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Following are some questions that our customers ask
We hope our answers are helpful to you.


Q:   Where are GLOBAL ROAMER OVERDRIVES manufactured 

A:     In British Columbia on the Pacific Coast of Canada.

Q:   What Models of Land Rover can be fitted with a GLOBAL ROAMER OVERDRIVE 

A:     The following Land Rover models can be fitted:
Series I, II, IIA and III models with four and six cylinder engines
Five spee
d Defender 90, 110 and 130 models with 1.41 ratio 230 type transfer cases 

Modified versions of Land Rovers with non-standard higher powered engines fitted with the 'Q' series 1.21 ratio transfer case.

At present we do not make an overdrive to fit the four speed LT95 gearbox used on Parentie models, classic Range Rovers and 101 Military Forward Controls. However we have a manufacturing agreement with another company that is planning to release such a product during 2022.

Q:   What Models of Land Rover can not be fitted with a GLOBAL ROAMER OVERDRIVE 

A:    We do not make an overdrive to fit Series models with the rare one-ton all helical transfer case.  If you have such a transfer case you will need to exchange your gearbox and transfer case to the standard type.

Q:   What are the benefits of fitting a GLOBAL ROAMER OVERDRIVE to a Land Rover 

A:     Fitting our overdrive will give you the following advantages:
When engaged, the overdrive reduces engine RPM by 28% in any gear.  Used in top gear on the highway, fuel consumption is reduced and the vehicle is quieter and more fun to drive. Used in other gears the overdrive can be used as a splitter between the normal gears. This is especially useful on Series vehicles as engaging the overdrive in third gear allows the vehicle to maintain speed on long hills.

The overdrive also reduces wear on the engine and drive components.  It can be used as a splitter gear between gears when climbing long hills.  When engaged in low range, it increases ground speed. This can be useful in sand conditions such as deserts.

Q:   Can a GLOBAL ROAMER OVERDRIVE be compared to a high ratio transfer case  (see discussion below)

A:     No, an overdrive cannot be compared to a high ratio transfer case.

Unlike the high ratio transfer case, the overdrive does not permanently alter the gear ratios on the gearbox, so overall vehicle capabilities are not compromised.

The usual high ratio transfer case offered on Series vehicles raises all the gear ratios 32% making the standard engine too weak to pull the vehicle up a hill in fourth gear.

On 90,110 and 130 models the high ratio transfer case not only degrades lower gear performance but decreases engine RPM on the highway by only 15% or less, versus 28% with the GLOBAL ROAMER OVERDRIVE.

The overdrive is also considerably easier to fit than a high ratio transfer case and can easily be moved between vehicles if required.

In our opinion, a high ratio transfer case is only viable on Land Rovers used primarily on motorways.

Q:   Is your ‘SS’ MODEL overdrive similar to the obsolete BEARMACH , FAIREY, SANTANA and TORO units that were produced for use on Series Land Rovers 

A:     No.  The construction of our ‘SS’ overdrive is very different as we use quiet epicyclical gearing without an oil reservoir.  The heritage models become noisy as they age.  They have separate oil reservoirs that are prone to leaks. The fine tooth couplings and needle thrust bearings are prone to failure.   They also do not have the power transmission capability of our overdrive and obtaining spare parts is difficult or impossible.  A perusal of the cost of used parts on websites such as E-Bay shows just how expensive these older units can be to repair or maintain.

Q:   Is your ‘DS’ model overdrive similar to the obsolete GKN overdrive that was produced for use on Defenders 

A.     The only similarity between the GKN and our ‘DS’ model overdrive is in the use of an epicyclical gear train that reduces engine RPM by 28%.

However, the GLOBAL ROAMER OVERDRIVE is a more robust unit than the GKN, with stronger gearing.

Another significant difference is that our overdrives have no complicated electronic or hydraulic controls and no slip clutches.  To engage the GLOBAL ROAMER OVERDRIVE you move a neat lever in the cab and the action is purely mechanical.

Another feature that sets our overdrive apart is that it does not have a dedicated oil reservoir like the GKN.  All models of GLOBAL ROAMER OVERDRIVE share oil with the vehicle transfer case.  This simple concept eliminates the need for dynamic seals and breathers.  The units require no service except to check the transfer case oil level at the recommended service intervals.

Q:   Does not having a dedicated oil reservoir make the unit more compact 

A:     Yes, both our overdrives are exceptionally compact units.   

At only seven inches in diameter (much smaller than other overdrives), the conical castings are easy to produce which keeps costs down.  Unlike some of the other overdrives, you do not need to move the exhaust pipe or other vehicle components during installation.

Q:   How does the shift mechanism operate 

A:     In exactly the same way as other mechanical overdrives. The engagement lever is situated on the transmission tunnel.

To engage the GLOBAL ROAMER OVERDRIVE you depress your clutch and move the lever forward. To disengage the overdrive you depress the clutch and move the lever back.

Q:   I have difficulty understanding how the epicyclical unit works. Can you explain this to me 

A:     It is not complicated. The drawing here shows a cross section of the unit.

