17 replies to this topic

[bob540]

A while after buying my mini (1994 carb) I started hearing a knocking/tapping sound coming from the nearside front wheel. One night driving home it got really bad all of a sudden and there was a scraping sound too so I pulled over, jacked it up and found the wheel was very loose (I reckon another 500 yards and the wheel would've come off!  ), took the wheel off and realised that the split pin was missing so the hub nut was just coming undone. I put it down to poor workmanship by the previous owner or his mechanic, spent 10 minutes cursing them, fixed it and moved on.

 

The knocking was still there though so I did a bit of searching on here and figured the bearing was probably damaged as the play would go away when the brake was applied. Sure enough the bearing collapsed on me a couple of days later so I had them replaced on both sides and the ball joints too for good measure. The knocking was still there though and there was still play in the wheel (not loads but a fair amount and it would go away under braking). A couple of weeks ago it started to get a bit louder one day so I took off the wheel and realised the split pin had sheared off completely and the hub nut was coming loose again!

 

My question is; was the bearing just not seated correctly using the flat washer method by my mechanic when he replaced the bearing or did the wheel coming loose the first time damage the hub or something else in such a way that the bearings just cannot be seated correctly? I'm hoping to just replace the bearing myself so I know it's seated properly but if you all think other damage has been done then I'm probably going to replace pretty much the entire drive assembly on both sides just to get a nice clean start with totally fresh parts. I should say that my mechanic isn't a mini specialist but he's really good, I just think he might have missed the seating procedure as I'm sure it's not common for most cars. Sorry for the long post but I figure it's best to give as much detail as possible and thanks in advance for your help 

 

[Spider]

Given that the CV Nut was loose for some time before being tightened the first time (that you know of), there would have almost certainly been damage done to the Tapered Washer, the Drive Flange and possibly the CV, so these should have been carefully looked at and also replaced as required. It would have also been a good idea to check the Hub for wear too.

[Dan]

  You need to strip and inspect the assembly to find the damage.  There are a few things that can be wrong.  If the end of the CV joint where the taper washer pinches it has had a deep notch cut into it by that washer when it was in the wrong place then it's almost impossible to get the assembly to pull up tight enough.  The taper washer will just slip into that notch every time yo try to tighten it even if you use the flat washer first.  If there is a more subtle mark there it can be linished off but if it's quite deep the CV should be replaced.  If the assembly wasn't tightening up due to corrosion on the CV shaft stopping the races moving into place then the CV should be replaced.   The hub upright can be damaged in a couple of ways.  If the outer races span in place then the bore can be too worn to hold them tight or the machined in place spacer can be worn down.  If they were forced in off square then there could be severe damage to all the faces in there.  I would replace the nut and taper washer as a matter of course at this point.

[bob540]

Thanks for the replies lads, what I was thinking of doing was taking off the hub nut this evening if the weather stays fine, seating the bearings with the flat washer and then putting it back together to see if there is still play. If there's no play then could I assume that the cv and hub are ok or is that just half-arsing it? Is it even likely that any of the parts mentioned are ok or do you just think I should assume they are not fit for purpose and go ahead and replace everything as I planned. I need new discs anyway so I'd basically be pulling the whole lot out for that anyway and I'm much more concerned with safety than having to fork out 1,000 for parts.

[Dan]

  Personally I don't think you should just replace everything, an inspection will show what you need to change.  The bearings currently fitted are now scrap and will have been damaged by the abuse, there is not really a way to tell if any slop left after you tighten them now is caused by damage to the hub or to the bearings themselves.  So if the slop goes away when tightened then fine BUT you will still need to replace the bearings themselves.  If the slop doesn't go away then you will still need to thoroughly inspect to find the damage as it could just be caused by the bearing.

[adcyork]

Which type of castellated nut are you using? Is it flat on the back or does it have a raised section?

 

I had the same issue you are having and found the root cause to be a distorted taper washer that had been damaged by the raised section on the contact face of the nut.

 

The correct flat washer torque sequence was used before the taper washer was fitted for final assembly but the CV nut loosened itself twice until I swapped to the flat back nut such as this: 

 

http://www.minispare...|Back to search

[bob540]

  Personally I don't think you should just replace everything, an inspection will show what you need to change.  The bearings currently fitted are now scrap and will have been damaged by the abuse, there is not really a way to tell if any slop left after you tighten them now is caused by damage to the hub or to the bearings themselves.  So if the slop goes away when tightened then fine BUT you will still need to replace the bearings themselves.  If the slop doesn't go away then you will still need to thoroughly inspect to find the damage as it could just be caused by the bearing.

I think I will take off the hub nut and seat the bearing correctly then see if there's any play, if there's not then I can just order the bearings, tapered washer and castellated nut and if there is still play well then I can take it from there, it's such a quick job that I might as well do it and I'll at least have a somewhat clearer picture of what needs replacing. Thanks for your help.

 

Which type of castellated nut are you using? Is it flat on the back or does it have a raised section?

 

I had the same issue you are having and found the root cause to be a distorted taper washer that had been damaged by the raised section on the contact face of the nut.

 

The correct flat washer torque sequence was used before the taper washer was fitted for final assembly but the CV nut loosened itself twice until I swapped to the flat back nut such as this: 

 

http://www.minispare...|Back to search

I'm not actually sure, I bought it from a mini specialist here in Ireland so I don't know. I'm fairly sure they get all of their parts from minispares but I don't know which one it is. I'll have to have a look at that when it's off this evening.

