart sticky speedometer

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John-B
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Dart sticky speedometer

Post by John-B » Mon Jul 08, 2019 7:51 am

Yesterday my speedometer was going up to 60 or 70mph quickly but then sticking there.
It took about five minutes to go down to 40mph and stick there. Eventually it returned to near zero when I stopped.
I'm pretty sure the cable is OK and that the speedo needle is sticking. Is there any way to cure this without taking the instrument out?
Next time I drive the car I'll change speed a lot to see if it loosens up. I drive the car at least every week all through the year so the speedo does get regular exercise.

silverdart
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Re: Dart sticky speedometer

Post by silverdart » Mon Jul 08, 2019 10:34 am

Very doubtful but, removal is very simple. Just disconnect the cable, pull out the ign. and h/light bulb holders and then by undoing the 2 thumb nuts the speedo can be removed.
Carefully prise off the chrome rim and then remove the screws holding the back on to get to the mechanism.
I would think a small amount of WD40 may do the trick.

Dave.

Christopher Storey
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Re: Dart sticky speedometer

Post by Christopher Storey » Mon Jul 08, 2019 11:02 am

I agree that taking the instrument apart is the way forward ( although it is possible that just releasing the cable connector perhaps half a turn might do the trick . I don't like the idea of WD40 which may leave a deposit although you could give it a try . I prefer to use switch cleaner which gets rid of gunge without leaving anything behind

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Re: Dart sticky speedometer

Post by John-B » Mon Jul 08, 2019 11:24 am

OK. I'll try to get it out but I hate bending backwards under the dashboard! :(

Sydsmith
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Re: Dart sticky speedometer

Post by Sydsmith » Mon Jul 08, 2019 1:17 pm

John The problem is very unlikely to be cable, the speedo would not stick, it may move around erratically if there was a cable issue but not stick.

WD40 is a definite NO, it is far too heavy for the mechanism and will clog it up.

You need watch or instrument oil in tiny quantity on the bearings, but lubricating a speedo needs very careful consideration.

Cleaning fluid will free off old oil and congealed gunge and clean the mechanism which may work for some time after, but you will also remove all lubrication from the mechanism which can be damaging long term.

The remedy is to clean the mechanism and re-lubricate it with a tiny amount of instrument or watch oil, given the price SP250 speedos go for these days, probably best left to a specialist. Syd

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Re: Dart sticky speedometer

Post by Sydsmith » Mon Jul 08, 2019 1:20 pm

Should have said be careful some cleaning fluids attack some plastics.

csm1406
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Re: Dart sticky speedometer

Post by csm1406 » Mon Jul 08, 2019 6:19 pm

Hi
Just had a new cable fitted & the fellow who did it said that the problem was not cable but the Right angle drive unit that comes out of the gearbox - or in my case the overdrive - It was in a bad way & I thought I would have trouble finding another - not so - Barry Thorne has them in stock - I purchased one & had it fitted & now all Ok. Out of interest the unit Barry supplied had fitting instructions that indicated that a spacer washer was required in the drive unit to avoid it binding & causing a problem . I have the instructions so if anyone wants a copy I can send it.
This may not be your problem but worth a look.

Good luck. I do have a spare speedo so if you want to check yours against this you are welcome to borrow it.

Cameron

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John-B
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Re: Dart sticky speedometer

Post by John-B » Mon Jul 08, 2019 7:17 pm

Thanks, Cameron. My cable was new five years ago but it might have got loose somehow.
I think it's more likely to be the instrument itself but it may be a while before I get it out for a close look.
I can judge the speed quite accurately from the rev. counter in top gear where the needle is always at the same angle in both instruments!

csm1406
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Re: Dart sticky speedometer

Post by csm1406 » Mon Jul 08, 2019 8:54 pm

Hi again
My speedo worked OK but was always erratic - The problem was with the Right angle drive which over the years with a bit of pressure on it caused the problem. Many of these units probably work fine for years - with my one it was definately faulty and the speedo now is solid - may be worth checking. If you want a copy of the instruction sheet - I can send it to you - may be worth having for future reference.

Cameron

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