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MG MG Y Type - Y type gearbox

Whilst I've got the engine out and at the "menders" my attention has been drawn to the gearbox. There is some play in the front bearing (1st motion shaft), so that needs replacing. The process according to the manual looks fairly straight forward except for re-assenbling the synchromesh after replacing the needle rollers. The manual shows a special tool made up from a modified gearbox part, making this is beyond me, so, my question is: is there an alternative way of re-assembling the mainshaft? without losing all the springs & balls etc.

Any advice would be very welcome

D P Jones

Hi Dave
Neil recorded how he rebuilt his gearbox. You can find it at on our website.
Peter Vielvoye

Hi David,
Unless you are fitting new springs to the sliding hubs, You don't really need to pull them apart.

It was a long time ago when I last did a Y or TC box, but I think I did dismantle the hubs so that I could rotate them to another spline. This was so the six synchro' balls had new ramps to ride on and I was trying to get the synchro to work as well as possible. The edges of the spline, where the synchro' balls run can get a bit rounded off.

I think I remember once using a hose-clamp and six short pieces of heavy wire to hold the balls in while I reassembled the hubs. Beware that if things don't go together first try, you might have ball bearings and springs flying around your ears! I don't remember doing it but assembling inside a clear plastic bag might be a good idea.

Bob Schapel
R L Schapel

Thank you all for your advice. I have downloaded the "how to" from the MGCC website. This has given me the confidence to tackle the gearbox and hopefully avoid having springs and balls scattering themselves around my garage.
D P Jones

I'm also in the process of 'doing' my gearbox. Until now the process has been very interesting and not too complicated.

To hold it in the vice I fitted a sturdy plate to the exhaust bracket holes (see picture)

Alas the laygear driven gear has broken teeth.
Tomorrow I'm going to look at a good used example.

I'm amazed how much the thrust washers cost and I'm investigating if the bearings are available from bearing specialists that don't charge the usual MG-premium.

That said, with the falling Pound parts that used to be expensive may be cheaper the coming weeks?

Willem van der Veer

a picture of the offending laygear....

Willem van der Veer

That looks like a very unusual failure Willem on the 4th gear end of the laygear - never seen one before.

Looking at the faces of the remaining teeth on 4th gear, I would deem the laygear as worn out even without the broken tooth. The faces on the teeth don't look smooth - or maybe it's the lighting ?.

While it is not good engineering practice to swap mated gears about, I have had quite a few Y-Type gearboxes made up of bits & pieces from donor gearboxes, and with new oil, have provided sterling service in cars driven for a thousand miles each year.

These gearboxes are tough, and will hang together well with less than perfect components in many areas.

That laygear is now a paperweight, so find a better one (used if fine), and I think you will be surprised just how good a job you can do yourself.

BTW - those bearings are just as expensive on this side of the planet. It's all about supply & demand in the bearing world.

Carry on & enjoy,


I'm thinking fatigue, or something has gone through it like a piece of input shaft bearing
How does the input gear look
In the pic the teeth to the right of the picture don't look (in the pic) to be meshing all that well, but that is the coast side so it is less important and hopefully an optical illusion
The teeth down to the left of the pic show the drive side and appear a lot better
The tooth immediately to the right of the broken one appears to have damage on the top of it which also points towards a visitor has been through there
William Revit

Wow Willem, that looks drastic! what does the mating gear look like? maybe something was in the gearbox and got jammed?

I found a 1937 6d piece in the bottom of mine! My box has never been opened in 45 years and has it's oil changed every 12 months or so.
My gearbox is now almost complete, thanks in the main to Neil Cairns and his "how to"
Replaced all the bearings, needles layshaft shaft etc. The most difficult part was seperating the mainshaft, the bearings were a tight interference fit in the case I resorted to removing the circlip from the centre bearing and levering the bearing out.

One oddity that I found which solved a mystery. In all the years (45) I've owned, the speedometer has been unreliable. It would be O.K. and fairly close to correct speed for a few miles, then after a while it would start to drop eventually down to zero, or, it would suddenly start jumping around. This behaviour I put up with for the 1st 30 odd years, but with the advent of stealth cameras I wanted to protect my clean licence I fitted an electronic speedo from a bicycle. I had already rebuilt/replaced the instrument, replaced the cable, examined the pinion drive in the gearbox and examined the worm gear as best as I could with box complete.

When I dismantled the box, before removing the propshaft coupling, I noticed that the spacer tube could be rotated without rotating the shaft.

