Calling all Moss box experts

My engine’s going to have to come out for a new rear seal in the near future and I’d like to try and address a rotational chatter coming from my gearbox at cruising speed. I have no idea of its rebuild history. It pretty much went back in the way it came out 18 years and 22K miles ago. Other than the chatter sound it’s behaved as well as can be expected for a Moss box. Double clutching has always been necessary to get it to go from 3 or 4 -> 2 if I’m going over 25 MPH but I don’t think anything can be done about that.

It appears my options are limited for new parts:

  1. The 2 large ball bearings on the main shaft input and output ends are available. Has anyone used them? They’re obviously aftermarket.

  2. The smaller caged roller bearing (C1843) on the constant pinion shaft is available again aftermarket. That looks easy enough to change but should I?

  3. The springs and ball bearings between the gears are available again aftermarket. Any reason to try and change them if the detentes have been functioning and it isn’t falling out of gear? I’m a little skittish about taking apart all the gears because of the headache of reassembly although I could possibly be convinced to be intrepid.

  4. The needle rollers on the main shaft 2nd/3rd gears (C18502) are available (aftermarket). But again that requires disassembly of the main shaft gear cluster right?

  5. The pinion shaft is available but I suspect it must also be aftermarket. I’m guessing this is ripe for replacement assuming the new part measures the same as the original and the original has any detectable wear?

  6. The full compliment of needle rollers for the countershaft cluster gear are actually available as official Jaguar spares believe it or not (C38573). Definitely do these right?

  7. A variety of countershaft thrust washers seem to be orderable. I guess that would need to be determined based on tested end float?

  8. Input and output seals are available, no brainer.

I’ve started perusing the manual about this and got confused straight away. There is an image (fig 7) titled dummy shaft, but the picture and dimensions appear to be of an actual countershaft. The dummy shaft doesn’t need to be that complex right? It’s just to hold the needle rollers in place? I’m also not sure why they tell you to insert it while you’re removing the rear cover and the shafts, and then immediately after that tell you to remove the dummy and let the counter sprocket fall into the box. If it’s just going to fall then why use the dummy shaft to begin with? Wouldn’t you want to turn the box on end with the end of the dummy hanging off the bench and remove it with the parts vertical so that the needle rollers are more likely to stay in place?

I do have a spare gearbox in bits out in the garage. I can’t recall the condition of the countershaft. It’s probably bad because the cluster gear on it was severely worn. But that could be used as the dummy correct?

What is the best way to reinstall this part with new rollers? I was reading old threads and someone said not to use any grease to hold them in place while you slip the countershaft through as it will impede oil circulation. I’m not even sure my idea to do it vertically would work because the ends of the rollers are conical so they’d just slip down inside. How do the pros do it?

Warning this thread might get long before this is all over :blush:

Also not sure how relevant but my original box is EB11689JS, so the shaved gear variety.


Not an expert but I did rebuild my own and it worked good for the 17 years I used the car before I sold it. Synchro down into second needed a careful change but the higher changes were fine and there were no funny noises.

You don’t need any fancy dummy layshaft, I’m pretty sure I used a piece of wood dowel, cut to length. I’ll check if I still have it for the measurements. I’m also sure I would have used grease for holding any needle rollers (thick water pump grease).

I did buy both big bearings and one was hard to get with the proper snap ring groove. I got that one from Robey, the other from a local bearing store.

Couple of things I remember, you probably want to check the state of the ends of the layshaft because they can get grooved up from the rollers. Also, look at the concentric rings on the synchro hubs to make sure that they still have reasonable depth left. I have a photo somewhere of a good one I’ll post when I find it.

Oh, and I changed the oil to Red Line MTL when I finished.

Thanks Clive, any help would be greatly appreciated. SNG has both bearings with the snap ring grooves, but as to whether they’re proper or not I can’t say just yet. Maybe I can compare them with the old bearings from my spare GB. It’s from an earlier car but is also an EB-JS box

So did you change both the needle rollers on the layshaft as well as the ones on the main shaft? If so was it much of a challenge to do the latter ones? It was always a bit of a mystery to me how one assembles those gears whilst compressing the balls and springs around the gears.

