Webmaster's note: This article appeared in both Marque One and Mascot and appears here with permission of John E. Davies. This installment was written before John was aware of my and Joe Way's (Sierra Specialty) efforts to make the 3/4" disc brake master cylinder available to enthusiasts. Content is the work of John E. Davies entirely. Other installments will appear in the future.
Early Twin bore Master Cylinders
The combined Lockheed clutch and brake master cylinder fitted to all Spridgets from AN5 to HAN8/GAN3 (Figure 1) is a heavy and robust unit, built like a battleship. Looked after correctly, it is capable of outlasting most of the rest of the vehicle and, amazingly, many original units are still in service, having received very little maintenance save regular renewal of their brake fluid and the rubber seals inside their bores. The bores in the units of the very early drum braked cars (AN5, HAN6 and GAN1) are each 7/8” in diameter but these were reduced to 3/4” when disk brakes were introduced with the HAN7/GAN2 vehicles. Anyone who converts a Spridget from early drum to disk brakes should be aware of this difference because using the early large-bore unit with the later disk brakes is not recommended: it will inevitably lead to larger than optimum brake pedal effort and may even be illegal. Abingdon never changed brake bits without good engineering reasons and it is really not a good idea to pick and mix brake components unless one is extremely expert and fully aware of the consequences of each change.
  tandem gif

Figure 1

Another thing to bear in mind is that matching the brake components can leave the clutch bits miss-matched! If the later small bore master cylinder unit is used with an early 9C or 9CG engine/clutch then clutch pedal effort will be too light and clutch pedal travel will be excessive. We shall return to this problem in more detail later on.


Despite their battleship construction, these early combined master cylinders can deteriorate and fail, the most common cause being pure neglect. Standard brake fluid is hygroscopic (that is, it absorbs water easily) and if brake fluid is not changed at the recommended intervals then the surface of the cast iron cylinder bores will rust (as will the insides of steel brake pipes). The result can be badly pitted bores and a short life expectancy for the rubber seals on the pistons. Many perfectly good units have been lost simply by being removed from a vehicle at the beginning of a restoration and then being left for years with brake fluid, pistons and seals all still inside. In the worst cases this can result in pistons that cannot be removed at all without specialist equipment, the whole thing being useful only as an expensive paperweight or doorstop. Anyone planning to ‘lay-up’ a master cylinder for a long time is advised to immediately dismantle it, thoroughly clean all its components and then immerse its cast iron block in a suitable preserving fluid (e.g. silicone brake fluid which is not hygroscopic). The threads in the holes which accept the brass brake and clutch pipe unions can also rust and become damaged and fragile with repeated use - stripped threads or other damage in this area is hard to fix and can also destroy the unit. Lightly tarnished or glazed cylinder bores can be restored with a hone but if the bores are pitted it is probably better to try to purchase a new or reconditioned unit, using the damaged one for exchange (providing it is suitable for reconditioning and providing the vendor will accept it). This is more easily said than done because new original stock Lockheed units are incredibly rare and frighteningly expensive, good reconditioned units – even from reputable MG/Healey suppliers – can turn out to be very dodgy indeed and there is a lot of confusion about what is and what is not available. For example, ebay sellers listing grubby second hand units will often say something like ‘this master cylinder is the Achilles heel of the car, impossible to acquire new’ and urge the gullible to buy it immediately. This article is an attempt to clarify matters in the hope that others may avoid the many expensive mistakes I made during my own master cylinder crisis. I am unable to describe this crisis in detail because there are only 48 pages in MASCOT but in brief, my problems began when a very reputable MG dealer rightly condemned my original GAN2 unit after honing because I had stupidly ignored it for 25 years. This same dealer then told me – wrongly and without a trace of sympathy – that new units are not available and that they could not help me. The crisis ended only after I had squandered a paralysing sum of money by acquiring and ultimately rejecting a string of dodgy bits and pieces. As a consequence, I possess an extensive collection of paperweights and doorstops coupled with a vastly depleted bank account.


