The braking system is arguably the most critical safety feature in any vehicle, and for classic cars like MGs, maintaining original components is often a labor of love. One often-overlooked element in the braking system of MMM (Midget, Magna, and Magnette) MGs is the brake cross shaft assembly. If you’re an owner of a classic MG from this era, you might be familiar with a wobbly handbrake or rattling noises emanating from this area. This article, inspired by insights from the Octagon Car Club Bulletin, will guide you through the process of rebuilding your MMM brake cross shaft assembly, ensuring your classic car’s braking system remains reliable and safe.
This guide is for enthusiasts who appreciate the mechanics of their classic vehicles and are looking to undertake a detailed restoration. While not strictly about “How To Remove Octagon From Car” in a literal sense, understanding the intricacies of components like the brake cross shaft is crucial for maintaining the integrity – and the iconic heritage symbolized by the MG octagon – of these classic machines.
Understanding the Neglect and Importance of the Brake Cross Shaft
The brake cross shaft assembly in MMM MGs often suffers from neglect, likely because it’s a welded unit. Reconditioning or replacement usually only occurs when it becomes completely unusable. Due to this, there’s limited information available on its rebuilding process, making this guide particularly valuable. The P-Type assembly discussed here is identical to J-types and similar to other MMM cars, with the possible exception of M-types.
Plan “A” – Minimum Work: A Quickly Abandoned Approach
Initially, a minimal intervention approach might seem appealing. The first thought is often to simply clean everything and replace the bronze bearing bush on the nearside end, along with bushes in the handbrake and ratchet support plate. The intention might be to use split bushes for the latter two to avoid removing welded components. This involves driving out old bushes and replacing them with split versions after cutting them off the shaft. This method, reminiscent of techniques used in pump industries, aims to circumvent major disassembly.
However, this plan quickly hits a roadblock. Removing the bush from the handbrake lever proves almost impossible. The thin-walled bush often becomes bell-mouthed and severely worn, making extraction incredibly difficult even with specialized tools.
Furthermore, uneven wear on the shaft becomes evident when the collar is freed and the handbrake lever is moved. Even a new bush wouldn’t compensate for this wear sufficiently to prevent the handbrake from wobbling, rendering Plan “A” unviable.
Plan “B” – More Work: Facing Setbacks with Metal Spraying
Moving to Plan “B” involves a more invasive approach: filing through the welds of one pulley and the handbrake arm on the shaft. This would allow removal of the handbrake lever and steady bearing for re-bushing, with the shaft then being metal sprayed and machined back to its original size. At this stage, the footbrake lever might still appear acceptable.
Before any disassembly, it’s crucial to sketch the shaft and lever positions, noting their angular orientations. The initial assumption might be that the factory used jigs for assembly and welding.
Filing through welds demands immense patience, which can be tested. Using an angle grinder speeds up the process, but introduces new challenges. The heat and vibration can potentially damage the shaft and surrounding components. Turning the shaft in a lathe to remove weld remnants also carries the risk of seizing the handbrake lever, potentially leading to bending or irreparable damage.
The idea of metal spraying also presents difficulties. It requires a groove to be cut into the tubular shaft, potentially weakening its structure. Combined with the cost of spraying, remachining, and the existing damage from initial attempts, Plan “B” becomes less appealing and ultimately, is abandoned.
Plan “C” – The Ultimate Rebuild: A New Shaft and Comprehensive Restoration
Plan “C” emerges as the necessary ultimate rebuild. Beyond re-bushing the handbrake and support bearing, this plan necessitates acquiring a new cross shaft. The remaining levers and pulley must be removed from the old shaft, and everything reassembled and welded onto the new shaft. The initial detailed sketches of angular positions become less crucial, as it’s discovered that pulleys and levers are keyed in position with shallow rectangular and woodruff keys.
Sourcing a Shaft and Reconsidering “Good” Advice
Enquiries to spare parts suppliers often reveal that new bare brake cross shafts are not readily available. One suggestion, considered alarming, might be to simply cut the shaft in half, insert bushes, and weld it back together.
This “advice” is highly questionable. The brake cross shaft is a critical component, and a weld can compromise its strength. Such a repair introduces a significant safety risk. While cutting and welding might facilitate bush replacement, it doesn’t address potential weaknesses in the shaft itself, especially concerning the footbrake lever access.
Therefore, fabricating or commissioning a new shaft becomes the only reliable solution. A drawing of the cross shaft is essential, and suitable material – like 1.125″ o/d x 8 swg wall thickness (0.16″, 4mm) Cold Drawn Seamless (CDS2) steel tube to BS1734 – should be sourced. Using a thicker walled tube than the original provides added strength, especially considering the woodruff keyways.
