15 replies to this topic

[mbolt998]

'79 Mini 1000. Ran it up to temp for the first time in 23y with fresh oil and various fuelling and cooling system refreshes. Seemed pretty good but then noticed lots of oil on the floor. Like a pretty big puddle. Turned it off immediately without waiting to see where it was coming out.

 

It was somewhere from the "back" of the engine (by which I mean the clutch end). Just now jacked it up on the nearside and more oil immediately started dripping out of the inner pot joint boot. Popped the boot off at the fat end and out came more oil.

 

That seal was never great back when I was using the car (23y ago). I remember the grease in there was always kind of mixed with engine oil but I never did anything about it.

 

Can I change that seal without taking the engine out?

 

[colinf1]

Should be able to change those seals, but you'll need to remove the driveshafts, so that means removing front hubs.

 

It can also leak if the driveshaft isn't fully seated in the diff housing, but as its been sat for so long, it would be worth replacing them both.

[Spider]

It actually sounds like the Plug inside the Joint is leaking or displaced.

If you strip down the Pot Joint, you'll find there's a Plug, much like a Freeze Plug, inside it to blank off where the Shaft Hole is. These can leak.

I have had great success in cleaning all the parts (super clean) and re-assembling with Loctite 243 on the Plug.

[mbolt998]

Thanks for the tips! The gameplan now then is to take it all apart and see if I can find this plug you're talking about. I may even improvise "special tool 18G461B" or whatever it's called that the Haynes Manual speaks of for removing the pot joints :)

[Spider]

Sorry, I was short on time earlier.

Here's a cut away sketch of the Pot Joint, you can see the Plug;-

 

You can see the Plug in this one;-

 

Plug out

 

 

[mbolt998]

Thanks for the more detailed information! But is the plug actually an oil seal? It looks like it might prevent grease getting from the inside of the joint onto the splines. But my understanding is there shouldn't be any engine/gearbox oil here at all, unless the seal where the shaft comes out of the diff has failed. But since I will be taking the pot joint off anyway I'll have a good look at everything.

[Spider]

The Plug stops Engine Oil getting in to the Pot Joint and likewise, Grease from the Pot Joint getting on to the engine.

If you're not sure, pop a Pot Joint off while you still have Oil in the engine.

Does the Oil stay in the engine or run out through the diff cap where you've taken the Pot Joint from ?

[mbolt998]

Yikes OK, makes sense, thanks! Hopefully all will be revealed.

[mbolt998]

The Plug stops Engine Oil getting in to the Pot Joint and likewise, Grease from the Pot Joint getting on to the engine.

If you're not sure, pop a Pot Joint off while you still have Oil in the engine.

Does the Oil stay in the engine or run out through the diff cap where you've taken the Pot Joint from ?

We will see but the oil now (and historically) is leaking through the pot joint. In other words, you take the boot off, and lots of oil pours out. That implies the plug to me. If it was the seal it should be leaking out behind the pot joint, between it and the diff casing.

[Spider]

 

The Plug stops Engine Oil getting in to the Pot Joint and likewise, Grease from the Pot Joint getting on to the engine.

If you're not sure, pop a Pot Joint off while you still have Oil in the engine.

Does the Oil stay in the engine or run out through the diff cap where you've taken the Pot Joint from ?

We will see but the oil now (and historically) is leaking through the pot joint. In other words, you take the boot off, and lots of oil pours out. That implies the plug to me. If it was the seal it should be leaking out behind the pot joint, between it and the diff casing.

 

 

If you think about the Pot Joints and the Diff Output Shafts, where is the 'Oil Seal' between these two ?

[mbolt998]

 

 

The Plug stops Engine Oil getting in to the Pot Joint and likewise, Grease from the Pot Joint getting on to the engine.

If you're not sure, pop a Pot Joint off while you still have Oil in the engine.

Does the Oil stay in the engine or run out through the diff cap where you've taken the Pot Joint from ?

We will see but the oil now (and historically) is leaking through the pot joint. In other words, you take the boot off, and lots of oil pours out. That implies the plug to me. If it was the seal it should be leaking out behind the pot joint, between it and the diff casing.

