Help please re. gearbox with overdrive

[p-B]

Hello, My recently acquired 1966 s-type (3.8S) has the synchromesh on all four gears (with the reverse left & back), but it's singing an unhappy tune ...particularly in 3rd, on overrun, & when the clutch is operated. Ken Jenkins suggests that this is most likely the layshaft bearings. That makes sense to me when I reason that - particularly with the load off ...the layshaft would in effect be free-spinning (being turned only by the prop-shaft) rather than being under load from the drive gears.

Ok so, despite having taken the precaution of a pre-purchase inspection ...I've been lay-shafted !

Budget spent - I now need to sort it out myself.. The ideal scenario would be to find a good cost-effective replacement, drop this one out... and slip the good one in ...Be that a temporary swap while I rebuild mine, or a solution.!

Unfortunately, the likelihood of my finding a good one ...ready to drop in, within the 'cost-effective' criteria is more than slim (I'd need a guardian Angel !). Still always the optimist.. before I can even start to look (and then assess my options) - I'd need to know two things:

Firstly, how do identify the correct box and overdrive from my car ?
Secondly, is it possible to tell if what I find is any good ...without being able to drive, feel & hear said box ? and overdrive ?

on the first matter ;
> the gearbox numbers should tell me, but am I correct in thinking that - there is an external web around the outside of only the later (all synchro) boxes ?
> Also are the 240 gearboxes the same as for the 3.8 ? (ratios and build strength ?)
> And are all the gearshift mechanisms and speedo drives the same, or are they different between the s-type and the MK.2, or 240 or 420
> And what about the overdrives, would I need a long one or a short one ? or perhaps there are more variations ?
> And are all the couplings the same for the prop-shaft, and the clutch between various models ?
> And finally ....are the clutch, clutch slave, bell housing, & rear gearbox mounts the same, or do I need some particular configuration for my car (3.8 litre ...which was built as an automatic) ?

I'd much appreciate any help you might be able to offer..

Thank you

Peter - Suffolk, England

photo from underneath of my car :

[PPV]

Hi, the 2.4 has completely different ratios from the 3.4/3.8. Gearboxes have a prefix of GB and if they are suitable for an overdrive I understand that there is a letter N at the end of this prefix for the Moss type. I am not sure if the later all synchromesh box has the same info on them as mine is a earlier Mk2 with Moss gearbox. I think synco boxes have JC prefix with JCN for overdrive ones.
There is a gearbox currently on E-bay for sale which may be worth a look.
Sorry not much help.
Regards,

[Martec]

Sorry to hear of your problems, looking at the picture it looks very like the full synchro and overdrive box I have fitted to my 61 MkII. I have found it a nice box to use if a little old fashioned in use, but suits the car.

In your situation I would take a recommendation of a good gearbox repair specialist and have my own known box and over drive rebuilt. It will not be cheap, but you will have a known good unit. You can save money by removing it yourself, if you are fit enough!

When I removed my own moss box and fitted this full synchro box I jacked it up, removed the front suspenstion (its a beam and so can be wheeled away) and sdropped the engine and gearbox onto a wheeled trolley. Far easier to accurately align the box and engine, its just very heavy but I use a half ton chain block and reinforce lifting beam, my wife sighted it whilst lifting and lowering.

Ten or more years ago a recon box and good overdrive cost me £800, what are they asking now?

If you are interested I can climb under tomorrow and get the numbers off it?

Brian

[p-B]

Thanks chaps, I do appreciate your taking the time to reply and help.

...best I can work out from the S-type Parts book (which I have on CD, in pdf format from the internet. But that's scanned images rather than text - so not searchable).., is that I have the later all-synchromesh gearbox with 'compact' (aka 'short') overdrive.

