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Wondering if Spit has the right diff fitted?


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1 minute ago, johny said:

Cliff, I would seriously recommend downloading a free manual from that site as this information is common to many cars and would help you learn a lot..... 

That sounds like a good idea. Didn't realise it was available as only joined last week. 

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Ha! Cliffs post count is up to 56 already.  I'm following this as I have not found my diff number yet and my phone was going buzz, buzz buzz, buzz.....as they all came in!

Handy to know where it is for us 'newbies' :)

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52 minutes ago, Jeffds1360 said:

Ha! Cliffs post count is up to 56 already.  I'm following this as I have not found my diff number yet and my phone was going buzz, buzz buzz, buzz.....as they all came in!

Handy to know where it is for us 'newbies' :)

Found the delete option now 👍. Think the volume of my posting is mainly because I have raised 3 separate issues in different threads and all have had quite a lot of responses, all very informative 🙂

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Just to update, I have tested again with GPS and Speedo is definitely reporting about 15% slower than actual at all speeds. 

Dividing the GPS speed by the reported RPM gives approx 18.5mph/1000rpm which I believe is correct for the car.

And if my maths aren't letting me down, I calculate that if the diff was about 4.1 the Speedo reading would be correct. So I think something has been fitted from an older car that had a diff with that sort of ratio. 

Happy to have got to the bottom of this now and explains why the test runs made before I found this seemed fast for the speed I thought I was driving at. Thought it was just being so low to the ground and all the noise lol

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a  4.11:1 with 185/70 13 gives 16.8 per 1000    ie 503  at 3000

a 3.63:1  should give you  19.01  per 1000  ie 57 at 3000

then it depends how calibrated the rev counter is  your gps gives the actual flat road speed but you are still going to guess the diff

as both diff and rev counter can be way out 

Pete

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Is a 3.89 18 then pete? , if the speedo is under reading it needs to be fixed. No mater what the ratio. Otherwise your in danger of speeding with all the danger that could entail.

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yes  3.89:1  gives 17,74  per 1000

sorry it needs a physical check of what diff and a calibrated rev counter  

with any equation  you need 2 of the 3 in place   not 1 of the 3 to get a result 

or youre just back to guessing or assuming    neither are  whats real 

you wont get a ratio result from a known speed and an unkown rev counter 

Pete

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Agreed. I know the tacho may not be accurate and besides, I'm only glancing at it so in reality, it was roughly 3000 rpm. Likewise, the GPS was varying between 54 & 56 (which of course could have been 56.9)

But all this has alleviated my main concern that I had a low ratio diff fitted and no overdrive which I would find a problem at cruising speeds.

I will identify the diff in due course but as suggested, sorting the Speedo is more urgent. Although I can mount the GPS Speedo from my pedal bike temporarily.

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23 hours ago, johny said:

I think we've agreed on here that the variation for diff ratios isnt corrected in the gearbox but in the actual speedo.

The correct one for yours should show 1000 (revs/mile) on the face...

Pic of my speedo attached. So does this mean it's the correct Speedo?

IMG_20210418_165427_750.jpg

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On 18/04/2021 at 16:57, cliff.b said:

Pic of my speedo attached. So does this mean it's the correct Speedo?

IMG_20210418_165427_750.jpg

What do the snt -62211/125 1000 relate to? Would help identifying my ones, also the makes triumphs used?

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all of the single rail gearbox cars had 1000 turns per mile speedos and they had different speedo drive gears for the different ratios so you could have a single rail box with the drive from a dolomite or something else. 

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41 minutes ago, DanMi said:

all of the single rail gearbox cars had 1000 turns per mile speedos and they had different speedo drive gears for the different ratios so you could have a single rail box with the drive from a dolomite or something else. 

Aha, I noticed yesterday that the engine block number is from a Dolomite, so guess the gearbox could be as well. Did Dolomites have 4.11 diffs?

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1 hour ago, clive said:

later dolly 1500 had 3.63. Just to add confusion.

Oh well, guess it will remain a mystery until I get to inspect everything more closely. 

Incidentally, although off topic from my original question, are there any differences between the Dolomite 1500TC engine and the Spit?

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