At 11:10 AM 10/25/98 -0900, Baker, G. wrote:
>.... My veh is a 1956 MGA, not chasis # but engine #BP15G-1444.
1. I've got no spacer tube on my 1st/2nd shaft (Moss 3461-140).
Probably never was one in that (early) model gearbox, but you could add one
if you like. I think it goes on the 3rd/4th rod, not on the 1st/2nd rod.
I believe this part was introduced at or shortly after the start of the
1600 (type) gearbox that came in just before the end of the 1500 engines.
And I think the tube spacer is intended to stop the motion of the 3rd/4th
shift fork/rod as it is entering 3rd gear position, such that the ball
detents in the 3rd gear hub and on the shift rod will fall directly into
the detent notches and not allow an overshoot condition which would
encourage it to rebound and pop out of 3rd gear. Other small changes were
also made at this time to reduce the pop-out-of-3rd problem, see more below
with item 6.
2. I've got no shim (Moss #461-280) on the input shaft. Could these be a
later or unnecessary modifications or has someone been there before me.
Someone has likely been there before you. I do not recall ever seeing less
than two shims (at 0.002" each in this location, and sometimes 3 or 4
shims. The idea here is to minimize end float for the input bearing in the
aluminum housing. Proper measurements and correct shimming can control end
clearance for the bearing at 0.001" to 0.003". Making the clearance zero
or less (interference) will defeat the front cover gasket and result in an
oil leak. Leaving axial clearance of more than 0.003" results in end float
of the input shaft on acceleration and deceleration in gears 1 through 3
and reverse (helical gear mesh with laygear) which may cause undo wear to
the bore of the aluminum housing. I know you've read my web page, so you
know how to fit the shims. Buy a few, they're cheap, maybe 2 each of
0.002" and 0.004".
>3. How do you suggest one removes the circlips holding the needle
bearings in the laygears and once they are out can they be replaced with
newer encased bearings I've read about? My layshaft does show significant
wear so the bearing should be renewed. Any experience in this would be
appreciated.
The encased bearings are interchangeable with the original loose needles,
and lots easier to use. Buy the shaft, buy the needle bearings, get
creative and get the circlips out somehow. Whatever you do, you will break
or otherwise damage them beyond use, so have new ones ready to install.
You should only have to remove two of the circlips, whichever two are
easiest to reach, leave the third one in place. I seem to recall retaining
one end of the clip with a small flat blade screwdriver to prevent rotation
in the groove while poking a sharp pointed awl under the other end of the
clip to lift it out of the groove, then putting the flat blade behind the
lifted end of the clip ring and bending it inward with a twist of the
blade. For sure the first clip you do is a knuckle torturing two-beer job,
but once you figure it out the second one is out in a minute or two.
>4. All my gears look pretty good.......to me..........but maybe I'm
missing what to look for. The reverse gear does have some very small
"lipping" on the gears but I think I'll just dress them. Other than the
minor wear on reverse the only real wear is on the Baulk(Synchro) rings,
the bushings and the layshaft.
If there are no obvious broken chips in the ends of the teeth, use a
Gibbonizer to gently touch off any sharp edges or burrs, bless the gears
and put them back in. Check the bushing in the reverse gear, usually
perfect but it doesn't hurt to check.
>5. I am in a quandry as to the Forks because I don't know what to look
for. I suspect they're worn but I don't know what warrants replacement.
It's a little subjective, but the forks should not rock excessively if
wiggled in the hub slot with the shift rod removed, and they should not
bind in the rotating hub with the shift rods in place. They likely had
0.002" to 0.005" of end float when new, but if wear has produced no more
than 0.020" end float now, they should be perfectly functional. This is
from no published source, but from some years of mechanical engineering
experience.
>6. Has anyone modified their 3rd/4th selector shaft by deepening the
detent so as to prevent jumping out of 3rd gear.