Jaguar's parts book subtitles both the 3-gear and the 4-gear synchromesh gearboxes with overdrive as having prefix JBN, however Autobooks and at least two parts suppliers mention the prefix JCN. Jaguar's original Service Book (workshop manual) does not say.

my S-type books only deal with the 3.4 and 3.8 cars (the S-type never used the 2.4 engine), so I thank you PPV for advising us that the 2.4 has different ratios. I've heard of one owner swapping his 2.4 out for a 3.8 ltr and that that fitted easily, so the bell housing to blocks fit. Because he retained the 2.4 gearbox w. o/d he wouldn't have noticed any change the ratios. However the parts book show the 3.4 and 3.8 bell-housings as having different part numbers. That may be due to a lighter clutch &/or slave cylinder and its mounting on the 3.4.?

my Autobook workshop manual only covers the S-type and the 420. And although it covers both the 3 and 4 gear synchromesh gearboxes - it make no mention of any differences for the 420. From which I might (with caution) assume they are the same. !?

Visual Identification (of the 4-gear synchromesh w.o/d gearbox) :
1. short overdrive unit (without extended cone). The underside of which has a single vertical lug & single stud for the gearbox mount (rather than flat two-holes in a transverse flange)
2. gearchange lever has a pronounced tapered locking cone under the gear knob (the earlier gearbox has a very small locking-nut cone)
3. the top cover to the gearbox is slightly raised pyramidal shaped (rather than flat)
4. gearbox number should have the prefix 'JCN' (I think !?)
5. the overdrive of the later type has external strengthening webs, and a square front cornered underside with big nut to RHS side (the earlier is smoother outside case profile, rounder underside, and a central filter nut).
6. The gear shift pattern is with reverse left & back (the 3-gear synchro later 'Moss' box has the reverse gear over to the right)
7. The clutch is the diaphragm type (rather than coiled springs).

Brian, I couldn't see any numbers under mine. The numbers on the early (3-gear synchro) box were stamped into a flat plinth on the top cover, but I don't know where they are on the all-synchromesh box. It would be reassuring to learn if they are JCN prefixed but I wouldn't wish to put you to the trouble of pulling the interior to find that for me.!

I cannot afford £800+ bills, nor spending half that to buy a used one - only to find it to be as bad.. So I'll have to pull this one out and learn to rebuild it myself. Thankfully, getting it out should be easier than usual (so I'm told) because this car was an automatic. And its broader tunnel allows the gearbox to be dropped without needing to take the engine &/or front suspension cross member out. Never-the-less that'll clearly be a whole lot of fun under the car on my own. But needs what may.., and all that. ...It is after all what our fathers would have had to do..

As and when I learn more I'll share it with you. Possibly be of help to others in a similar situation.

cheers, Peter

[Martec]

Hi Peter, again sorry for the situation you find yourself in, all in not lost, but I am concerned for your saftey with your idea of removing the box from underneath.

My dad was a motor mechanic and told me of this practice of unbolting the box and dropping it onto his belly and manouvring it and himself from under the car, but that was on the early light weight cars with dinky gearboxes.

It can be done but a number of considerations need to be taken into account. As I have removed the engine and moss box in a oner from the car and then separated they and refitted the replacement full synchro box and overdrive I know how heavy the box and overdrive is and I would not want to be trapped underneath them!

In the past on smaller engines I have lifted up the gearbox, CAREFULLY slid the input shaft into the clutch spline (lowering it now will bend the shaft) and with the dowl pins engaged my wife has screwed up a couple of bolts at the top of the flange. With the Jaguar box and overdrive I used a chain block with the engine sat on a trolley.

I have removed and refitted a transaxle from our 944 porsche but I made a cradle for the transaxle to bolt into and securely fitted this to a very large trolley jack, so a similar arrangement can an nodoubt has been done in the past for this engine and box. The other point is the engine is only supported at the front, NOT at the back, so you would need to make up some arrangement to support it at the back. I have an original manual car with a narrow tunnel and I can't even get a mirror on a stick up beside the box and I could not undo the top bolts of the bellhousing.