As I mentioned I do have a spare old layshaft I could use as a dummy although it would be just that length. Not sure if it’s sufficient or not.

I’m not sure what exactly I could do about wear to the concentric rings. They kind of are what they are yes? Those parts can’t be purchased new. I could have a look at the ones from my spare box but given the state of the counter shaft sprocket it’s unlikely to be much better in that regard.

I did this job back in 1988 so I can’t remember everything but I did dismantle another EBJS Moss box last year that I sold to a fellow lister on the forum here, This box from a '62 car that was totaled in the early 70s and I had it in storage since then. It actually appeared to be in better condition than my own box.

I used the Haynes manual and I probably needed my hydraulic press and a bearing puller to get the large bearings off. I don’t think the whole job is too difficult so long as you’re careful and follow the manual.Gaskets for the box weren’t available at the time so I made them from brown paper. I replaced the seals of course and there were never any leaks.

I can’t find the dummy layshaft and I’m not sure how useful the manual diagram is. It only needs to be the same length as the layshaft cluster and doesn’t need to be the exact diameter, just big enough to stop the rollers falling out. I might have used a piece of 3/4’ EMT conduit which is almost as thick, and if cut with a tubing cutter, has suitably rounded ends.

Here are some pics of the spare box that was actually in better shape than my own.

The synchro hub friction brakes which I think are still ok, still have some definition. I’ve seen a lot worse. Also, no chips on the synchro teeth The greasy stuff is LPS3 from nearly 40 years of storage:

Here is one of the internal hubs the synchros run against:

The inside roller track of the layshaft cluster and the 1st/reverse straight cut teeth (the ones that cause the characteristic whine):

And a bunch of the parts.

Redline MTL is the ONLY oil to use in a Moss box! It makes a WORLD of difference!

Ray L.

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Wow, those first gear teeth on the cluster gear gear look amazing. I’m jealous. I haven’t seen mine yet but I’d be shocked if they looked that good. Those synchro hubs look new also. Mine are probably near flat. Lucky lister to have received that box from you !

So it looks like you did take it down pretty far. How does one manage to compress all the detente springs around a gear at once to slip it on? Is there some special tool for that?

The pictures I posted are from the spare gearbox which I was checking over before selling it. I really can’t remember everything that I did to rebuild my own but I took it down much more than this one. I’m sure I’d remember any real problems and I don’t, so it must have been reasonably straightforward.

Good luck with your rear main seal. Just make absolutely sure that’s what it is.

I always thought I had that problem too until I did some engine work about 12 years ago (rings and valves). I had replaced the rope seal when I first rebuilt the engine in about 1990 and it was still good. The leaks were all running down to the back of the engine and unfairly incriminating the rear seal.

After careful re-assembly of the timing case, head, sump and camshaft piping, I never had any more oil leaks at all.

Erica. I have no experience with rebuilding a moss box myself but it is my understanding that it is possible to get the synchro cones rebuilt. (Regrooved?). If you are having problems with downshifts it might be something to look into. My 64 has had a synchro conversion but a moss box e type that I test drove while looking had no problems with gearchanges. No double clutching into any gear but first as long as you did not rush it.

I’m pretty sure it has to be the main seal Clive. it’s coming out the bottom of the bell housing, and it’s starting to affect the clutch. I unfortunately let the car set up without starting it for several years while renovating my house and ever since putting it on the road again the seal has been leaking a lot. The upper end is about 99% dry.

I’ve heard rumors about this process myself Geoff. The problem is that I can’t confirm it with anyone that’s had it done. There’s one lesser known vendor out there that claims to do it but but it’s a big question mark. If it’s so great, why don’t others do it also and why don’t parts places sell rejuvenated gears? It just seems like a big expensive gamble since I’m a pretty accomplished double clutcher at this point.


