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MG Midget and Sprite Technical - Jacking using the diff case

Did I dream it or was there a comment in a recent thread that said it was a bad idea to jack up the rear of the car by placing a jack under the differential? If so, what is wrong with doing that?
Chris H (1970 Midget 1275)

The drain plug is right at the bottom so jacking direct could strain this area. I always use a piece of wood with a hole drilled in it to spread the load. Apart from that I thought the diff casing was the preferred jacking point.
Steve Church

Most jacks have a cup which allows the weight to be spread around the diff plug.
Personally I use as is but with the addition of thick cloth to avoid metal to metal contact.
Gary lazarus

Same as Steve - block of wood with hole in it.
David Smith

I have a drain plug that's flush with the case, and used a shaped cup on the jack without wood.

A
Anthony Cutler

Thank goodness for that - I place a block of wood with a hole in it around the drain plug and place the jack under that. I thought for a horrible moment that I was doing something terrible (did somebody actually say no to using the diff?)

Chris
Chris H (1970 Midget 1275)

Hi Chris,

you can search for previous threads on this topic and find it, I remember the discussion you are probably referring to and there was discussion about whether it could cause trouble or not

Remember that the whole car only weighs in at about 1500 ~ 1700lbs, with maybe only a 1/3 of that at the rear axle when you jack it up (there ought to be no driver or passenger weight when you jack, and any of the engine and front bumper weight in front of the front wheel center will counterbalance). So what the drain plug sees is probably less than 500 lbs.

the advice above about using a piece of wood is wise. I've just jacked right on the plug for all of these years and never seen it make any difference. The rear end that I just overhauled (after subjecting it to that treatment for over 15 years) looked as good as new when I inspected it (housing, threads and plug), if that is anything to go by.

Though, now that my housing has pretty black paint on it I might start using a block of wood, just to prevent scratching it!


Norm
Norm Kerr

As Norma says

Yes I saw that comment and it worried me a bit too as my drain plug used to stick out so far (and only went in a few threads) and my car is too low to get my jack under it even without a bit of protective wood or rubber

I bought a couple of new drain plugs and they were the same length so I cut one down and installed it on another diff oil change

I try when possible to use a block of wood with a hole drilled (both hardwood and soft wood have split when I used them)

But I realise when the car goes into a garage they dont worry about a piece of wood or cloth
Nigel Atkins

Always jack the rear on the diff housing, but we use a rubber insert in the jack, never had a problem, doesnt slip and doesnt damage the threads or the plug whatsoever.

The front is more of a concern in my opinion. Spreading the load with a small plank can lead to slipping, etc. Luckily we jack our up on the sump guard, which due to its design prevents the car from slipping rearwards.

PeterJMoore

Peter. Good idea using the rubber insert. Also your concerns about the front. The bottom of the cross member is quite thin even when new, so a piece of wood across the chassis legs does spread the load, but as you point out can slip with disasterous consequences for the radiator etc.
I do use a piece of 4"x 2" and I 've been thinking about screwing a couple of hooks in the back to grip the cross member to prevent it slipping and maybe cutting out the shape of the saddle in the wood to stop that slipping, or use your idea of the rubber insert at the front too.

Bernie.
b higginson

We have seam welded the rear edge of Wills cross member at the front, allowing for a touch more strength when jacking without the sump guard on.

My own shell is going to have a modified crossmember to allow for safe jacking, even something simple like replacing the sheet with thicker material and adding a cross bar of 1" box or similar to prevent slip and a good grip for the jack.

One of hundreds of small modifications i'll be making to the new shell.
PeterJMoore

At the front I use a piece of 19mm ply cut to size - keep meaning to thread a small bolt into the centre of the ply to locate in the crossmember drain hole - sort of sliding / shear key.

R.

richard boobier

This thread was discussed between 08/10/2010 and 09/10/2010

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.