Gearbox

[Norton]

Hi.
1973 S3. Understanding the manual gearbox.
Studying partslists etc, there is an oilpump at the end of the mainshaft. Also reading / partslist on saloon car gearboxes, also oilpump but not on OD gearboxes, as there is an oilpump in the OD unit. Are ( some ) bearings pressure lubricated?

Gearbox on my car showing signs of needing an overhaul. Rumbling noise at idle, diappearing when pressing clutch, gearstick moving in third and generating heat during prolonged driving in third. l have been able to get a 4 speed box fron a 69 420G with compact OD. I was thinking either replacing gearbox with this or using parts from this box. ( with no oilpump ). But understand they are not complete identical to a S3 box, there are some parts with different partnumber.

Any advise?

Rgds Harald.

[angelw]

Hello Harald,
If you use the 420 Gearbox with the OD intact, it will fit into the S3 without any modification whatsoever; even the tails-shaft remains unchanged.

If you use the 420 Gearbox without the OD unit, the Main Shaft from the S3 Gearbox will have to be used in the 420 Gearbox. The Oil Pump of the S3 Gearbox is part of the aluminum Gearbox extension and therefore, fitting it to the 420 Gearbox is simply an assembly process.

The noise you describe is invariably caused by the Reverse Idler Gear. The noise is also there when the car is in motion, just not so obvious due to road noise and other Gear noise emanating from the Gearbox.

The following two pictures show the Reverse Idler Gear, the Lay Cluster Gear and the First Motion Shaft (just visible at the extreme left of the picture) assembled. I have a rig where this assembly of gears can be run up to speed so as to determine if the Reverse Idler Gear is noisy. The noise will be obvious when the Reverse Idler Gear is in the forward position and will disappear when slid back to the Reverse Gear engagement position. Even under close examination. it will be difficult to detect any visual defect in the Reverse Idler Gear, but its the slight damage to the area of the Reverse Idler Gear that engages with Reverse Gear that makes the noise when the Reverse Idler Gear is in the forward position and the area that engages with Reverse Gear is engaged with the Lay Cluster Gear.





The following picture shows the rear face and Main Shaft for a Gearbox ready to accept an OD unit. The Main Shaft is shorter and the nut shown in place doesn't exist with a non-overdrive setup.



The following picture shows the typical damage sustained by the shaft the Reverse Idler Gear runs on. The damage is in the area of the position of the Reverse Idler Gear when engaged with Reverse Gear; rather significant considering the short overall time Reverse Gear is engaged compared to Forward Gear running time.



The following picture shows the Reverse Idler Shaft we manufacture in-house using better material and more appropriate heat treatment than the original part.



Regards,

Bill

[lowact]

Does the 420 gearbox have the mountings for the clutch slave cylinder?
Is the 1st gear ratio sufficiently the same?
What is yr diff ratio, compatible with an OD?
When did you last check the gbox oil level? Brgs/shafts wear when there is no oil, oil drains out when seals get old.

[angelw]

Colin Wrote:

Does the 420 gearbox have the mountings for the clutch slave cylinder?

Hello Colin,
No, I don't believe it has. I've converted Gearboxes without the clutch slave mounting lugs, by spot facing the two location areas, drilling and tapping the case to take threaded studs and then a press fit spacer onto the studs.

Regards,

Bill

[Norton]

Hi. Bill, thanks for information and confidence boost to dive into the box. Been ages since I done anything like that.
Noise, I was thinking about the layshaft.
The noise are present when car is moving forward. Understand thath it is wear / damage to the idler gear, not wear on the shaft that makes the noise? The shaft you make, is that usually in stock?

Colin, I have not yet seen the gearbox I bought ( its in transit ). Don’t know about 1. gear ratio. Are they usually different?
From photos it dont have lugs for slave cylinder as Bill confirms.
I have a 2.88 diff so not compatible with OD. OD unit on aquired box is .72, will end up with final ratio of 2.07. With a 3.54 it would end up at 2.55, probably the best set up? A 3.31 would give 2.38, still on tall side.

