Throwout bearing

additional trans snout collar picture.
The metal failure, ( galling ) was stunning and disappointing, the throwout bearing was replaced at no charge, but the snout was not.This time I will hope for a better result...

for my education...
are those two pieces stationary (as far as not rotating) and the sleeve with the bearing (upper pic)just slides back and forth on the shout (lower pic)?

I would assume the two pieces are made of dissimilair metal (to reduce friction). what would be the expected clearance?

besides a clearance problem, is it possible there is an alignment where the pieces got asquew and caused the intial stick, then galling

quote:

is it possible there is an alignment where the pieces got asquew and caused the intial stick, then galling

I am really at a loss to see how that failure occurred.I trust you have inspected the crankshaft pilot bearing for wear, but I don't really see that as a contributor to this failure.

What about the bushings on the clutch cross shaft?

Larry

LF, would the clutch cross shaft item 1006?
if so, I was sort of thinking the same as one side was pushed ahead of the other

Chris, the parts shown appear to have the galling at the bottom of the carrier & the ZF nose. I dab a little grease on the radiused fingers and nose-piece when assembling, but I've never seen galling that bad! Normally, all you see is a polished area where the loaded parts slide on each other. All the moving parts are cast iron and run metal-on-metal with no lubrication except what gets dabbed on during assembly.

The radiused fingers are designed to push on the approximate middle of the sliding throwout bearing carrier, just like rocker arms on a valve. Either debris got caught in between the carrier and ZF nose, or a misalignment somehow occurred. If the nose-piece got loose on its 3 allen bolts, you would have had a massive lube leak, so I dunno. Is it possible the pilot bushing is badly worn?

quote:

LF, would the clutch cross shaft be item 1006?

Yup

I still really got nothing on this.

Very odd

Larry

are those two pieces truely both cast iron?

the dry static friction of cast iron on cast iron is "stuck together" (CoF>1). a little grease will make it slippery (CoF <0.1). I would think one should be a mild steel [CoF ~ 0.4)

If they are both cast iron, maybe the local vibration prevents a true static and the dry sliding CoF would be about 0.2. a dab of lube still sounds like it would be highly desired

The pieces are both machined steel, the failure I believe is from no lubrication between the throwout bearing and the collar it rode on, I knew it was impossible as I worked through the problem but in the end it was true, galling from one surface to the other acting like glue. The transmission was also rebuilt, did I leave that out? The point on the collar where it stuck was at the furthest retraction ( top of the pedal). I was able to actuate the assemble numerous times in half measures before it totally failed.

If you look opposite the gall area, I wonder if you might see a small dimple or dent as a shiny spot that forced no clearance in the galled area.

I have been doing a little googling to "learn" a little bit about throwout bearings and I noticed some (I think GM) have a recess in the bearing slide for grease



HEY RON McC,

How are you adressing this when you put my ZF togetther?

Jack and JFB are correct, I think, but on reassembly all will be thoroughly checked.
No one had herd of this before, at least in my circle of gear head friends. I have been jinxed
with a bunch of crazy problems that have kept me wrenching for the last 5 weeks! I think it was all those mean things I did when I was a kid.
Is it the 13th?

would having a groove cut in the ID to hold a little grease be an improvement?

JFB, maybe, but I don't think so, I have a theory on what went wrong and after I receive the new collar I will test it out and let you know.

If you can (for my education) could you get some mic measurements? Maybe even a more general photo?

Are you replacing the guide tube? (photo 2)

I looked at the old retaining spring on the galled throwout bearing and I was shocked how towed in the spring was

I use molybdenum paste instead of grease or anti-sieze.

The clearance between the throwout bearing and the collar is 90 thousands. I think the problem was with the wire retaining spring that hold the bearing housing to the actuating fork in the bell housing. the picture illustrates the "right" and "wrong". The "wrong" was really wrong on the part, I had to straighten the arms out to reach the "wright" position. The warning is if the arms are not straight the assembly may have problems!

The other problem was no lubrication, I used wheel bearing grease on the collar and on the fork arms.

The throwout bearing housing is highly machined and if not attached correctly, well I believe could have caused my galling problem

Proper retaining spring placement. I am keeping my fingers crossed and stabbing it in tomorrow, if you don't hear from me again it worked.