As you are in an unfortunate situation why not turn it to your advantage, and inspect the clutch and release bearing whilst it is apart. Removing the engine and box is not too bad, I found removing my year 2000 S type engine considerably worse, no manuals, no precedent written up, half the torque setting not available and the hassle of disconnecting the mass of wiring looms from engine and gearbox. The main problems are having lifting gear strong enough for the combined transmission weight (1/2 ton chain block is fine and lifting the front of the car high enough (30 inches springs to mind, leaving the rear wheels on the ground) unless like 'Oldtimer' you are lucky enough to have a car lift.

Just somethings to consider whilst you make your plan of attack, honestly removing an engine and box is no big deal as you say our fathers did (or atleast mine did) just keep yourself safe that is the important point.

Best wishes
Brian

[PPV]

Peter, just a few points. I totally agree with Brian, I have found the gearbox to be very heavy and would not like to handle it underneath, perhaps a visit to Stoneleigh in March may help with identification, weight and bits? Nevertheless you do neet a cradle to support its weight as just using trolley jacks on your own is risky.
Regarding the gearbox number besides being on the top cover it should also be stamped on a lug at the left hand rear corner of the gearbox casing according to the Mk2 manual although I have not seen this myself.
I can't quite see enough detail from your picture to see the overdrive etc but as your car is a converted manual car then the gearbox/overdrive could be a mixture. You could do a quick check by noting the revs for some standard speeds, say 30 or 40 mph (assuming the speedo is correct!) and compare to the figures in the service manual.
Just before engaging in all the work do you know that the gearbox oil is correct as many years ago a friend had his filled with 20/50 engine oil and it made a terrible noise but once the correct oil used it made a big difference. I guess though that the clutch operation especially on 3rd gear does point to layshaft issues.
Regards,
Paul

[p-B]

Thanks Brian and Paul for your cautionary warnings - good advice. I will bear them in mind and configure something to take the weight. ... Just thinking about it as I write - I have a hydraulic motorcycle lift that may be adapted. That is wider and very much more stable than trying to balance the gearbox on a 1/4 ton trolley jack or my middle-aged belly. All I need to do now is to get the whole car two foot off the ground..

The later all-synchro gearbox, which I'm now sure that I have - because of the gate (left & back for reverse) is specified to have Hypoid / EP90 gear oil, whereas the 3-gear synchro Moss gearbox is specified to use SAE 30 motor oil. I changed the gear / overdrive oil and checked / cleaned the filters just a couple of hundred miles ago.

Yes I'll be checking the clutch and thrust bearing while it's out. And it seems like I'll also have to pull the overdrive apart as well, because that is slipping under load. (rather neat as it works like a kick-down - but alas... not correct

Thanks again, keep the advice coming.. Peter.


p.s. ....just spotted the overdrive ID plate on Brian's photo. Above the filter on the LHS.. Thanks Brian.

[Martec]

Your comment about a filter reminded me of a potential problem, The brass plug you see below the identification plate is stated as a filler plug, in practice fill the gearbox and it overflows into the overdrive and fills it. Start it up and allow to run for 10 minutes and the level will drop a little top it up again and your done.

IF you decide to be concientious and clean the filter, take the plug out and run a screwdriver in all the way and carefully use this to persuade the filter out and support the filter on its way out and back in, otherwise it will drop into the casing!!!??//.

Brian

PS hypod 90 is correct, this last time I seemed to have difficulty in finding someone to supply it and ended up with 'carlube'. A check the other day and it was a good colour and level.

[p-B]

Excellent Brian,

I recall the fun with the filter, it's not the most convenient of setups is it !?

However, I don't think we topped up the gearbox after running it. We did run the engine after changing the oil filter, because we were concerned with it leaking (and it did .. we then found that the filter casing was cracked .. twice !). re. the gearbox oil - I presume you need to engage the synchro as well - as I understand the gearbox oil pump is in this unit.. But I may have misread that ?