Had the car little less than a year, oil level was ok when I got it. Changed the oil and checked it before we went on a longer trip. It was on this trip I discovered heat build up on third ( western part of Norway, roads requiring much third gear ).

Its going to be a winter job, using the «new» box or rebuilding the original with parts from the «new» one? Have to decide when job have started.

Oil pump: its obviously pumping oil, but to were? Bearings?

Rgds Harald.

[christopher storey]

The oil pump supplies oil at about 5lbs/sq.in pressure ( ie very low pressure) to the shaft bearings

[angelw]

Harald Wrote:

Oil pump: its obviously pumping oil, but to were? Bearings?

Hello Harald,
The needle roller bearing of the gears and of particular importance, with regards to the oil pump delivered bearings lubricant, is the Drawn Cup, Needle Roller bearing pressed into the First Motion Shaft and interfaces with the front journal of the Main-shaft. This bearing is rather well shielded from splash lubrication and therefore, needs the oil supplied via the centre oil gallery of the Main-shaft.

We normally have stock of the shaft we make that the Reverse Idler Gear runs on.

Regards,

Bill

[Norton]

Thank you all. Next step will be to get the box out and look into it.

Reagrds Harald

[Norton]

I finally got the gearbox I been waiting for. It is stamped KZN412. Turns and shifts freely. Overdrive solenoid hav only one wire attached, slate with violet tracer whitch don’t make any sense. Solenoid is pointing rearwards and wire is the one to the left. Positve or negative? Or does i matter? Box from a 420G w neg earth.
Got it late yesterday and had leave for work early today, but after a quick count the ratios approx 3:1, 1.9:1 and 1.4:1. ( revers 3.4:1 ). I don’t know what ratio is supposed to be on a -73 S3.

[Norton]

Hi.
Draining oil from a compact A type OD?

Cleaned the box, lifted off top cover and removed bellhouse, looks good so far. Drained it, but when going to drain the OD I became bewildered. There are four boltheads on underside at aft. Whitch one for draining oil? See photo. My guess is no. 1 the big one. I loosened it but then hesitated and retightened it. Have not been able to find information here or any internet site. And what are the other 3 bolts?

Have recounted input / output in all gears, are as the S3 manual specifies.

Thanks, Harald.

[mgcjag]

Google search...... Laycock de Normanville overdrive....lots of info and pdf file service manual.....also detailed in the Jag service manual for models useing this o/d.....XJ6......Steve

[Norton]

Thanks.
Finally got it. Did google search many times, all types of laycock OD’s turned up - except compact A type. You prompted me to try again and finally I got hold of service manual for a 420G whitch have a compact A. Which is what my box & OD came from.
Manual shows draining is from no. 4. No. 1 holds the acumulator, no 2 oil pump & no 3 main operating valve.
Harald.

[Norton]

Hello, help needed.
The OD’s oil sump contained more than oil, some metalparts which I cannot identify. Anyone any idea? See photo.

The smaller narrower parts I’m pretty sure are from thrust washer that should be in planet gear carrier, similar to the one behind uni-directional clutch. ( curvator and thickness ). Parts list / service manual don’ give details of carrier. Larger parts similar material ( non magnetic yellowish ) but I can’t find anything like that in parts list either

Small bent pin probaly unsuccessful used to lock planetary gear shaft.

OD not completely dismantelled, thrust ring assembly on sliding member with bearing still in one piece. ( the one with 4 studs on whitch operatng pistons act via bridge piece ). But no way theese pieces can have escaped from here.
Annullus still attached to rear casing due to stubborn speedo drive, need correct extractor. But from manual / parts list nothing like theese chunks in that area.
Any idea anyone?

( Also posted this on jagstyperegister )
Thanks, Harald.

[christopher storey]

Harald : I suggest you send your picture and description of the debris to Overdrive Repairs in Sheffield ( very helpful people in my experience) and see if they can tell you

The email address is info@overdrive-repairs.co.uk

and the website is https://www.overdrive-repairs.co.uk

I am pretty sure they will be able to provide you with spares as well

[Norton]

Hi.
Thanks, been emailing overdrive-repares with good response. They suggests that chunks are pieces of maincase centre bush. Didn’t even know about such a bush as it was completely adsent except some remains in the bottom of case. Parts list not very informative about such details. See photo, no bush.
I am know figuring out what parts I need and trying to put it back together. New problems will probably show up.
Rgds Harald.

