EH Holden Part Synchromesh Gearbox Substitution.

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1 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 through to the HK series. From the 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 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

2 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 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

3 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 enquiries@earlyholdenparts.com.au Web:

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