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MG MGA - Clutch Arm Shattered - Ever see this?

I found the reason why my clutch stopped working:

http://mgablog.com/archives/2005/06/clutch_problem.html

Doesn't seem like too common of a problem ... anyone ever see this or know how it might have happened?
Rich

Rich,

It is not completely clear from the photo.
You say that the clutch arm is broken, but it seems to be OK and still attached to the throw out bearing.
Is it only the bearing (carbon ring and steel carrier that is broken)? That is, the circular ring that has the two pivots.

Mick
Mick Anderson

I can't tell either...too much garage and not enough detail of the problem in the picture. The carbon beaaring is shattered and I can see one retaining clip, but can't see if the rest of the actual arm is there.
Jon Bachelor

I have never seen that problem with a clutch, but I am willing to take a guess as to the cause.
When the clutch is in the compressed position, with the six coil springs fully compressed, it has stuck in that position. After the operating lever has retracted, all of a sudden the springs have released.
If the lever and throw out bearing had fully retracted it could not have been hit, but not having been pushed back by the clutch it was only partially retracted.
Any other theories?

Mick
Mick Anderson

The arm is ok - the circular cup is shattered and the carbon ring is completely missing.

Barney Gaylord offered a theory via email that I thought was interesting. He thinks that perhaps the bearing ring had completely worn away and the consequent friction resulted in this damage.

As I can't find the carbon ring anywhere and there's nothing but dust, this seems pretty likely.
Rich

I agree with Barney. If the carbon ring had shattered, you would have found pieces of it in the bellhousing. When my father taught me to drive, many years ago, he stressed the point that if I was stopped for longer than 10 or 15 seconds, shift into neutral and take your foot off of the clutch! After seeing the bearing used in the MGA, I think that this is good advise. Reduce wear any time you can. This practice also reduces wear on the crankshaft thrust bearing.
Ed Bell

Is there "no" remains of the carbon ring?
It seems to still be visible in the photo. Is that just an illusion? Is the black area that shows just the metal?
If there is no carbon ring at all, but only the grooved seat in the metal, the carbon ring has not worn, it has fallen out. But where is it now? If it fell out, the gearbox input shaft would still support it and the next time you used the clutch the ring would be crushed.
This is a puzzle.

Mick
Mick Anderson

Mick, look on the floor in front of the bellhousing. Could be pieces of the carbon ring?
Tom

Tom,

I also thought that the pieces in front of the bellhousing could be part of the carbon ring. That is why I asked the question.
We have been given confusing information, firstly the lever was broken into "about a dozen pieces", then we are told it is not broken at all.
Then we are told the carbon ring is "completely missing", but there seems to be parts of it, although you can't be sure.
We need an absolutely accurate description of what is there and what is not there.
I have seen many carbon rings worn down level with the grooved metal seat without ever seeing the damage in the photo.


Mick
Mick Anderson

Fair enough. I just used a magnetic screwdriver to sort through the pieces, and it turns out that some of them are from the carbon ring after all (hard to tell from visual inspection, but easy with a magnet).

I've found about 1/3 of the carbon ring in several pieces. There is one large piece, from which it is easy to see that the wear was not parallel with the ring surface. Rather, the ring is worn away at an angle. I'll upload a photo later if necessary.

The rest of the pieces are from the circular ring that holds the bearing in place. The arm itself (up to the ring) isn't damaged - just the ring, of which about 1/3 is broken up(and mostly, but not entirely accounted for in the miscellaneous pieces).

The circular ring itself is ground down smooth, to shiny metal, at an angle. This will warrant a photo later when I get back. The metal is ground closest to the lever. Farther away from the lever, it appears to be completely untouched.

Rich

Sounds like the release bearing was not properly installed.
dominic clancy

Rich,

This is getting interesting.
I hope that you don't mind a couple more questions.
If we call the carbon "the ring" and the metal holder "the holder".
Is some of the ring stil in the holder? If so, how much?
Are the clips still in the two pivots of the holder? Are both pivots still fitted in the arm?
Do the two pivot areas, on the holder and the arm, both show their contact areas polished?
Are the locknuts still tight on the eyebolts of the clutch assembly?

Mick
Mick Anderson

Hi Mick,

There is no ring left in the holder.

The clips are still in the two pivots of the holder and both pivots are still fitten in the arm.

Not sure what you mean by the third question - the pivots themselves are not polished at all, but the portion of the holder near both pivots is. It appears that the top portion of the holder which is broken off was pressing at an angle into the clutch. This area may have gotten thin and then broke off.

The locknuts are still perfectly tight.

-Rich
Rich

Ok, more photos have been uploaded to http://mgablog.com/archives/2005/06/clutch_problem.html.

I think I found the rest of the carbon ring. Lots of black powder poured out of the clutch when I removed it from the flywheel.

It basically appears that the retainer cup was pressing into the clutch at an angle. The carbon ring eventually wore through and the retainer ring was then ground up at an angle. Eventually, the friction weakened the metal and the top of the ring broke off.

