I have two leaks I would like advice on. A small on from the Speedo drive. A larger one from a brass ‘lever’ at the gax of the gear box - front of the overdrive. There are some bolts on it.i could nip them up…but since I have no good idea of what it does I thought best to consult the oracles. It may some part of the mechanism that links the overdrive to fourth gear?
Dave,
Which OD?
There is an o-ring on the speedo drive OD, and the lever is what the solenoid acts on to engage the O/D. There is also an o-ring on the shaft which the lever is attached to. The interlock for top is electrical - a switch on the G/B top cover closes when the transmission is in 4th and that enables the switch on the binnacle to operate the solenoid.
Not sure what the overdrive model is. The car is a MK2 1962 with the Moss box. Here is a pic of the place with the leak.
I added a marker dye to the oil that shows up with UV light. Great stuff. is this something i can fix with the box insitu?
There’s something odd about that picture. The lever I’m thinking of is on a shaft which passes through the O/D at 90 degrees to what your picture shows (i.e. the pivot is not longitudinal).
You can replace the speedo o-ring in situ, but the shaft for the lever I’m thinking of goes right through the body of the O/D to where the Solenoid acts on the other end (The lever is actually just used to set the datum when adjusting the solenoid operating lever on the other side of the O/D). I don’t think you can change the o-rings on the lever in situ, if that is in fact where your leak is.
The U/V tracer stuff is quite useful.
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Dave, the “lever” circled in your picture is actually a bar, which holds in place the two shafts on which the lower and reverse gears revolve. There are rubber seals inside the aluminum housing. Unfortunately there is really no way to change them without pulling off that housing, which means gearbox out and on a bench.
The Laycock DeNormanville OD box is an added complication because you have to be careful how you pull it all apart.
However, there is a quick and dirty fix. You could drain the oil, remove that bar, clean up the area, smear some sealing goop all over it, put the bar back on and refill the oil.
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The Mk2box is a Type A overdrive and the smaller one on XJ6 and S-type / 420 etc is ‘Compact Type A’.
Rob - I will try you quick and dirty fix first 
I just take out the bolts, remove the bar etc ? No complicated springs, danger of things coming loose inside, any other advice ?
Andrew - the speedo o ring- is it on the speedo cable end or sitting in the gearbox drive unit? Again any advice welcome before I start fishing around in there.
Dave
There are a couple of variations. Basically the worm is held in by a sleeve, and the sleeve is held in by a grubscrew. Usually there is an o-ring on the OD of the sleeve to seal to the case, and another inside to seal the worm.
The speedo takeoff is generally at the bottom of the case, so you can either drain the oil ahead of time, or have it self drain immediately after you’ve removed the takeoff.
Putting the worm back in is sometimes a bit jiggery pokeryish… resist the temptation to tap it in, but rather pull the worm back, rotate one tooth, feeling for when it bumps and thread it back in.
Dave, just remove the one bolt and the bar. Nothing else will pop out.
The bar fits into a slot in each of the two shafts; its purpose is to prevent them from turning and moving out. Try not to turn the shafts, but if you do just turn them back with pliers so the bar will fit back in.
You need the surface clean and dry, not oily, so the goop will stick. Use a soft pliable goop such as Permatex No. 2 because someday somebody will want to scrape that stuff off when they replace the seals.
Thanks guys. A project for next weekend I think
Started work yesterday.
Rob the ‘bodge’ on the bar and bolt at back of the gearbox went well. Some of the bolt thread was stripped in the housing so getting it all back together was tricky. In the end a copper washer instead of the spring washer was the tiny amount necessary for the bolt to start on a good thread and she snugged up. Lets see how it holds up - but looks good.
Andrew the speedo drive came out easily. Ran in to a problem with the sealing ring on inside of the brass shaft though. I assumed it was just an o-ring and gave it a poke to pull out. All I got was this spring ( see pic)
. Obviously what was in there was a proper oil seal which I have now banjaxed. The rubber part was still in there so I put it all back together for now.
