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MG TD TF 1500 - Later gearbox, 3rd & 4th shifter positive stop mod

Hi all,

Having just had my TF, and therefore late, gearbox rebuilt, it has been pointed out that due to minor variations in replacement shafts etc, the circlip on the front of the 3rd & 4th shifter shaft may result in the location ball not being fully into the indent on the shaft.

The mod is to tap a thread into the small extension bearing, already bolted onto the remote control housing. A small 1/4" set screw and locknut,(+ Loctite) can then be fitted and with the top of the gearbox removed, third gear selected. The screw is then adjusted until the ball drops fully into the shaft indent, and locked. On my gearbox this resulted in the circlip groove disappearing into the gearbox front case, and therefore not usable. If the circlip was fitted, the ball would not be fully into the shaft indent, probably not critical, but clearly not desirable.

With a new gearbox the distance between the circlip and the indent was originaly hopefully spot on, but replacement shafts may not have been so accurate - we're only talking about very small variants here. On the other hand in engineering terms a circlip is not supposed to take numerous side knocks, which is what happens each time you change into 3rd gear, the most common gearchange movement.

Have others heard of or used this mod ? Any thoughts as to it being sound and of benefit? Certainly when a gearbox top cover is off, it would be worth checking that the ball is fully into the indent when 3rd gear is selected. If the mod is done the set screw and locknut need to be made very secure, and the depth of the protruding screw noted. I must admit that the use of a 'positive stop' circlip feels slightly more comfortable, but not if the ball is not fully located into the shaft indent.

I must repeat that this concern only applies to later TD and TF gearboxes with the long 3rd @ 4th shifter shaft fitted. I look forward to the comments of others.

Cheers,

John

J C Mitchell

Hi John. I'm aware you are talking here about TF & late TD boxes. I offer the following words of caution to those planning their first gearbox rebuild. On completion of the reassembly if you wish to view the operation of the box under "road" conditions it is necessary to use a modified lid. This consists of a cut down lid (the one I used came from a Morris 10) & is the full width of the box but only about 30mm long. This ensures that the shafts are firmly held in their correct operating positions by the 3 balls & springs, allowing an internal examination whilst selecting the various gears. Operation of an early box without the lid, if the 3/4 synchro balls are not peened over, will result in them exploding into the box! Don't ask me how I know. Cheers.
Peter TD 5801

P Hehir

Hi Peter,

Interesting comments re the 'safe' operation of the gears, using a cut down lid. Presumably you do this with the gear box on the bench, but it would also be useful to check selection on an attached gearbox in the car. My only comment would be to make up a small metal spring retainer bolted to the rear of the opening, so as to not upset Morris 10 owners!

I am surprised that there have been no other comments on this issue, an important one when considering the correct selection of 3rd/4th gears, on late T type gearboxes.

Cheers,

John
J C Mitchell

Fair call John! I didn't chop up the Morris 10 lid, I just borrowed it (& am about to return the item ). My exploding experience happened on a bench after spending the day stripping & rebuilding the box. You certainly could use it in situ as you suggest (but I would resist the temptation to drive it that way!) Having said that I suppose you could chock the front wheels, put the rear axle on stands & take her for a drive, thus eyeballing the box under road conditions. Essential to keep digits, glasses, tools, foreign objects & OH&S inspectors well clear. Not that I'm advocating this, mind you! Cheers
Peter TD 5801
P Hehir

I should've added you'd probably get showered with gear oil though!
P Hehir

Hi Peter,

I wasn't seriously advocating starting an engine up with a cut down cover on the gearbox, but with an assistant on the starting handle, and one rear wheel jacked up, each gear could be then be checked.

I didn't really think you'd cut a Morris 10 cover, but why was it cut by someone else ? - just wondered !

Cheers,

John
J C Mitchell

I guess if the choice is to leave the lid lying in the grass in a car wrecking yard or put it to some good use? ... This operation was performed about half a century ago & it is now a valuable aid to gearbox restoration. Saw a similiar cut down lid in a Sprite gearbox mechanic's box of tricks here in Sydney quite recently, so the idea is not new. Hope someone swings this thread back to your initial query! Cheers
Peter TD 5801
P Hehir

This thread was discussed between 09/03/2014 and 11/03/2014

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