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Hello folks, just curious....looks like I may have a duff overdrive in my '62, and since I'm not entirely sold on the gearbox in this car, I'm wondering if it's possible to upgrade to a later gearbox w/od.
And if so, how hard are they to find?.... I'm expecting most of you will recommend I just swap in a 5-speed, so please fire away.
I would hazard a guess that such a gearbox would be pretty hard to find in Costa Rica, but what do I know ? ...now if one's looking for party girls, you're in luck down in Jaco Beach...
Schmitty
I drove my Mk2 for years with its old Moss box and overdrive. I've regularly defended the Moss gearbox as not being as bad as it's often painted and with work the change quality can be improved. I'd taken the view that if I swapped it, it had to be for something significantly better at no great cost or difficulty. That left the options: stick with the Moss, swap to a Toyota Supra W58, or swap to Jaguar all synch with overdrive. The Toyota boxes are getting thin on the ground and much more expensive than a few years ago. Some are offering the W59 box instead, but it's a truck gearbox with what I consider unsuitable ratios. There are quite a lot of Jaguar all synch with o/d around, but many are out of XJ6 cars and have a short tail complicating the fitting. I was fortunate to find a KCN (Jaguar 240) gearbox for a few hundred pounds. Trying it on my workbench, it seems excellent with a very nice action. My only criticism is the gear stick seems a bit long. I prefer the shorter one on the Moss box.
My advice is look for a Jaguar JCN or KCN gearbox. They have the long tail and are a straightforward swap. It's worth updating to a diaphragm clutch at the same time. The KCN boxes are from the 240 and many think them unsuitable. In fact, they differ only in having a higher first gear which might even be seen as an advantage. The overdrive from the 240 operates at lower pressure and has less springs, but by most accounts works fine in a 3.4. If not, it can be modified.
You get two overdrive units that were used by Jaguar in our era. Both 0.77 to one ratio. You get the long tail overdrive that was fitted to the Moss Box and the short tail A Type (so called compact overdrive by Jaguar engineers) fitted to the Jaguar all Synchromesh gearbox. The upgrade to the newer Jaguar gearbox is worthwhile. You will have to source or have manufactured a correct length propshaft. This does not apply to the Mk2 based Daimler V8. That has a split propshaft.
Get hold of Dave Twigger at Overdrive Spares in Rugby. He knows more about Laycock DN Overdrives than most on the planet. He is a most helpful gent & more than happy to help even if he sells you nothing. Changing to modern gearboxes can become an expensive affair.
You get two overdrive units that were used by Jaguar in our era. Both 0.77 to one ratio. You get the long tail overdrive that was fitted to the Moss Box and the short tail A Type (so called compact overdrive by Jaguar engineers) fitted to the Jaguar all Synchromesh gearbox. The upgrade to the newer Jaguar gearbox is worthwhile. You will have to source or have manufactured a correct length propshaft. This does not apply to the Mk2 based Daimler V8. That has a split propshaft.
Glyn, I don't think that applies if you stick to Mk2, 340, 240 gearbox and overdrive. It would be the case if swapping to a transmission from another model. The A type compact overdrive on the Mk2 JCN/KCN gearbox has a not so compact long tail on it. If I have time tomorrow, I'll measure mine to be absolutely sure.
I have a Synchro/Compact OD in mine & my one donor has a Moss/Longtail OD (converted from Auto). Maybe the conversion from Auto to Manual bodge is the reason. The car is a BITSA which is why they must have fiddled with the propshaft.
Seems you are correct. Same propshaft for the below: C26658
Sorry for poor info.
Mk I / Mk 1 3.4
Mk II / Mk 2 2.4 & 240
Mk II / Mk 2 3.4, 3.8 & 340
S-Type 3.4, 3.8
Last edited by Glyn M Ruck; 11-25-2023 at 06:32 AM.
Trying to be logical, I'd ask what's the difference between JCN, JBN, and JDN gearboxes apart from the prefix, that they went in different cars (Mk2, S type, 420) and that, in some cases, they had slight differences in the tailpieces of the overdrives that attached to them? Unless I'm missing something, the component parts seem to be all the same. The same question can be asked of the three boxes without the N for de Normanville.
Chris, Another attraction of the overdrive gearbox: nowadays most people want to have a flap on their steering column to swap gears (even though they hit it by accident more often than intentionally). How neat is it to have the same on a 60-year old car that does the same thing (even if only between 4th and 5th speed)?
More seriously, I guess your problem is finding the box and transporting it to Costa Rica. I found my gearbox on eBay and collected it and probably got a bargain. A lot of private sellers aren't enthusiastic about getting involved in shipping. Also, you don't want to risk a dud. It might be worth contacting Ken Jenkins (UKJag) to see what he has in stock. It will cost more than a private seller, but you'll have more confidence that the box will work.
Absolutely ~ Ken Jenkins is a very capable & honest guy. He would never supply junk. I spoke to him on Skype for a friend with an Auto & Orlando swears by him.
Last edited by Glyn M Ruck; 11-25-2023 at 07:09 AM.
I don't wish to belabour the point but, in the case of the S Type at least, there were two different length propshafts between Moss + Longtail OD Unit & the Jaguar + Compact Short tail OD Laycock DN unit. It appears that C26658 that Barratts have in stock & I indicate above is for Moss + Longtail OD units only including early S Types. (It is the model I restored so know the best & for a moment I thought I must be loosing it as we definitely had 2 different length propshafts. One from the Auto conversion to Moss + longtail OD & my original that we had new UJs fitted to, corrected runout & re-balanced). The Jaguar all synch box was only offered on S Types from March 65 and initially in short supply & offered as an option. My car was built January 1966 & No 4 off the local production line. All SA built cars had Jaguar all synch gearboxes & LDN Compact ODs or Auto. All were 3.8s.
So I would say that Mk2s, 240s & 340s fitted with Jaguar all synch gearbox & short tail compact OD will also have a different propshaft length.
I apologise for the confusion.
S Type Parts Manual.
Last edited by Glyn M Ruck; 11-26-2023 at 10:23 AM.
Glyn, I suspect that a Moss box from a Mk2 was used to convert your donor from auto to manual. The manual Mk2 cars always had a long tail gearbox and shorter prop shaft, while the S type and 420 had short tail gearboxes with longer prop shaft. As a result, your donor would also have had the shorter Mk2 prop shaft. I think the changes in part numbers over the history of the prop shaft were due to updates in UJs, diameters, etc, rather than changes in length.
I don't know why the Mk2 cars had a shorter prop shaft. I can only guess that it was to avoid a potential vibration problem in the original live axle 2.4 litre MK1.
I guess the lesson for Chris is that if he buys a gearbox and overdrive that's not from a Mk2, 240, or 340 (not JCN or KCN), he also needs a plus 3.5inch prop shaft.
The Jag Club of Cape Town disagree with you. I phoned them. There are 2 different length propshafts between Moss + Longtail & the Jaguar + Compact. That includes late Mk2s, 240 & 340. Maybe their Chairman is wrong.
Last edited by Glyn M Ruck; 11-26-2023 at 10:52 AM.
Glyn, That's not a Mk2 gearbox. The photo below is a Mk2 gearbox. It's not a good picture, but it's from more or less the same angle as yours and shows the much longer tail on the overdrive.
I've just measured my gearboxes. The all synch is 832mm from front of bell to rear face of tail flange. The Moss is about 850mm +- 5mm, which I don't think justifies a different prop shaft. (Measuring the Moss is more difficult as it's on the car and access is uncomfortable).
11-24-2023, 10:26 AM
Later MK 2 gearbox/od fits earlier cars?
