Diff ratios (again)

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simonjrwinter
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Diff ratios (again)

Post by simonjrwinter » Wed Nov 20, 2019 8:35 am

At some time in the future I’m planning on replacing my MGB V8 axle (3.07 ratio) with a Jaguar item.
I was planning on using a standard (ie non PL) Diff.
The current diff ratio is just about perfect for my needs, decent acceleration and high geared in 5th for long runs so I’d like to stick with that.
However, I’ve been told that the Jag 3.07 diff is quite rare and difficult to get hold of.
Would something like a 3.3 ratio make much of a difference?
Simon
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David Large
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Re: Diff ratios (again)

Post by David Large » Wed Nov 20, 2019 9:26 am

When we built our BRA in the 1980s we used, if I recall correctly, an MGB back axle with an MGC automatic differential which was either 3.3:1 or 3.6:1. When I changed it to an MGB V8 diff of 3.07:1 the difference was huge. First gear (an LT77 gearbox) suddenly became useable instead of being too low for any benefit. Cruising became much better but the harshness of acceleration became a bit less. But for me the 3.07 was and is great for the car.

David

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StewbieC
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Re: Diff ratios (again)

Post by StewbieC » Wed Nov 20, 2019 2:04 pm

I use a T5 5 speed box and that suits a 3.54 diff perfectly.
More popular ratios are 3.31, 3.54 and 3.77.
3.07 were fitted in the XJ6/12 as a none locker.
The difference from a 3.9 standard MGB Diff to the 3.54 Jag diff was not massive, but noticeable. So I'd imagine that the 3.07-3.33 would be slightly less noticeable should you not be able to find a 3.07. I know Dave Woodward is also after a 3.07 and has been for a while.
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kdavies3
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Re: Diff ratios (again)

Post by kdavies3 » Wed Nov 20, 2019 7:58 pm

I'm building the the Sebring with a 3.54 PL (derated) and a T5 recommended by Ben at Simply Performance.
The over driven 5th in the T5 will give a nice cruise.
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Re: Diff ratios (again)

Post by Jerryedmans » Sat Nov 23, 2019 12:05 pm

I used a 3.3:1 which I sources through simply performance. Gerry had recommended 3.3:1 powerlock which was hard to locate. In the end Simply Performance got hold of a 3.54 and arranged for an ex Lister Jag gearbox specialist to change the crown wheel to male that 3..3:1. I can't comment on other ratios as this is the only one I've driven, but first gear is properly functional and 5th gear gives 70MPH at just under 2000rpm making for efficient motorway driving. My experience with Simply performance was a bit hit and miss but they got there in the end.
Good luck
j

michaellloyd
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Re: Diff ratios (again)

Post by michaellloyd » Fri Dec 13, 2019 2:39 pm

Hi Simon, I have just read your post on somtime changing your rear axle,if you do decide to change it I would be very interested in buying your mgbv8 rear axle,no rush of course. Mick.

simonjrwinter
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Re: Diff ratios (again)

Post by simonjrwinter » Fri Dec 13, 2019 2:53 pm

Pm sent
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