Conclusion: there was insufficient compression in the coupling, rear bearing, spacer tube, worm gear, shims, centre bearing train, allowing the speedo drive to stop rotating at times (the propshaft coupling was tight up against the end of the splines judging by the marks it left behind). Fix: i've made up some extra thick shims and will assemble the group without the rear extension to finally check.

Hopefully the engine will be back from the machine shop next week.
D P Jones

Thinking back, i can remember towing our old racer on a trailer and accidentally left it in gear. When we unloaded at the track it had a clunking noise in the back- On inspection we found a tooth plucked off the crownwheel where it had been rocking on it on the trailer.
Could this be the cause of your tooth failure ????

William Revit

Today I picked up a very reasonable used example, and I was unload some TD parts in part exchange, so my hopes are up.

The vendor had two layshafts. One good an one badly rusted (he had to cut the gearbox housing in two to extract it).
He tried beadblasting the rusted one but he blew off a piece just like the ones missing from my gear.

Like on my layshaft it broke away adjacent to one of the round (balancing?) holes that are in the gear.
Probably these holes cause a weak point?

Willem van der Veer

and another picture

Willem van der Veer

I don't think the teeth look worn?
Or maybe I don't know what to look for?

Willem van der Veer

The side of the teeth which is most easily seen in the image, is the overrun side, not the drive side. It would be unlikely for that side to be worn, so it might be a reflection which gives the appearance of wear.

I have two or three lay-gears which have similar failure, in my shed. I got them in a box of bits from an old MG mechanic. I assume they are weak there if the four holes (drilled in the front of the gear) are too close to the teeth. From the appearance of the other three holes in your lay-gear I am guessing that was your problem. I am only guessing that the positioning of the four holes varies from lay-gear to laygear. I will have a look at my spares to see if this is the case.

Bob Schapel
R L Schapel

Just dug in the shed ... see image. Yes, holes vary in position. The two (broken) top lay-gears and the bottom left are similar to yours. They have holes close to teeth. The bottom right lay-gear has holes well back from teeth and so would be stronger. It is a pity the two bottom lay-gears have wear on first gear. I wonder if the stronger ones were made later... and when the design was changed.

I guess this means that we should always look for a lay-gear with holes well back from the teeth! (Not that we get much choice nowadays!)

Bob Schapel

R L Schapel

Thanks Bob for these pictures; very interesting indeed. It would confirm my suspicion that this is a weak point in the gear.
Alas the 'new' used one also has the 'holes in the teeth'. It's a shame I didn't know this 'killer fact' before, as it would have been a nice bargaining point.

I'll proceed with cleaning the gearbox and reassembling it with new roller bearings.
The pins were all within spec, so I'll be reusing them. This may be frowned upon, but I'm wary of low quality new parts and these proved their worth in the last 60 odd years.

Due to these delays I'm unfortunately not able to have the car ready for the Remscheid Y-treffen next weekend (as if the hobby budget wasn't overdrawn by quite a bit already).
Willem van der Veer

Isn't this site great
After how many years, and now on here is the answer to what must be an old problem looking at the choice of dead gears-
That cluster on the RH side lower of Bob's pic. looks to be the one to go for
Thanks for sharing --something else to try and remember
William Revit

Hi Willy,

<<Isn't this site great>>: that's exactly what I thought when I saw the photos!

Shall we share this knowledge with the TD/TF crowd or keep this knowledge to ourselves in our hunt for good examples? ;-)
Willem van der Veer

Sorry Willem and William, I have already started a thread under TD/TF to ask for information on the subject. I want to know how common the problem is. (You have both already confirmed it is not uncommon.) I would also be interested in when the design was changed ... and if the weaker gears were the early ones. (Do you know the origin of other broken gears?) Apologies also for accidentally missing a couple of your earlier posts .... hence a couple of my posts repeated points that you guys had already made.

You might be interested in the answer to a question on the TD/TF thread regarding the reason TC boxes are stronger. I got out the scales and camera. Y/TD/TF lay-gears weigh 400 grams. TC lay-gears weigh 600 grams! See image of the two side by side.

Bob Schapel

R L Schapel

Of course we wouldn't (and couldn't) hide this knowledge. As good neighbours we often take a peek over the BBS-fence.

The difference between the TC and TD shaft is amazing.
Willem van der Veer

This thread was discussed between 16/06/2016 and 29/06/2016

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