Different Diffs

Technical advice Q&A

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lyons
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#1 Different Diffs

Post by lyons » Mon Aug 14, 2017 2:24 pm

Can anyone tell me if a XJ series 3 limited slip diff will fit in an e type cage.

If not, can someone explain what are the differences are !

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christopher storey
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#2 Re: Different Diffs

Post by christopher storey » Mon Aug 14, 2017 5:57 pm

I am not an expert on this, but I have no reason to believe that an XJ diff cannot be fitted into an E. However, I have some recollection that there are differences in the caliper mountings which have to be accommodated, so I don't think it is a straightforward swap. The ratio is also fractionally different IIRC 3.06 rather than 3.07. Peter Crespin is probably your best bet for definitive information

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JagWaugh
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#3 Re: Different Diffs

Post by JagWaugh » Mon Aug 14, 2017 7:28 pm

The Diff unit itself can be swapped into the E pumpkin - this means your inner fulcrums, output shafts, and caliper mounts all stay the same.

If you want to fit the brake calipers from the SIII XJ to the '60s diff casing you need to grind some meat off the calipers to get past a web (do this before you have the calipers plated or rebuilt).

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44DHR
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#4 Re: Different Diffs

Post by 44DHR » Mon Aug 14, 2017 7:29 pm

Irrespective of the diff itself, the lower fulcrum brackets bolted to the diff would need to be E Type ones, as the XJ ones would be a different angle and offset so would not fit the E Type cage.
Regards,
Dave
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#5 Re: Different Diffs

Post by PeterCrespin » Tue Aug 15, 2017 1:03 am

What year is the S3 XJ?

Mid-eighties had a Dana for a while - recognizable by absence of a drain plug and a square-ish rather than round input flange.
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

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lyons
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#6 Re: Different Diffs

Post by lyons » Tue Aug 15, 2017 3:33 pm

Thanks for all replies.

This looks like a real possibility with a few changes to brakes and brackets.

P.S. Assuming it is a LSD, how do I determine the ratio if the there is no tag fitted ?

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Jaglex
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#7 Re: Different Diffs

Post by Jaglex » Tue Aug 15, 2017 4:07 pm

Just count how often you have to turn the propshaft - flange to get the halfshaft flanges doing one (or ten) full turns. If it is hardly more than 3 rounds, it's a 3.06 or 3.07 : 1, id it's a little less than 3 turns it's a 2.87 : 1 and so on.
Happy turning
Alex
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#8 Re: Different Diffs

Post by 288gto » Tue Aug 15, 2017 5:09 pm

44DHR wrote:Irrespective of the diff itself, the lower fulcrum brackets bolted to the diff would need to be E Type ones, as the XJ ones would be a different angle and offset so would not fit the E Type cage.
Regards,
Dave
As Dave says, and remember those lower fulcrum brackets will need re shimming to the diff so the fulcrum shafts line up with the irs cage.

To easily check it is a Limited slip diff, when you turn one output shaft the other should turn in the same direction. On a standard diff they will turn in opposite directions.

If you take the cover off the back, the ratio is stamped on the crown wheel.

Make sure you use the correct diff oil or additive if it is a Limited Slip Diff.

Simon
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#9 Re: Different Diffs

Post by Bobb » Tue Aug 15, 2017 9:28 pm

I stuck one in my S 1 1/2 with the 2:88 ratio. With my slightly smaller 185 (modern sizing) tires, I get the same speed in gears as the original size tires with the European 3:07 gears. Over here, most E-Types came with a much higher diff (3:54(?)) for stop light acceleration.
I used the newer brake calipers too. Works great!

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#10 Re: Different Diffs

Post by Hugo » Fri Aug 18, 2017 12:11 am

Jaglex wrote:Just count how often you have to turn the propshaft - flange to get the halfshaft flanges doing one (or ten) full turns. If it is hardly more than 3 rounds, it's a 3.06 or 3.07 : 1, id it's a little less than 3 turns it's a 2.87 : 1 and so on.
Happy turning
Alex
It's easier to jack up one wheel and halve the results. I would suggest that 3.06 and 3.07 are the same? Diff ratios are always a weird ratio (such as 11/41) so that the same teeth don't co-incide too often. So unless they have come up with two pairs of numbers that give almost exactly the same ratio but not quite, these two will be the same, just rounded up or rounded down.
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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#11 Re: Different Diffs

Post by christopher storey » Fri Aug 18, 2017 9:06 am

Hugo : I am pretty sure that the 3.06 diff is something like 49/16 . The 3.07 is 43/14. The two are certainly different from each other, the 3.06 only appearing in XJ6 cars as far as I know