Two questions 1.Can I just replace the internal sealing ring with an o-ring. 2. Anyone know the size of the o rings ?
I have taken measurements of the ones I have and plan to order a selection box of viton o-rings. The plumbers ones I have to hand will never last in the oil.
Dave
The lip type seal is more intended for rotating shafts, where an o-ring would be more intended for non-rotating applications, although with reliable lubrication an o-ring can work.
Lip seals are specified by the housing bore diameter, shaft diameter and width or thickness of the step where it fits in the housing.
Any bearing shop should be able to get the right one given those dimensions.
But I do not see any lip seal in the Mk2 parts catalogue.
I took apart an XK140 OD unit I have here and there was no internal seal at all on that shaft, just the outer o-ring as can be seen in your picture.
I wonder what’s going on there?
I did some research and found a seal for the inside of the bore :C32592J* Speedo Pinion Seal. Common to lots of Jaguars, MGS, etc. It is not shown in the exploded diagramme on the manuals or on the online suppliers who use them.
SNG Barratt confirmed it is the right part when I sent a picture. Mystery solved - or I guess we could wait until it arrives and I fit it and it works before victory is declared.
Dave
Very good research!
I see C.32592 is shown in the Borg Warner automatic trans for my '74 XJ12 and fits inside C.21297 bushing.
So perhaps you have a later modification to your gearbox?
Bad news - it is not the right part. Here is the one I pulled out beside the much smaller one I got. The really bad news is I tore the old one getting it out. Now I am completely stuck.
I am starting to think that my speedo has an after market upgrade. My MG TF speedo has basically the same set up - but without an inner seal. There is however a company (From the Frame Up) who do a modification to insert an o ring. I have just done that on the MG and it works a treat.
In the end now I have the old one out I will be able to eventually track down a replacement. Then I just need to figure out how to get it in…
On to the supplier today to see what they say.
The supplier was stumped. Has nothing list similar with the right size. Was going to ask around but nothing yet. In mean time I need to me able to move the car at least. I had a rubber blanking grommet/plug that is a great fit.
I know this is not even a semi-permenant fix but it should hold the oil in long enough to be able to move the car around the garage.
What kind of pressure does the gear box build up ? Could it last for a short run if needed ?
The top of the gearbox normally has a vent to atmosphere, so it does not build up any pressure, although the rotating parts throw oil around quite a lot. Your plug should work indefinitely.
You have a caliper, so measure the ID of the bushing and OD of the shaft, in inches. The seal is probably a standard inch size, but that may depend on in what country this modification was done.
Thanks Rob. Good to hear.
The seal sits into a groove cut into the sidewall of the bushing half way down. I need the height and depth of that grove and there is no way my caliper will get in there. That said I have the old seal and hopefully confident that will be enough.
If not then I was thinking of getting a new modern seal of the correct internal diameter and having the top of the busing milled out to take it. i.e at the end of the assembly where the speedo cable screws in mill out enough to seat a seal.
Since this would have been simpler in the first place I am wondering why they didn’t do it originally…
I am very surprised to hear that. That is the sort of groove normally intended for a simple o-ring seal, not a lip seal.
I thought since you pulled out a lip seal, it would be in a simple stepped bore, similar to the seal in the tail shaft, as I think you are suggesting.
That is probably what my XJ12 has.
I wonder even at the need for a seal here, unless the bushing points downward and the speedometer cable would tend to collect oil through there and eventually get up to the cabin.
I wonder if you might be better to look for a replacement bushing in the original configuration. What is your gearbox number?
given your present circs
I would be fitting an o-ring, if there is a recessed groove that can accommodate one
that is what I did when I overhauled a BW8, (but that is the correct part that came out)
If the entire job of the o-ring is to stop low pressure oil migrating past the inner shaft or outer bore, and there is a recess, I cannot see why an o-ring would not work at least as well as a lip seal
you may be able to measure OD, by making a small length and lowering into the groove