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MG Midget and Sprite Technical - 1500 gearbox rebuild

I have searched this BB through all the years, spent many tens of hours, but not found the answers to these questions. I open this way not to glorify myself, but to let y'all know I respect you and don't choose to waste your time.

I finally got my 79 midget engine running well enough for a trip around the block, and confirmed a nasty growl in first gear. So I pulled the engine and tranny, and opened up the gearbox. Most everything looks ok, the springs behind two of the 1-2 synchro hub detent balls were broken, but most obvious was the extreme wear on the teeth on the reverse idler gear, and the outer gear of the 1-2 synchronizer. I observed before disassembly that these gears (partially) engaged when in 1st, although I cannot imagine why, unless BL just couldn't figure out a way to stop it. Most of the "1500 gearbox" posts I read described this 1st gear noise, but few the cause. 2 made reference to the "fact" that they were "supposed to".

1.) Is the 1-2 synchro outer gear "supposed to" engage the reverse idler gear with the tranny in 1st? If not, how do I stop it, If so, how do I prevent the new gears (ordered Moss yesterday) from suffering the same fate.

2.) In spite of the numerous warnings I got, I managed to pop open the 3-4 synchro (and loose the balls, see also Moss). I have determined for sure that the bullnose side of the inner gear faces 4th, I have deduced that the grooved side of the outer gear faces 3rd. Can anyone confirm or dispute this?

Engine repairs will follow tranny.

PS If it makes a difference, this is an "older" 1500 gearbox, with 21 teeth on reverse idler and 15 on reverse main.
M S Powell

Hello MS, I have rebuild my 1500 year or so back. It had previously suffered a nasty loud rythmic rattling sound when pulling away and driving in first gear( almost grating sound in first gear )I found on stripping the gearbox apart that the idler was chipped and worn badly - replaced it with new one.

I have read somewhere as you mention that the rev idler is mean't to be engaged when you select first - I can't see where now - could be Haynes manual...

John Barber

thank you, John. I got my info from Ian, on this site. Many of his other suggestions (to others) have been totally consistent to my own knowledge and observation. it makes no sense to me, I considered taking my reverse idler and 1-2 outer synchro gears to a shop and having the offending edges REMOVED. But I bought new gears, instead. It just seems to make no sense to have a synchronized 1st, if shifting into first under motion grinds reverse. And I thought Ford was the "Better Ideas" people!

Anyway, any thoughts on the 3-4 synchro hub thing? The real question boils down to "are the detent balls supposed to engage the edge set of detent slots in the outside ring of the synchro hub when the tranny is in 3rd, or in 4th"?
M S Powell

I can't recall the 3.4 re-assembly in detail from memory right now - but I did take photo's of the mainshaft re-assembly setp by step it may help. Look here

its under the gearbox rebuild pages .. I have some more photo's if this does not show enough to work it out...

John Barber

I have a few more pictures if needed. I did a rebuild shortly after John.

I can't remember how things all work though without going through the pictures to remind myself. I will take a look tonight.

John, long time no see, did you get your car going again?!

Malcolm Le Chevalier

John, the final pic in your gearbox section answered my question. Thank You.
M S Powell

John, the final pic in your gearbox section answered my question. Thank You.
M S Powell

Hi Malcolm - no still work in progress I am afraid - and the going is slow at the moment due to other committments.. I have seen your stream of notes and progress - keep going at it Mate....
John Barber

No problem MS - its good that its proved useful ...
John Barber

This thread was discussed between 08/07/2013 and 13/07/2013

MG Midget and Sprite Technical index

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