Next weekend I'll check that level. Thanks it could be a major factor in the noise (always the optimist

[stephenriley]

Did you get that gearbox out? I have a similar problem to yours and was wondering how easily the box came out. Regards Stephen

[B87UL]

I have a 1965 3.4 ltr S type MOD, documentation shows the gearbox prefix to be JBN.

The physical appearance seems to match correctly with the numbers, but I have not cross checked the gearbox stamped numbers but have no reason to suspect they will not match.

I am not particularly conversant with Jaguars however I have completed automotive work in 56 countries, so not an absolute beginner. Having said that I have noticed discussions so far seemed to have missed three points regarding identification.

The all synchromesh box was used with both coil and diaphragm clutches.

The rear mountings on these overdrive gearboxes were changed on RHD at chassis IB52078 for 3.8ltr and IB 2192 for 3.4 ltr to be similar to the Automatics.

The 3.8 ltr and 3.4 ltr overdrives are different. The accumulator bores and hydraulic operating pressures are not identical. This would normally lead to potential overdrive “slip” if a 3.4ltr unit was used with a 3.8 ltr

In the latter instance the factory must have numbered the respective units accordingly to enable correct production call offs. It MIGHT be reasonable to suggest that gearboxes with OVERDRIVES were prefixed JBN for 3.4 ltr and JCN for 3.8 ltr to differentiate. Obviously this numbering is guesswork and I stand to be corrected.

Details taken from S type service manual.

[oldtimer]

Hi All,
I suppose I might as well add my peneth.

I've read through this thread a couple of times and Peter, sorry for the dilemma you find your self in.

I owned a 1966 3.4 S type from '67 for a number of years, a really fine motor, certainly not the fun car that the Mk 2 was but superior in so many ways especially as a well appointed fast, comfortable cruiser. the IRS did it.

Now then, I simply don't accept the claim that the floor pan and its recess to accommodate automatic transmission is larger than when a manual gearbox is installed. Jaguar are too tight fisted to provide alternative transmission tunnels. I rest my case until somebody confirms otherwise.

Next. Please take note of Martec's health warning. If it falls on you it won't hurt. It'll kill you. So no chances ah.

The simple and quickest way to remove the lump is again as Martec suggests. Front suspension out. Propshaft and exhaust off. Engine and G/box out as one using approved engine crane and correct chains.

Jacking - I would suggest large blocks of would and four very short axle stands to raise the vehicle in the horizontal plain.

I fitted a 4.2 litre 3x carb engine using the original 3.4 all syncro box and overdrive as yours clearly is. I commuted at weekends from London to Anglesey for five months followed by several years of commuting 38.5 miles each way each day at eighty / ninety mph. So there is no problems on that front.

Now to the G/Box and overdrive. When this job is done do you want to have the confidence to drive to the south of France on holiday or be fearful of going to the end of the street ?
Before embarking on this marathon I would love to know what parts are available to overhaul them both. Remember overhaulers are likely to replace the minimum and within a price which may not be the best option.
It's too late at night (cos I'm an Oldtimer) to start a full description of a G/Box function but I have my reservations in regard to Ken's suggestion that the lay shaft bearings are at fault. The lay shaft gears are one lump mounted on needle rollers with a 1/2 inch shaft running down the centre. Yes it could contribute to the noise but then so could the bulk ring on third gear and so it goes on. Open it up and have a look is the only answer.

As MARTEC says I have a four post lift for such jobs but have to admit the mind is willing but the body aint any more

Oldtimer

[piman]

Hello B87UL,

for what it's worth and this was a Triumph gearbox. I had a whine start on mine and that was indicative of layshaft bearings as the mesh is wrong when the bearings wear, replacing them and the gearbox was good again. That said if the layshaft bearings are worn I would expect to find other parts will need replacing. It is the most economical repair if you can do the job yourself.

Alec