Which axle xk 140 ots

Just curious; The original 140 OTS with OD has a 4.09 axle; would the engine pull ok if an overdrive were to be installed in a non-overdrive car with the standard 3.54 axle?

Not an XK but my 3.8 ‘S’ managed to pull OD with a 3.07 diff so I can’t see why not, I am in the process of playing that G/box behind my 3.4 ‘S’ but this will have the 3.54 diff.

plenty of torque and rpm available…but why not just change diff ratio to 3.27 or even 3.09. First gear is barely useable with even the 3.54. Enjoy 65mph…at 2200 to 2400 rpm. I plan to make the change this fall or winter during layup. Nick

Yes I think ratios are
And yes great cruising car

Thanks men. How difficult would it be to change diff and where would one find these parts?

OK, I see Moss has these gears. How difficult is it to make this change? Also, what advice as to whether to change to a five speed tranny or just go with a lower ratio gear set and stick with the four speed?

What country do you live in? If we are talking about 4HA in North America, there were lots vehicles that used the equivalent course-spline Dana/Spicer Model 44 variants. Jeep and Studebaker groups will be conversant.

yes, in USA tons of parts and people that can do it in 2 hrs…once they have access to the differential. The jeep rock crawler people do it all the time…basically the Salisbury 4HA is a Dana 44…common. So not only the ratios that were Jaguar factory options,but many other ratios are available. As you are at 3.54…you are on the best side of the ratio divide. SO…as to access…either the entire rear end sub assembly comes out…springs and axle…OR and I like this option…the fuel tank comes out and then with car on a lift the differential case is right there in front of you…No worries about springs, shackles etc…but either way: You just need to find a Dana 44 jeep type place that is willing to do it. My plan is in jeep guys home shop, is to take the fuel tank out there: …then it is all his…to roll onto space for the lift. Parts can be used or new…with that choice…easy…choose NEW. They know to always use new bolts, They will also know to match the prop shaft splines.

Many diff ratio to rpm at mph converters on line…just need your tire radius or diameter, loaded…which for most of the 600-16 available today I wouild put at about 27.0 to 27.8. The tires are usually listed as about 27.7 to 28.36 not loaded. So maybe just use 27.5 Diameter and play around with different ratios on the converters… (your gear ratio if asked is “1”, 600 may not work as a width number, so…use a modern equivalent, 185 is close, aspect would be 80 or 82, and of course 16 inch…You can put in various rpm, varios diff ratio, and see your mph at whatever rpm. This is a view of the diff, (a 2HA) with fuel tank out in a 120. My guy saw this and said…sure, no problem. Nick


I converted my XK 140 FHC SE by changing the original 4.09:1 diff for a DANA 41/11 (3.73:1). I was advised that in case of the standard version the engine would rev rather high at cruising speed (at least much higher than we’re used to nowadays). The 3.73:1 ratio is a kind of compromise between acceleration and comfort and I never regretted my choice.
Note that the DANA 41/11 diff is not a “Jaguar ratio” but fits perfectly and does the job.

Bob K.

so…there are two “sides” of the ratios available in the Dana…Salisbury…the change is in the 3.70 range…if above it…say the XK140 overdrive 4.09, then you are limited to ratios 3.73 or so…to the numerically higher…(lower gears) say, 3.92, 4,09, 4.11 and so on…unless you do an entire pumpkin change…but can’t do just a ring & pinion. If below it…say you have a 3.54…then you can go to 3.31, 3.27, 3.09, 2.92 whatever…in that direction…low numerical, taller, higher end ratios. So the XK140s with OD had 4.09…but without OD had 3.54. There are various opinions on what a "good cruise rpm is:…some personal, some mathematic as in piston speed, (Road and Track used 2500fpm), or where torque and HP graphs meet. Using 27.8 tire diam loaded, and at 60 mph, a 3.54 gives 2567rpm, a 3.27 is 2371, a 3.09 is 2241. (a 3.73 is 2705rpm). Actual tire size may vary a few tenths by brand: …won’t make much difference.

3.27 is an ENV ratio. Haven’t heard of it in a Salisbury context. The vast majority of ENV 120s were 3.64, and I believe most of the Salisbury cars were 3.54 (at least in the European markets). Other Salisbury ratios were 3.07, 3.31, 2.93 and even 2.45. There were a number of lower ones too - 3.77, etc.
I’m very happy with my change from ENV 3.64 to 3.27. I haven’t yet checked revs & speeds against a GPS but I’m pretty certain that at 70mph the revs are about 2,800. That’s with Michelin X 165 x 16 tyres.The speedo must already have been reading slow, because at that speed it’s barely showing 60mph. Nice and relaxed on the motorway, now.

Just trying to decide which car to buy; 140 with OD or 140 without OD. Am I correct in reading the car with overdrive has a final reduction of 3.58 (4.09 x .875 = 3.58) vs 3.54 standard without?

That sounds about right to me, but I’ll leave it to the overdrive experts!

From memory, the reduction created by the O/D is 22%, not 12.5%…that would give you a 3.19 final drive.

OK, I’m sure now I don’t know. Various websites give as either. 875 or .80 but I don’t know how to tell. Jacking up the rear end will only give the rear axle ratio.

