[BOUNCE mgs@Autox.Team.Net: Message too long (>10000 chars)]
Date: Thu, 15 May 1997 08:51:39 EDT
From: barneymg@juno.com (Barney Gaylord)
Subject: Re: Pulling gearbox, what else?
Steve,
On Wed, 14 May 1997 22:58:25 -0700 you write:
> ..... '74 B has been complaining when I shift. ..... decided to
>pull/rebuild the tranny.
> .....
>My questions: What else should be done while Di's out of commission? Any
tricks/hints on insertion/removal of various pieces/parts would be
appreciated. .....
I've gone a few rounds (well, OK, many rounds) with MGA gearboxes, and no
big deal, no special tools required, you can do it. I wrote this for
some MGA guys a while back, but most of it is applicable to MGB as well.
Have fun.
Subj: Rebuilding the gearbox
When you open the gearbox, there are a few specific things to look for.
First count all the teeth just to be sure that they're still all there --
that shouldn't be a problem.
When you disassembled everything, you'll probably find the lay shaft to
be worn somewhat where the needle bearings run against it. You should
probably replace the lay shaft, but it's a judgement call when you see
it. If it doesn't look too bad, and you drive the car in a civil manner
(yeah, sure), you may opt to put the original back in. But personally, I
thrash the crap out of the thing, and I expect to keep it another thirty
years or so, so I figured a new lay shaft and needle bearings to be a
good investment. They're not the most expensive parts in there, and I've
done it for two gearboxes now.
You may also consider replacing the big ball bearing on the input shaft.
It's a pretty rugged part, but it depends a lot on its past history of
maintenance and such. The best way to check this bearing is to run it
before you yank the engine and listen for noise. With the engine running
and the selector in neutral, depress the clutch pedal for a few seconds
to let everything stop rotating and listen, then let the pedal up and
listen again. If you hear a fairly loud hissing noise when you let the
pedal up, that's the input bearing telling you it's tired. To muffle the
engine noise, it helps to get another person to put their foot over the
open end of the tail pipe and nearly stop it off, not enough to kill the
engine mind you, but almost. When the parts are in your hands, try
wiggling the outer bearing race. These big ball bearings do have a small
internal clearance, so a little wiggle is OK as long as it turns smoothly
without any noticeable scratching sounds. It should be very smooth to
the touch when rotated with a little oil in there. If you find a lot of
wobble or nasty noises, it's a gonner for sure.
Check the syncro rings after removing the side cover but before
disassembling anything else, press the brass ring as tightly as possible
against the mating cone surface, then try a 0.020 inch thickness gauge
between the flat surface of the brass ring and the adjacent steel
surface. If the feeler gauge fits without binding, the syncro will
probably work OK for at least the next 40,000 miles or so. Check the
brass rings again after disassembly. Look at the angled surfaces on the
triangular ears, and compare the most worn ones (probably second gear
syncro) with the least worn ones (probably fourth gear syncro). If
you've lost nearly half the thickness of the triangular ears, it's time
for new parts. I've never known them to wear out the conical working
surface, just the outer ears.
Check the working surfaces of the brass shifting forks where they mate
with the grooves in the sliding steel sleeves. When new these fit almost
like crankshaft bearings, just a couple thousandths inch of clearance.
After 100,000 miles they get a little loose and wobbly but will usually
still work just fine. Don't worry too much unless they're really sloppy.
My original gearbox has about 150,000 miles on it, and the forks were
working OK. I swapped them out for some younger ones recently, but only
because I had some extra ones laying around and put in the best I had.
Check the bore holes where the shifting rods slide in the aluminum
housing. They should be a very close fit with little or no perceptible
clearance. The ones inside of the main part of the gearbox are usually
perfect. The rod in the remote control tower can be a different story.
This one is exposed to road dirt from underneath (housing is open on the
bottom), and the aluminum bores can get pretty sloppy, especially the
rear bearing hole. Also, check the spherical aluminum surface where the
shift lever seats in the remote control tower. Somewhere way past
100,000 miles this surface gets badly worn, and the shift lever action
gets sloppy. If I remember right, the flat top surface of the spherical
part should sit about flush with a flat surface inside the housing. Of
three gearboxes I have (or have had) I have only two of these housings.
