Rolls Royce and Bentley Rear Axle and Driveshaft Modifications

Differential overhaul and upgraded ratios. 

We offer a rear axle overhaul service and are able to supply exchange units from stock for all early post war cars. The ratios available are as follows:

Model Original Ratio Ratios We Offer
Bentley MkVI 11/41 (3.72:1) 12/41 (3.42:1) and 13/40 (3.08:1)
Bentley R Type 11/41 (3.72:1) and 12/41 (3.42:1) 12/41 (3.42:1) and 13/40 (3.08:1)
Bentley R Type Cont 12/41 (3.42:1) and 13/40 (3.08:1 12/41 (3.42:1) and 13/40 (3.08:1)

Knowing which ratio will suit your motor car best

When it’s time to overhaul, an upgraded rear axle ratio is a great way to enhance your MKVI Bentley, R type Bentley, Rolls Royce silver Dawn or Wraith. The 4 ¼ engine is very well suited to an intermediate ratio from the later R type Bentley 12/41 (3.42:1). This ratio gives lower engine revs for cruising, and also allows the torque provided by the engine to be used to far greater benefit, especially when pulling away fully loaded in 2nd gear. All in all, it will greatly improve what is already extremely good and offers approximately a 10% raise over the standard 11/41 (3.72:1) axle ratio. 

The 4.5 Litre MKVI Bentley, Silver Dawn and later R type Bentley’s are well suited to the “Continental” ratio which is approximately 18% over standard. The more powerful engine copes with this ratio very well and is an excellent upgrade for cruising giving lower engine revs and improved fuel consumption with the added benefit of more useable torque within the short rev range these early post war cars have. This equates to: 54.5 mph at 2000 RPM and 69.7 mph at 2500 RPM.

The Rolls Royce Silver Wraith standard wheelbase has a ratio of 11/41 (3.72:1)  and is already “geared up” with the addition of 17” wheels. Depending on the fitment of heavy coachwork, or the kind of work a limousine may be asked to carry out, we recommend keeping the car standard or opting for the 12.41 (3.42:1) intermediate ratio. Contact us to discuss your exact requirements.

Rear wheel bearings and drive shafts

Over the last few years we have encountered more and more rear wheel bearing failures, so much so that we now always recommend changing the bearings if they are of the original type. It is worth remembering that many of these original bearings are now over 70 years old and in that time have received no service at all, The bearings give little or no indication to the driver that they are rough or worn and very rarely will we encounter an owner that has complained of a noisy bearing so why change them?

The answer is quite simple and the consequences of ignoring them are very serious and costly, As the bearings have aged the lubricating grease inside the sealed bearing case has turned to a soap like substance thus no longer lubricating the roller balls that make up the bearing, as time goes on the bearing gets hot and can eventually lock solid! At best the bearing centre will often spin on the drive shaft rendering it useless for overhaul so new shafts will need to be found, at worse the free play in the shaft will ruin the rear axle and the shaft could shear off completely, this could happen at any speed so being mindful of what’s going on at the back of your car is very prudent.

The method we use to fix the problem

After many years working with Norman Geeson, renowned Rolls Royce and Bentley axle and drive shaft specialist, we have adopted his method to eradicate any future problems with these bearings. The axle half shaft is stripped down and inspected for damage and wear then thoroughly cleaned. We then move into our machine shop for damage or wear rectification and final polishing of the axle seal surface. The bearing housing is modified in the lathe to take a larger double row bearing that is pressed into the housing and then we modify several other components to be able to accommodate the larger bearing. The whole assembly is then pressed onto the half shaft and an interference fit safety collar is also pressed in place at a force of 35 tons. The shafts are now ready to do at least another 70 years work!

Services

  • Exchange axles available from stock

  • Exchange half shafts available from stock

  • All axle ratios kept in stock

  • All axles built to the very latest specification

  • International shipping

  • Fully guaranteed

  • Axle advice given freely

  • Fitting service available here in our workshop