Wear and tear take their toll on even the most robust machinery. Eventually things wear out and need an overhaul. The Hydramatic transmission is no exception, but mercifully thanks to their superb build quality and substantial design, overhauls are an infrequent occurrence. Many cars are still running on their original transmissions which have never been re-built.  I have experience of several Rolls-Royce cars that have covered over 200,000 miles before their transmissions have needed anything more than band adjustment and the odd fluid change. Often, provided these transmissions receive the recommended maintenance at the specified intervals they will cover vast mileages and give decades of reliable service. 

Minor fluid leaks are a common problem, but provided the fluid level is kept topped up they don’t affect the operation of transmission if they are not too serious. The output shaft oil seal is a regular culprit, together with the torus seal. Transmission fluid is very searching rest assured it will find the tiniest gap between parts. In my experience, I have yet to see the hydramatic transmission that did not leak to some extent. Back in the 1950’s and 60’s oil seal technology was not sufficiently advanced to withstand the high temperatures and chemical attack endemic in any automatic transmission.  Today owners are more fortunate. Oil seals are now readily available which are able to withstand such environments. Wear in the moving parts is also considerably reduced by the advent of modern transmission fluid, which provides greater protection than could have been achieved back when the cars were new. 

Hydramatic transmissions are really quite pleasing to drive when properly set up. However, if they or their control linkages are not in the best of health they can be a source of great irritation. The overhaul of these transmissions is not for the faint hearted. They are selectively assembled and not easy to understand at first glance. In depth knowledge of how they operate is essential to diagnose faults effectively. 

It is advisable for an owner to be watchful for symptoms which may indicate impending problems. In brief, if having drained the transmission the fluid it is found to be very dark in colour and smelling burned, the transmission should be investigated without delay. It is probable either a clutch or brake band is slipping which in turn causes tremendous heat build up. Slippage is not always caused by worn friction linings in the clutches or brake bands. Internal fluid leaks may reduce the hydraulic pressure available to operate the servos which in turn operate the clutches or brakes. 

Whilst driving the car, make sure that the transmission changes gear cleanly and does not slide into gear, listen also for any rise in engine speed during gear changes. If slippery gear changes are in evidence again worn clutches or brake bands may need attention, however this is not always the case. An incorrectly set throttle valve or worn throttle linkage may also give rise to such symptoms.

Whilst driving the car note the quality of the gear change when the transmission is changing from 2^nd to 3rd gear whilst accelerating. A sharp snatch or a bang from the transmission may indicate the bands need adjustment and or the throttle valve may need adjustment. 

It is also worth noting the speed at which the gear changes take place. (Please see the tables of change speeds at the end of this article.) Again if a transmission is not changing gear near to the speeds indicated in the tables, an owner would be wise to have the fault investigated without delay. 

If an owner is not conversant with automatic transmissions, overhauling a Hydramatic is perhaps not the best place to start. It is often a surprise to people how very heavy a fully assembled Hydramatic transmission is. It would not be advisable to try to remove a transmission without the aid of a suitable transmission jack.  Unless an owner is well placed to buy, make or loan the necessary special tools and has sufficient mechanical experience to confidently tackle an overhaul. It is by far the best policy to seek the advice of Graham Whitehouse or a similar specialist used to working on Hydramatic transmissions before attempting an overhaul. 

Having started to overhaul the engine in my Silver Cloud II, I felt concerned about simply re-fitting the transmission without making sure it was in 1^st class order. It was leaking from all the usual places, and I felt third didn’t sound quite right. I had overhauled several more modern automatic transmissions successfully and had always enjoyed the complexities of their overhaul. My need to understand the transmission, together with a desire never to experience transmission troubles on the road led me to the conclusion that I should re-build the transmission. My First step toward this was to look into the acquisition of a factory workshop manual. 

My search for a workshop manual by great good fortune led me to the door of Graham Whitehouse. Graham, a vintage and classic car enthusiast and Silver Cloud II owner is based near to Halesowen in the West Midlands. He is one of the world’s foremost experts on historic automatic transmissions. In particular Graham and his team specialise in the repair and overhaul of Rolls-Royce hydramatic transmissions and those of later periods. He and his team are able to supply anything your heart might desire when it comes to Rolls-Royce automatic transmissions, from a re-build kit for your tired Hydramatic to the total replacement of the Hydramatic transmission with a modern substitute. 

