Gearbox Conversions


Some options / tips for converting your Gearbox …


  • Replace 4spd gearbox with 5spd L series gearbox
  • Converting a 3.7LSD to 3.9LSD

Replacing 4spd gearbox with 5spd L series gearbox

Borrowed from The dot point summary of what needs to be done follows the new section just below. results will vary from car to car.

This new section just below, written after converting standard height 1984 Brumby/MY 4 speed D/R 4WD to :
'91 L Series 5 speed manual D/R 4WD 3.7:1
The 5 speed D/R 4WD gearbox weighs about 56 kilograms
Work was done using a car hoist and transmission jack. My second preference is to remove engine and then gearbox with car on ground. Other people have removed engine and gearbox as a whole from under car stands. Others used stands and left engine in place to remove gearbox. Not a good feeling in Newcastle during the earthquake!
Questions that rise before doing conversion likely to be answered here.
The main components needed are numbered, with info , options and tips below

1.0 Gearbox

single range or dual range 4WD The dual range has a shift rod on the right hand side from the selector box towards the front, the single range (ie , no low range) does not. Don't buy/fit the box you don't want ! Ensure you get the clutch fork, and release bearing and its two retainer clips
Final drive ratio ( diff ratio)
Generally '85 - '88 was 3.9:1 ……… '88 on was 3.7:1
The gear ratios on offer varied between models, years and diff ratio
TIP : drain oil before moving or working on gearbox

2.0 Shift Lever Assembly

1 > 5 & R, 4WD and support stay that bolts at rear underside of hole. Best position of the bolt depends on how all gearbox mount and cross member changes affect it. My new hole was 19mm , centre to centre, to the left of the factory stud, M8 thread
OPTIONS: (a) use entire L Series lever assembly and use L Series console components as the two levers now share the same shift boot and surround, or : (b) retain the MY 4WD selector and modify to suit new box and explore your console options.
TIP: (a)Fitted flat rubber to top of stay bracket to minimise metal to metal contact between stay and underside of tunnel (b)Hole in tunnel needs a plate fixed at front as hole is now way too big

3.0 Wiring Loom

Get this including about 150mm past the connector plug. 4 wires on MY plug, 6 wires on the D/R 5 speed
INFO: Reverse switch is on LHS of box 4WD dash light switch is at the top at the back Low dash light switch is on RHS of box
MY 4WD dash light switch is at the base of the lever itself. One wire is black, an earth I think. The other is blue ? Extend this to the new loom.
TIP: Test all switches for correct operation in place. CRC 556 is handy to wash out and lubricate dirty malfunctioning switches. Switch might also need extra spacer washer to make it work correctly in its positions.
INFO: MY connector plug on car side Reverse switch wires, green with white trace line , green with yellow trace line Low range dash light, blue with red trace line Earth is the black wire
L Series six wires consist of two reverse wires that hook to both the MY reverse wires, the 4WD dash light switch wire and its earth (black), the low range dash light switch wire and its own earth wire (also black). The two earth wires are connected inside the car/dash side of the connector plug, so I will bridge these two earths to make one less wire to connect up. Sorry , forgot their colours.

4.0 Flywheel and Clutch

(a) If already 8 " EA81 flywheel and you are happy with its ability you can use a Gemini 1.6L petrol engine clutch disc (R7926W), it is 8" and splines fit the 5 speed input shaft splines. Very cheap option. I used this option and happy so far. I also retained the MY spigot (pilot) bearing
(b) heavy duty for sand work, big tyres etc, Later model EA81 had 9" clutch and flywheel
(c) EA82 flywheels have reportedly been fitted but is not a recommended option as the engine block needs grinding to clear flywheel, you'll need to transfer the timing marks, and some say there is a bolt hole difference in the flywheel to crank. The ring gear position may also move requiring starter motor spacing changes, so needs to be checked for correct and safe operation.
All options use the L Series clutch release bearing and fork
TIP: Flywheel to crank bolts can leak oil from crank case so these bolts need to be sealed on threads