Figure 2

Contrary to much popular and professional belief, brand new 7/8” combined master cylinders for drum braked Spridgets have been available for years, manufactured by Caparo AP Braking Ltd. in Leamington Spa, Warwickshire. At first glance, these units (Figure 2) look identical to the original Lockheed ones but a close examination reveals that the information cast into the sides of their blocks is different, something that will worry only the most dedicated concours fanatic because these marks cannot be seen after installation. These units are made to the same specification and quality available in 1959 but incorporate improved materials developed in the intervening period: the surface finishes are improved and the rubber compounds are good up to 120 degrees instead of the 80 degrees of natural rubber. The result is astounding, and – as a bonus – the price is much less than that quoted by some leading suppliers for a reconditioned old unit of dubious provenance. AP Braking sell only to the trade, but their product is available to everyone from several distributors in the UK (Leacy MG, Moss Motors Europe and AP Braking’s own distributor, Seltech Engineering Ltd.). Spridget owners with drum brakes can therefore sleep soundly unless of course they have upgraded their engine and clutch, in which case they will be suffering insomnia for an entirely different set of reasons as hospitals are not usually very comfortable places.


The owners of early disk-braked Spridgets, however, are not so lucky because the small bore 3/4” unit has not so far been re-manufactured, probably because the 7/8” unit is suitable for a much larger range of vehicles including MGAs and more mundane applications which include industrial machinery and fork-lift trucks. The good news is that the company ‘Past Parts Ltd.’ in Bury St Edmunds -




can re-sleeve a 7/8” unit to 3/4” using stainless steel which means it won’t corrode, a valuable advantage for vehicles which are stored for long periods - and the total cost still compares favourably with that for a reconditioned unit from specialist suppliers. Other companies will perform this re-sleeving too, but I can personally recommend ‘Past Parts’ because my own GAN2 car possesses one of their re-sleeved master cylinders and I can certify that the job was performed to a very high standard, using machinery and expertise imported from my homeland Australia where this sort of re-sleeving is a very common place activity.


One problem still remains for the disk braked owner: after re-sleeving, one still needs a set of 3/4” pistons and these are not generally available. We should all make strenuous efforts to preserve any small bore pistons which still exist because they are probably the most valuable part of any rusty old 3/4” unit. The pistons are often in good serviceable condition, even if the rest of the thing is scrap. However, Past Parts can fit new pistons when re-sleeving cylinders from 7/8” to 3/4” because they have had them made specially for this purpose.


We now return to the problem mentioned earlier which confronts, say, the owner of a Frogeye who wishes to upgrade to disk brakes (because he wants to stop at cross roads) but who also wishes to retain the car’s original 9C engine and clutch. A perfect solution to this problem is to ask Past Parts to re-sleeve only the brake bore of a brand new 7/8” AP-Braking combined master cylinder. Both brake and clutch will then work precisely as Abingdon intended, the re-sleeving job should be less expensive than a 2-bore job and one set of 3/4” pistons can supply two Frogeyes! As far as I am aware, no one has yet tried this experiment - but Past Parts has assured me that it is perfectly possible. I have two good 3/4” pistons in one of my expensive doorstops and I am prepared to donate one to anyone who would like to try this, the only proviso being that they agree to write a report for MASCOT describing the result.


Please note that I have deliberately not mentioned prices because they may change. These early combined master cylinder units are not cheap but they are one of the most vital parts of the car and this is not an area in which to attempt a slight economy. Be very wary of old second hand units, check the price catalogues of all leading suppliers and obtain firm written quotes (not estimates) for any work that you commission. In my view, the Caparo AP-braking / Past Parts options which I have described provide safe braking and offer extremely good value for money. And no, I do not have shares in either company, I just wish everyone safe braking.


I thank Ken Ewers at Caparo AP Braking and Nigel Wigg at Past Parts Ltd. who very kindly read my manuscript at short notice and provided extremely useful extra information. Any errors remaining are mine.


John E. Davies (Member 3443)


  *Reprinted with permission of John E. Davies