The main reason for penning this particular article is the frightening number of these brake assemblies that I see which are either built up absolutely incorrectly or at best way out of adjustment. The normal warning signs being that the brake adjusters are screwed right in, almost to the extent of making one believe there are no linings on the shoes. This problem is very widespread in the USA but it also appears on home territory and is not confined to owners, invoices from professional specialists combined with the obvious faults shows no common ground. What is very obvious is that the proper rebuilding procedure is not widely known or followed. Hopefully more brake assemblies will now meet the objectives of this article as shown below.

To rebuild the later type front brakes so that the correct brake shoe self wrapping action occurs both in a forward direction and in reverse. Ensuring that the front brakes, when applied, provide the designed retarding power in either direction. To correct the omissions from the parts and workshop manuals. Any mention of the Bentley MKVI brake assemblies includes the relevant Rolls-Royce models.

The history of the front brake and incorrect brake assembly

The early Bentley MkVI hydraulic front brake was based on the mechanical wedge front brake arrangement that was used on the Bentley MkV of 1939/40. Fig 1 shows the external linkage of a 1940 Bentley MkV, note the mechanical link at the top of the king pin with another universal link under the leather cover. Wedge brakes are notoriously difficult to design so that they provide the correct feed back to the driver, and from the driver’s point of view can be alarmingly difficult to control. The main reason is that the input effort to output load is not linear along the travel of the wedge, and they can tend to be fierce in action and to stick or release slowly. Try extracting a wedge that has been holding a door ajar under some pressure and you will realise just how efficient a wedge can become, and how difficult to release. Having discussed the down side of wedge brakes, if you are faced with stopping a heavy vehicle with limited input effort they certainly can provide the application efficiency as long as you are not too concerned about controllability. In short if you are travelling on ice, water or have slight brake unbalances….don’t ring us!

Cost and the practicalities of transmitting the driver’s effort to the foundation brake at the road wheel end would have caused the shift from a mechanical operation to hydraulic operation, of at least the front brakes. The fairly new fangled hydraulic brakes having been around the best part of 10 years and more without killing the masses in their Wolseley and Morris cars. In October 1944 the initial R-R drawings, in this case drawing RF 3127 covering the kingpin and yoke assemblies showed a hydraulic front brake. Fig 2 illustrates this design, still a wedge brake but with hydraulic operation. The parts of the cylinder are made up of out sourced components from Girling and in house produced parts like the cylinder body.

This design was to last from the introduction of the Bentley MkVI in 1946 until approximately June 1950, the hydraulics powered the foundation brake arrangement shown in Fig 3. Viewing the available drawings shows that the original intention was to mount the hydraulic hose to chassis pipe connection off the shock absorber body instead of the chassis. Unfortunately the inter shoe linkage was original attached adjacent to the trailing shoe as shown by the red arrows which tended to pivot the shoes around the link pivots instead of the adjuster tappet. A service bulletin later instructed retrospective reversal of the linkage so that it was fitted at the position of the blue arrow. This service bulletin was indeed needed as the brakes were subject to dragging. Moreover as Fig 3 shows, no one altered the parts manual even up to 1952, and to this day owners are mislead by this image. It should be noted that this brake arrangement was also used on the rear brakes right until the “S” series of cars were launched in 1955.

At Bentley MkVI chassis B-1-GT, Silver Wraith WME –1 and Silver Dawn SCA-1 the front brakes were altered completely, including the brake drum. Fig 4 illustrates the foundation arrangement of this later front brake, particularly important on this parts list view is the position of the off stop pin, which is correct. This brake was designed to produce maximum retardation without the disadvantages of a wedge operation, and it achieves those objectives extremely well.

Unfortunately neither the parts nor the workshop / service manuals are very helpful in rebuilding this late type brake correctly. The former shows the position of the clevis link Fig 5 in the place of the off stop pin and the latter are missing a number of vital paragraphs and fail to explain the importance of the cylinder positioning.

The only known complete drawing of this front brake that shows the correct assembly is contained in scheme number PL 5693, which was the original design scheme. Fig 6 shows part of the drawing for this scheme in which the red arrow clearly depicts the off stop position at the front end of the cylinder.

Fig 7 shows the writer’s correction of the assembly of the late type cylinder previously shown in Fig 5, note the correct positioning of the ‘clevis pin’ and ‘(off) stop pin”. The latter always being at the front of the wheel cylinder.

Comparison of Fig1 with Fig 8 shows how the changes affected the exterior of the brake from 1940 to 1950.

There are at least five different ways of assembling this late brake assembly, only one is correct. The three most frequent errors are to position the “off stop pin” at the rear of the hydraulic cylinder instead of at the front, see Fig 9. Having the “W” link hooked onto the trailing shoe only instead of passing through the shoe and engaging in the anchor plate. Finally, in the extreme, failure to engage the sprag link into the recess at the rear end of the hydraulic cylinder.