Transmission " how to" assembly guide

There just wasn't a lot out there on how to guides for this- so here's my version


(With assembled 1st input/2nd layshaft /3rd output motion shaft)
This is where the transmission is having parts replaced, but not affecting tolerances...
The only parts replaced were the 3rd synchro ring and input shaft...

1>Clean cases- lots of crud accumulated in the tail housing especially

2>Put 2nd motion shaft (laygear) in case with biggest toothed gear side forward, do not try to
    insert shaft yet

3>Insert 3rd motion (output) shaft assembly in without 3/4 synchronizer assy on it. 

4>Line up rear bearing hub with the round locating disk at the 10:00 position looking at rear of the case.

5>Gently tap in bearing hub with soft hammer until tip of 3rd shaft is in blank space of laygear,  then slide 3/4 synchronizer assembly on shaft and tap bearing hub in the rest of the way flush to the back of the case.

6>4th gear synchronizer will try to fall off. Make sure synchronizer outer blocks are inserted into synchro assembly.

7>Insert needle roller bearing in 1st motion (input) shaft cup or on snout of 3rd motion shaft.  I apply some bearing grease for startup lubrication.

8>Insert 1st motion (input) shaft til over 3rds snout.
 It will not go in if laygear is pinned in place or if synchro rings outer blocks are not in the assembly!
  Slide in until circlip on bearing reaches housing.

9>There are 2 oiling spacers with grooves on them that go on either side of the layshaft. Big one up front, small to the rear. Insert these (I used a telescoping magnet) then use a smaller diameter rod to line up with layshaft to the other gears

10>Attempt to insert layshaft pin while not fumbling oiling spacers and pushing out roller bearings. The layshaft pins notched end goes towards the front with the notched side "up" (look at the front cover- you will see)

11>If you succeed in that, then the front oil cover /clutch arm holder and
big bearing spacer shim can go on. 

>>Make sure transmission can spin without binding.

12>At the tailshaft there is a large bearing spacer shim against the bearing hub on mine.

13>The speedo gear goes over a tiny half round key in the shaft. No key= no speedo.

14>A distance tube goes over the output shaft. Flanged side to the back.
Shims separate the end of the distance tube from the tailshaft bearing on mine

15>The reverse gear is placed in the case with fork notch to the front,  pin is inserted from the rear of the case with indent to the front.  This notch accepts a bolt with a pointed tip to hold it in position.

16>The 3 shift forks are placed in the appropriate holes from the rear. Make sure the rear fork bolts are wired. 
If they get mixed up, you can set the forked side on the table and look at the indentions
in the shafts.  This is determined by how far they have to go into the transmission.

The order of shaft holes from the table is
lowest = reverse shaft
middle= 1/2 shaft
highest= 3/4 shaft

17>Do not put in the shift rod pills yet, they will fall into the hole and cause problems. Do them last.

18>Place the 1/2 bronze fork (has 2 holes in it) over 1/2 synchronizer and slide the rod through- lining up the notch with the bolt hole in the fork.

19>Place 3/4 bronze shifter fork on 3/4 synchronizer and slide rod through- line up hole

20>Place reverse shifter fork over reverse and slide rod through- line up hole

21>Insert shift rod bolts, nuts, washers (DON'T drop any!) through shift forks into shaft.

should look like this afterwards...

22>The shift rod forks kind of nest together with reverse running over the top of the rest.

23> Bolt the rear housing to the main case- being careful not to disturb shims and keeping shift rods from being bound up.  The shift fork selector needs to stay towards the reverse plunger. Then its selector paddle goes between the forks afterwards.

24>Shift interlock 

 goes around the rear tabs of the shifter forks and envelops the selector paddle to keep it inline with the selector forks. (keeps it from falling away)  Its mounting plate fits into the indent of the housing.

Interlock is the mowog piece 

25> Install shift tower, plastic bushing should snap in to lower shift cup.  6 bolts- 4 long, 2 short. Check shifting action with screwdriver into upper shifter cup.

26>Insert 3 shift pills rounded side down into top left of case with springs and bolts following them.

27>Seal up side plate, re - check all bolts- is the drain bolt in??  11/16"

>>If everything shifts and turns good,
Replace rear transmission seal while you're at it then put on the 1 5/16" tail nut to torque specs.

About 3 qts of oil and you're ready to go...check the dipstick
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It's a 3 synchro- but close enough...

OY! Vat a day! watch for parts store seals...

Got the gearbox back together.  Everything seemed right, not many leftover parts..so we're good. Lol

The nice "new" transmission was bolted to the engine and filled to capacity. 3 US qts from empty.
Engine took 4.5. Blew out oil cooler prior to refill and trying Castrol gtx 20-50 per popular request.

Note: o'reilly and autozone tried selling a rear transmission output seal for the mgb that is NOT right ! It may be for a overdrive- but not the 68-80 4 speed.
 473234 p/n

Autozone on the left, one that works to the right.