[Norton]

Hi.
Things have progressed. OD now back together and paired with its original gearbxox( from 420G ) and bench tested ok. Obiviously not under load.

Gear box finally out of -73 S3. Started to dismantle, top cower and bellhousing. But so far unable to remove rear extension. Following service manual, removed speedo drive, seven bolts also a bolt on top front of extension.( What’s the purpose of this bolt? ). Manual says « draw rear extension from third motion shaft». ( third motion shaft and main shaft, two names for same part? ).

Extension is moving about 4mm then stops dead. Tried to gently tap it rearwards, also wedging with two wooden wedges but it will not move more than those four mm. Have not dared to use much force.
It can be turned freely around, and looking into the 4mm opening something is turning with the extension. Could look like outer bearing race except it have a slot. Oilpump? See Photo.

Is there something I am missing?
Thanks, Harald.

[lowact]

Yep is oil pump, which is fixed to the housing and comes off with the housing. Bearing in the other end of the housing is a snug fit onto the main/3rd motion shaft. That 4 mm is as far as you can move before the bearing has to start to come off. Keep tapping, make sure yr working square.

[Norton]

Hello.
Thank you. Kept on tapping and off it came. Tapped out countershaft and took out first motion shaft.
And then next obstacle. Item 6&7 service manual. (see photo).
6: Is it the large nut, the one in front of main shaft?
7: to dislodge which bearing? Mainshaft from rear bearing?

And is 6&7 really necesarry at this point?
Also reading service manual of S type, 4 synchro box. Here theese actions ( 6 & 7 ) are described after mainshaft is out. Theese gearboxes are essensially identical.

Am I right in thinking mainshaft may be removed first?

Rgds Harald.

[angelw]

Hello Harald,

6: Is it the large nut, the one in front of main shaft?

No, its the nut in front of the First Motion Shaft bearing.

7: to dislodge which bearing? Mainshaft from rear bearing?

The bearing on the First Motion Shaft.

And is 6&7 really necesarry at this point?

You only have to carry out these steps if you're going to replace the bearing and can be done at anytime prior to replacing the bearing.

Also reading service manual of S type, 4 synchro box. Here theese actions ( 6 & 7 ) are described after mainshaft is out. Theese gearboxes are essensially identical.

Clearly, a different person wrote that manual; see my comment regarding your previous question.

Take note of the advice to keep the reverse gear pushed up firm against the remainder of the Main Shaft assembly. To ignore this warning will result in the loss of the needle roller from the gears into the bottom og the gearbox housing. Not the end of the World if this happens and your intention is to replace them.However, if you were going to reuse them and they are original, different toleranced rollers may have been used in different gears. This is OK, but mixing different tolerance roller for the one gear should not be done.

When reassembling the gearbox, ensure that the companion flange nut is torqued up good and tight. There is no torque specified for this nut, as it kept from coming loose by a split pin, but it should be tight, as the oil pump drive and speedo drive gear are driven only by the clamping force applied by this nut. Don't tighten the nut, find that a slot in the nut and hole in the shaft don't align, then back the nut off until alignment is achieved; this is just asking for the oil pump drive to slip in the future. Instead, machine, or lap material from the interface surface of the nut until alignment for the split pin is achieved when the nut is torqued up tight.

Regards,

Bill

[Norton]

Hello Bill.
Thank you, that clarified a lot. Have looked over things, without actually doing anything. Trying to be ahead of things.
Brings me to next steps, with reference to service manual.

8: think I understand this one, but still gives only about 16mm clearance before it will foul forward/constant gear on layshaft.

9: fine, but after 16mm forward movement it will foul countershaft.
I cant see that countershaft can be moved more out of the way, and looks very much like drawing in service manual.

10: Is rear bearing supposed to be removed when mainshaft is only moved 16mm forward? Is it a loose fit?

And just to be sure, reverse lever pulled rearward / reverse disengaged?

Rgds Harald