The one I use is really good, but the other is really badly worn, both in
the rod bores and in the spherical seat. I could easily sleeve the
bores, but fixing the worn spherical surface is cost prohibitive (too
damned expensive). I think the only reasonable fix here is new (used)
aluminum part.
Check for wear on the selector parts, Selector-1st and 2nd gear,
Selector-3rd and fourth gear, Selector-reverse gear, and
Lever-front-selector; also the tips of the fingers on the Interlock Arm.
If the corners of these parts are worn and rounded off, that's OK, it
just makes it slicker shifting. But if you can't find any flat surfaces
left (completely rounded off the parts), then the shifting will be quite
sloppy. You should best check the feel of the shift lever before you
start, while you can still drive the car. When you move the shift lever,
if you have trouble finding the right gate or the throw seems to go too
far, especially into 1st 2nd or reverse, or if it tends to get stuck
badly in 1st 2nd or reverse, then the selector parts need to be replaced
or refurbished. If you're a real craftsman type person, you may be able
to weld up the worn surfaces and file them back to the right profile, but
I think this would take a lot of patience. I would do it in a flash if I
needed to, but so far I have enough good parts to pass.
[Next paragraph not applicable to MGB]
[MGB may skip to Reference label]
Now lets see, yours is a '57 so it's a 1500 like mine. This gearbox has
a sliding spline joint where the propeller shaft mates to the rear of the
gearbox. Inside here is a bimetal bearing like a big copy of a kingpin
bushing, bronze inside of a steel liner. To check this one you shove the
drive shaft front yoke in to the normal working distance and try to
wiggle it. When new the working clearance is just 0.002 inch like a
crankshaft bearing, no perceptible clearance with oil in it. If the yoke
can wiggle more than few thousandths of an inch, it's a problem. It
probably won't self-destruct in normal use, but it can cause a vibration
in the drive shaft at speeds over 30 MPH. But what's also nasty is that
it beats up the rear seal in short order and the oil leaks out. In one
case when mine got especially loose, a new rear seal was completely shot
in two weeks. Adding oil daily will save the gearbox but leaves a
hull-of-a-big oil puddle where you park.
The fix for a bad drive shaft support bushing is not easy. On new cars
this is a non-serviceable part, only because the dealers don't want your
car stuck in their shop while the aluminum housing goes out to a machine
shop for bushing replacement. The parts books don't list the bushing at
all, so you have to buy a new rear housing. The MGA books do detail this
bushing as a replacement part, and Moss even has a number for it, but in
the real world it's made out of "Unobtainium", so you can't buy one (I
know, because I searched persistently for two years).
When this bearing gave out on me last summer, the only immediate fix was
to get a new (used) rear housing from the British bone yard. I got the
only good one they had out of six that they checked, and it only fit the
later 1500 gearbox that belongs in my car (internal rear seal), but was
still in need of a rebuild at the time. The early 1500 gearbox that I
had rebuilt and had in the car at the time has a different rear housing
(external rear seal). In a pinch I bought one of these also and
installed it just to get back on the road, but with a sloppy bushing, the
seal wouldn't hold up. I have since rebuilt the original gearbox and put
it back in the car -- no more seal problem.
Now you want to know how to fix the bushing? I went to my local bearing
supply house and bought plain bronze sleeve bearings. The original
bimetal bushing is 1.375" ID x 1.500" OD x 2.75" long. The new bronze
parts weren't available in that length, so I bought three pieces each
2.00" long. I intend to cut one in pieces 0.75" long and install a 2.00"
piece and a 0.75" piece end to end in the housing. The original bushing
was a bear to remove, being in a bore with a shoulder way down inside. I
had to make a thick double-D washer to put in behind the bushing and pull
it out with a large threaded rod, washers and nuts. The new pieces
should press in OK, but being thin wall parts, they will probably need to
be honed to final size. I swear I'll get around to it one of these days,
that's my spare tranny and I want it ready if it's needed.
