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MG Midget and Sprite Technical - Rear hub nut torque figure ?

Hi,
Does anyone know what the big rear hub nuts on a Mk 2 midget should be tightened up to, torque-wise, please ?
I can't seem to find the number in any of my manuals/books.
Thanks.
Squibby
M W Sutherland

Only ever done it up "tight", and then bend the lock tab back in place. It can't go anywhere. So don't worry about it. If the lock tab has never been off before you can reuse it. I've never replaced mine, and it's fine.
Lawrence Slater

I did mine to 100+ lb/ft. It's worth buying the correct spanner I got mine from *bay USA.
Tim Dalton

at 100 lb/ft I'm amazed you didn't strip the thread! the nut is super-skinny and only needs to be tight enough to remove any play between hub and casing.
David Smith

I did a quick search through the archives.
courtesy of Bob T. "My BL Manual for the Mk3 Midget lists the torque for the hub nut as 140 lb/ft."
Tim Dalton

How do you know that 140lb/ft isn't a misprint and that actually it should read 40lb/ft?

I'd expect that anything much over 40lb/ft will compress the soft steel of the locking tab.

How did you check the torque using the correct spanner?

I think the consensus in the past has been between 40 and 80lb/ft. I forget what I've used on my car, without a lock tab.
Daniel Thirteen-Twelve

I don't think they are 140 lbs ft. I looked in the BL manual and I couldn't see a torque for the hub nuts. It's in section H4 and it's quite brief with no torque there. It talks about the gasket and oil seal and just states assembly is the reverse of the removal procedure. The only torque of 140 lbs ft I could see is for the pinion hub. i.e. the big nut on the front of the diff. This is mentioned in the next section H5. Once you go over 100lbs ft often things start breaking.
Greg H

This has been discussed so many times in the past! The nut needs to be tight enough not to work loose, which is largely why it has the big tab washer. And it isn't compressing anything. But with a nut that size and the fine pitch thread there is a real danger of stripping the thread, or it jumping and cross threading if you overtighten it. Certainly 140 ft lbs is way too much and is likely to ruin the axle casing (which is softer than the nut).

Most shade-tree mechanics wouldn't have a means of combining a torque wrench with a spanner that fits the nut anyway. Just do it up "grunt tight" with a bar or lever about 18" long. But do make sure that the locktab is in good condition and well fitted.
Guy

As has been mentioned before, they do need to be very tight, not just quite tight.

Although the nut is quite thin, it is a large diameter and therefore has a huge surface area of thread.

If not tight enough, it is possible for the bearing to compress the washer, due to cornering forces imparted by the wheel, enabling the nut to become looser.

I recently dismantled an Austin A30 rear axle and had great difficulty undoing the LH hub nut. I was using all of my weight with a 3-foot bar and I still couln't get it undone. It was at this point that I discovered that the A30 did NOT have a LH thread on the LH side. Even so, I didn't strip the thread, either.
Dave O'Neill2

Hi guys,

Dave O'Neill2 is right.
I, too, used to spread that mis-information about that nut "not needing to be tight", until some more knowledgeable folks chimed in here, with first hand experience of ruined rear axle housings caused by too-loose hub assemblies. Even though the lock tab might prevent the nut from turning, the concern is that if it is not fully tight then the clamping load on the system will be too low and the hub /bearing would be able to squirm around and erode the housing / threads.

One of them reminded me about calculating the proof load of a fastener that size and I was thoroughly convinced that 140 ft lbs is the correct torque:

Hub nut torque (not shown in the manuals): 140 ~ 150 ft-lb. This size of Grade 2 nut, diameter 1.5" - 12 threads/inch x 1/4" thick is physically capable of more than 900 ft-lb of torque.

Don't worry, you can not strip that thread. That is, unless some previous person has left it loose and the thread has been eroded by the nut shifting around under use (that has happened).


My advice is to get a breaker bar and get it good and tight, the next time that you are in there.
Apparently, the reason why the manual didn't cite a number is because there is just so very much safety margin between 140 ft-lb and 900 ft-lb. Probably every shop (back in the day) had a very long wrench with that 1 7/8" on one end and a mechanic standing on the other.

":oD
Norm
Norm Kerr

Opps just seen my mistake. I meant socket not spanner..
You can get them from the USA online quite cheaply.
Tim Dalton

Well all I can say, is that I should have ruined my rear axle several times over then, or I have the brute strength of a gorilla. The only tool I have ever used to tighten my hub nuts, is a large adjustable pipe wrench, with about a foot long handle. And I don't stand on it.

It's never come lose, and the bearings have not worn prematurely. Must be pure luck. That's a lorra lorra luck for 34 years. :).

I can't help thinking, that if 140lbs was/is indeed needed, that since pretty much everything else that needs torquing is quoted with the appropriate figure, this must be one huge oversight, or it just needs to be "tight".
Lawrence Slater

Lawrence, that's my experience too! Maybe it is just one of those things with a wide tolerance so it doesn't matter whether it is just tight, or ultra extra tight. Just so long as it isn't loose!

Actually last time I did them up I used a portable bench vice as I couldn't find my big adjustable . - No the vice wasn't attached to the bench at the time! Just used the jaws to grip the nut and then a length of bar through the body of the vice to turn it up tight.
Guy

I do them up well tight but nowhere near 140 - the threads often don't seem to be that good a fit - slop/engagement - probably because its unusual to have such a large diameter and such a thin nut - the ratio just looks wrong.Quite a few axles have been stripped by overtighening.

Many I've seen have been driven undone/tightened with a chisel !

When I bought my present Midget to restore - my brother gave me a present - another socket set but 3/4" drive !! - never thought I'd use it, but hub nuts, front pulleys etc have proved me wrong - had to make a reducer to fit my 1/2" torque wrench though.

R.
richard boobier

Many thanks everyone !

Is the LH nut ( nearside ) on a LH thread then ? It doesn't say that in the manuals either ?!

My car is a 1964 1098cc, but I've swapped from wires to 4-studs and am using a rear axle from a 4-stud 1969 1275 Mk 3 Midget, with the 3.9 diff instead of the 4.2 that was in my wire wheel axle.

Cheers once again.

Squibby
M W Sutherland

Yes, the LH hub has a LH thread. It is actually stamped on the face of the nut.

I remember reading - in 'More Healeys' IIRC - that the early Frogeyes had a RH thread, but they had problems with them coming loose.
Dave O'Neill2

OK - thanks Dave.
M W Sutherland

This thread was discussed between 24/12/2011 and 28/12/2011

MG Midget and Sprite Technical index

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