Don’t Call It Hydra-Matic: The Rolls-Royce and Bentley Automatic Gearbox


From 1953 to 1978, British automaker Rolls-Royce manufactured its own versions of the General Motors Hydra-Matic transmission for use in Rolls-Royce and Bentley luxury cars. One version was very similar to the Hydra-Matic used in American cars and trucks, but Rolls-Royce later created an improved aluminum-case version with modifications to provide smoother shifting. This version was offered in some versions of the Rolls-Royce Silver Shadow I and Bentley T Series from 1966 to 1969. The older version remained in use in the big Phantom V and Phantom VI limousines until 1978.

Although the Hydra-Matic transmission was first used by Oldsmobile and Cadillac, the final user was not a GM division, but Rolls-Royce, which used its own license-built versions of this highly successful GM transmission from 1953 to 1978. This included an unusual, short-lived variation for the early Rolls-Royce Silver Shadow and Bentley T-Series — the last iteration of the original Hydra-Matic transmission. In this installment of Ate Up With Motor, we take a look at the upper-crust British career of this venerable American automatic transmission.


On an article like this, it bears repeating in boldface type: I CANNOT to tell you how to fix any of these transmissions, I DO NOT sell (or buy) parts for them, and I can’t help you find parts! If you have transmission maintenance, repair, or troubleshooting questions, I strongly recommend that you seek out the factory service manuals and/or consult a transmission specialist familiar with older automatics. (I am NOT a mechanic and am NOT qualified to give troubleshooting or repair advice.)


As we recounted in our original Hydra-Matic article, users of this revolutionary early automatic transmission included not only GM divisions, but also a surprising number of other automotive marques, including Lincoln, Kaiser, Nash, and Hudson. Most non-GM automakers purchased complete transmissions from GM’s Detroit Transmission Division (which became Hydra-Matic Division in October 1963), even using the Hydra-Matic name in their marketing and even badging. The exception was Rolls-Royce, which manufactured its own versions of the Hydra-Matic transmission under license in Crewe, England, for use in Rolls-Royce and Bentley passenger cars. (Rolls-Royce owned Bentley Motors from 1931 until 1998.)

Both before and after World War II, Rolls-Royce chief engineer W.A. Robotham (abbreviated “Rm” in internal memoranda) had taken a keen interest in the latest developments in American automotive engineering. Although that was a somewhat controversial point within the company, Rolls-Royce routinely purchased examples of other manufacturers’ cars for testing and evaluation, including American models from Buick or Cadillac, and Robotham visited the U.S. in 1932 to examine the latest automotive developments firsthand. During that visit, he saw some of the early work on the Military Transmission project, which subsequently evolved into the Automatic Safety Transmission and the original Hydra-Matic.

1942 Oldsmobile B-44 H-M badge

The Hydra-Matic transmission made its debut in late 1939 as an option for the 1940 Oldsmobile, and became a Cadillac option the following year. American passenger car production temporarily ceased in early 1942, but Hydra-Matic was used in a number of wartime armored fighting vehicles. After the war, it saw widespread use both inside and outside of General Motors. (author photo)

Although wartime activity was the major priority for Rolls-Royce from 1939 to 1945, some passenger car development work continued during the war, including early experiments with automatic transmission. In 1944, one experimental car was fitted with a Brockhouse Turbo-Transmitter, a torque converter transmission later offered in the limited-production Invicta Black Prince, while in 1945, a Hydra-Matic transmission was apparently installed in “Big Bertha,” an eight-cylinder Silver Wraith limousine. (There may have been earlier Hydra-Matic tests as well; journalist Laurence Pomeroy, later technical editor of The Motor, reportedly recalled driving a Rolls-Royce so equipped during the war.) Robotham and design chief Ivan Evernden found the postwar Hydra-Matic greatly improved from early examples (thanks in part to extensive wartime use in light tanks and other military vehicles). It was now a reasonably well-sorted transmission that could be adapted to the needs of Rolls-Royce and Bentley without too much difficulty.

In March 1946, Robotham flew to Detroit to talk to GM executives, including O.E. Hunt, vice president of the corporate Engineering Staff, and John F. (Jack) Gordon), general manager of Cadillac, whom he had met during his earlier visit to the U.S. From these meetings, Robotham learned that the Detroit Transmission Division was preparing to greatly increase production capacity, anticipating increased demand for Hydra-Matic internally and the possibility of outside sales. However, Robotham confounded nearly everyone he spoke to at GM by insisting that he didn’t simply want to buy Hydra-Matic transmissions; he wanted Rolls-Royce to license the manufacturing rights.