Having ascertained he could supply me with a workshop manual I paid Graham a visit to gain a better insight into just what I would be taking on.

I was warmly welcomed by Graham and his staff. Before I knew it I was being shown around their impressive premises. Graham kindly spent some considerable time explaining how he tackles the overhaul of Hydramatic transmissions. His advice to me was no nonsense clear and concise, and his enthusiasm for elderly Rolls-Royces palpable. He was kind enough to take the trouble of showing me a dismantled transmission to illustrate the kinds of problems often encountered during an overhaul. He went on to tell me that he does not consider the Hydramatic transmission really in the realm of most mechanics. This is due to the way the transmission is built and adjusted - by selective assembly. Anyone thinking of carrying out an overhaul needs to be equipped with the necessary range of special tools and adjusting shims, a variety of replacement springs etc, together with a testing rig. 

 I was still determined I wanted to tackle my own transmission re-build, so I took a workshop manual away with me to study in detail.

I studied the schematic diagrams and carefully read the manual for a couple of weeks until I felt at least I understood the design clearly. I paid Graham a further visit to discuss some slight modifications he thought to be a good idea. I came away with a Hydramatic overhaul kit, some modified valve springs, and some useful advice on where I might encounter problems.

In all Graham could not have been more helpful. I came to look forward to visiting him because he treated me like an old friend and shared his vast knowledge of automatic transmissions freely. I really cannot imagine a more helpful company, or a more charming and helpful man than Graham Whitehouse. 

Having dismantled the transmission, I washed all the components in cellulose thinners. With everything as clean as possible I placed all the components into plastic ice cream containers to ensure the parts were kept clean. Part by part, I inspected everything minutely.  Everything seemed to be in excellent condition except for the forward drive rear planet gear set. To test the planet gears I spun them fast by blasting the individual gears with compressed air. The sound of each gear spinning on its bearing pin should be the same. One of the gears in my rear epicyclic unit sounded distinctly off tone. A visit to Graham soon had the offending bearing pin replaced. Satisfied with the condition of the remaining internal components I turned my attention to the appearance of the external components. 

The cast aluminium bell housing had oxidised.  These large castings have a habit of warping. The warping causes a leak to develop between the bell housing and the main casing. I left mine with Graham who arranged for it to be re-machined and blast cleaned. 

 Early Silver Cloud II’s had their transmission casings painted in a light metallic gold finish to match the finish on the engine crankcase.

I sent the transmission casing, sump etc along with the engine crankcase to specialist in Gloucestershire to have them refinished. A metallic gold polyester base coat was applied. This exactly replicated the colour of the original finish. The job was completed with the application of several coats of polyurethane lacquer which, once baked on provides an extremely durable barrier against oil and fuel. At the same time I sent all of the fasteners and plated parts to be re- plated. This proved to be a very expensive exercise! From looking at other cars it would appear to me the Silver Dawn and Bentley MK VI/ R type had their transmission casings painted black, as do some Silver Cloud III’s. 

Following the workshop manual I meticulously overhauled every part. I fitted new clutch plates and springs in both forward drive clutches. I replaced all of the sealing rings in the servo assemblies, governor and oil pumps etc. These sealing rings look exactly like piston rings, there are several differing sizes used in the transmission. All the original neoprene piston seals were also replaced with modern Viton seals which did not require the rather fiddly metal seal spreaders to be fitted with them. Graham’s kit provided replacements for every consumable part. I thoroughly cleaned the control valve unit. This complex little unit took some considerable time to overhaul. During dismantling I found two large lumps of dirt inside it. Goodness knows how they got in but they would have done the unit no good left in there. Graham recommended that I should change the 1^st to 2^nd gear shift spring. The original spring was specified to be 27.50mm long. Experience has shown this spring length often causes the transmission to miss 1^st gear and start off from stationary in 2nd. Alternatively, the transmission may change into 2^nd gear far too early.  Either situation places undue strain on the engine and transmission. Graham offers a modified spring of 31.50mm to prevent this happening. With the longer spring fitted the transmission holds 1^st gear until the car is travelling at about 8 MPH. All the other gear shift positions are unaltered by this very sensible modification.

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