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MG Midget and Sprite Technical - Gear box rebuild request please

20 miles prior to arriving at Cadwell Park for a Track Day, during a gentle gear change into 3rd, it went bang, stripping teeth of the 3rd gear on the lay gear side. It's still unknown why this happend, possibly debris, but there is no sign of a forign body in the box only the remains of 5 teeth. So possibly gear fatigue.

I have a spare gear box to go in which I have used previously and have these questions;

1) The gear lever extension used to rattle very loudly above 6000rpm (engine is 1380 with 288 deg cam etc..). It's unclear whether the lever extension was rattling or whether it was acting as a sound path for a rattle originating deeper in the box? What can I do to minimise this type of rattle (very loud tizz)?

2) I have the Haynes Manual to guide me checking the box over. Should I assume this is a good guide or are parts of this procedure unnecessary, or, can (you guys) recommend further checks, clearances etc.?

Many thanks as always, I trust every one has had a good 'Safety Fast' summer. Although I see Michigan still has some 20C weather!..and our Aussy contigent is approaching Spring!

James Eastwood

Pic is old box.


James Eastwood

Not a very technical reply from me but just in case you didn't know -

for the 1275 you can buy an anti-rattle kit which I think would be the replacement parts

'O' Ring TRS710

Button 2A3467

Spring 2A3390

which are 'o'ring for bottom of gear lever, plastic/nylon cup and spring that goes beneath the cup

the kit QTK5 from MGOC is only £3.45

This might help if the present parts are worn (difficult to see, I think)

If you have the removeable metal cover then replacing a worn Grommet- Gear lever ACA5208, £2.46 might help

It looks like the earlier g/boxes had only one plate to hold the lever in pace and the later g/boxes had two plates the bottom one with a slot to middle - you could make sure the plate(S) are screwed down securely

The later levers look canted and with possible(?) some sort of built in anti vibration (I can't remember ever see one of these so I'm not sure)

The 1500 has a Plunger- Anti rattle 22G2286 and Spring- Anti rattle DAM2768 both 45p each
Nigel Atkins

Nigel, many thanks for your detailed reply or anti-rattle vibrations with the part no.s also. They are nowall duly noted!

Just in case any one needs it the old box will be going as 'spares or repairs'.

Regards, James
James Eastwood

Drain your old box and check for particles... these are the predictor of a box about to let go...

A
Anthony Cutler

James, no problem, I just looked up the MGOC parts web page - http://www.mgocspares.co.uk/acatalog/sec_midget.html

my gear lever tizzes at higher revs (not so well made Escort quickshift, second one I've fitted) I just use the noise as a audable rev limit warning

Spridgets - not just for summer :)
Nigel Atkins

James, you probably want to sell the old gearbox in one piece. But if you decide to sell it in parts I would like to buy the mainshaft ( 3 rd motionshaft) 22G146 from you.

Thanks in advance.

Pascal
pjw Seezink

James sorry to hear of your bad luck but if you are selling parts ill have your first gear the big one not the lay gear.mgblue74@hotmail.co.uk


b bithell

James

It's hard to tell from the photo, but do you have a bronze spacer between 2nd & 3rd gear, or is it the stell spacer whihc is part of the third motion shaft?
If the former, it's not a 1275 'box.
Dave O'Neill 2

Dave, thanks. I had a look at some other photos and think that it is a bronze bush. More to the point though my spare box is definately from a 1098. Is the 1275 box better in any way? I see it has the same ratios as the 1098.

Also I understand some gear boxes had cones but later ones had bulk rings, again is one more robust than the other?

Regards, James
James Eastwood

Dave, thanks. I had a look at some other photos and think that it is a bronze bush. More to the point though my spare box is definately from a 1098. Is the 1275 box better in any way? I see it has the same ratios as the 1098.

Regards, James
James Eastwood

If you have the early 1098/Morris Minor type 'box with the bronze spacer, it also has bronze bushes on 2nd & 3rd gears rather than needle rollers.

