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Retro-fitting remote-acting brake servos, Kunifer-10 pipework & silicone brake fluid

Discussion in 'Steering, brakes & Suspension' started by Nigel, Jun 20, 2009.

  1. Nigel

    Nigel Member

    Canvey Island, Essex, UK

    Written & Compiled by Nigel A. Skeet

    Here is an update of an an edited, non-illustrated article, which was previously published as follows:

    Nigel A. Skeet, Tech Talk, "Fitting Remote Vacuum Brake Servos, Kunifer-10 Pipework & Silicone Brake Fluid", Transporter Talk, Issue 66, August 2003, Pages 12~15.

    For several years, my father had been complaining about the excessive physical effort, required to apply the brakes of our 1973 VW 1600 Type 2 and asked whether I could fit servo assistance. I had to concede that on the few occasions I had needed to brake heavily, it had almost been necessary to use both feet, owing to the combination of front disc brakes and no servo assistance.

    Fitting a vacuum assisted servo unit of any type, requires a source of vacuum, which is typically derived from the inlet manifold (or manifolds) of the engine. The inlet manifolds of the twin Solex carburettors, fitted to the 1972~83 VW 17/18/2000 Type 2s, make standard provision for the brake-servo vacuum connection, but this needs to be added to the vertical down-pipe of the VW 1600 Type 2 inlet manifold, below the single Solex carburettor; requiring the temporary removal of the inlet manifold and hence the engine. A non-return valve must be incorporated into the vacuum hose, as close to the inlet manifold, as is reasonably practical.

    In principle, I could have fitted a brake master cylinder, pushrod and a direct acting, vacuum servo unit, from a 1972~79 VW 17/18/2000 Type 2, but this would also have required the associated front torsion-bar suspension beam, with servo mounting bracket, as shown in the photographs I obtained some years later.


    RHD, 1972~79 VW 17/18/2000 brake-servo mounting bracket

    Notice that the asymmetrical brake-servo mounting bracket, mounted on the torsion-leaf tube assembly, is positioned on the right-hand side for RHD, and that it is angled in two planes, to align the axes of the brake-servo unit and the brake master cylinder. Hence, if one desires to retro-fit vacuum brake servo assistance, to a RHD, 1971~79 VW 1600 Type 2 (which has non-servo-assisted, front disc brakes!), there is no point retro-fitting, a front-suspension, torsion-leaf tube assembly, salvaged from a LHD vehicle, which has its brake-servo mounting on the left-hand side.

    Fabricating and fitting a servo mounting bracket to our existing suspension beam, would have been possible in theory, but even with a pattern to copy, I believe it would have been far from straight forward, to obtain the correct bracket shape and position alignment. Welding such a bracket to the suspension beam, would require particular care, to avoid overheating the torsion leaves inside, which would otherwise cause them to lose their temper and hence their springiness.

    Owing to the paucity of 1972~79 VW 17/18/2000 Type 2s in the British breakers' yards, it was decided to fit twin remote servos (one servo per hydraulic circuit), assuming we could find a suitable donor vehicle. Remote servos were rumoured to be used on the VW Golf GTI Mk 1, but I never had the chance to inspect any. Sometime later, in 1988, I chanced upon a pair of ATE (i.e Alfred Teves GmbH) remote servo units at my local breaker's yard, installed in a 1975 BMW 518i. I later learned that they were used on several models of right-hand drive BMW (including the 2002 and 318i), during the 1970s.

    Remote-acting brake servos - side view of cradle & servos


    Remote-acting brake servos - oblique view of cradle & servos

    Last edited: Jun 20, 2009
  2. Nigel

    Nigel Member

    Canvey Island, Essex, UK

    Written & Compiled by Nigel A. Skeet

    It was not practical to mount the servo units, on the front-suspension beam or anywhere in the immediate viscinity of the master cylinder, so they were suspended in a homemade, 25mm square-section, welded, tubular-steel cradle, bolted beneath the chassis, using existing holes in the longitidinal chassis members, rearward of the front jacking points, straddling the central warm-air duct, as shown in the photographs. The schematic diagrams show the hydraulic brake circuits, before and after modification.

    Remote-acting brake servos - view from right-hand rear underside of my 1973 VW 1600 Type 2


    Remote-acting brake servos - view from rear underside of my 1973 VW 1600 Type 2


    1973 VW 1600 Type 2, factory-stock & modified hydraulic brake circuit, incorporating two remote-acting, vacuum-assisted brake servos


    Sometime before I embarked upon this project, I had read about Dow Corning silicone brake fluid, available from Automec. Having discovered that silicone fluid was kind to human skin and paintwork, didn't lead to vapour lock or corrosion problems, owing to its non-absorption of water, had good lubricating and thermal conduction properties, had a higher boiling point than conventional polyglycol, DOT3 or DOT4 specification brake fluid and was compatible with the existing components, gave a whole new meaning to the concept of low-maintenance, high performance braking systems. Never again having to change the brake fluid at two year intervals, was regarded as a great boon.