Not enough hands for pics during the install, will try a transmission write up though.
At 103* I was racing the heat.

The only other vehicle that is as easy to pull and fit a drivetrain into is a jeep cj.  Simplistic and robust!
Anyway... in a mere 4.5 hours.. the car went from many many pieces to a working, very nicely shifting , better accelerating machine.  Just seems zippier. Especially 2500 rpms up. Probably the fact the valves are opening and closing like they're supposed to

And as soon as the last bolt was turned clouds and rain (first time in 2 weeks) started rolling in.  And the temperature dropped 13*.  Lucky me.

The transmission at a glance and other problems v2.1

So since 3rd gear ground when being shifted moderately hard, the teardown begins.

Bam, torn down.


Shift rods and gears, blah blah blah

 Springs from shift 3/4 shift collar and balls went flying.
There are thicker springs and "pills" for the shift rods themselves on the left upper side under the bolts, dont confuse the 2 types.



Offending culprit just like Byron said .
It cracked through the thick portion.

Oh- and there's another problem! The first motion shaft is shot! "new" one on the way...

That little piece on the right is supposed to be attached to the piece on the left.  It was in the tail of the box!

V2 update:

Good news, after ordering a new batch, I found my synchronizer ball that went flying.  While torquing the engine head it rolled from under the dolly. Figures.

Instead of chasing it and loosing it again I came up with an idea so astounding, so revolutionary, that it should be patented.

First -
get a laundry basket lined with towels. Work in this zone so your balls wont go anywhere.
Second-
 put the springs and balls in the synchronizer- when they go flying again, you'll thank yourself.
Third -
put a large hose clamp around them
Fourth -
inset assembly partially into hub
Fifth-
Whack center hub with soft blow hammer and if everything goes right- you're done!

balls go into cavity with springs- then go flying everywhere!

patent pending , all rights reserved, TM etc... etc....

Rocker shaft rebuild

So instead of 11 to 20 per rocker arm the originals got new bushings.
Its not hard, just time consuming.
  The old bushings get pressed out with a vice and 2 sockets. I used a 3/4- 1/2" drive and a 1/2- 3/8" drive as a pusher.

Heres the fun part- the new ones get pressed in with seam "up".
Done right? Feeling accomplished??

Next take out the adjusting screws
And grind off the rivet head.
Someone said they punched the rivet through- I'd like to see how they did that.

Drill both oil weep holes through the bushing using the rivet hole through to the inner oil port and the upper side hole as a guide.

Done- right?  The official reamer size you need is .6255.
 Why .0005 was needed i dont know.
So the .625 cared for drill bit was chucked up, table vice set up for distance. And with a moderate speed and lots of oil...

After the part was deemed perpendicular to the bit it was drilled.

Then tested on the new rocker shaft. They went on  but took some effort to slide on the shaft.

I ran them on the bit by hand 3 more revolutions at the top of the fluting. 

This gave them a machined match feel to each.

I ran the small oil port bit back through to open the ports again.  Then clean all the bronze shavings off.

The old grooved shaft vs the new setup.
I filled the shaft with oil prior to installing on the new head.
Note the original shaft- rear side (left) worn terribly, front (right) that got little oil in good shape.  Weird.

Off with its head! Straw that broke the camel

Pulled and cleaned the oil pan, it had a bunch of gasketing on it.   Found that 4 oil pan bolts went m.i.a. , probably shook loose.  No chunks in the pan sans some non magnetic gasket maker.

2 things were noticed-  Thinking that #2 was the straw to #1

1.  chunks of crap in water passages of the head impeding water flow.  I flushed the block- but never took off the head to clean it out

2.  thermostat blanking sleeve was turned so the head passage had no hole facing it. May have been     bumped when changing out the gasket.  I drilled smaller holes next to the original blanking holes so there will not be that problem again.

So heres the head, cylinder 4 looks like it was warm.  Note the clogged water ports.

Heres with old head gasket, note gasket sealer...

Heres the block itself, lots of gasket.

Stamping on the pistons. Cant distinguish if overbored or not

After polishing w the nylon wheel the pistons got shiny!
pointing to new water ports with the drill bit

Cylinder 4 appears to have a different piston in it.  May be the lumpy idle.
I took the liberty of drilling 3 more small holes on the non exhaust side of the deck where the blanked areas were to keep this from happening again..  hopefully

So on to the rocker shaft and arms and bushings.

Most reliable car ever- pulling drivetrain.

After 120 miles of driving, mg reared is ugly head.

So i started pulling the drivetrain so the new head could be put on and get 3rd gear synchronizer swapped.

Luckily the bolts are still easy to turn thanks to antiseize

Why does this one have a steel fan instead of a plastic ?

Everything out, drippy oil pan off 3.5 hours.   

102*, calling it a day...