1275 Gearbox rebuild

[brucek]

Having put my rebuilt 1275 MG Midget engine into my convertible and toured around France, Switzerland and Italy (just) with fortunately no apparent major issues, I now have to do some work on the gearbox. The gearchange in all four forward gears appears fine - possibly a little 'sloppy' but there does not seem to be much whine or evidence of excessive wear. However, reverse gear is a different matter. Selection of reverse is usually OK but it jumps out of gear more often than not and occasionally struggles to select. Clearly a problem that needs sorting.

So this autumn/winters project is to rebuild the 'box. I have never done a gearbox rebuild before but have decided it's time to rectify that The engine and box will be coming out the weekend after next but in preparation for what could be quite a long, slow and possibly frustrating job, do any of the wise guru's on here have any top tips, hints and advice before I start?

I know most would say don't do it (springs and small bits apparently fly off in all directions from time to time) but the price of reconditioned boxes or type 9 conversions are just a bit prohibitive at the moment.

All points gratefully considered. Will try and keep a photo journal too as you don't see many gearboxes rebuilt stage by stage on here

Thanks in advance

Bruce

[bmcecosse]

Good luck with it! It's a long time since I did a Minor box, although I have done a few Mini boxes more recently. It is all quite straightforward - I'm sure someone who has more recent experience will come up with a guide. I'm certainly looking forward to seeing your pictures.

[brucek]

Thanks Roy. As soon as I start the stripdown, I'll post up a thread for folks to follow.

[IslipMinor]

Bruce,

You say that the gear change is a bit sloppy - what gear lever have you used? The 948 is different from the 1098/1275 and will be very sloppy - is that the problem?

[brucek]

Mmm it could be and I have read that too. I think I still have the original Midget stubby somewhere and I was going to try that before I got the box out. I must admit, when I got the engine many many moons ago, the only thing I didn't do when I drove the car it was in was put it in reverse so I have no idea if I inherited the problem or whether it was the gearlever. It seemed OK when I bench tested it but gave problems when actually in the car. If it turns out that this solves my problem, I'll probably rebuild the 1098 box I have which is definitely in need of some repair. If I can't find the stubby to compare, what is the difference between the 948 and 1098/1275 levers? is it the length or diameter of the ball end?

[IslipMinor]

The difference is the length below the ball. The 948 is shorter, so if fitted in the 1098/1275 does not engage properly with the socket that connects through to the selectors.

We were always disappointed when we fitted a 1098 box to the original 948 engine, that the change was sloppy. It wasn't until after the restoration and the 1380 engine + Toyota 5-spd had been fitted that I found this out! Tried a 1098 lever in the box, then languishing in the garage, and found all the slop had disappeared. We had driven it for >10 years with slop! Oh for the internet and forums like this years ago.

[brucek]

Thanks for the clarification Richard. Unfortunately, having cleared out the garage and store sheds in prep for the engine/gearbox out next weekend, I can't find the original stubby gearlever - must have chucked it out last time I had a clear out.

So - I currently have two gearlevers - one that is in the car now and a second one. One of these was almost certainly with the 1098 box that went with the 1098 engine I had in the car previously. On the assumption that one of them must be right, I'll compare the two over the weekend and see if there is any difference. If they are the same, I will assume they are both 1098 levers. If that is the case then the 1275 gearbox rebuild is still on cos the slop will have been caused by something other than poor slection owing to a short gearlever. Holmes you are a genius

[katy]

If/when you do the gearbox rebuild watch the rear main bearing. The new replacement ones are slightly different than the originals. The inner race is slightly thinner and needs a spacer on the front of it to make up the difference. The one I just did, the spacer came w/the new bearing but no instructions about it.
There was a thread on here a coupla months ago about it, with pictures showing the difference.