    Silicone brake fluid is miscible (i.e. will mix) with conventional polyglycol brake fluid, but is immiscible (i.e. will not mix) with water. This implies that if silicone fluid is contaminated with polyglycol fluid, which had previously absorbed water, the silicone and polyglycol fluids will mix together freely, but the water will separate out from the mixture, boiling at 100 °C (assuming standard atmospheric pressure of 760 mmHg at sea level!), after the brake pedal is released, to cause vapour locking, or freezing below 0 °C, causing blockage of the hydraulic system. At high altitudes, water boils at temperatures, much lower than 100 °C, owing to reduced atmospheric pressure.

    Not wishing the new silicone fluid to be contaminated with conventional polyglycol fluid, the mixing with which, would have undesirable side effects, the servo units and the existing braking system components, were cleaned internally, using iso propyl alcohol; all except the rear brake-pressure regulator, having been disassembled prior to cleaning. As a precaution, all the master cylinder, rear slave cylinder and front caliper hydraulic seals and dust covers, were also renewed.

    When the servo units were disassembled for cleaning, the hydraulic seals were inspected and showed no obvious signs of wear and so were re-used. The servo unit cylinders, master cylinder and slave cylinders were easy to clean thoroughly, but without splitting the calipers in two, it would have been virtually impossible, to completely remove the sludge which had accumulated in all the internal nooks and crannies, during the preceeding 16 years.

    Contrary to popular opinion, polyglycol hydraulic brake-fluid absorbs the majority of moisture, by osmosis, through the semi-permeable, flexible hoses, close to the road wheels, rather than via the vented fluid-reservoir cap, in the cab. This moisture diffuses very slowly, through the fluid, so the majority of any internal corrosion, would be in the brake calipers, slave cylinders and neighbouring pipework. Being wary of disassembling the pressure regulator, owing to the spring-loaded internal components and the unlikelyhood of internal corrosion, owing to its remoteness from both the flexible hoses and fluid reservoir, this was simply flushed through several times with alcohol.

    Employing patience, copious quantities of releasing oil and firm but gentle use of the socket wrench, the two sets of four bolts (holding the matching halves of the two calipers together), finally unscrewed; without shearing or damage to the bolt heads. It was fortunate that the O-ring seals between the caliper halves were in good condition and that I had not discarded them, because I later discovered that the ATE caliper service kit, did not include new O-rings! With hindsight, I could probably have obtained suitable O-rings from a specialist, industrial hydraulics, wholesaler or industrial seals manufacturer, which are likely to be listed in Yellow Pages and Thompson's general purpose directories or trade directories, such as Kompass, Kelly's and Sale's, copies of which are to be found in the reference section of many public libraries.

    Prior to splitting the front brake calipers in two, I had initially wondered how to remove the hydraulic pistons, but finally hit upon the idea of pressurising the caliper with my tyre inflator (i.e. footpump), using a discarded brake pipe union and a piece of thick-walled, rubber tubing with Schräder valve (old ones are usually discarded when tubeless tyres are renewed) as a connector. Several years later, I was intrigued to see this idea, published in the February 1995 & October 1999 issues of VW Motoring, as reader's Top Tips, independently submitted by two other readers; yet another case of great minds thinking alike!

    As I would have to incorporate additional hydraulic pipework, I took the opportunity to upgrade the whole system, using 3/16 inch, Kunifer-10, cupro-nickel tubing (manufactured by IMI Yorkshire Alloys Ltd. - now commonly available through motor factors and car accessory shops, at quite modest cost); a marine grade alloy, comprising 90% copper and 10% nickel, which is more corrosion resistant than either conventional zinc coated, steel bundy tubing or pure-copper tubing.

    This avoided the need in later years, to replace corroded steel tubing, as it finally succumbed to the ravages of time and weather, plus negating the chore of trying to remove polyglycol fluid and sludge, from the old pipework, in preparation for using the silicone fluid. Costing about £7~£8 per 25 feet length, in 1988, I considered Kunifer-10 brake tubing, a cheap and worthwhile investment. It also proved to be easier to bend and flare than steel tubing. Owing to their location, it was impractical to connect the remote-servo units, to the master cylinder using single lengths of brake pipe, so in-line connectors were also incorporated. Having rerouted the pipework, it was also necessary to fit grommets and additional pipe support-clips, in strategic positions.

