626 Modern Lady Magazine

Hydraulic Brake PumpsThe old trial and tribulation years of research anddevelopment can sometimes be a costly endeavor. Inthe early days of hydraulic systems a Frenchautomaker, Robert Citroen, designed a car called theCitroen. One of the neatest things that this car offeredwas a hydraulic leveling system. Rolls-Royce used theRobert Citroen patented hydraulic system and rede-signed the complete system to work with their hy-draulic system.

The Silver Shadow series started with a hydraulicsystem that was designed by the French and re-engineered by the English. Need I say more? Thistime around let’s just talk about the brake pumps inthis short technical article.

The original brake pumps that were fitted to theoriginal cars were heavy industrial diesel injectors thatwere used on locomotives. They were adapted byCAV, a company that Lucas owned.

Our dear friend from “The Shadow’s Corner” said fromthe start of the very first Shadow through the earlySpirit and Spur series there were problems with brakepump barrel and plunger assemblies. Camshaft drivenplunger type brake pumps started with the beginningof the Silver Shadow Series V8 engines.

There are two extra eccentric cam lobes on the enginecamshaft. As the engine rotates, the plungers areforced upwards by the connecting pushrods. Theseare kept in continual contact with the eccentric lobesof the cam by the internal return spring in the brakepumps. As the plungers are moved downwards by thespring, the brake fluid is drawn into the pumpsthrough the open inlet ports of the brake pumps. Anon-return valve internal of the pumps ensures thatfluid in the delivery lines is not drawn back into thepumps. As the plungers are forced upwards againsttheir internal springs, fluid pressure closes the non-return valves in the inlet ports and opens the outletports to the supply lines. This allows fluid to startcharging the accumulator spheres.

Both pumps are mounted centrally, front and rear, onthe tappet cover in the middle of all V8 engines. Theyare behind and between the intake manifold and

by John Palma

Cutaway section ofthe revised mineraloil pump.

Modern Lady Magazine 627

screwed on top of the tappet cover. The front pump isknown as hydraulic system pressure one and the rearis system is two. The two brake pumps circulate thefluid in the system and create fluid pressure for thebraking and leveling hydraulic accumulators.

This design has stayed the same through the end ofthe 6.75 litre V8 engine. The old Crewe built BentleyContinental R series and the new Corniche also usethe original 6.75 Litre engine with the original hydrau-lic system. The Silver Seraph and the Bentley Arnage,with the BMW V8 and V12 engines, use the BMWdesigned braking system incorporated into the laterseries cars.

These brake pumps were used in early and late seriesmotorcars that used both brake fluids … RR363 ormineral oil. The brake pumps may appear to be the

same but they are not interchangeable. There areseveral ways to determine the difference between thetwo pumps. The RR363 pump is NOT painted greenon the reservoir housing. Also, the feed pipe is con-nected to a larger diameter threaded nipple which islocated at the top of the outlet adapters.

The early type mineral oil brake pump has a quarterinch diameter threaded nipple that connects to thefeed pipe of the accumulator. There is a green plasticring around the top adapter and the outer pumpreservoir housing is painted green. A later revisedmineral oil brake pump was made when supplies ofthe older style were depleted. The top threaded outletadapter identifies the revised pump. It has a stakedoutlet adapter and has the same green identificationdisc.

Rear prakepump mountedon top of tappetcover at back ofengine.

BRAKE PUMPS, continued

628 Modern Lady Magazine

Close-up of rear brake pump mounted in place on top of tappet cover,under the engine s intake manifolds of a late 6.75-liter V8 engine.

Hydraulic Brake Pumps, continued

Cutaway section of the completeEarly Silver Shadow 6.2 liter V8 engine

and hydraulic brake pump and accumulatorassembly s components. Shows the new high

plug position, the camshaft driven hydraulic pumpsmounted in the V and the hydraulic accumulators

(on the right) which are initially filled with nitrogenat a pressure of 1,000 lbs./sq. in.

The early pump had inter-nal seepage problems.Mineral oil seeped past theplunger and mixed with theengine oil. This causedexcessive use of mineral oil.The modified multi-grooved type plungerdesign stopped the mineraloil from seeping past theplunger and mixing withthe engine oil. The revisedpump is a non-serviceableitem except for the replace-ment of the pump housing‘o’ rings.

Given the right set of cir-cumstances the plungercould stick at the top posi-tion in the barrel. Theclearance in the barrel andplunger assembly was notenough, particularly if theengine was switched off aftera long hard run. The

already extremely high under bonnetengine temperature would spikeeven higher when the engine wasshut off. The engine camshaft playsan important part in this problem. Ifthe position of the camshaft brakepump lobes are in the most upwardsposition when switching off theengine for a short period of time, thecamshaft lobes continue to compressthe plunger in the brake pump in theupwards position. When restartingthe engine, the plunger returnsprings would not have enoughpressure to return the plungers to thebottom position.

Modern Lady Magazine 629

Remember my short technical articleabout having no gas in the brakeaccumulator spheres if the enginewould quit while driving in traffic ...NO BRAKE AT ALL? Well, here isanother scenario for you.

Imagine both brake pumps experi-encing the problem of being over-heated and sticking in the upwardposition. Now, picture yourselfdriving along as you normallywould, applying the brakes as youstop for traffic and not noticing thewarning panel light on because it isdifficult to see in the daylight. Eachtime you apply the brake peddle youare depressurizing the stored pres-

sure in the accumulator spheres andyou are unaware that you only haveone or two applications left to stopthe car from rolling. Again … NOBRAKES AT ALL.

The worst two years for this problemwere 1984 and 1985. However, CalWest has said that any year of SilverShadow or Silver Spirit could experi-ence this problem given the right setof circumstances and that numerousaccidents have been caused bysticking brake pumps with thedrivers claiming that they had nobrakes. When the cars had cooledand were examined, no fault couldbe found. This was because the

pumps had sufficiently cooled andwere now functioning normally.

Rolls-Royce had taken steps to correctthis problem. They redesigned thecamshaft so that the brake pump lobeson the camshaft are offset from eachother. This means that only one brakepump can fail at a given time if the rightset of circumstances would arise. Theyalso increased the tolerance betweenthe pump plunger and barrel. Thismade the pump less likely to stick.However, this caused more fluid tobypass the plunger into the engine.That caused them to develop thegrooved plunger which is now in use.

Bottom of page shows the same picture of a late mineral oil rear mounted brake pump showing engineintake manifold system over top of brake pump. this view of the rear brake pump can only be viewedwith the engine removed from the car.

◆◆◆