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GT6 3.27 Diff Wanted


Nigel Clark
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2 hours ago, Nigel Clark said:

The Dolomite 1850 has identical ratios to the GT6/Vitesse 2 litre box.

That's what I have Nigel. Personally I find the close-ratio box and 3.27 diff gives a tall first gear on my 2.5PI Spit. But the high speed cruising (with O/D) is great! The tall first gear probably gives the diff an easier time, but if I was to have the box re-built I would have the wide ratios from a 1500 Spit. I think Triumph knew a thing or two and realised wider ratios were more appropriate for their torquey, less revvy, stroked engines. Or maybe torquey engines and wide ratio boxes simply suit my driving style better? A lot of this is down to personal taste and driving style.

Cheers, Richard

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I'm still a bit torn...

I really like the idea of relaxed cruising with the 3.27 final drive and reckon that the 2.5 litre engine with its long stroke and ample torque will pull the high 1st gear.

Then again, as my thought process goes, 3.63 diffs are more widely available. And this ratio would give better acceleration through intermediate gears, with reasonable cruising in overdrive.

The only certainty is that a 3.89 final drive in a GT6 with a bigger engine is too low.

Decisions, decisions!

Nigel

 

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Was out in the GT6 this morning in the rain so didn't want to go too fast due to lying water and poor visibility... I was watching both speedo and tacho but in 4th O/D I was doing an indicated 56 - 58 at 2000 rpm... I think the speedo requires recalibrating!

(J-type O/D from Dolomite 1850 - is that 25 or 28%?)

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25 minutes ago, Colin Lindsay said:

Was out in the GT6 this morning in the rain so didn't want to go too fast due to lying water and poor visibility... I was watching both speedo and tacho but in 4th O/D I was doing an indicated 56 - 58 at 2000 rpm... I think the speedo requires recalibrating!

(J-type O/D from Dolomite 1850 - is that 25 or 28%?)

The J type from an 1850 Dolomite should be 25%.

Nigel

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2 hours ago, Colin Lindsay said:

Was out in the GT6 this morning in the rain so didn't want to go too fast due to lying water and poor visibility... I was watching both speedo and tacho but in 4th O/D I was doing an indicated 56 - 58 at 2000 rpm... I think the speedo requires recalibrating!

(J-type O/D from Dolomite 1850 - is that 25 or 28%?)

Or the tacho needs recallibrating!😉

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Considering how old and the tolerances of discrete components used I would not be surprised if it read wrong!

All the ones I have fitted & ever tested against a calibrated Fluke caused me not to touch or add a means of adjustment. I think there might have been a screwdriver slotted variable resistor?
Maybe there were errors at different points and was no point in linear adjustment? Can't remember. Never disbelieved them at any RPM. I have a modern TSSC one now.

 

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Colin what speedo drive is fitted if your car as your using a Dolomite 1850 J type box, if ratios are the same then I assume the speedo drive should be consistent with a GT6 but are the speedo heads comparable.

I’m interested as I have one to put in my Vitesse but it’s a single rail so needs internals fitting into a 3 rail case. I did my daughters Mk2 Spit with 1500 box internals and J then need to use some weird US spec speedo drive.

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46 minutes ago, Peter Truman said:

Colin what speedo drive is fitted if your car as your using a Dolomite 1850 J type box, if ratios are the same then I assume the speedo drive should be consistent with a GT6 but are the speedo heads comparable.

I’m interested as I have one to put in my Vitesse but it’s a single rail so needs internals fitting into a 3 rail case. I did my daughters Mk2 Spit with 1500 box internals and J then need to use some weird US spec speedo drive.

It's a 3-rail Dolomite 1850 box with WM prefix, but the speedo head is original non O/D GT6 Mk1. The angled speedo drive was fitted by me to adapt from non O/D to O/D but should be the proper version for the GT6.

Tomorrow I'll bring a sat-nav and see how far out the speedo is, and report back.

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Colin I was alluding to was the worm and pinion drives in the O/D, the Spit 1500 with J type O/D could have 2 different worms 5 or 6 start and correspondingly  2 different pinions with 18 or 20 teeth ( the non O/D appear to have 1 of 5 different pinions with 20 to 25 teeth).

By comparison the Dolly 1850 non O/D 3 rail and single rail appear to have different worms and pinions with the single rail having 2 pinion options too. The worm is the same part No as the non O/D GT6, 157028, couldn't find the corresponding GT6 pinion

But the Dolly 1850, 3 rail and single rail J type O/D both have the same worms and pinions, worm NKC45 (blue) and pinion NKC48 (grey 20 teeth)

So it would appear the speedo worm and pinion drives should be compatible between the Dolly 3 rail 1850 and GT6, don't know about the speedo head though & it depends on what diff ratio is fitted too!

for info I've attached a spreadsheet I made when trying to determine what was the best worm and pinion for the Mk2 Spits conversion from 3 rail to single rail internals in a 3 rail box casing with a J type overdrive and using a 4:11 diff, I won't say its definitely right but it was the best info I could find. 

Gearbox Speedo Worm & Pinion Drive.xlsx

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