5.0 L Series clutch cable

Prior to dismantling and removing from car to do this work on MY clutch pedal and cable set up, mark the angle of the cable on the pedal box as a guide to mount L Series cable in the right direction out of the firewall. Remove whatever supported the MY clutch cable outer on the clutch side of the pedal box, I found it best to drill out spot welds if possible to preserve the pedal box, and reinforce pedal box wall with 1.6mm plate riveted in place on the borders. Mounted the L Series cable with sufficient spacer for cable to operate centrally within the outer cable. I used 1.6mm reinforcement plate plus 6mm of steel plate and welded in place, another 1.0mm spacer may have been ideal. I also used high tensile M6 1.0mm pitch bolts, 40mm long , to hold cable outer mount to pedal box
TIP: L Series pedal boxes don't fit MY. It's clutch pedal fits MY and '91 model had a longer lever action on cable, less pressure required, so pedal choice best made before fitting cable mount to block, ie , drilled holes.

6.0 Tail shaft

OPTIONS: (a)Use the L Series two-piece tail shaft with centre bearing. A support bracket needs to be made and installed. See Subinator ? for links to his photos Advantages: Cost and availability
(b) have a single piece shaft made to measure (230mm longer than MY ?). Going rate about $350 Disadvantages: Cost and availability

7.0 Rear Diff

ratio to match new gearbox front diff ratio, if not the same.
You need to check this for yourself or you are likely to wind the front diff against the back diff if ratios not the same when putting into 4WD and stuff your new gearbox
TIP: Through filler plug hole mark first tooth and count number of teeth on crown wheel of each diff eg: 3.7:1 have 37 teeth and 3.9:1 have 39 teeth

8.0 Gearbox mounts and crossmember

(a) stronger looking mounts already fit gearbox, if you can make it fit into the MY body, good luck!
(b) convert MY crossmember and mount brackets to suit gearbox much easier as it only involves a rat tail file, a vice and half a brain. I elongated the the two holes in the cross member where mounts bolt to by about an extra 4-5mm outwards. The metal bracket that fit between rubber mounts and gearbox, their holes were elongated also to match the L Series gearbox mounting holes, elongated further in on one side and further out on the other side .
TIP: I ground off the little locating tit on the side of the mount that sits on cross member as it got in the way. It is there to stop the mount turning when tightening bolt. I held it straight while doing this.

9.0 L Series Console

if option 2.0 (a) , the shifter boot and housing, the handbrake console , and coin tray INFO: Shifter console front to MY radio console = 30mm gap
Further Notes
Starter motor spacing:
Due to variations in housing dimensions between where the starter motor fits and the front face of the gearbox bellhousing which mates to the engine block, spacers have been used by some people, and not by others.. Measure the difference if any and make appropriate changes to suit. From my original MY gearbox and the L Series the difference was 4.0mm, so I made a ring shape spacer of 4.0mm aluminium Changing flywheels may alter the distance between the ring gear and the starter motor drive cog when it engages, it may then grind or jam. If a starter motor jams it can catch FIRE, so too your workshop, shed and or house as a result. SO BE AWARE
metal sheet/plate is available in 1.1, 1.6, 2.0 , 3.0 , 5.0 & 6.0 mm I needed 4.0 mm spacing and so used 4.0mm aluminium sheet.

I also found that after gearbox installed and running the engine was tilted forward and ended up putting 5mm of spacer washers between chassis and the plate that the sway bar, radius rods and gearbox cross member bolt to. Three M10 bolts each side. Also re-adjusted the engine stay to suit. This also helped with the clearance problem between the gearbox and the inside of the tunnel on the drivers side. Clearance on the LHS is ample.
Clearance was a problem Only on the RHS. The gearbox I fitted has a cast knob at the top on the right with M10 threaded hole. It is not used in my installation and could have been removed for better clearance . Others have done this. The tunnel is double skinned and at the front right top of this double skin some panel beating can help with clearance of the box.
Before gearbox removal , the DOJ's on the axle stubs came off easily after removing just the horizontal ball joint bolt each side and removing radius rods completely and outta the way.
Use commonsense and work safely.
Good Luck!