With the help of Jack Gordon, Robotham arranged a meeting with GM president Charles E. Wilson. Wilson was as puzzled as his subordinates had been about the economic logic of Robotham’s proposal — the 5,000-unit annual production estimate Robotham cited, though extravagantly optimistic for Rolls-Royce (whose typical annual passenger car production over the next 25–30 years, including Bentley cars, would be roughly half that), was very small beer by GM standards. Nonetheless, by the end of the meeting, they had reached an agreement, at least in principle.

Robotham’s account doesn’t explain why he was so emphatic about building Hydra-Matic rather than buying complete transmissions, but we’ll hazard several guesses. Company pride likely had something to do with it, but it may also have been significant that his trip to Detroit came less than a year after V-E Day. After six years of a conflict during which many thousands of tons of supplies and matériel had ended up at the bottom of the Atlantic Ocean, it’s understandable that Rolls-Royce might have been uneasy about relying too much on an overseas supplier for an essential subsystem, and there were at that time almost no local alternatives if the supply from the U.S. were to be cut off for any reason. (We assume the Brockhouse torque converter unit was judged unsatisfactory; its subsequent automotive career with Invicta was brief and unhappy.) Beyond that, Great Britain’s postwar Labour government was putting considerable pressure on industry to increase exports, and the cost of importing transmissions would likely have been high, even if GM’s unit price was reasonable.

After his return from Detroit, Robotham’s attention shifted to other matters (he subsequently became head of the company’s new diesel engine division, ending his involvement with passenger car development), so his memoir offers no insights on why it took an additional seven years before Crewe began production of the automatic gearbox. Aside from the various practical and logistical challenges involved in any transatlantic manufacturing agreement, particularly in the era before fax machines and email, Rolls-Royce may have opted to wait for the introduction of the revised Dual-Range Hydra-Matic, launched in the U.S. in the fall of 1951, which offered a much greater degree of manual control for the driver than did earlier Hydra-Matic transmissions.

1954 Rolls-Royce Silver Dawn (black) front 3q by Andrew Bone (CC BY 2.0)

Automatic transmission was first offered on Rolls-Royce and Bentley cars in 1952, but the option was initially confined to export cars, which at first used imported transmissions built in Detroit. Crewe-built automatic gearboxes became optionally available on British-market models, including the Rolls-Royce Silver Dawn and Bentley R Type, in October 1953. The Silver Dawn, offered with a factory-built steel body as an alternative to the traditional rolling chassis, had a British list price of £4,605 5s 10d with purchase tax; automatic brought the total to £4,704 9s 2d, equivalent to more than $13,000 at the contemporary exchange rate. We don’t have contemporary U.S. list prices for these cars. (Photo: “Rolls-Royce Silver Dawn (1954)” by Andrew Bone, which is licensed under a Creative Commons Attribution 2.0 Generic (CC BY 2.0) license)

Rolls-Royce also attempted to bring the automatic gearbox up to expected Crewe standards of finish and production tolerances, a Pyrrhic effort that only added to the new transmission’s teething pains. For example, early Crewe-made transmission brake drums had a smoother surface finish than the ones made in Detroit, which turned out to cause erratic shifting (we assume by making it harder for the brake band to securely grip the drum). In most such areas, Rolls-Royce eventually conceded that it was attempting to fix things that weren’t broken, and decided that the better part of valor was to follow GM’s lead.


Automatic became available on Rolls-Royce and Bentley export cars in 1952, initially using a batch of imported Detroit-built transmissions fitted with Rolls-Royce driveshafts and a tail extension incorporating the power takeoff shaft needed to drive the mechanical brake servo (a curious device Rolls-Royce had used since 1924). Rolls-Royce announced the automatic as an option for British-market Rolls-Royce and Bentley models in the fall of 1953, priced at £99 3s 4d with purchase tax (equivalent to about $278 at the contemporary exchange rate), although few production cars received Crewe-built automatics before the end of the year.

The automatic gearbox became standard on the new Rolls-Royce Silver Cloud and Bentley S Type in 1955. Rolls-Royce also sold some transmissions to Armstrong Siddeley, which offered the automatic as an option on the Sapphire 346 from 1954 to 1958, and later to BMC for use in the Vanden Plas Princess 4-litre (though not the later Princess 4-litre R, which used a Borg-Warner automatic behind its 3,909 cc (239 cu. in.) Rolls-Royce FB60 six). The Jensen 541S, which used the big 3,993 cc (244 cu. in.) Austin six, also offered the Rolls-Royce automatic, although later Jensen models with Chrysler V-8 engines adopted the Chrysler TorqueFlite transmission instead.

