TSEngel@Comcast.net
Date: Thu Jul 23, 2009 10:55 am
Subject: Re: Re: 2nd question
Ed,
Drive out the roll pins that secure the inner yoke to the
transaxle output shaft
With the shaft assembly loaded inward (ie, the car sitting on it's
suspension), look through the roll pin bore and observe how well
the inner and outer holes align. Without any shims, the yoke
slides on too far, the holes overlap, and the through-opening
that remains is sort of a catseye shape.
The idea is to install shims behind the yoke, in the bore
surrounding the transaxle's output shaft, moving the yoke outward
until the inner and outer holes align. In a perfect world, the
idea would be to produce a stepless, smooth bore for the roll pin.
In the real world, the shims are available is limited
thicknesses, and there's almost always some minor step.
In the beginning, the outer hole in the yoke will be too far
inward. As you shim it out, it will cross over the perfect
alignment point and end up too far outward. With the shim
thicknessess available, you can move the hole in 0.005"
increments. Shim until the mis-match is just one shim too much.
The odds of perfection are not in your favor. If removing one
shim leaves the outer hole too far inward, and putting that last
shim back in leaves the hole too far outward, then go with the
latter case... one last shim too much.
If you stop one shim short, then as the roll pins are installed,
the yoke will just slide outward on the shaft until the yoke's
hole aligns with the shaft's hole (which is now further out), and
there will be no compression load holding the end of the yoke
against it's seat in the transaxle.
If you go one shim too far, then when the roll pin is installed,
the yoke will be drawn inward to align the holes, pressing it
firmly against it's stop, and holding there by the extra
compression on the roll pin. The split in the roll pin provides
it with sufficient compliance to work with that negative fit, so
it acts as a spring. A solid pin or bolt would not be capable of
doing that.
If you shim to one increment short, then the roll pin will hold
the inner yoke out, off it's stop by whatever the final mis-match
was. Then the yoke will be free to wobble and slide in and out
as the suspension loads and unloads. Continuously working the
slop is more damaging to the parts, and subjects the roll pin to
fatigue cycling, than a few thousandths of constant compression
fit due to the spring effect of the split roll pin.
Slide the yoke off the shaft. Look in the bore surrounding the
shaft to locate any existing shims and withdraw them. A dental
pick can be a useful tool for that. Inspect the shims. If
they're still in good condition, they can be re-used. Add or
subtract shims as required, re-assemble and check the hole
alignment. Repeat as required until the outer hole (the one in
the yoke) is as close as possible to aligning with the inner hole
while still being too far outboard.
When you install the roll pins, note that one end is tapered.
If it's not, then grind a short tapered lead on the end. Insert
the taper into the bore first, and drive it home.
There are special pin punches made for roll pins. Instead of
having a flat end, there's a raised bump in the center. The
bump fits into the roll pin's hollow center and serves to keep the
punch centered on the pin. You can drive the roll pin with a
common, flat end pin punch, but the registration bump really does
make the task easier.
Note on removing the roll pins:
I've had several roll pins crack in service right at the shear
line between the output shaft OD and the yoke ID. As a result,
the long thru-pin becomes three short pins. Since there's likely
to be some small step mis-match between the bores in the yoke and
shaft, especially if the shims are not present, the ends of the
pieces of sheared pin catch on the steps.
As a result, the pin doesn't drive out easily. Even with your
best shot, and a stout hammer blow, the pin doesn't move. If
you run into that, keep in mind the possibility of a fractured
pin. Avoid just hammering away on the pin, since each hammer
blow is going directly into the differential support bearing, and
you really do not want to damage the bearing.
I usually support the yoke from below, using a length of iron
pipe supported on a trolly jack. Raise it until it applys some
upward pressure on the yoke. Then hammer downward. With that
set-up, the pipe acts as an anvil, and the worst of the hammer
blow doesn't get to the bearing.
If the roll pin is fractured, prepare for a battle. I've used
easy outs, vice grips... anything I can think of to "withdraw"
the sheared ends of the pin. A bigger hammer, and driving it
through, isn't always the best answer.
Good luck,
Tim Engel
----- Original Message -----
From: ed law
To: lotuseuropa@yahoogroups.com
Sent: Thursday, July 23, 2009 7:58 AM
Subject: [lotuseuropa] Re: 2nd question
>
> Im referring to the thin ones as there is a lot of droop
> at the in board universal end where it enters the case
> ---ed