A DIY Diversion: Crafting the Shaft
Instead of relying on machine shops, a hands-on approach can be taken. With access to a lathe and the ingenuity to create a milling attachment, crafting the new shaft becomes a rewarding endeavor. Building a vertical slide attachment for the lathe allows for milling keyways at the correct angles, demonstrating the resourceful spirit often found in classic car restoration.
Parallel Rebuilds and Bearing Considerations
Serendipitously, another opportunity for a rebuild arises. This parallel project allows for refining the removal process, finding that cutting the old shaft in half and machining away welds is cleaner and easier than the initial struggles. This also highlights variations in original components, as some assemblies might have serviceable original roller bearings on one side, requiring only a bronze bush for the other.
Regarding bearings, the original assembly might use a combination of bronze bushes and needle roller bearings. For a complete rebuild, upgrading to needle roller bearings at both ends can be considered. While original 2mm diameter needle rollers might be obsolete, alternatives can be sourced. Adapting modern bearings might require custom inner sleeves and slight adjustments to the shaft bore dimensions. The advantage of assembled needle roller bearings is the hardened outer track, offering improved durability compared to the original setup.
| Photo 1: Comparing bearing types – standard (left) and upgraded needle roller bearings. |
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Image showing standard and needle roller bearings side-by-side for brake cross shaft assembly.
Addressing a Worn Footbrake Lever
A common issue discovered during disassembly is a worn footbrake lever. While it might seem serviceable when assembled, cleaning reveals play and slack. Bushing the original lever might be considered, but its thin wall thickness makes it unsuitable. Welding and re-machining also prove problematic due to gripping difficulties and concerns about strength.
The most robust solution is often to fabricate a new footbrake lever from steel strip. Using a thicker gauge steel than the original enhances durability and ensures reliable performance.
| Photo 2: Original thin footbrake lever (left) contrasted with a new, thicker lever (right). |
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Image highlighting the difference in thickness between old and new footbrake levers.
Reassembly and Welding: Putting it All Back Together
With new bushes pressed into the brake lever and ratchet mounting plate (reamed and bored to size respectively), and components cleaned (grit-blasting is effective), the stage is set for reassembly.
| Photo 3: A single set of rebuilt brake cross-shaft assembly parts ready for assembly. |
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Image showcasing the various components laid out before final assembly.
Keys are fitted to the new cross-shaft, ensuring a snug fit with levers and pulleys. Before welding, shaft ends are plugged to prevent distortion of bearing bores. The footbrake levers are positioned first and welded, carefully checking orientation against workshop manuals. The collar, ratchet support plate, handbrake lever, and arm follow, with meticulous attention to the asymmetrical ratchet mounting plate orientation.
Pulleys are then fitted and welded, alternating weld sides to prevent tipping. MIG welding offers convenience, though the harder weld metal might pose challenges for future reconditioning. The handbrake retaining collar is positioned and secured with a pilot-drilled screw.
| Photo 4: Assembled brake cross-shaft, showing standard and roller bearing configurations. |
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Image of the completed brake cross shaft assemblies, one with standard and one with roller bearings.
Lubrication Considerations
Original needle roller bearings often have a blank inner plate, meaning lubrication from the offside pipe primarily serves the needle roller bearing. The nearside bronze bush is drilled to allow oil into the hollow shaft, lubricating the hand and footbrake levers. Maintaining the shaft half-full of oil, supplied through the bush, is crucial.
Upgrading to needle roller bearings at both ends necessitates bearings with off-center drilled backplates to ensure oil circulation and maintain a higher oil level within the shaft for improved lever lubrication. While there’s no sealing at the shaft ends, potential solutions like soft O-rings or felt washers could be explored to minimize oil leakage and prevent dirt ingress.
Conclusion: No Shortcuts to Proper Restoration
Rebuilding a MMM brake cross shaft assembly is a task demanding determination and access to basic machinery. There are no shortcuts to a proper restoration. Many of these assemblies are likely in a worn state, emphasizing the value of a thorough rebuild. This guide demonstrates that with careful planning and execution, it’s perfectly achievable to restore this critical component, ensuring the continued safe operation of your classic MG.
This project, while detailed, ultimately contributes to preserving the heritage and driving pleasure of these iconic vehicles, each bearing the proud mark of the MG octagon.
Inspired by the work of Geoff Taylor, Octagon Car Club Bulletin.