Although Rolls-Royce made no secret of the new automatic’s Detroit parentage, they sternly advised the press to describe the transmission as “the Automatic Gearbox” rather than as “Hydra-Matic,” which was (and remains) a registered trademark of General Motors. (We assume the license agreement did not include the rights to use the Hydra-Matic name on transmissions not built by GM.) Nonetheless, the Rolls-Royce transmission was very similar to its American-made cousin, even sharing the same ratios: 3.82:1 in first, 2.63:1 in second, 1.45:1 in third, 1.00:1 in fourth, and -4.30:1 in reverse.

1956 Rolls-Royce Silver Cloud I saloon (blue) front 3q by Charles01 (CC BY-SA 3.0)

The four-speed automatic gearbox was standard equipment on the Rolls-Royce Silver Cloud and Bentley S Type, introduced in 1955, although some sources indicate that a few cars were built with the earlier four-speed manual transmission by special order. (Photo: “1956 Rolls Royce Silver Cloud I, Castle Hedingham, Essex, September 2008” by Charles01, which is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) license; it was resized 2022 by Aaron Severson)

Like the Detroit-built Dual-Range Hydra-Matic, the Rolls-Royce automatic gearbox had three driving ranges, which Rolls-Royce labeled “4,” “3,” and “2.” “4” range started in first gear and used all four forward speeds; “3” range locked out fourth gear until high speeds; and “2” kept the transmission in second gear in most conditions, as well as allowing second-gear starts. When the first RHD automatic cars were unveiled at the Motor Exhibition at Earls Court in London in October 1953, some credulous British journalists assumed these controls were a Rolls-Royce exclusive, apparently unaware that the Hydra-Matic transmissions used in some quite ordinary GM cars and trucks now offered the same features.

Crewe-built automatic gearboxes had revised hydraulic controls that prevented the transmission from automatically upshifting in “2” range (in L, Dual-Range Hydra-Matic would eventually shift to fourth gear to prevent over-revving) and eliminated the provision for part-throttle kickdown. You could still trigger a downshift by pushing the accelerator all the way to the floor, but because kickdown changes exacerbated the transmission’s tendency to shift with a thump, Rolls-Royce recommended selecting the “3” or “2” range to execute a 4–3 or 3–2 downshift, which was smoother and often quicker. Crewe-built transmissions also had a tail extension incorporating the power takeoff for the brake servo and the oil pump for the hydraulic ride control unit used on some models.

Like the contemporary Hydra-Matic transmission, the Rolls-Royce automatic gearbox had many virtues. Low-speed “creep” was minimal, and the split torque arrangement in third and fourth gears (in essence, a partial mechanical lockup) reduced the effects of slippage in the fluid coupling. There was no way to manually control the 1–2 shift or to hold first gear, but you could choose whether to start in first or second, and the “2” and “3” ranges provided useful control of the intermediate gears. It was possible to shift quickly between “2” and reverse to rock the drive wheels free of mud or snow, and the use of front and rear oil pumps allowed push-starting in a pinch. With proper maintenance, the automatic gearbox was also reasonably robust.

To our knowledge, Rolls-Royce didn’t offer comparable manual and automatic cars for back-to-back independent road tests during the brief period in which the automatic was still an optional feature, but automatic-equipped models had respectable performance for the period. With its dual oil pumps, the automatic undoubtedly consumed significantly more power than a manual gearbox did, and overall gearing wasn’t ideal for unrestricted European roads, but the low (high numerical) first gear and modest slippage in the higher gears provided some compensation.