Found it: http://www.mmoc.org.uk/viewtopic.php?f= ... it=gearbox

[katy]

Forgot to mention that I figured out a trick for re-assembling the 3 springs and balls in the synchromesh hubs. With the hub on the bench, if you look on the side of the hub you'll see 3 holes about 1/8" diameter , these holes line up w/the springs. What I did was to put the spring in, put the ball on the end and pushed it in as far as it would go, then I stuck a straight pin in the hole and jammed the spring closed. Did all 3, put some grease on the balls to hold them in place and then slid the outer sleeve over the hub and balls, still had to persuade it a bit but not as bad as trying to do it w/holding the balls and springs against the full spring pressure. Once the sleeve is in place you can remove the 3 pins.
Also be aware that in the 1st and 2nd speed gear going onto the hub that there is another plunger in there and the gear has to go on the hub in one specific location.

[mike.perry]

I am using a 1098 lever in a 1275 box which works perfectly. The only noticable difference between the boxes is that the 1275 has a shorter throw into first and a longer throw into reverse, sometimes it is easier to drop the handbrake before selecting reverse

[brucek]

Another question: The 1098 Midget 'box and the 1275 Midget 'box have almost identical gear ratios. The only difference appears to be that the reverse gear ratio is different. The 1098 Minor 'box has both different forward gear ratios and has bronze bush bearings as opposed to the needle roller bearings that the Midget uses. Now the important bit - Is there any way to tell EXTERNALLY whether the 1098 gearbox you are looking at is a Minor or a Midget one? Is there a casting number/ID number or any other way of telling them apart?

My guess is that there are a lot of Minors currently running round with a later gearbox that is actually a Midget one but won't know it. Also possibly that there are more of the stronger Midget 1098 gearboxes around than we might think IF it is possible to identify them without pulling them apart. Any thoughts/ideas/comments ??

[IslipMinor]

Bruce,

The 1098/1275 Spridget box had closer ratios than the Minor:
[frame][/frame]
Also, as you said, they had needle roller bearings for the mainshaft gears, instead of the Minor's bronze bushes.

There were two different helical angles in the Spridget boxes, A and B gears, just to add a bit more complication! The 1275 Spridgets had the quieter B type gears as original fitment, and also had a reverse light switch built into the remote housing, which none of the other boxes had.

For exchange gearboxes, BMC were believed to provide any of the 3 options, Minor (bronze bushed), A Type or B Type gears (needle roller) without reference to the proper fitment.

As far as I know there is no reliable external identification. The layshaft is stamped and can be seen through the side cover, once it is removed, and from the Moss catalogue, the Minor 1098 is 22G83, A Type gears is 22G76 and B Type gears is either 22G232 or 22G1100.

[brucek]

Excellent many thanks Richard. At least there is a relatively easy way to check which is which now. Does make you wonder how they identified which box was which when they had them in store at the factory

[brucek]

Well, I think I may have solved my gear selection problem - it appears to be as Richard suggested.

In the attached photo, the lever at the bottom is the one that was in the car, the lever at the top is my spare. There is a clear difference in the size of the shaft before the ball on the top lever meaning I was inadvertently using at 948 lever instead of the correct 1098/1275 one . That should save me a LOT of money and buys Richard a beer

So, for now, I'm going to put the gearbox rebuild thread on hold (sorry Roy ) until I can test the theory (the car is off the road for the time being whilst I fit a second wiring loom owing to 'issues' I encountered in Italy!!) but hopefully I'll be able to report good news soon.

Once I know all is OK, I'll start to strip down my 1098 Minor 'box and rebuild it as a spare 1275 Midget one so I will have a known top spec spare to call on if I need it

Thanks guys for your help/advice - just shows how useful the ol' forum really is [frame][/frame]

[bmcecosse]

Well done sorting that out! This is what makes this forum the best I have found..... And bu99er - I was on the edge of my seat for the gearbox rebuild.......