Not I, but .... the workshop manual section FF (exactly one page) describes
the modification from the factory with the 1600 gearboxes. Shallower depth
of drill hole for the 3rd gear rod detent spring can be achieved with a
small shim button in the bottom of the bore before the spring is installed.
Two detent notches in the shift rod were deepened by 0.018", which can be
achieved by changing the shift rod to the later production part, or if you
have an "in" with a machinist you may have the two cylindrical notches
ground deeper (not the center one). Also check the length of all the
detent springs under load, the book gives the details of load vs length.
Personally I have no problem with the original design, as by now my car has
trained me to keep my hand on the shifter when downshifting into 3rd gear
at speed, so now I never notice it pop out of 3rd gear (like it used to).
>7. I don't see a lot of wear on the thrust washers but plan on mikeing
them. Is there anything to look for with these? I notice Moss sells three
different sizes.
One size for the front, four different sizes for the rear. These are
hardened steel washers running in oil in the lowest part of the gearbox, so
usually not much wear. If you don't change the laygear the original
washers are the ones to use. Rear washers are available (or at least
spec'd) in 0.003" increments. Can't recall where I saw it, but I think the
end clearance (dry) is intended to be 0.004" to 0.008" (2 washers = 4 oil
spaces). A little more clearance probably won't be noticeable, it just
adds up to a little extra backlash in the gear train as the helical gears
can float axially. If you're like me and always on the gas or on the
brakes, you'll never notice. If you're in the habit of lugging the engine
under load below 1000 rpm you may get a resonant rotational shaking of the
engine on the rubber mounts which may take advantage of said backlash and
shake your neck accordingly, reminding you not to do that.
> I plan on renewing baulk rings, layshaft, springs, needle bearings(four
sets), bushings(3), gaskets, roller bearings, seals, and possibly thrust
washers. Any other thought?
Thrust washers are probably okay. New gaskets, seals, lay shaft and needle
bearings are a given. Most springs are likely okay, but check length
against load per spec's in the book. If you buy new ones, check them also
before installation.
Bronze bushings and interlocking ring on the layshaft I have only replaced
after I have damaged them during R&R. I have not known them to wear out in
service. Either the gear is locked while engaged with no relative rotation
on the bushing, or the gear is free-wheeling on the bushing with no load.
For the big ball bearings, rotate them in your fingers with a small thrust
load and a bit of oil inside. If you feel any vibration or scraping
greater than perfectly smooth, or can hear any noises from within, replace
the bearing. The input bearing is more prone to wear than the center one.
I have very little experience with the tail bearing in the 1600 box, but
the same test applies.
One last big headache may be the big steel/bronze bushing carrying the
sliding spline drive shaft front yoke in the rear of the 1500 gearbox. Two
years of hunting says this part is made out of Unobtainium. For
replacement I used a plain bronze bushing procured from the local bearing
supply house. Original bushing is 1-3/8" ID x 1-1/2" OD x 2-3/4" long.
New bronze bearings do not come that long, so buy two pieces each 2" long,
cut a 3/4" long piece from one and install it along with the 2" long piece
to make up the 2-3/4" length. I have one in service now for 30,000 miles,
no problem. And these plain bronze bearings will not need to be honed
after installation.
When you place the drive shaft front yoke in this bearing with a little
oil, there should be no perceptible side play. Any noticeable radial
motion here will quickly destroy the rear seal, allowing the oil to escape
from the gearbox, possibly causing catastrophic failure of this rear
bearing, the drive shaft yoke, and maybe the housing as well (been there).
First clue that this may be happening is a nasty vibration coming from the
drive shaft, very similar to the effect of a bad u-joint.
For a much detailed synopsis on what to look for in worn parts during the
gearbox rebuild, see this web page:
http://www.ntsource.com/~barneymg/mgtech/gearbox/gt101.htm
Have fun with the tinker toys,
Barney Gaylord
1958 MGA with an attitude
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