Thursday, September 7, 2017

Air suspension on Bentley GT and Flying Spur series cars


The Bentley GT-series were the first cars from Crewe to use air suspension instead of conventional steel coil springs.  In doing this Bentley followed the lead of corporate parent VW (and Audi) along with Mercedes, BMW, and Land Rover.  Air suspension allows for lowering the car at speed, raising it for clearance, and even leaning into corners.  It’s a more sophisticated system but it does introduce some new service problems as the cars age.



Coil springs sag with age, but since 1966 Bentley had provided means to shim the springs to compensate.  With that, coil springs usually last 20 years.  Air springs don’t sag, but the rubber air bladders can crack and leak, and when that happens there is no compensation – they must be replaced.  Air springs may begin leaking when the car is five to ten years old.  Note that air leakage in the struts is seldom visible, even if it's sometimes audible.

The air bladders surround the shock absorbers in these cars, which means they are serviced as a unit.  Older Bentley motorcars had separate coil spring and shock units.  

In the Bentley parts catalog a Continental GT air strut is somewhat more expensive that a comparable shock and spring for, say, a 1997 Continental R.  As of this writing, OEM Bentley front struts are about $2,500 each.

Bentley GT cars have a sophisticated multilink suspension that is shared with other VW/Audi models.  When removing the struts it is necessary to disconnect several of the suspension links and it’s common to find the top links have all broken or deteriorated.  If that’s the case they should be replaced too, which adds another $300 apiece at the Bentley parts counter.


Upper suspension links usually need replacement when struts are changed

The rear suspension uses similar components but seems to be a bit more durable, perhaps because the struts go up and down but do not twist for steering.  When the rear suspension needs service the issues and corrective actions are the same.

One benefit of the GT’s shared mechanical platform is that many parts interchange with high end VW/Audi cars, often at lower prices.  The Bentley parts are the same in some cases; in others they are slightly different.  Many buyers of secondhand Bentley cars will choose the VW replacement parts even if they are slightly lower performance, given cost savings of 10-40%.

Aftermarket front strut for Bentley GT


Furthermore, shared platform parts are often available from aftermarket suppliers giving even more range of choice, performance, and cost.  As of this writing (fall 2017) it's possible to save more than 50% off the cost of genuine Bentley struts with good aftermarket units.  For the most demanding applications, only the genuine stuff will do but for the other 95% of the time . . .

Most Bentley dealers will stick to the genuine Crewe parts bin.  Independent Bentley specialists are free to source parts anywhere.  One caveat:  If a car is repaired with genuine Bentley parts at a dealer the whole repair will be covered at any Bentley dealer in the country.  Genuine parts put on by an independent will also be warrantied at any dealer, but not the installation labor.  Repairs with aftermarket parts will only be covered by whatever warranty is offered by the parts supplier and shop.

Another point to keep in mind is that strut replacement may be within the skills of a mechanically inclined owner, but the Bentley laptop test system will be needed to clear faults and bring a flat suspension back to life.  If you have a car whose suspension has gone flat, simply replacing the failed parts will not return it to function.  The computer must be reset.

Luckily there is a modestly priced answer for that, too.  The VAG system will run on any Windows laptop and costs less than $500 and do everything but programming.  You can buy a pass-thru system to add dealer-level test and programming for approximately $2,000 more but you also need a subscription to the online Erwin system.



© 2017 John Elder Robison

John Elder Robison is the general manager of J E Robison Service Company, celebrating 30 years of independent Bentley, Rolls-Royce, BMW/MINI, Mercedes, and Land Rover restoration and repair in Springfield, Massachusetts.  John is a longtime technical consultant to the car clubs, and he’s owned and restored many fine British and German 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.

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