The 'E' Type Forum

I have just checked my 3.8 Roadster and I see that it has, from new, a 3.30 diff. Not one I have come across before. I converted my FHC to a 3.07 but cannot for the life of me recall what it was before. I like the 3.08 , a lot, but if I was very critical I would say that second can be a bit high in certain traffic conditions, but 4th could be higher! so its the 5 speed argument again I suppose. Anyway, rather than just change the 3.30 to a 3.07 what is the collective view on the ratio?

Jaguar changed the ratios a few times during production between 3.07 and 3.31 and back again. Most US destined cars had 3.54 diff. If you plan on touring Europe with the OTS go for 3.07 but otherwise for hooning around our congested roads the 3.31 will be fine. The only thing that may really irritate you is the different driving experience and expectations between the two cars. Avoid the 2.88 as it is too high - I have it in my OTS - but it is a pain around town. There is a mph calculator you can use to give you an idea of how big the differences will be between the two final drives: http://wahiduddin.net/calc/calc_speed_rpm.htm

I have the 3.31 diff in my S3 and I love it, acceleration is brilliant.
However the engine does rev higher than a 3.8 does (red line 6.5K compared to 5.5K). If you arent going to use the car for long distance touring and you want off the line acceleration then I would seriously think about keeping it. Not as raw as the 3.54 diffs.

Andrew..all the road speeds / rpm for 3.331, 3.07 & 3.54 are on a chart on page A.5 of the Jag manual

thanks Ian. I should have added that whilst the 3.07 diff feels too high in second, the problem is exacerbated by the difficulty of a low speed double de clutch into first with the Moss box. If I had the 3.07 with a synchro, and I do, it may well be the better option. I still think that if you are travelling on a german autobahn and you feel like a speed test in the E, then it doesn't really matter if its pulling 5500 rpm with a 3.30, as you won't be at that speed for very long. Perhaps the real key to driving a series one on long distances and enjoying it is to drive it at the speed it naturally settles into. In my FHC with the 3.07 it balances out at 85/90. Above this where it has bags of pull , the engine is coming on cam and working, so its back to the 85/90

I have a 3:31 in my 3.8, its all I know and I have found it fine in any gear. It was a bit of a pain at high speed doing around 80 would be 3200 RPM.
That's changed now since I have a 5 speed box.

Dave

thanks Dave. I think I will stick with this ratio. If for no other reason than to experience it .

Understand all the above, except about 3.07 being a bit high in second. I've got a 3.07, and pull away in second extremely easily, no clutch slipping, and accelerate hard from the start, so doesn't seem too high at all. If anything, I'd like a higher ratio - or 5 speeds.
Dave, wouldn't 80 be 3200 revs on a 3.07 diff? (Handbook shows that I believe) Thought it would be higher on the 3.3

Malcolm : the 2+2 always had a wider ratio box ( usually KJS ) than either the Moss box or the EJ all synchro box . Your 2nd gear is considerably lower than on the other boxes

Oh, right, thanks. Didn't know that!

Like Dave,

I have a 3.31 in my 3.8 lightweight copy and it is brilliant at Goodwood, Snetterton and Mallory track days. Then for driving home the T5 0.8 5th gear is ideal for fast cruising on the motorways.

I prefer the 3.31 to a 3.07 and I have had both . I like to use a sports car as the makers intended so I find the 3.07 a bit too high a ratio - but if you like relaxed cruising.....

regards Barrie

malcolm wrote:Understand all the above, except about 3.07 being a bit high in second. I've got a 3.07, and pull away in second extremely easily, no clutch slipping, and accelerate hard from the start, so doesn't seem too high at all. If anything, I'd like a higher ratio - or 5 speeds.
Dave, wouldn't 80 be 3200 revs on a 3.07 diff? (Handbook shows that I believe) Thought it would be higher on the 3.3

Its been a few years since I drove mine without the 5 speed so it could have been 3500 RPM. It was tiring with a st.st exhaust and worse with the hood up.

Dave

christopher storey wrote:Malcolm : the 2+2 always had a wider ratio box ( usually KJS ) than either the Moss box or the EJ all synchro box . Your 2nd gear is considerably lower than on the other boxes

The box certainly changed over time Christopher, and the 2+2 often had a different standard diff ratio compared to its SWB stablemates, which has the effect of closing or widening the overall gearing, but are you sure the actual ratios varied between contemporary LWB/SWB models?

I haven't heard that before and the part numbers for the gears (and layshaft with all four gears on it) are identical in the S1 2+2 and SWB parts books?

Pete

I have done a bit more research into it, Peter, and it does seem that some early cars did have EJ manual boxes although of course the vast majority of the LHD cars were automatics . Most manuals , however, had initially EJS and later KJS. The position is not helped by the fact that the Borg Warner Model 8 Automatics had EJ prefixes ! The relative ratios were

EJ 1.00,1.27,1.74 , 2.68

KE and KJS 1.00 , 1.389 , 1.905 , 2.933 which were effectively the Mark 2 saloon ratios

Interesting what you say about part numbers. My S1 catalogue does not in fact deal with the 2+2 at all !

christopher storey wrote: Interesting what you say about part numbers. My S1 catalogue does not in fact deal with the 2+2 at all !

Nor does mine. I was using J38 the 2+2 spares book, which has identical cluster part numbers to the S1 SWB 4.2 gearbox, although shafts and casing etc differ.

I think the ratio changes were made over time and across all models, rather than differences between models built at the same time. There was always tge option of special-order close ratios of course, and once the later box came in perhaps one had the option of asking for earlier cogs too?

Pete

I'm another fan of the 3.31 ratio.

In my 1962 FHC Moss boxer it seems an ideal compromise between lusty acceleration and civilised motorway cruising, even at, er, significant speeds.

All of the specialists that I've spoken to reckon that it's the best all-rounder in a 3.8.

Hi

What has to be done and how on the speedometer with any modification of the diff ratio ?
Can it be a DIY solution ?

Michel

Just checked my handbook, and it says that my gear ratios on a 3.07 diff are the same as on all other models.
I like the way that 60, a nice round number for me for some reason, comes up at 4600 revs in second, comfortably short of red band. But second still doesn't appear "high" at all.

Nice feedback here, as always. 3.31 it will be staying as then. Anyone recommend a good diff overhaul company for me please? I have used Dana and there is no issue with them except price, delay and hassle getting to them. I am sure there are others who can do this easily. Thx.