Hi all, recently I drove my '36 sedan to the NZ National Rally - about 200km. Being about 3L capacity it would easily handle a higher top ratio. While at the ‘Show and Concours’ event I got talking to a visitor, who told me that post-war ENV CW&P will fit the pre-war housing. Ed Nantes has previously indicated that early 120 and MkV had a suitable 3.8 final drive. Three questions please: Can anyone suggest a source for a 3.8 CWP set ex-Jaguar? Can anyone tell me what other UK cars had ENV diffs with this or similar ratio? Can anyone offer practical advice on what to do/what not to do in this potential swap?
many thanks
Chris Lovell-Smith NZ
To be more precise.
The whole ENV diff assembly [ not just the CW&P] can be used in an SS. It takes a little bit of modification
The top and bottom mounting holes in the banjo casing are 1/2 a hole out [ easily fixed.]
And the half shafts have different splines. so one needs to do a some mix and matching of spider gears and shims. But it’s been done , My brothers SS1 had that done in the late 70s.
But firstly, what ratio does the car have now? . I would think a 4.25 would be ideal, A 3.77 was the ratio in a 3 1/2 litre SS100 which has about 400cc more than your saloon at present and is noticeably lighter. Could it be you car has a 4.55 ?
My 3 /12 litre saloon has a 4 .27 ratio and this works well.
There is a tendency for owners to assume that a longer diff is automatically better. Various reasons are put forward , “Uses less fuel, doesn’t work as hard and so will last longer.”
But inreality the fuel costs are miniscule in the total cost of owning and running one of these cars and it’s not always a given that an ever longer ratio will use less fuel, It still takes the same amount of energy to drive a car at a given speed.
AS for wear . Wit modern oils and the mileage driven a well rebuilt engine will outlast the owner.
The reality is they like it to be quieter. But wind and tyre noise from these cars is always going to be much louder than a modern car[ which is what they are using as a yardstick.
I had check with my car on the freeway . 60 mph , noise level X , so put the car into neutral, noise level very little different.
And as the diff ratio gets longer, the acceleration deteriorates. Unless you are running in sprints. found that changing from my initial 4.27 ratio to a 3.77 ratio cost me half a second at the Geelong 1/4 mile sprints.
The really annoying rato issue is the 1st gear In those days the English often referred to it as "emergency low"and happily always started off in 2 nd.
I’ve never personally need to pull tree stumps out but if I did jaguar 1 st gears would be a blessing.
Gearspec here when rebuilding Moss boxes make new 1st gears with a higher ratio. Not a vast difference but it means the teeth can be made stronger and well, every little bit helps. The 3.77 ratio was only in Xk 120s [ over drive] nty Mk vs.
New 3.77 CW&Ps for 3 1/2 litre SS 100s seem to be available , at a price. But one needs to know precisely what ratio you are starting with now before changing to another.
Further to Ed’s comments, about 20 years ago I did a “cut and shut” to a Mk V diff. I used a 3.54 Mk 1 diff, cut the axle tubes off about 1/3rds out from the diff centre and cut the MK V diff axle tubes off about 2/3rd from the diff centre. We turned out the inside of the MK V tubes (very minor) and slid them over the MK1 diff. After alignment and size checking we did plug welds to join the 2 housings together. Also re-checked the housing for alignment after welding. Also swapped the spider gears over to change from fine to coarse. Re-inserted the MK V axles and presto. In the 3.5l Mk V this was in my opinion excellent. I feel it is better than the Toyota 5 speed G/Box conversions as every gear is “longer” as opposed to an extra gear. also the Toyota box is from a 4 cyl car, first is very low. Having said all that, I have just done another conversion achieving the same. Again a 3.5l Mk V. car. I obtained a Mk 8 sailsbury 4HA diff housing, used a 3.54 CW & P carrier from a MK 1 or 2, 3.54 gears from a XJ40 (machining required) and all brakes from a Mk V. Upon installation, found there were no S/Absorber mounts for the old lever arm shockers, had to weld a sub frame above the diff for telescopic shockers, and brackets to hold the handbrake cables. All very messy, but seems to work well. I agree with Ed, little / no economy gain, just a quieter car (mechanically) a lot less “busy” at highway speeds - Rex Wallis / AUSTRALIA Ph 0447796098