Tuesday, November 3, 2015

Sudden Brake Failure in Shadow-era Rolls-Royce and Bentley Motorcars



How do you know the brakes in your Shadow-era Rolls-Royce are safe?  If you are like most people you trust the warning lamps on the dash.  When you start the car and you see the lamps glow, flicker, and go out – you know they work.  Lamps out - brakes safe.  You expect the lamps to warn you if either system loses pressure, so you can stop the car before brake pressure is lost.



Can that system fail?  Last week, I learned that the answer is yes.   Shadow brakes can fail without warning.  I know because we had it happen to a car in our yard.  The only thing that saved the car from crashing into the building was the simultaneous shift into park and stepping hard on the emergency brake.  And when the car stopped we realized we would not have been so lucky if the speeds had been higher – those tricks won’t do much at 60mph.

The next morning we hooked pressure gauges to the test points and read 2,000psi on the rear circuit, but just 1,300psi on the front at idle, rising to 2,000 as the engine sped up.  That puzzled us because the pumps were recently changed, and the accumulators were freshly charged on rebuilt blocks.  Why the low pressure? 

There was no obvious reason the front circuit should have been low.  And an even bigger question remained – how did the brakes fail with those system pressures?  1,300psi at idle is low, but it’s still plenty to stop the car.  And the rear had full pressure all along.  So what happened?  The pressures must have fallen to zero on the test drive, and we were at a loss to how that could have happened.

We did a flow test, which one circuit passed and the other came close.  That didn’t answer the failure either, but it raised a question.  What would account for low flow in a newly rebuilt pump circuit?  We have seen that happen with collapsed lines from the reservoir to pump, but these lines looked good.  

We suspected the answer might lie in the hydraulic reservoirs, located on the left fender well just forward of the firewall.  We started removing the screws that hold the cover in place - something that never happens on most Silver Shadow cars.  Why would you remove the cover?  You can see the fluid through the sight glasses, and you fill through the caps on top. The unit itself is seldom taken apart.  But it should be, as our exploration revealed!


The first thing to check was the intake screens in the reservoir and that is where we found our answer.

Sludge in a Silver Shadow hydraulic reservoir (c) JE Robison Service



What you see in the photo is a solid inch of sludge, and the intake screens are actually collapsed from the force of the pumps trying to suck solid sludge through the fine mesh.  Take a look at this comparison:



You can see how the pump was straining for a long time to pull fluid through those clogged strainers. Intake restriction is surely a cause of pump failure in some of these cars.  And it can get worse - if a pump fails it can seize and damage the pushrod or even the cam. So you can see how this gel issue can turn into major mechanical trouble in addition to the obvious hydraulic problems it causes.

I was shocked to find such a gelled mess of fluid, but the car in question had been stored for 10 years, and a review of online forums reveals quite a few instances of brake fluid gelling in cars and motorcycles during long term storage.  We have actually seen that ourselves, as shown in this photo of what we found in a Jaguar XK120 brake reservoir after being parked 6 years.




The fix for this - on the Rolls - was to remove and clean the reservoir, and replace the screens.   

For the sake of comparison, this is what a disassembled reservoir looks like on a car in our restoration shop:




A restored RR363 hydraulic reservoir from a Silver Shadow (C) JE Robison Service 

After cleaning this car's reservoir, we also replaced the suction lines to the pumps, and thoroughly flushed the system.  But flushing only goes so far.  After running the car 100 miles this is what we found on removing the reservoir top again



As you can see the rear circuit has turned rather dark, and there are little bits of debris accumulating in the tank.  In these cars the rear hydraulic circuit powers the level control, and we have known the rams to build up sludge, some of which seems to be making its way back to the reservoir.  The photos below show the level control circuit on this car, which was a repository for more sludge:





The cure for that: Take apart and clean the level control circuit.  In this car, the level control hadn’t worked, and the owner had said to ignore it. But we could not do that, when we saw how it was polluting the clean fluid in front. We took apart and cleaned both rams, cleaned the valves, and blew clear the lines. In retrospect I see that the level control failure was due to gelled fluid preventing proper operation. It worked once this was done.

So one takeaway from that is that the whole system should be cleaned and serviced, even if the owner does not care about self-leveling.  What seems like a place to economize on service (level control) could well end up a cause of rear circuit brake failure.

The other takeaway is that the reservoirs should be opened up and inspected when these cars receive major brake service, or when they are serviced after long-term storage (more than one winter.)  There is no external sign of sludge in the reservoir, and if you don't open it up and look your first clue may be the total and sudden failure of the system.

This inspection is a nuisance, with 14 screws holding the cap in place, after which the screens and plates have to come off.  And if the reservoir needs to be cleaned you could be into a half-day project.  But do it anyway, in the interest of safety!  The lesson of this car is that the fluid reservoir should be checked before the car is driven.

And when the reservoir is filled, be sure to use the RR363 fluid that's made special for these cars.  Ordinary brake fluid does not have the castor oil lubricant the brake pumps require, and substitution of a different fluid can lead to brake pump wear and premature failure.  That's a failure that's easily avoided - just use the right stuff!  It is ok to top these systems with DOT3 fluid in emergency but if that is done the RR363 should be put back in at the earliest opportunity.

And one final thing – why didn’t the warning lights come on?  In some of these cars the warning lamps are at the end of long dead-end pipe runs.  In this vehicle, the line to the sensor was jammed by gelled fluid, and there was no live connection between the sensors and the fluid they were supposed to monitor. Yet they looked good from outside!  That just shows how appearances can deceive.  Particularly since this car originally had the warning lights lit, and they went out when the car was first started up.

The advice in this article applies to 1965-1980 production Rolls-Royce and Bentley motorcars that use pressurized RR363 hydraulics.  This includes all Corniche, Shadow, Wraith, T Type, and T2 built in that period.




(c) 2015 John Elder Robison
John Elder Robison is the general manager of J E Robison Service Company, celebrating 30 years of independent Rolls-Royce and Bentley restoration and repair in Springfield, Massachusetts.  John is a longtime technical consultant to the Rolls-Royce and Bentley clubs, and he’s owned and restored many fine British motorcars.  Find him online at www.robisonservice.com or in the real world at 413-785-1665

Reading this article will make you smarter, especially when it comes to car stuff.  So it's good for you.  But don't take that too far - printing and eating it will probably make you sick.


1 comment:

Brian McLean said...

Nice points John, thank you!

-Brian McLean (LRX11290)