1957 Bentley S1 saloon (silver) front 3q by Steve Glover (CC BY 2.0)

From the fifties into the eighties, Rolls-Royce and Bentley cars generally differed little save for their grilles and badging. A Bentley S Type was somewhat cheaper than a comparable Rolls-Royce Silver Cloud — by £127 9s 3d (including purchase tax) in the home market, equivalent to about $357 at the contemporary exchange rate — but remained a very expensive car. It was also quite large by British standards, stretching some 211.8 inches (5,378 mm) on a 123-inch (3,124-mm) wheelbase, although its overall width of 74.8 inches (1,898 mm) was modest compared to contemporary full-size American cars. (Photo: “Bentley S1 (1957)” by Steve Glover, which is licensed under a Creative Commons Attribution 2.0 Generic (CC BY 2.0) license)

It probably helped that the engines with which the Rolls-Royce and Bentley transmission was paired were not too different from those with which the American-made Hydra-Matic had been paired: initially, a big F-head (intake over exhaust) inline six, replaced in 1959 by the new 6,230 cc (380 cu. in.) L410 V-8 — an all-aluminum OHV engine with oversquare dimensions, wedge combustion chambers, and hydraulic valve lifters, like the latest Detroit V-8s. (Before we inadvertently start any arguments, let us hasten to note that the L410 was not a copy of any American V-8 engine. However Rolls-Royce did adopt a hydraulic valve lifter design developed by Chrysler, again opting to manufacture the components in Crewe.)

As for refinement, by the fifties, single-coupling Hydra-Matic transmissions were reasonably civilized in gentle driving, especially with a little finesse in throttle application, but shifts were noticeably firmer than rival torque converter automatics, something that became more pronounced if the bands and throttle valve linkage weren’t properly adjusted. Since automatic transmission was still uncommon outside the U.S., British and European buyers had few points of comparison, but the jerkiness had become a sore point for American customers.

To keep pace with the rapid-evolving U.S. market, the Detroit Transmission Division introduced the thoroughly updated Controlled Coupling Hydra-Matic, which superseded the Dual-Range Hydra-Matic in most passenger car applications for 1956. Controlled Coupling Hydra-Matic (discussed more fully in the the second part of our history of early GM automatics) replaced the older transmission’s multi-disc front clutch with a “dump-and-fill” second fluid coupling and used sprag clutches instead of brake bands in most normal driving. The redesigned transmission was significantly smoother, but also even more complex and expensive than before, which appears to have been a commercial miscalculation. Most non-GM customers shied away, opting instead for cheaper automatics from rivals like Borg-Warner.

Rolls-Royce Silver Cloud II L410 V-8 engine in situ by Herranderssvensson (CC BY-SA 3.0)

The long-lived Rolls-Royce L410 engine made its debut on the Rolls-Royce Silver Cloud II and Bentley S.II in 1959. Named for its 4.10-inch (104.14-mm) cylinder bore, it initially displaced 6,230 cc (380 cu. in.). Rolls-Royce did not quote output figures (except where required for type approval in export markets), but modern sources report that the early L410 had about 240 gross horsepower (equivalent to about 179 kW), with as-installed net output of 183 hp (about 136 kW) and 258 lb-ft (about 350 N-m) of torque — obviously not a particularly high-strung engine, even for its era. (Photo: “Rolls-Royce Silver Cloud II engine” by Herranderssvensson, which is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) license; it was resized 2022 by Aaron Severson)

Had Rolls-Royce been simply buying Hydra-Matic off the shelf, they would have had a number of options at that juncture — continue with the single-coupling Hydra-Matic (which remained in production for light truck use into the early sixties), switch to the dual-coupling Hydra-Matic, or consider new alternatives like the Chrysler TorqueFlite — but having only recently established production in Crewe meant that Rolls-Royce were committed to the existing transmission, at least for the moment. (Interestingly, in 1957, a V-8 prototype was fitted with a Buick Dynaflow torque converter transmission, perhaps for evaluation purposes. It was replaced with a four-speed Rolls-Royce automatic about two years later.)


Add a Comment
  1. 1. Thank you for new content.
    2. I appreciate the research undertaken to provide this new content. Entertaining and informative. Job well-done!
    3. I learned that Rolls switched to Chrysler-style lifters for their OHV V8 engine; they did prototype work with Buick lifters and had camshaft lobe failures. Not surprising–Buick lifters (Nailhead/Nailvalve era) had no crown, the Buick camshaft had no taper, and the Nailhead lifter bores were not offset on the lobes. The Buick Nailhead lifters were not intended to rotate in their bores. I don’t know of any other V-8 OHV engine that intentionally does not spin the lifters. Lifter spin reduces wear.

    1. The Chrysler lifter design is mentioned in the text, as it was another example of Rolls-Royce engineers considering a problem, deciding existing American technology offered the best solution, and then arranging to manufacture it in-house. It’s also clear that developing the V-8 involved a pretty steep learning curve in various respects.