 

EDIT: I was looking at minispares there and I know the hub nut on mine is the brass coloured one so if the 34mm is always that colour then that's the one I have. I'll order the 1.5/16" one when I'm ordering parts. I may buy a socket for it too.

Edited by bob540, 28 April 2015 - 12:50 PM.

[adcyork]

Put some pics up of the nut if you get chance

[spiguy]

Which type of castellated nut are you using? Is it flat on the back or does it have a raised section?

 

I had the same issue you are having and found the root cause to be a distorted taper washer that had been damaged by the raised section on the contact face of the nut.

 

The correct flat washer torque sequence was used before the taper washer was fitted for final assembly but the CV nut loosened itself twice until I swapped to the flat back nut such as this: 

 

http://www.minispare...|Back to search

 

Couldn't it be that the split taper washer was binding up on the CV joint - ie due to a groove on the CV -  giving a false torque reading (as described by Dan above), and then when you replaced the nut / split washer (I assume you replaced the washer) it didn't happen that time as new parts were in use (I imagine a new washer might clear the groove as you tighten up, as it hasn't been compressed yet).

 

I just can't see how a hub nut can back itself off unless the torque applied is false due to binding, and then subsequently movement occurs which releases the binding, leaving the nut loose.

[adcyork]

 

Which type of castellated nut are you using? Is it flat on the back or does it have a raised section?
 
I had the same issue you are having and found the root cause to be a distorted taper washer that had been damaged by the raised section on the contact face of the nut.
 
The correct flat washer torque sequence was used before the taper washer was fitted for final assembly but the CV nut loosened itself twice until I swapped to the flat back nut such as this: 
 
http://www.minispare...|Back to search

 
Couldn't it be that the split taper washer was binding up on the CV joint - ie due to a groove on the CV -  giving a false torque reading (as described by Dan above), and then when you replaced the nut / split washer (I assume you replaced the washer) it didn't happen that time as new parts were in use (I imagine a new washer might clear the groove as you tighten up, as it hasn't been compressed yet).
 
I just can't see how a hub nut can back itself off unless the torque applied is false due to binding, and then subsequently movement occurs which releases the binding, leaving the nut loose.
 

 
No. When I had the failure, it was less than 1K miles after a completely new build where the only reused part was the swivel hub. 
 
Torque relaxation occurred due to the raised section on the contact face of the nut causing distortion of the split taper washer by localised yielding of the contact surface This allowed the nut to break past the split pin and loosen off.
 
The washer was replaced as was the nut, for a flat backed item and I have never had an issue since.

In bob's case, the groove and subsequent false pre-load setting would make sense in the instance of the second failure but not in the first.
 
bob540 - can you post a picture of the washer and back face of the nut?

Edited by adcyork, 30 April 2015 - 09:04 AM.

[spiguy]

Interesting. Forgive my ignorance, but what mechanism is it that causes the unwinding of the nut on the front anyway? I can understand how this can happen at the back, where you have a stub axle and the bearings and hub rotate whilst the nut is stationery, but since at the front the whole assembly rotates together, I can't quite imagine what happens that forces the nut past the split pin and off?

[adcyork]

As the torque relaxes, the CV shaft and all of the other components are no longer under any axial pre-load so they can slide back and forth through the hub bearings by a small amount. This causes the CV shaft and inner bearing race to move out of alignment with the hub axis due to the inner and outer races of the taper roller bearings now not being seated correctly in relation to each other.

 

The drive flange, loaded with wheel forces in X Y and Z is now only held square to the CV shaft by the splines, of which a small amount of movement is possible.

 

This loading of the drive flange during braking, acceleration and bump causes a misaligned rotation force on a small part of the nut face which then causes the nut to work loose and break past the split pin.

 

Try putting a round bar in a piece of tube that it slightly larger and you'll see that combinations of for, aft, up and down motions result in a rotational component force. 

[spiguy]

That makes sense. I guess the amount of play in the interface of CV to flange via splines would have a considerable influence on that mechanism of undoing the nut.

[bob540]

Sorry I'm only replying now lads I couldn't go at the car until today 'cause of the weather. I took the hub nut off and used the washer method to tighten up the whole lot to 210Nm. Everything was perfectly tight, no play at all but after driving it for 15 or 20 minutes I can hear that the play has come back again. I took pictures of the bottom of the nut and of the cv joint, I'll attach them both. There seems to be a pretty decent groove in the cv, do you think there's a point in checking the hub or can I just assume that it's damaged?

Attached Files

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•  IMG_2015050410623.jpg   32.06K   41 downloads

[bob540]

Ok so I used the washer method to tighten up the whole lot and the play that was there before when I grabbed the wheel at 9 and 3 was gone (happy days), there is still play though if I grab the wheel at 6 o'clock, it doesn't budge if I grab it at 12 o'clock though. There's quite a bit of movement, though some of that could be just the suspension, and it makes a squeaking sound as it moves. Anyone got any ideas what it could be? I'm thinking a rubber bush just 'cause of the noise and I've had a look and they could probably all do with replacing but haven't got a clue if that's where the movement is coming from.