    I had previously purchased a metric brake-pipe spanner to dismantle the system, but I didn't possess the appropriate tools for fabricating brake pipework, so a tube bender and flaring kit were hired for 3 days, from a local tool-hire shop, whilst I was home from work over the long Christmas holiday. Cutting the new brake tubing to exactly the right length, plus bending, flaring and trial fitting, was a time consuming affair, taking a total of three days, working more than 10 hours per day. I finally completed and fitted the last of the 28 pipe unions, at about 2.00 AM, on a rather cold morning after Boxing Day; with just enough time for a snooze, before I had to return the tools to the shop, at 9.00 AM that morning.

    After filling the system with silicone brake fluid, it was bled in a revised sequence, which involved bleeding the front brakes' remote servo unit before either of the front calipers and similarly for the rear brakes' remote servo, before the rear slave cylinders. This task completed, the system was fully pressurised, by my father stepping hard on the brake pedal, whilst I inspected each of the pipe unions for leakage.

    Much to my surprise and relief, only 3 of the the 28 unions, showed any sign of weepage and this was easily rectified by tightening the unions by less than one flat (i.e. less than 60° turn of the spanner). Several days after seemingly completing a successful installation, it was noticed, that brake fluid was dripping, from the vacuum canisters, of the remote servo units; having leaked past the seals of the hydraulic cylinders.

    Following the leakage, I enquired about ATE remote servo, service kits (ATE part No. 03•0671•9929•2), for which I was quoted a price of £156•58 (including 15% VAT) per servo unit, in 1989! It was thus decided a better option, to buy two new, identical, remote servo units (ATE part No. 03•6119•5212•4), from Hatchlands Autos, in Redhill, Surrey (the local ATE agents, near my then place of work), at a total of £515•67 (including 15% VAT and 25% trade discount). After fitting the new units, the system checks and bleeding operations were repeated.

    Buying second-hand ATE remote servos, proved to be a false economy, principally owing to the exorbitant cost of service kits. Whether this is also true, of the remote servos made by either Lucas-Girling or AP-Lockheed, I don't know, but it would be advisable to check, before embarking on a similar project.
    Last edited: Jun 20, 2009
  3. Nigel

    Nigel Member

    Canvey Island, Essex, UK

    Written & Compiled by Nigel A. Skeet

    Fitting the vacuum servo assistance has certainly made driving more relaxing, now that we don't have to strain our leg muscles when using the brakes, whereas before, I almost felt the need to use both feet on the brake pedal, on those few occasions when emergency braking was required. So far, there have been no problems with the braking system, nor any need to top-up the silicone brake fluid, which whilst the van has been layed-up these past few years (for further modification and refurbishment), will have protected the steel hydraulic components from rusting, which very likely would have occurred, had the system been filled with water absorbent, polyglycol brake fluid.

    Prior to modifying the braking system, the only work I had done on brake hydraulics, was to replace the two rear slave cylinders, on our VW Type 2, some years before. I have since used silicone fluid in the hydraulic clutch of my 1974 Triumph Toledo and intend to also use it in the braking system, in the near future, when I replace the now corroding steel pipework, with Kunifer-10 alloy tubing and upgrade the system to dual circuit.

    Since installing silicone brake fluid in our 1973 VW Type 2, in 1988, I have learned (see Charles Bulmer, "Arresting Developments", Car Design & Technology, December 1991, Pages 82~84) that it does exhibit some potentially undesirable characteristics. Although silicone fluid does not absorb water, it does tend to dissolve air, which comes out of solution, as air bubbles (rather like a case of 'the bends', in deep-sea divers), at high altitudes, where the atmospheric pressure is lower; causing some feeling of sponginess when braking. Another factor which may lead to a feeling of sponginess, is silicone fluid's greater compressibility (i.e. volume is reduced by application of external pressure), at high temperatures.

    Both these conditions might become manifest, during mountain driving, when descending long, steep hills; with prolonged use of the brakes. We haven't undertaken any serious mountain driving, since installing the silicone fluid, so I don't yet know whether this is likely to pose a problem. I have always adopted the lorry driver's maxim, that one should descend a hill in the same gear, as one would need to ascend it, so I tend to make relatively little use of the brakes.

    Several years ago, a university colleague of mine, who was a keen amateur rally driver, related a story concerning his father, who had decended a hill, controlling the speed of his Ford Transit van, by means of the brakes, rather than the gears and engine. His father later discovered the brakes had become so hot, that the paint had burnt off the road wheels! If this seems implausible, consider a VW Type 2, with an all-up touring weight of 2•0 tonne, descending a 1-in-10 (i.e. 10%) hill, at a modest constant speed of 30 MPH, using only the hydraulic brakes and no engine braking.