 

 

If you think about the Pot Joints and the Diff Output Shafts, where is the 'Oil Seal' between these two ?

 

I assumed that the seal on the diff would keep all the oil in. So the output shaft would just be an output shaft that spun around. I'm still a bit confused. Is the output shaft hollow and actually full of oil?

[Spider]

,,,,,,. Is the output shaft hollow and actually full of oil?

 

From the Sump, yes.
 

[mbolt998]

OK managed to get the pot joint off with some difficulty. I made the special tool:

 tool.jpg   53.95K   9 downloads

 

inserted it behind the joint, and then whacked a cold chisel in between the tool and the back of the joint.

 

Here is the hole in the driveshaft which presumably feeds oil into the back of the joint:

 

 driveshaft.jpg   53.23K   9 downloads

 

And here is the joint, after cleaning it up a bit:

 inside.jpg   79.79K   7 downloads

 

I tried filling the top with paraffin to see if it leaked past the plug. It didn't. But I'm guessing that when the car is running the hot oil in there is under higher pressure?

 

 back.jpg   73.77K   4 downloads

 

So I guess I change the seal anyway. But I think the plug must be the real source of the leak, as Spider said, because the oil was going into the joint and coming out of the boot. If it was the seal it should have been coming out behind the joint. But I guess with oil everywhere it's hard to be sure.

 

So should I bash the plug out (with a piece of aluminium rod maybe?), clean it up and loctite it back in?

 

Or replace the whole joint? The Haynes manual speaks of more special tools that hook into the subframe somewhere for removing the outer driveshaft from this joint. But mine just disconnects with a squelchy pop as the boot comes off, the balls fall out, and the inner part of the joint slides out. Is this supposed to happen? Or is my whole joint knackered anyway?

 

Thanks again for all the help!

[Spider]

So should I bash the plug out (with a piece of aluminium rod maybe?), clean it up and loctite it back in?

 

Or replace the whole joint?

 

The Oil isn't under any pressure and it won't pour in to the joint (unless the plug is missing altogether !). If you leave your joint long enough under 'test' as you have it, you'll eventually see the paraffin coming through, but it might take a week. Remember, the oil you are seeing in the joint got there probably over months and it was probably only 1/4 of a cup or so.

If the joint is in otherwise good condition, knock the plug out, they are not super tight, a piece of aluminum would be good, just something so you don't distort the shape of it. These are an odd ball size, I couldn't find a commercially available replacement. As suggested, you can clean it all up and fit fit it with a sealant, I find Loctite works well here.
 

[mbolt998]

 

So should I bash the plug out (with a piece of aluminium rod maybe?), clean it up and loctite it back in?

 

Or replace the whole joint?

 

The Oil isn't under any pressure and it won't pour in to the joint (unless the plug is missing altogether !). If you leave your joint long enough under 'test' as you have it, you'll eventually see the paraffin coming through, but it might take a week. Remember, the oil you are seeing in the joint got there probably over months and it was probably only 1/4 of a cup or so.

If the joint is in otherwise good condition, knock the plug out, they are not super tight, a piece of aluminum would be good, just something so you don't distort the shape of it. These are an odd ball size, I couldn't find a commercially available replacement. As suggested, you can clean it all up and fit fit it with a sealant, I find Loctite works well here.
 

 

Thanks! It sounds like this plug can't be the main source of my leak then. Because it dumped like probably a litre or two in a few minutes. So I will have a closer look for that. The plug is probably also leaking which is why there was always a bit of oil in that joint for as long as I can remember. William of Occam never owned a mini.

 

Update: I've just popped the seal out of the diff and, like some of the other formerly rubber components on this car it's become completely hard and brittle. So I think what happened is as soon as things warmed up and expanded a bit it no longer made a seal.

 

So the gameplan is: replace both seals; loctite the plug anyway (because that joint always had oil seeping into it); probably do that on the other side too while it's off; return to square one via the longest route possible.

Edited by mbolt998, 14 May 2022 - 09:55 AM.