The late 1098 Midget/1275 'box has the steel spacer, needle rollers and closer ratios.

AFAIK only the smooth case 'box had cone synchronisers.
Dave O'Neill 2

I've had 2 do that - one on second and one on third. going to see if I can meld them back into one. is the laygear an expensive bit? suspect it might be...
Rob Armstrong

Rob, sorry to hear you've also suffered, but what can we do to avoid this happenning? If it's debris then would a magnetic oil drain plug help, or a strategicaly placed strainer to catch the debris out of the oil as it's thrown off the gears? More regular oil changes (I had just filled the box with fresh oil). I don't particularly think it was gear fatigue as the gear box was under light load when it happened.

I believe the basic gear layout was re-used for the Mini, but with different input and output shafts. Therefore the gear box gear sets were in production up until the 90s, in which case they would be plentiful. Perhaps the forum will concur or dispute the Midget/Mini commonality for gears sets.

Regards, James
James Eastwood

I've fixed it with a type 9 :). Dad has a few mini gearboxes lying about so I can check the teeth numbers if it's an unkown quantity.

I suspect I could have avoided it by driving slower. But where's the fun in that? :p
Rob Armstrong

Pascal - I can check mine when it comes out if you want - I'm exchanging it for my spare, so, if you can wait a couple of months as I'm not ready to come off the road yet ......
rachmacb

Rach
You have a 1500 box.
That is NOT a ribcase.

Pascal finaly getting to the white one?
Onno Könemann

Onno - I have more gearboxes than shoes - being that sort of woman :)!!!! They live outside my house too, so I don't even have to find storage inside (although, outside is becoming more difficult ...!)
rachmacb

why on earth have you got a ribcase?!
if you got the parts go and get a proper midget then ;)
Onno Könemann

James and Rachel, is it possible to see a number on the laygear (after removing the sidecover) on the waist between the largest and second largest gears ?
22G83 is for a Minor, if this is the case with your box sorry but I allready bought such box thinking it was a Midget box.

If the number on the laygear is 22G232 or 22G1100 this is a Migget box with the correct mainshaft.

Rachel things must go very strange will I not be in G.B. on the 12 th of june next year but if possible I would prefer to have the part earlier.

Of course I will pay for the part and postage costs my e mail adres is : pseezinkmonkeytailhomedotnl

monkeytail = @ dot = .

Yes Onno I allready have stript a lot of parts of the white one but I hope to finally start with the restoration this winter.

Pascal




pjw Seezink

Early 3 synchro mini gears are similar in layout to the Spridget box - although I've never bothered to find out if they are interchangeable as 3 synchro Mini boxes are probably rarer than Spridget boxes these days...

The much more common 4 synchro Mini/Metro box is a different animal and the parts are not interchangeable
James B

I did once salvage some gears from a Special Tuning SCCR 3-sync Mini 'box. First gear & laygear were u/s unfortunately. Second & third are the same as Spridget - 1st & laygear were too, but not salvageable.
Dave O'Neill 2

Onno - I DID drive a 1275 recently - and, funnily enough, two owners of 1275 ended up driving my 1500 ...!

Pascal - I'll e-mail you
rachmacb

I tripped my spare box last night and have two questions;

1) The v. loud rattle over 6000rpm, appears to be coming from the sellector rod rattling in the sellector forks, in a side to side motion when in gear. The remaider of the gear level does not have significant play in it. Qu - what can be done about this?

2) When measuring clearances if the Haynes manual say for instance clearance must be within 2 to 5 thou, how sensitive is the gear box to these. Should I aim to bring the clearances down to the minimum for the quietest gear box. Or is the box not that sensitive and anything in the range is ok?

Thanks.

Pic shows car at Brans with old g'box still running.


James Eastwood

This thread was discussed between 30/10/2010 and 02/11/2010

MG Midget and Sprite Technical index

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