Just on the side, the early 1500 gearbox needs a different propeller
shaft as well. the output shaft in the early box is 1 inch 10 spline.
The output shaft in the later 1500 box is 1-1/16 inch 10 spline. Since I
didn't notice this at first, I ran the later drive shaft in the early
gearbox for 30,000 miles before it destroyed the rear bushing. Sometimes
we all have to learn the hard way. The early drive shaft is also 5/8
inch longer to match the shorter rear housing and output shaft of the
gearbox. I think that's what finally got to the bushing -- not enough
length of engagement.
[Reference]
As for the rest of the internal stuff, just be sure that the parts are
all there and nothing's broken. When you reassemble it, the front cover
has a gasket and some thin shims for the front bearing. The bearing has
an external snap ring. The idea here is to tap the bearing back to seat
the ring solid against the housing, measure the extension of the outer
bearing race from the face of the housing, measure the depth of the
counter bore in the front cover and add the thickness of the paper
gasket, then fit enough shims to take up most of the clearance. Leave a
thousandth or two of clearance just to be sure the gasket seats properly.
The book just says to reinstall the original shims, but I find that
these often get mutilated somehow and need replacements. Stick them in
place with some grease to hold them during assembly.
If your front cover is original, it won't have a rubber seal. But it is
common practice to fit a front cover from a late 1600 of MK-II gearbox
which has a rubber seal. I have installed an early MGB front cover to
accommodate the MGB clutch and flywheel assembly (OK, so ask). This
cover uses the same seal as the late MGA parts. Any cover with the seal
and the seal itself will work with you original input shaft. Now you
remember that little split pin in the bottom of the bell housing?
There are gaskets for the front cover, side cover, front housing to rear
housing joint, shift selector cover, and two more for the remote control
tower. Also a plastic washer at the speedometer drive fitting, and a
felt seal on the oil dip stick (maybe not available separately). Gaskets
are pretty cheap. Buy the whole gearbox gasket set if you can. You will
also need the rear seal. The internal seal for the late 1500 box is
reasonably priced and easy to get. The external seal for the early 1500
box is a financial rip-off but generally be still available. There is
also a seal on the speedometer drive shaft, but you can change that one
any time in the car.
[Next two paragraphs are specific to MGA]
You also want to check the rear rubber mount. These are only moderately
expensive, but a real pain to change, being a press fit steel shell in a
thin aluminum housing. Be careful here, as the aluminum monkey ear on
the rear housing is easy to break off. You surely can remove the old
mount without a press if your willing. Start by drilling out the rubber
all around and remove the inside steel tube. Then you can carefully
hacksaw through the steel shell from the inside. Saw in the upward
direction, toward the inside of the housing, so when you leave a small
kerf in the aluminum part it's on top where it won't break out.
You may be able to tap the new mount into place with a hammer, but only
if you can support the aluminum ring all around with a steel tube like a
giant wrench socket. These things are supposed to fit really tight.
They come new with a light coat of paint on the outside. I think you can
chemically remove the paint, but if you sand it off the part may end up
being loose in the housing. I had one that kept slipping sideways in use
and had to wrap a bungee cord around the rear housing and frame to keep
it in place. Fortunately, that's the one that took a dive last year, so
I don't have that problem any more. If you're the least bit queasy about
breaking the aluminum monkey ear, take it to a shop with a press and the
proper punches and dies. And it's best to do this when it's
disassembled, so you only have to deal with the smaller aluminum housing.
Oh! And be sure to put the rear mount in from the right side -- take a
look at the picture in the book.
That's about it. This one's pretty easy to work on. It only has two
large ball bearings and they're held on with jamb nuts, not a very tight
fit. Just don't loose the spring loaded bits. It's frustrating to have
to place an extra parts order for one little spring and two steel balls
just because they went flying under the bench somewhere and you can't
find them. And that's usually on the last day when you want to finish
the job, so it makes you wait another week or more for the last few
parts.
Well, trust me, it's not a big deal to rebuild an MG gearbox, and you'll
get one hell of an ego trip when it's finished and running again. Let me
know how it progresses.
Keep me informed,
Barney Gaylord -- 1958 MGA
Naperville, Illinois
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