Jaguar diff

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Rusty77
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Jaguar diff

Post by Rusty77 »

Hello,

Has anyone out there converted a jag diff ratio.

I currently have a 3:54 and based on info form another post it looks like i should be lolling at a 3:07 or 2:88 to run with he top loader that I am seriously considering.

Is it an easy conversion as i currently have a diff 50% stripped.

Alternatively, does anyone know of a 3:07 diff that is available. I only need to the diff unit as I have all the swing arms, brakes etc....

cheers

Pete
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Roger King
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Re: Jaguar diff

Post by Roger King »

Ed at Ward Engineering is the man to do this for you. I don't like working on diffs myself as getting correct mesh is a truly black art, and if wrong it will most definitely whine!
If you are going for 3.07 with a toploader, I'd strongly advise a wide ratio 'box rather than the HEH-E close ratio. Driving around town will be a real pain with the C/R 'box and the long diff, you'll spend your life slipping the clutch. 2000rpm in 1st with the CR 2.32 1st gear will give you 21mph, whereas with the WR 2.78 you will be doing 17. 2500rpm will give you 36mph as against 31mph with the WR. You really don't want to run the engine much below this in real world driving, so you'll be around town in just 1st and 2nd which ain't much fun. 3.07 is a long ratio and it pays off on the motorways, definitely, but I would strongly advise WR gears to suit. The 3.07 will give you around 85mph at 3500rpm which is just about what you want, and will be the same with either box - the WR just makes it nicer getting there. The 3.54 will lose you over 10mph at the same revs, but would be a bit more squirrely around town. My car has a 3.07 with WR 'box (T10) which is great, but first still feels a bit long pulling away. Depends what you want!

Edit - I really wouldn't advise a 2.88.
Paul Blore
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Re: Jaguar diff

Post by Paul Blore »

Just to add a counterpoint to Roger's advice, I have exactly what he has advised against, a close-ratio Toploader with a 2.88:1 diff.
First gear is pretty tall, but it makes it a useful gear rather than just for pulling away and I've never regretted my choice. The only difference is that I have a big block engine.

Paul
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Roger King
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Re: Jaguar diff

Post by Roger King »

Paul Blore wrote:Just to add a counterpoint to Roger's advice, I have exactly what he has advised against, a close-ratio Toploader with a 2.88:1 diff.
First gear is pretty tall, but it makes it a useful gear rather than just for pulling away and I've never regretted my choice. The only difference is that I have a big block engine.

Paul
True... but you have just got through a clutch - don't know how many miles you've done in it. Not a job I like to do too often.
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Roger King
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Re: Jaguar diff

Post by Roger King »

Having said all that, I'd better come clean about the Sunbeam Tiger. These came from the factory with a Ford 260 V8, lowly 8.8 CR and only a 2V Autolite carb, giving just 164bhp (don't know bmep or torque figures offhand). They all had toploaders, all close ratio HEH-E boxes. And they all had a live axle, open, with a 2.88 ratio! They did have significantly smaller rolling radius 13" wheels which made a big difference, but nevertheless they were very long-geared. I know, I had one in the late seventies.
Paul Blore
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Re: Jaguar diff

Post by Paul Blore »

Roger King wrote:
Paul Blore wrote:Just to add a counterpoint to Roger's advice, I have exactly what he has advised against, a close-ratio Toploader with a 2.88:1 diff.
First gear is pretty tall, but it makes it a useful gear rather than just for pulling away and I've never regretted my choice. The only difference is that I have a big block engine.

Paul
True... but you have just got through a clutch - don't know how many miles you've done in it. Not a job I like to do too often.
Having taken the clutch our Roger, there was very little wear on it and could have gone straight back in again. I've replaced the friction plate just as a matter of course, but the pressure plate was like new and has been reinstalled. It now looks likely that the slight slipping I had coming out of the garage in Mulhouse was simply down to adjustment.
I've never had to replace a clutch on any car I've owned due to wear, so I must be very gentle with them. I replaced the Dino clutch, but that was within the first month of ownership, so is unlikely be down to me. :lol:

Paul
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Roger King
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Re: Jaguar diff

Post by Roger King »

Just to aid the discussion on gear ratios, I quoted above that with a 3.07 diff and a CR toploader 1st gear, the car would be rolling at 21mph at 2000rpm. As a test I have found that my everyday car needs to rev at 4000rpm to do 21 in 1st (It's no daily shopper, it's a 3.0 petrol BMW 6cyl estate). This indicates the problem I'm referring to. 'Our' kind of petrol engine should, ideally, not be run at lower revs for prolonged periods of time. They may drive fine and feel perfectly OK, but depending on components and setup, 1500-2500 rpm will be speeds at which the carburettor(s) will be running on the transition circuits, not main jets, which cannot be tuned properly. This could have implications for borewash etc. Likewise the ignition system will be still halfway up the advance curve which, again with aftermarket components, is not likely to be perfectly matched to the engine requirements unless several hours have been spent on a rolling road with weights, springs, lockouts etc. at set rpm. This kind of motor is best run to be on the main fuelling circuits with all ignition advance in. For most US V8s, particularly those tuned for 'go', this will be very roughly from around 3000 upwards. This is where they're most efficient, give most power and are less likely to suffer damage. As a race engine builder told me many years ago, 'it ain't revs that kills motors, it's chugging' - and, within reason (I wouldn't recommend trying to rev a 460 to 12,000), he was right. These ain't diesels!

Edit - None of these comments are aimed at Paul - I've driven in convoy with him over a large number of miles now and he's a lovely driver!
Maxakarudy
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Re: Jaguar diff

Post by Maxakarudy »

Talking about diffs Roger, what have you used in your Cobra, a Jaguar P/l with Jaguar casing or the original style?
cobra427differential_600.jpg
427 diff pictured
Martin
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Paul Blore
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Re: Jaguar diff

Post by Paul Blore »

Maxakarudy wrote:Talking about diffs Roger, what have you used in your Cobra, a Jaguar P/l with Jaguar casing or the original style?
What do you think? :roll: :lol:
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Roger King
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Re: Jaguar diff

Post by Roger King »

Well, no, actually - you've found the one chink in my armour.
The ally casings were being quoted at £3500 just for the casing when I was looking. And they were unobtainable anyway (not entirely sure why they quoted). It also seems to have been a particularly weak bit of design with little scope for improvement, and pretty much every Cobra going these days seems to use the Jag casing with adapter brackets, so that is what I have. The internals are all the same: I have a 3.07 Powrlok, with a 3.54 PL as back up just in case. And it doesn't matter which you have, they are a complete b*stard to fit.* Easily the nastiest job of the entire build.

There are also a number reports on the US forums of folks having issues with the aluminium diff casings due to differential (haha) thermal expansion of aluminium casings containing steel gears when they get hot, which put me off somewhat.

* - in a Kirkham, that is. Not so bad in a Hawk.
Last edited by Roger King on Fri Mar 25, 2016 10:22 am, edited 2 times in total.
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