At 06:52 PM 10/22/01 -0500, Phillip Farmer wrote:
>....
>What holds the axle in place if you can just drive it out?
The rear axle rotating half shaft is held in place by the wheel bearing,
which is a tight press fit on the shaft. The Pinion Pin, sometimes called
Planet Gear Axle, is held in place by a steel cross pin (pinion pin peg),
which in turn is held in place by a peening over of the edge of the hole
after the pin is installed.
>Apparently the roll pin (pinion peg) is sheared. The pinion pin rotates
>with the gears as the cage turns. I assume this was potentially a major
>potential problem. The gears should rotate on the pinion pin. Is this
>correct?
Correct. The rears should rotate, but the pinion pin should be fixed in
the housing.
>What could have caused the roll pin to shear? The ends are still in place.
You have a serious question there. Every one of these assemblies I have
ever seen that was original has a solid steel pin in the position for the
"peg", never a roll pin. (Anyone may feel free to correct me if the later
MGBs were built with roll pins here.) Even at that these steel pins are
know to sheer on occasion. When one wheel wants to spin slightly under
hard accelleration in lower gears, there is a heavy radial load on the
pinion shaft. This load is in a direction perpendicular to the axis of the
peg. If there is a little clearance between the shaft and the mounting
bore, the shaft will work back and forth a little in the housing. If the
peg is a tight fit in both the shaft and the housing, then said heavy load
will be applied directly to the peg, with the possible consequence of
eventually sheering the peg from accumulated stress (ie, long term stress
failure).
I have mixed feelings about this mechanical arrangement. While the solid
steel peg is likely to be stronger than the roll pin, the roll pin may
conceivably be able to flex enough to relieve the stress of the described
motion of the pinion shaft. However, continued flexing of a tempered
spring steel roll pin can also cause fracture failure. If it were my
design I would like to see a solid steel peg installed loosely with a
little more clearance around the peg that around the pinion shaft, such
that the shaft could bear firmly against the housing without stressing the
peg, and the peg could serve solely to prevent rotation of the shaft.
Now about removing that broken peg. We have done exactly that at a club
tech session earlier this summer. See photos and notes here:
http://www.chicagolandmgclub.com/photos/a_diff/index2.html
You start by drilling out the burr in the peened side of the housing at the
exposed end of the peg. Then you drive the peg out from the other side
with a small diameter punch. And I sure wish they would have made the
drive-out hole a little larger diameter so you could use a larger
punch. We did two of these in one day, as we were swapping out the better
bevel gears and thrust washers into the replacement differential while
changing the final drive gear ratio. One of the units had a broken peg,
and I'm sorry we didn't get a few more pictures at that point. We had the
same problem in that the peg was in three pieces, and the center section of
the peg was not aligned with the hole in the housing.
You can use a thin cut off wheel in a hand grinder to make a slot in the
end of the pinion shaft. Then you can use a large screwdriver to rotate
the shaft to align the peg with the hole in the housing. Good luck with
finding the correct orientation for the shaft. Turn a little, tap the peg,
turn some more, tap the peg again, and keep at it until the peg comes
out. This may be even tougher than it sounds, as the peg itself will quite
likely have a nasty burr at the point where it sheered (at two sheer
points). You may have a good clue at the proper position when you tap the
peg and the shaft no longer turns.
And if that fails, and you're sure the pinion shaft is free to turn in the
housing, then use a large diameter punch and a BFH to drive the pinion
shaft out of the housing without regard for the peg by hitting the shaft on
the end nearest the peg. Once the pinoion shaft is out you can knock out
the three pieces of the broken peg with a smaller punch.
Oh yes, and when you do succeed (and you will with proper persistence),
hoist a cold one for the bunch of us, and then come back and crow a little.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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