Drivetrain Options, Gearbox, Clutch, Diff etc.
The EJ Holden, and the EH were fitted with a three speed partial synchro gearbox. This box was carried on until the early HK. These boxes have produced some classic, some legendary, and some sad stories. They do suffer from a lack of parts availability these days, with gear synchro drums being very hard to get in good condition. These boxes are also known as crash boxes, due to the exact sound they make when you try to force them into first gear (has no synchro) at the wrong time! They are rebuildable with a kit, and a bit of time, but if you are after something a little different then…
You can put in a multitude of other boxes. The conversions are too numerous and detailed to mention, so I’ll go over a few common ones here. A three speed all synchro box is a pretty easy conversion to do as it bolts up to your original motor, as long as you have the clutch, bellhousing and everything together. You will need some other things, including a different length tailshaft (depending on which vehicle you are modifying), a speedo cable, modify your crossmember (will fit straight into an EH auto floorpan), a perhaps a floor shift would look nice. Putting an aussie four speed in is just about the same, but you have to make sure you have or put a six cylinder front shaft on your box which must be shorter. Similar conversions, include Saginaw four speeds, and Muncie four speed (but parts are not easy to get for this one)
So if you’re stuck, and can’t get parts or want to make a total change. What are the alternatives? The Japanese gearboxes are very popular, so why not try one of them. We have had millions of them sent over here, so parts are easier to get. One of the most popular is to convert to a Toyota Celica four or five speed. This is a particularly tough little box and will comfortably handle the power from a hot six.
There are many versions. The steel case is one of the easier to get and fit, so go for one of them. If you want a bit more of a safety margin, you may consider having the front cluster bearing replaced for a needle roller type. Tougher and more expensive is the Supra five speed. There is some very good and factual Toyota box info at this website
Fitting kits are available for these and some other Japanese boxes from The Castlemaine Rod Shop, but you may even find one in the trading post.
To do the conversion you will need a bellhousing conversion, a clutch, crankshaft end spigot bush, speedo cable, clutch slave cylinder (not for cable operated clutches of course), modified cross member, special tailshaft yoke, tailshaft and a shifter boot.
Now travelling further back in the car, make sure your tailshaft is the correct length, balanced, and you have good uni’s fitted.
The diff however is another story. The banjo diff that the EJ/EH came out with has ratios varying from 3.89 to 2.78, and each ratio has its purpose, and you will have to find out which one suits your needs. There are limited slip versions available, but parts are very very scarce for these.
The other alternatives that you have is to fit a salisbury type diff from a later holden, which you can get in LSD a bit easier. You can get a Borg warner diff from a VN-VS Commodore, cheap to buy, gives you disc brakes, but the cost of the conversion is the same as a NINE INCH!!! GRRR, BEEFY. Very expensive to buy, this is one chunk of a diff with about a thousand different ratios, and is about as strong as Hercules in the morning. But if you are not into doing a hundred wheelies a day, you can get by on a banjo, and while we are one the subject, think about upgrading to rear wheel discs. But that’s another story, perhaps one that someone else could fill us in on….