EH Holden Part Synchromesh Gearbox Substitution.

The 3 speed part-synchromesh gearbox or "crashbox" as it has come to be known

was the standard transmission available on all Holden models from the original 48-

215 through to the HK series. From the 48-215 through to the EK series, this gearbox

was housed in a 2 piece casing consisting of an integral cast iron bellhousing and

main case and a removable extension housing in cast aluminium alloy, although very

early units had a fabricated steel extension housing. The EJ series saw a re-design in

the casing arrangement with the introduction of a removable cast aluminium alloy

bellhousing, cast iron main case and a cast aluminium alloy extension housing. The

bellhousing and main case received minor alterations with the introduction of the EH

179 manual model and this gearbox was then carried through to the HK series. The

internal gearsets for the later type crashboxes had minor revisions to accommodate

larger bearings and revised internal shifter forks, but essentially they were the same

from 48 to HK to the point where the later, slightly more durable internals can be

fitted to the 48-EK casing with only minor modifications to the case.

With the introduction of the HK model, Holden offered a new 3 speed all

synchromesh transmission as an option over the standard part synchromesh gearbox.

This new all synchromesh gearbox then became the standard transmission from the

HT model onwards as the crashbox was discontinued at the end of HK production in

mid-1969.

The all synchromesh gearbox has a strikingly similar appearance to the crashbox in

that it also consists of a removable aluminium alloy bellhousing, red-oxide painted

cast iron main case and an aluminium extension housing. The obvious difference is

the all synchromesh box is physically larger and heavier as it was also designed to be

used behind the new Holden V8 engine introduced with the HT model.

The only carry-over parts in common to both gearboxes are the oil filler plug and

plug gasket and the rubber rear support/mount. The two gearboxes are also very

different in that the shifting arrangement is also completely different and

incompatible. While both gearboxes have 2 levers on the shifter cover sideplate, they

operate very differently. The crashbox uses the front lever to shift all 4 gears and the

rear lever internally switches the "gate" from the R-1 gate to the 2-3 gate. On the

steering column , the levers are coupled together such that when pushing and pulling

the gear lever back and forth through the neutral gate , the control lever and rod

moves up and down, acting on the rear lever on the sideplate which then governs

which gate the selector lever will shift.

The all synchromesh gearbox also has 2 levers on the shifter cover sideplate. Unlike

the crashbox, these two levers operate independently whereby the rear lever

operates Reverse and First gears and the front lever operates Second and Third

gears. As a consequence, Holden had to re-design the internal column shifter

components for HK models so that the two lower column levers operated

independently of each other. In all earlier model Holdens, the shift levers are coupled

as described above and will not successfully operate the all synchromesh gearbox.

The 3 speed crashbox has long had a very deserved reputation as being weak and

unreliable, especially when exposed to any kind of extra load such as towing or

mildly modified road car engines. This lack of durability and reliability would be

compounded greatly under competition use, as has been demonstrated in current

historic racing cars. This then adds to the problem of finding suitable replacement

parts for the crashbox. I well remember as a teenager going with my Father

searching for a new main cluster gear for our family HK Kingswood wagon in about

1979-80. The crashbox had been out of production about 10 years at that time and

even then parts for them were difficult to source and relatively expensive. Since my

own involvement in owning, operating and restoring early Holdens from the early

1980`s onwards, finding decent, useable used or occasionally new parts for

crashboxes has been a difficult and expensive exercise. Most people opted to fit the

later and virtually bullet-proof all synchromesh 3 speed gearbox because it was

cheaper for the whole conversion than for just the parts alone for the crashbox. The

only issue owners had was the fact that the all synchromesh gearbox could not be

operated by the original column change on 48-HR models and required the fitment of

a floor mounted gear change.

In the early 1990`s, from both customer and a personal demand I developed an all

synchromesh shift conversion for FE-HR model Holdens whereby the all synchromesh

gearbox could be operated by means of the original column gear lever. This was

done by developing a new set of column gearshift internal levers and spacers based

partly on the original FE-HR type and partly on the HK All synchromesh type as well

as a modified original gearshift tube. The result was a complete system to operate

the all synchromesh gearbox that would fit into the unmodified standard steering

column on FE-HR models. I have offered this conversion for road cars for nearly 20

years now and it has proven to be very popular among early Holden enthusiasts

because of the virtually "factory stock" appearance of the conversion , the

convenience of synchromesh on first gear in modern stop-start traffic and the cost

effectiveness compared with rebuilding the crashbox. The cost of rebuilding a

standard crashbox can exceed $1500 in parts alone with labour additional to that.

The days of purchasing "good used" crashboxes from parts recyclers are long gone ,

whereas good used all synchromesh gearboxes can be had readily for under $200 at

time of writing. The cost of converting an EH or other early Holden to all

synchromesh 3 speed is generally comparable to the cost of rebuilding a crashbox

alone but comes with the benefits of reliability and driveability. Any early Holden

fitted with anything warmer than a stock red six, let alone a race prepared engine,

will destroy a crasbox in very short order even for road use. The all synchromesh

conversion maintains the original character, feel and appearance of the original

transmission without the reliability and cost issues.

Below are some comparison pictures showing both gearboxes and both steering

columns.

Prepared by Roger Hancock, B.Eng. (Aerospace) RMIT - owner at Holdenman

Restomotive. Ph. 0408 349 185 Email: enquiries@earlyholdenparts.com.au

Web: www.earlyholdenparts.com.au