Be sure to use loctite on all bolts when re-assembling
1. Put vehicle on Jackstands
2. drop exhaust
3. remove center consoles/shifter knobs, etc
4. remove bolts holding tranny to bell housing
5. remove sway bar
6. pull axles off stubs
7. remove drive shaft
8. plug end of tranny, or drain gear oil
9. remove starter
10. unhook speedo cable
11. disconnect any other connections to tranny
12. place jack under tranny and just take the weight off
13. take off tranny crossmember nuts
14. remove tranny mounts from tranny and crossmember
15. remove tranny and tranny crossmember
Can use 8" EA81 flywheel and pressure plate with gemini clutch friction plate used in all 1.6 litre petrol Holden Geminis. Splines fit 5 speed. Use 5 speed cluth throw out bearing and carrier
1. remove ea81 pressure plate/clutch
2. remove ea81 flywheel
3. replace rear crank seal if needed , seal sizes 76,93,10 mm
4. grind edges of opening at bottom of bellhousing so the ea82 flywheel will fit without rubbing
5. transfer timing marks to ea82 flywheel if needed
6. . replace pilot bearing in ea82 flywheel
7. install ea82 flywheel
8. . install ea82 clutch/pressure plate
9. raise 5 speed D/R tranny into opening
10. install tranny crossmember
11. attach tranny to motor/bell housing
12. attach original tranny mounts to tranny and crossmember
13. prepare ea82 drive shaft. (If mounting into a Brat or Wagon no mods are necessary, if mounting into a hatch, the shaft must be shortened.)
14. weld carrier bearing mount into place
15. install ea82 drive shaft
16. weld carrier bearing mount into place
17. install sway bar
18. install exhaust
19. install axles
20. connect speedo cable
21. install starter
22. re-connect remaining tranny connections
23. install interior ea82 boots/consoles

Converting an open diff to lsd centre

I recently did such a conversion, you will need a diff with some kind of lsd centre (viscous or clutch type).
This type of conversion is mainly for older model subaru's which have different ratios to the later models that came with lsd.
It is a pretty simple job really. I am going to presume you have got the backing covers off both diffs ready to go. Keep both diffs seperate, that is two distinct working piles.

  • Remove stub axles
  • On the LSD - place a screwdriver through the roll-pin hole on the stub axle, and use the arc of a claw hammer to pull the stub axles out - they are attached with circlips so they do just pull out.
  • On the open diff - you will need to undo the locking bolts from within the stub axles — I found that an 8mm 1/4" socked got one side out - the other side, I had to drill out. The bolts are actuall torque heads so the correct socket would go a long way to making this easier.
  • Once you have the axles out, undo the retaining bolts on the side of the diff and take the bearing carriers out.
  • Keep the sides and shims separate — check bearings for wear, replace if necessary.
  • The open centre diff centre will come out quite easily then. The LSD needs to be turned sideways a little and coaxed out. Can take a little bit of fiddling to get it to come out. Then again you may fluke it and it will pretty much fall out in your hands.
  • Take the crown wheels off both centres by undoing the bolts around the wheel. Now, put the crown wheel from your open diff on to the centre from the limo. This is going back in to the original housing from the open diff.
  • Before it will go in the hole, you will notice on the inside left hand side of the diff housing there will be two raised sections just near the side opening. Compare it to the LSD housing. You will see what I am talking about. You need to get a grinder and get rid of the raised bits. You will not get the centre back in if you don't.
  • Once you can get the centre in, reassemble the diff using all the original parts from the open diff. All you should have done in reality is put the LSD centre in to your old diff.
  • To work out the ratio of your open diff, count the teeth on the crown wheel and pinion. A 3.7 will have 37 teeth on the crown and 10 on the pinion (37/10), etc…
  • Finally you want to check that there isn't too much backlash (free rotation/slack/play in pinion shaft before crown wheel engages) in the diff, or that the diff is too tight.
  • Adjustment is made by moving shims from one bearing case to the other (if it is too loose, move a shim from the side furthest from the crown to that closest — i.e. moving the crown closer to the pinion)
  • Always keep the same total number of shims


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