[brucek]

Not going to disappoint you Roy! - and any others for that matter - always wanted to do a 'box but never quite had the nerve. My only real worry was having to repair my only 1275 in view of the time it could take and the money it could cost. I really didn't want to run into problems that would mean the car was laid up until I could sort things out. Now that (I hope) my cars ability to actually run is not dependent on my completing the 'box rebuild, I can take my time with my spare and 'enjoy' the experience whilst also putting together a useful (and valuable) replacement 1275 box at the same time. To start things off, here is a photo of the candidate 1098 Minor box in its original, very dirty condition! [frame][/frame][frame][/frame] Bit of cleaning required I think but the bench is cleared and we're ready to go ahead with the stripdown.....

By the way - I forgot to thank katy for the additional advice - i'm sure it will prove very useful in the weeks ahead. Great also to get some advice from over the pond - I have many cousins in Canad - primarily Kelowna BC but also on the East coast too, all of whom are hoping that, very soon, I live up to my promise to bring the convertible over to Canada and fulfil one of my driving ambitions - to travel the entire length of Highway 1 (Trans Canada Highway) in the Minor - another story to tell no doubt

[bmcecosse]

I've driven most of H 1 - but not in a Minor.....

[brucek]

Time for a quick update: Spent most of this week researching gearboxes! Sad I know but true. I have to make some use of that anorak I have

I was fascinated by the fact that 1098 Midget boxes have exactly the same ratios as the 1275 Midget boxes but, from the outside, at least, they are identical to each other and to the 1098 Minor box too. As mentioned before, the 1098 & 1275 Midget use the stronger needle roller bearings and are more resilient, esp when using the greater power of the 1275 engine. After some trawling I think it is possible to identify which are Minor and which are Midget boxes without having to rip them apart.

The key is to look for a stamped serial number on the first motion shaft just behind the splines on the smooth part which can be seen when the box is out of the car, or, if you are lucky, with a torch through either the top or side inspection hatches.

If your 'box has the number 22G171 - this is a Minor 1098 box and has the standard bronze bush bearings. Perfectly adequate for the 1098 Minor but not so good on a 1275 engine.

If your box has 22G172 or 22G229 then this indicates a Midget 1098/1275 box. It seems there were two gearsets used in the 1275 - an A and a B gearset. Not sure what the difference is but the two numbers allow you to determine whether you have A or B sets.

So, to complete the research, I need to ask you for your help in confirming whether this number check is accurate. If you are in your garage over the next week or so, here's how you can help.

If you KNOW you have a Minor 1098 gearbox in your car or in the garage, please check and post whether your number agrees with mine (from the 'box in the photo in an earlier post). I'm almost certain that this is right for the Minor but a few others to confirm would be great

If you KNOW or THINK you have a 1098 Midget or 1275 Midget box in your car or garage, please check and post to confirm the first motion shaft number. These are the ones I'm most interested in.

Why all this hassle??? well, if the numbers above are correct and you can determine which box is which from them, there could be a few benefits:

i) you will know if you have the 'stronger' box in your car or in your spares to use when the time comes
ii) you will be able to identify the best box for your use from the pile of gearboxes you have in the garage (and maybe sell the rest to make a few quid?)
iii) you will be able to quickly and easily identify which box is available when you go to see a job lot of spares in amongst which are a bunch of old gearboxes

But most importantly, you will be able to pick up the odd bargain at an auto jumble when you see someone advertising a 'Minor' gearbox for £30 and you discover that it is actually the better Midget box!

So, I think I'm going to put my rebuild on hold for now until I can source one of the stronger boxes to rebuild, otherwise the costs will be huge in changing both the bearings and gearsets for the 1275 into a Minor 1098 case. As soon as I have the right box, I'll start the strip down so I know the completed box is completely refurbished.

Please do help with the ID numbers if you can

THIS PUBLIC SERVICE ANNOUNCEMENT WAS BROUGHT TO ALL FORUM MEMBERS BY BRUCE K - general good ol' bean and will happily welcome a pint from anyone who seriously benefits from this

[MarkyB]

Thanks for the info.
Could you post a picture of where the number is stamped, a picture is worth 1000 words you know

[les]

I rebuilt a 1275 mg box a while ago and can confirm the 1st motion gear shaft is 22g229. I also have the component numbers and gear teeth numbers if you want to compare when you strip the box.