That's my best guess. Although one thing I'm not clear about. It seems that the retainer cup and ring have some freedom of movement that would ensure the ring is always parallel to the clutch. So how could this happen?
Rich

Rich,
Your flywheel ring gear looks normal to me, as I have a similar looking ring, although I may not see what you are seeing. Regarding your carbon ring holder( throw out bearing), it appears that it somehow got cocked against the pressure plate "fingers". In the parts manual they are called release levers. Check the levers in the pressure plate, where they would press against the throwout bearing. Chances are that they show damage. Check that the remains of the throw out bearing housing move freely in the clutch arm, although I believe that you state above that it does. When you install a new throw out bearing, you should check for free movement of the bearing in the arm, as your failure may have damaged the existing unit.
mike parker

If an MGA clutch fork is anything like a B, also check your bushings in the fork and the bolt that holds it to the bellhousing, a lot of play in there could be the culprit. Have had it happen to me before also.
LUVMYMG

Rich,

I only see your four new photos of 19th June by going to:

http://mgablog.com/archives/2005/06/

The URL you give above only shows the older photos.

Mick
Mick Anderson

Rich,

Is the throw out bearing free to move on its pivots? I don't like the look of that discoloration of the arm near one of the pivots. Could it have been red hot and seized the pivot? That would explain the angled wear. Even if it is now free, does it show signs of having seized?
I still do not see why there is no carbon ring remaining in the groove of the bearing. Even if it wore down to the metal and then broke you should still have the carbon ring in the remaining half. These carbon rings are an interference fit at "cherry red" temperatures, as stated in my mga twin cam Workshop Manual. If you took a throw out bearing and smashed it to pieces with a hammer, each segment would still retain its piece of carbon ring.

How does this sound:
The clutch was normal until the carbon ring wore down to the metal.
The metal on metal contact then heated the throw out bearing to cherry red temperature.
The carbon ring fell out and then was hanging on the gearbox input shaft, only to be smashed next time the clutch was used.
The heat between the the metal surfaces increased until the throw out bearing was seized on one pivot (see discoloration in photo).
The bearing collapsed due to the heat and the now uneven wear.
I assume that you are replacing the clutch assembly. If not, carefully check the surface that mates with the throw out bearing, including the three "mouse trap" springs.
I would seriously consider changing the throw out bearing operating arm.
Although you cannot tell from the photo, I think that the flywheel ring gear looks OK.

Mick

Mick Anderson

Back when I was changing a couple of clutches a week, this kind of failure was not uncommon, especially on cars driven in city traffic. It is the result of the bearing remaining in contact with the pressure plate in operation. This is driver error - resting foot on pedal, or hydraulic malfunction keeping pressure in system, or driven plate wear causing the pressure plate release plate (part the bearing contacts)to come back so far that the slave cylinder bottoms out. This last may also be a possible consequence of people putting longer pushrods in, usually to "fix" an earlier hydraulic malfunction (air in system); it may work when the driven plate is not worn, but as the DP wears the release plate comes back further until there is no place for it to go. Most of the time the release plate will be blued and/or heat checked, and will show wear from contact with the cast iron cup of the release bearing. In really bad cases, I've seen the release plate itself disintegrate, allowing the release bearing to grab one of the pressure plate fingers - NOT pretty! In any event, once the bearing is worn to the point where the cast iron contacts the relase plate, it will generate a lot of heat if it remains in contact for more than a few seconds. The clutch would still work for a long time IF you only used it whilst shifting, but if you had been doing that you wouldn't have a worn out bearing in the first place! The carbon ring is a shrink fit in the release bearing cup and will fall out if the cup gets hot enough; once it breaks from any cause there is nothing to keep the pieces in the cup. Long ago you could buy the carbon ring and shrink fit it into your old cup.
FRM
FR Millmore

Thought I'd add this. I had a similar failure. The Throw out bearing came apart. In my case it turns out the thrust washers in the engine fell into the oil pan. This allowed more slop in the crank shaft and I think caused the bearing to come apart. I have never heard of this happening but thought I'd mention it anyway.
Pete Kohne

With all the added info...I'd say Mick's assessment is probably fairly complete. The carbon ring is great in compression, but horrible in tension. This would also be worsened if water were to splash into the bell housing and onto the carbon ring during a very heated moment...though a bit of an imaginable stretch. Inadequate/missing grease on the arm's bearing's pivot point could have caused a cocking of the bearing. Extraordinary play in the arm's center pivot bushing could also allow uneven wear. The exact cause may or may not be determined, but the end result is clear.
Due to the cost (parts/labor) of a repeat offense, a careful inspection of the arm should be made before even considering reuse, especially with any discoloring (weakening) of the arm's bearing-pivot contact/support.

I've only separated six MG drivetrains and all used the carbon bearing showing no abnormal wear. Lucky...perhaps, but this fellow's experience begs me ask all if the roller bearing type would have also failed/seized under the same probable causes...
Jon Bachelor

Since I had to take out the gearbox for a rebuild this winter, I took the opportunity to install a roller-type throw out bearing. Mind you, that was only 700 miles ago but so far, I am totally satisfied. I am not in a hurry to take my foot off the clutch any more and there is no rpm loss when pressing the clutch either.

Karl
Karl Leclerc

The bushing and the through bolt at the pivot point of the release arm are subject to wear and are replaceable. They should be replaced with a new clutch. As for poor driving habits there really is no fix for a Loose Nut Behind the Wheel.
R J Brown

Hi Karl. Did you install a release bearing retract mechanism on your car? I have heard one is necessary to prevent burning the ball bearing out. Cheers! GLenn
Glenn

This thread was discussed between 18/06/2005 and 21/06/2005

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