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#12 Re: Different Diffs

Post by Hugo » Fri Aug 18, 2017 10:09 am

christopher storey wrote:Hugo : I am pretty sure that the 3.06 diff is something like 49/16 . The 3.07 is 43/14. The two are certainly different from each other, the 3.06 only appearing in XJ6 cars as far as I know
That's interesting - and rather perverse if you ask me. If they already have the ratio, why would they look for another pair of numbers (the top number is usually a prime) to give exactly the same ratio, then manufacture the gears for it?
40/13 gives you 3.07. How do you get 3.06? It might be 'something like' 49/16, but not quite! That's rather a lot of teeth for a diff, too.
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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#13 Re: Different Diffs

Post by Jaglex » Fri Aug 18, 2017 11:18 am

@Hugo:
Jacking up one wheel is not the best option if you have a LSD.
I doubt you can turn manually the input shaft of a LSD if one of the halfshafts is not turning.
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#14 Re: Different Diffs

Post by Hugo » Fri Aug 18, 2017 2:02 pm

Ah yes - I hadn't thought of that.
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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#15 Re: Different Diffs

Post by christopher storey » Fri Aug 18, 2017 10:02 pm

Hugo : at some stage, Jaguar changed from Salisbury to using, for a period, a direct supply of the Dana 44 gear sets, which had earlier been supplied to Salisbury. I cannot tell you why the ratio changed from 3.07 to 3.06 for the XJ6, but change it did . I do not know why you think the number of teeth are large, as in earlier days the ratios such as 4.27 used a gearset with IIRC 47/11 teeth, and of course, where the continuous torque requirement is higher , as in a saloon weighing about 50% more than an E it would be , it is desirable that the load is spread over a greater number of teeth in the driving gear so that the point loadings at the tooth face are reduced

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#16 Re: Different Diffs

Post by Hugo » Fri Aug 18, 2017 10:30 pm

Yes but it's a trade off, as are so many other things in engineering; the more teeth, the bigger the crownwheel, and the heavier the whole assembly becomes, which in turn would add to the unpsrung weight on a car with conventional suspension.
I might be quite wrong about the numbers being bigger than normal - that's just how it struck me when I read it. I did a couple of back-of-an-envelope calculations to work out what 3.06 was, but I didn't get 3.07 with any of the numbers I tried.
Not that things like this are of any interest except to nerds like me.
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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#17 Re: Different Diffs

Post by JagWaugh » Sat Aug 19, 2017 6:14 am

Hugo wrote:Yes but it's a trade off, as are so many other things in engineering; the more teeth, the bigger the crownwheel, and the heavier the whole assembly becomes, which in turn would add to the unpsrung weight on a car with conventional suspension.
I might be quite wrong about the numbers being bigger than normal - that's just how it struck me when I read it. I did a couple of back-of-an-envelope calculations to work out what 3.06 was, but I didn't get 3.07 with any of the numbers I tried.
Not that things like this are of any interest except to nerds like me.
52/17=3.0588

Primes tables for hunting tooth gearsets are part and parcel of gearbox design. The tooth count problem in a diff isn't so much weight as getting a pair of numbers which are sweet for the given size of the pinion and gear. (You don't want a 3 or a 127 tooth pinion - something between 10 and 20 is more appropriate.)

If you're restricted to a single pair of gears and DP then you can't always find a pair of primes - one prime is a compromise.

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#18 Re: Different Diffs

Post by Hugo » Sat Aug 19, 2017 7:58 am

Do they both need to be primes? Smaller number makes no difference, does it? Just the number of times it divides (or doesn't divide) into the higher one. In other words, how often the same teeth hit.
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#19 Re: Different Diffs

Post by christopher storey » Sat Aug 19, 2017 10:18 am

No, they are not both primes usually , but one of them often is a prime . So, of the commonly used gearsets on our Jaguars , 3.07 are 43/14 , 3.31 are 43/13 and 3.54 are 46/13 . I cannot remember what 2.88 is but it may be 46/16 and the earlier special order 2.93 which was used on e.g. some D types was IIRC 38/13

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#20 Re: Different Diffs

Post by Hugo » Sat Aug 19, 2017 11:55 am

Actually I don't think either has to be a prime, as long as the two are as individble as possible. How would you work that out I wonder? Fascinating, isn't it. Like the fact that radial engines always have to have an odd number of cylinders in each bank. Or the intriguing question of how far up the bore a piston will be when the crank is at 90 degrees (or alternatively, what angle the crank will be when the piston is half-way up the bore). I presume this latter is a factor of conrod length to stroke?
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