Look at Roger’s first post under “gearbox ratios” a bit further down the page…overdrive: .779.

3.54 with Moss or All synchro box and OD is perfect. Means the OD is for highway/>60mph only.
With 4.09 even fast country road driving means going back anf forth between OD and 4th.
Dont understand why Jaguar used the 4.09 in the XKs with OD

With XKs, as with other Jaguars as well, there are four major factors that impact on overall gearing which with a factory delivered/unmodified set up, with have a matching calibrated speedo/odo so your speedometer reading is within legal accuracy tolerance (which back in the 1950s where legislation existed was usually +/- 10%, albeit the ‘better’ marques such as Jaguar with SMITHS speedometers usually did much better than 10%).
The GEARBOX: See my previous advice on GEARBOX Ratios noting the speedometer drive is from the output shaft, thus is accurate regardless of being in 1st, 2nd, 3rd or top gear, with Top Gear for XK gearboxes always 1.00:1 ratio.
The OVERDRIVE: Simply a case of WITH Overdrive or not with Overdrive, and always made by Laycock DeNormanville - thus the ‘DN’ suffix on the Chassis Number of an XK factory fitted with overdrive. Laycock DeNormanville made a large range of Overdrives of different ratios and of different torque carriage capability, thus with an XK engine with lots of Torque Overdrive was only enabled if in top gear - other makes with less torque engines would often enable Overdrive in Top GEar and intermediate gears - such as Austin Healeys) But the OVERDRIVE unit always had a plaque on it, that decoded to the Ratio and Model Specification, those for XKs being…
28/1390/00 . . . .||XK140|
28/1516/00 . . . .||XK150|
28/3020/00 . . . .||XK150’S’|
28/3034/00 . . . .||3.8 XK150|
28/3038/00 . . . .||3.8 XK150’S’|

Note in all these cases, the 28 prefix denotes the Overdrive has a 28% ratio.
With cars fitted with Overdrive, the speedo drive is from the overdrive output shaft…

The REAR AXLE. Jaguar offered a choice of rear axle ratios with the earlier XK120 ENV differentials, and a slightly different choice of ratios with the later XK120, and all XK140/150 Salisbury Rear Axles, but for XK140 with manual (only) or automatic the standard ratio was 3.54:1 or with manual/overdrive 4.09:1 was standard - but other ratios were optional, albeit you really needed a good reason re your intended usage of car, to deliberately choose an optional ratio. Don’t underestimate the skills of Jaguars engineers in selecting the best all round drive line ratios for 99.9% of their customers usage, with the special ratios usually chosen for racing cars, then for sprint events (and rarely/never with OD) or long distance events…, so go away from standard at your own peril/risk/choice…

The TYRES. Without stating the obvious the output rear axles from the Differential, then turn the wheel/tyre - so you now have a fourth ratio to consider based on the standard 6.00 x 16" Dunlop Roadspeed tyres as fitted new to every XK. The tyre manufacturers will quote rolling radius of each particular tyre size, at there recommended inflation pressure, but please appreciate a brand new tyre will have a larger rolling radius than a used tyre with worn down tread, and also note a tyre will ‘grow’ in radius to some degree based on centrifugal force at high speeds. These ALL affect the rolling radius and thus the final speedometer calibration, and thus the quoted +/- 10% (or better) tolerance achieved.

If you look at your speedo… see below from an XK140 DHC…

Note the small numbers underneath the odometer - in particular the 1200
1200 is the number of speedo drive revolutions as taken from the output shaft of the gearbox (and thus input drive to speedometer) that goes through a 3.54:1 rear axle fitted with 6.00x16in Dunlop RoadSpeed tyres to give the XK140s calibrated revs per mile, thus speed in mph…
If a different rear axle ratio is fitted, a different number (revolutions) is shown (eg 1120 for 3.31:1), or if a metric km/h speedo, different again (eg 740 with a 3.54 axle), and with a Mark 2 saloon fitted with 15in tyres, different again, and in the 1960s when radial tyres first became optional, and then standard - different again given the different laden radius characteristics and radial ply tyre sizes relative to cross-ply 1950s tyres…
If you modify your XK140 from its factory standard specification, a speedometer can be recalibrated by the specialists who have access to the necessary internal parts…, presuming you do want a reasonably accurate speedo given the unavoidable tolerances typical of new to worn out tyres, different pressures and different speeds… Or fit a Sat Nav unit - and have an accurate speedo at all times (except when inside a long tunnel)

Thank you Roger for your very clear explanation of the question. Unfortunately, my feeble comprehensive abilities deny me from understanding the final reduction in the rear axle on the 4.09 with OD fitted. Can you explain the 28% ratio?

Nick, I want to disagree with this. Yes there are two dif cases as you say. But I (myself) put a 3.54 gear set in a Mk7 that had 4.27. And a 3.77 2HA in another mk7 that had a 2HA. In both cases I didn’t just switch the ring & pinion but the whole lump (Carrier?) I did not have to change the axle housing. Thankfully no one told me I might need to measure and adjust. Both actually worked out very well. The 3.54 went into my own car and I enjoyed it greatly. I never noticed any noise. I hesitate to say it would always work out but I was 2 out of 2.