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yorkshire_spam

Spitfire Speedo issue

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After hibernating for a few months over winter (and getting the diff rebuilt) I took the Spitfire for a thrash over the moors to the CT P+P monthly meeting on Friday night.

The speedo starts fine.... but gets to somewhere between 20 and 30 mph and won't go any higher no matter how fast the car is actually going....

Any ideas? Speedo itself? cable? Speedo angle drive? Gearbox output?

 

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Does the odometer work normally - or does it give up at the same point?

If the odo gives up at the same point then I'd suspect slippage in the drive somewhere (drive gear, angle drive or cable).  IF the odo works normally, I reckon the problem is in the speed head itself.

Nick

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On 07/04/2018 at 10:31 PM, yorkshire_spam said:

The speedo starts fine.... but gets to somewhere between 20 and 30 mph and won't go any higher no matter how fast the car is actually going....

 

Mine has just started doing something similar, but I get to around 60mph and then starts to drop back even though road speed is increasing, lift off the gas a bit and it increases, all a bit odd. This is on a Speedo that was fully refurbed and calibrated 18 months ago, so will likely be going back....

Darren

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I've once had an issue with an angle drive where the drive stub that goes into the gearbox was spinning inside the gear in the angle drive (they are a friction fit).  This is why I asked about the odometer.

Nick

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So I finally got around to testing this, I did a run last night on the way back from CT Pendle and Pennine meeting, the GPS measured 9.2 miles, the odometer 9.4 miles. So the odometer is not giving up when the speedo does. (Roughly half that distance was at 70ish MPH with the speedo showing around 40mph)

On 4/8/2018 at 9:51 AM, Nick Jones said:

If the odo gives up at the same point then I'd suspect slippage in the drive somewhere (drive gear, angle drive or cable).  IF the odo works normally, I reckon the problem is in the speed head itself.

 

Looks like it's the speed head!

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Well.... I removed the speedo and stripped it down. No signs of any issues. :confused:

I cleaned it, lubricated it and re-assembled it. I'll refit it and retest it when I get chance.

 

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So I refitted the speedo and took it for a test run yesterday, same problem.

I re-stripped it AND the spare I have to compare.

I've set the spare to be the same odo reading as the original, just in case I need to press the spare into service.

One thing I noticed, with the mechanism in the case the "drag cup" seems to be binding/rubbing on something, with the mechanism out of the case it seems to be completely free.

Further investigation required.

 

DSC_1240.JPG

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1 hour ago, rustbuckit2011 said:

Err..

Why dont you just fit the spare? That IS what it is for isnt it?

 

Yeah, that's what I'll do now. I've swapped the faces over (I'm not a big fan of the "lavender" coloured KPH numbers that the spare had.)

Once the spare is in I'll re-re-strip the original and see if I can figure it out.

Setting the tumblers on the odo is a right pain in the bum!

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7 hours ago, yorkshire_spam said:

Setting the tumblers on the odo is a right pain in the bum!

There is a knack to it, and you need a set of those watch-mending screwdrivers.  I usually acquire the knack just as I'm finishing, then have plenty of time to forget it before the next time.

Nick

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12 hours ago, Nick Jones said:

There is a knack to it, and you need a set of those watch-mending screwdrivers.  I usually acquire the knack just as I'm finishing, then have plenty of time to forget it before the next time.

Nick

After a good few attempts I settled on assembling it all on the axle but out of the unit, then using masking tape to hold it all together, remove the axle and re-fit to the assembly. Yeah, I wish I could find my jewelers screwdrivers, they are "in the garage somewhere". 

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