  2. An excellent review. Thank you!

  3. Aaron, while automatic transmissions in luxury cars are not my jam, reading your wonderful scholarship is. Thank you!!!Jir

  4. Aaron, great to see new content here, and to the same high standard as ever. I wonder if RR’s decision to licence and build, rather than merely import was due to to government currency restrictions regarding Sterling and the US Dollar?

    1. I had the same thought, particularly when I saw that Rolls-Royce arranged to pay for the imported transmissions used in 1952–1953 cars in U.S. dollars. My understanding is that in that period, for a British company to pay for a transaction in dollars would have been only slightly less politically fraught than arranging to pay in bone marrow! However, Robotham’s account makes no mention of political considerations like that when he went to the U.S. in spring 1946.

      Also, if the rationale for licensed production was political, I have to think GM management would have been less puzzled. Wilson, surely, would have understood the impetus for local production due to import restrictions, unfavorable currency exchange rates (although it’s notable that the trip took place well before the subsequent devaluation of the sterling), or the costs of importation. The only explanation Robotham’s memoir offers for not wanting to import the transmissions rather than build them is that it was “unthinkable.”

    2. I drove a Rolls for a wealthy fellow in the early had the exact same radio/cassette player as my ‘86 Cheney S-10, albeit with gold plating.

      A nice ride. What I remember most was it was quiet, and there was little or no plastic in the interior

  5. Coming in a bit late..many years ago I read that when RR received the first batch of Hydra Matics, they were shipped dry (of course) and RR as was their procedure, decided to “improve” the finish of the internals parts by cycling walnut hulls through them. This caused problems (I think the walnut oil messed up the rubber seals) and GM told them to stop doing that.

    1. I’m just glad that anyone is still reading, having gone years without new content to speak of.

      With Hydra-Matic, it’s clear that Rolls-Royce made a variety of efforts to gild the lily, as it were, generally ending with the crew in Crewe having to concede that there was no good in fixing what wasn’t broken.

      The one really substantive change they made from a mechanical standpoint (prior to the aluminum-case version used in the early Silver Shadow) was eliminating the forced upshift from second to fourth in Low range. With the Dual-Range Hydra-Matic, GM had concluded that it was better not to let the driver override the automatic controls to the extent that it risked over-revving the engine; you could delay upshifts, but no further than the hydraulic controls would otherwise allow at WOT. Rolls-Royce apparently felt that if a driver manually selected “2,” they damned well wanted second gear and shifting up should be at their discretion. This might have improved performance a bit, because with the GM units, the automatic upshift in Low was to fourth, not third. Winding out in second and then shifting to “3” would probably give slightly better acceleration. How many Rolls-Royce drivers would have bothered, I have no idea, since it would seem likely to spill milady’s mustard.

  6. Echoing others’ comments, it’s great to see some new content and the older articles continue to be prime points of reference. A bit of a tangent but the mention of Robotham’s name being abbreviated to two letters in internal memos reminded me that when I joined the Rolls-Royce aero engine business in the mid ‘90s (which had been separated from the car company since 1971), the Derby part of the company was still using this convention to the great confusion of those of us who worked at other sites. I’m not sure when it died out, but not long after.

  7. Still reading!

  8. Another great read, and I thank you for it. Not that I’m in the market for one, but couldn’t R-R at least put at the column shift on the left of the column for RHD cars?

    And that steering wheel (styling wise) is more suited to a bus.

    1. And that steering wheel (styling wise) is more suited to a bus.

      Which wheel? The Silver Cloud wheel does seem rather bus-like, perhaps because until the Silver Cloud II in 1958, power steering was a pricey extra, and some allowance had to be made for the chauffeur on cars without power assist. (Cars with power steering did get a smaller wheel set closer to the dash, but the difference in diameter was about an inch, and so I think it would take a practiced eye to spot the difference.) The two-spoke wheel in the Silver Shadow doesn’t strike me as particularly bus-like, although I can’t say I find it particularly attractive or in keeping with the general ambiance. A detail, I guess, but at these prices, the details ought to be exquisite.

  9. I only discovered this site about a month ago and it is now my favorite auto site along with Mac’s Motor City. I really appreciate your in depth dives into various models and technology. I hope you continue to publish more as I can’t get enough!

  10. Thank you for a very informative amount of info on RollsRoyce/Hydramatic transmissions.
    My daughter is interested in a 1956 Armstrong Siddely fitted with automatic transmission,when I queried the seller is it automatic or preselector he said someone told him it was the same as RR used.
    That car is now a lot more interesting as a result of your information thank you.

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