    Under these conditions, the four brakes would have to dissipate heat, at a rate of 26kW in total (an average of 6½kW per wheel), corresponding to the rate of loss of gravitational potential energy. This would be even greater, if a heavier vehicle, higher speeds or a steeper gradient, were involved. Compare this, with a typical electric kettle, which rapidly becomes too hot to touch, having an electric heating element, of less than 3kW. With no water in the kettle to absorb the heat, the electric heating element would overheat and explode; blowing the lid off the kettle, as I have personally observed!

    During the early quarter of 2000, I obtained (on a sale or return basis!) an Eberspächer BA6 under-floor, auxiliary petrol-fired heater, which may be fitted in place of the under-floor heating system duct. Unfortunately, the required location for the Eberspächer heater unit, corresponded to the position of the ATE remote servo units, I had fitted in 1988. Hence, I would again have to modify the braking system, if I wished to fit a BA6 unit.

    This would involve either relocating the servo units, which I believe to be impractical, or obtain a brake master cylinder, pushrod and a direct acting, vacuum servo unit, plus the associated front torsion-bar suspension beam, with servo mounting bracket, from a 1972~79 VW 17/18/2000 Type 2. Not wishing to do either of these things, I shall investigate the practicalities of using a different Eberspächer unit.

    To enhance brake cooling, some vehicles are fitted with cross-drilled discs or ventilated discs, which if not fitted as standard, are sometimes available as an after-market accessory. Cross-drilled replacement discs, made by Rossini Performance Products (see Paul Knight, "How To: Bay Bus Stoppers - Brake Upgrades", Volksworld, September 2002, Pages 86~89 and James Hale, "How to Modify VW Bus Suspension, Brakes & Chassis for High Performance", Veloce, Speedpro Series, 2002), were then available for the 1973~79 VW Type 2, from Car Parts Direct, priced at £98 per pair, which was nearly twice the price of the standard replacement discs. Although this might seem expensive, it is comparable with the price of standard replacement discs, for the 1971~72 VW Type 2.



    Cross-drilled & grooved brake discs, for air & water-cooled VWs


    Another recently anounced brake upgrade (see New Products, Volksworld, January 2003, Pages 17~18), to 1968~79 VW Type 2s, is the fitment of Porsche 944 front brake discs & calipers, to 1968~70 VW Type 2 front wheel spindles (the kind to which drum brakes were fitted), using a special custom spindle adapter bearing and brake caliper spacer kit, available from Harry Harpics, in Westcliff-on-Sea, Essex. If one wishes to upgrade the 1971~79 VW Type 2 in this way, it will be necessary to fit the earlier type wheel spindles.


    Charles Bulmer, "Arresting Developments", Car Design & Technology, December 1991, Pages 82~84.

    "Fluid Dynamics", VW Motoring, October 1999, Pages 66~69.

    Paul Knight, "How To: Bay Bus Stoppers - Brake Upgrades", Volksworld, September 2002, Pages 86~89.

    James Hale, "How to Modify VW Bus Suspension, Brakes & Chassis for High Performance", Veloce, Speedpro Series, 2002.

    New Products, Volksworld, January 2003, Pages 17~18.


    Automec Equipment & Parts Ltd., 36 Balmoor, Buckingham, Buckinghamshire, MK18 1RQ, Great Britain.
    Tel. 01 280 - 822 818 Fax. 01 280 - 823 140
    Internet website: http://www.automec.co.uk e-mail: info@automec.co.uk

    Paul Miller (Proprietor), Harry Harpics, Volkswagen & Porsche Engineering,
    2 Brookside Works, Springfield Drive, Westcliff-on-Sea, Essex.
    Tel. 01 702 - 391 756

    IMI Yorkshire Alloys Ltd., Leeds, LS1 1RD, Great Britain.

    A. P. Lockheed Brakes, Automotive Products Ltd., Tachbrook Road, Leamington Spa, Warwickshire, CV31 3ER, Great Britain.

    Alfred Teves GmbH, P.O. Box 900 120, D-6000 Frankfurt 90, Germany.

    Car Parts Direct, 160 Burton Road, Derby, DE11 1TN, Great Britain
    Internet website: http:/www.carparts-direct.co.uk
    For cars upto 20 years old Tel. (UK) 01 332 - 290 833
    e-mail: sales@carparts-direct.co.uk

    Parts for Older Cars (Fittapart Centre), 1 Southwell Road, Mansfield, Nottinghamshire, NG18 4EH, Great Britain
    Internet website: http:/www.carparts-direct.co.uk
    For cars more than 20 years old Tel. (UK) 01 623 - 658 041 ask for Martin Mosley
    Fax. (UK) 01 623 - 421 257
    e-mail: martin@carparts-direct.co.uk
    e-mail: martin@partsforoldercars.co.uk
    Last edited: Jun 20, 2009

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