There is a guy (is it Walt something?) somewhere in the Mid-West who does Jag work, has a process for “rejuevenating” Moss synchros, I believe by lapping them. He claims it restores “as-new” operation. Never heard from anyone who’s actually done a before-after, but his price was reasonable.

On parts, I’ve always heard there are many replacement parts that are not correct. In particular, the large bearings with the external snap rings, the groove is in the wrong position, rendering the bearing unusable.

Disassembly/assembly of the Moss is straight-forward. Just follow the manual. As gearboxes go, it’s about as basic as they come.

One thing - Make absolutely certain you replace the rivet that stops the first gear selector sleeve from over-travelling. Otherwise, you WILL be sorry, when your gearbox gets stuck in first gear in traffic. AMHIN…

Ray L.

Oh crap. I was afraid of this. I ordered both of them. I’ll dig out the old ones from my spare box and measure them to be sure. Hopefully that problem was resolved.

Yeah there is an older fellow at Vintage Jag Works that talks about remachining them. I was hoping someone that has had this service might chime in. I’d be too nervous to experiment here.

It’s been a lot of years since I tore down the spare g-box for storage. I can’t recall having removed a rivet though. Where is it and why would it need replacing? Does the head get worn down from use or something?

If I can’t even change the main bearings on this box, I may just forego the entire affair and just change the front and rear seals. There just don’t seem to be enough parts available to warrant the extra risk.

It’s on the piece on the main shaft the selector ring slides on. It limits the travel of the 1-2 selector ring when going into 1st gear. The rivet eventually wears, allowing the ring to go too far, where it gets stuck, and can be very difficult, it not impossible, to get out of 1st gear.

This happened to my gearbox after it was rebuilt. The rebuilder did NOT replace the badly worn rivet. The result was it would sometimes get stuck in 1st, and I had to, literally, grab the stick with both hands, and pull as hard as I could get it back into neutral. Disassembling the gearbox was NOT an option I was willing to consider, so I found another, much simpler, approach. I removed the top cover of the gearbox, and machined a split nylon washer that slipped over the shifter rail, between the gearbox cover and the selector fork, to limit the travel of the rail, hence the travel of the selector ring. This kludgey fix has been in-place for 20 years now, and works perfectly. I actually think this is a better solution that the stupid rivet, as it really does not wear, and could be easily replaced if it ever were to fail.

Here’s a picture of the offending rivet:

You can just barely see the rivet here:

And the whole article about the problem:

Ray L.

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Just a thought. You may want to post a question about the synchro’s on the xk and the saloon lists. There are likely a number of people there experienced with Moss boxes. Another source would be the etype uk forum. Can’t hurt to ask.

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Do you recall who re-re-rebuilt my engine? Talking the walk isn’t the same as walking the walk :wink:

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So that was him? Oops!

Ray L.

Ray, you’re a machinist of some repute! You could be the Moss synchro hub guy! Aren’t you looking for a retirement gig yet?


You have to have realistic expectations. A Moss box, even when brand-spanking-new, had sluggish synchros. It’s just the nature of the beast. The Moss box was designed in the '30s, for 1-ton trucks, not sports cars. It’s built for reliability, not performance. And, at that it excels. They are near indestructible.

Since the synchros are steel-on-steel, there’s not much can be done to improve the synchro action. The one major “dial” you can turn is the oil you use. Redline MTL is, bay FAR, the single best thing you can do. Lapping the synchros, as Walt whats-his-name did/does, is about the only remediation that can be done to the actual hardware. Anything else would require re-designing the whole synchro interface - not remotely practical.

Ray L.

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YupI’ve used MTL for about 10 years. As I mentioned the only thing my box can’t do well is downshift to 2nd. It’ll do it as a straight shift if I’m below 25mph, but above that I need to double clutch and rev match which I’m very good at now.

Yeah I was thinking about the lapping part. I’m not sure what that exactly. Is that rejuvenating the concentric rings on the hub?