Global Roamer Corporation

Inside our overdrive is a rotating planet carrier (E) that is driven by the main gearbox output shaft. Three shafts (G) are held in the planet carrier and rotate with it. Three planet gears (H) rotate about the shafts (G). Sun gear (J) is placed in the center of the three gears (H) and annulus gear (L) is placed on the outside of gears (H). Annulus gear (L) is connected directly to the output shaft of the overdrive to which is mounted a gear to replace the topmost gear in the transfer case. Bolts (F) hold the overdrive together inside casing (U).

When the overdrive is not in use a clutch locks sun gear (J) to the three planet gears (H) and as a result the annulus gear (L) is forced to rotate at the same speed as planet carrier (E) and there is no overdrive effect. Note that in this mode none of the gears is actually working - all the components are rotating at the same speed about the center.

When the overdrive is in use a clutch locks the sun gear (J) to housing (U) and the sun gear can no longer rotate. As planet carrier (E) rotates about sun gear (J), planet gears (H) are forced to rotate about shafts (G) and the effect is to cause annulus gear (L) to rotate 28% faster than planet carrier (E) thus giving an overdrive effect.

Q:   Are the gears and clutches very highly stressed 

A:     No, the gears and clutches are not highly stressed.

As the torque is divided among the three gears the stresses are much lower than would be the case with a single gear train. And, as the three gears are placed 120 degrees apart all side stresses in the assembly are contained. The whole overdrive assembly rotates supported by one large deep groove ball bearing. It is a very simple concept.

Epicyclical overdrives are not new of course. Many British cars in the sixties were fitted with them. However, the GLOBAL ROAMER OVERDRIVE is the first epicyclical overdrive for a Land Rover that employs a simple mechanical shift mechanism. There are no electrical solenoids, relays or microprocessors. A lot of thought and testing have gone into the design and we have patented the concept.

Q:   How difficult is it to install a GLOBAL ROAMER OVERDRIVE   Can I install it myself 

A.    The overdrive is not difficult to install. Most owners find they can do the job in about three hours using normal shop tools.  On Series vehicles a hole has to be drilled in the transmission tunnel to accommodate the shift lever.  On Defenders it is a straight bolt in job and no modification is made to any bodywork.

Q:   What about service and maintenance 

A:    We have put a lot of thought and effort into making this product as simple as possible.  Anyone with a good mechanical aptitude can install and service the GLOBAL ROAMER OVERDRIVE.   It is lubricated with transfer case oil so there is no independent oil level to maintain and no drain plug or breather to leak.  It has no dynamic seals.  It can be dismantled using common workshop tools.

If you ever have to service one of our overdrives you will note that we have used simple metric ball bearings that can be purchased from regular bearing suppliers. The syncromesh internal components are stock Land Rover parts that can be purchased from your normal parts supplier.

When servicing your overdrive, observe that the correct oil to use in the transfer case is an API-GL4  MTF.  Do not use oils labeled API-GL5 as such oils are hypoid rear axle oils that may be corrosive to the bronze synchros in the overdrive.

The GLOBAL ROAMER OVERDRIVE was made in the tradition of the older Land Rovers. It is virtually indestructible!

Q:   How reliable is a GLOBAL ROAMER OVERDRIVE in an expedition environment 

A:    Your GLOBAL ROAMER OVERDRIVE can be used with confidence on the most demanding expeditions and will greatly reduce the cost of fuel. We suggest you take a basic seal and gasket set with you and pack your original drive gear and cover in your spares kit, although it is extremely unlikely you will need it.  Seal kits can be obtained from our distributors. Our experience shows that no other parts need be carried.

Q:   Can I install a GLOBAL ROAMER OVERDRIVE on a vehicle with upgraded power engines 

A:    On Series vehicles the SS GLOBAL ROAMER OVERDRIVE will easily handle the extra power provided by the installation of the popular 200Tdi engine or engines of a similar power.  In such cases the model SX-COV transfer case oil cooler must be fitted.

On Defenders your DS GLOBAL ROAMER OVERDRIVE can be used with confidence up to the rated torque on the R380 gearbox which is 380Nm. This is equivalent to the output of the popular 2.8 TGV engine conversion or popular ‘Stage 1’ re-chip of the TD5 motor.  In these applications the oil cooling DS-COV transfer case cooler must always be fitted.

Several tuning companies offer conversions that boost engine output beyond 380Nm. In high speed driving, at such power, the oil temperatures in the gearbox and overdrive may become excessively high leading to lubrication breakdowns and subsequent failure of the gearbox, transfer case or overdrive.  There is no warranty offered on an overdrive that has failed due to overheating.

If you do choose to fit a GLOBAL ROAMER OVERDRIVE to a vehicle with power output in excess of 380 Nm we strongly suggest that you fit an oil cooler to your transmission. You should also install our oil temperature gauge DX-T to the DS-COV transfer case cooler and monitor this gauge to avoid overheating the transfer case oil when driving at high motorway speeds.


For some years now Land Rover drivers have been offered higher ratio transfer cases (HRTC) as an alternative to overdrives in both Series and Defender models. The vendors of these products make claims like ‘eliminate the need for an overdrive’ or ‘a stronger alternative to an overdrive’.

In our opinion, these claims are misleading and do not give the whole truth about the products sold. In a question and answer format, we state our case below.

Q:   How does a HRTC work 

A:     What a HRTC does is permanently alter the ratio between the engine RPM and the speed of rotation of the vehicle wheels. This is done by dismantling the transfer case and substituting a new set of high range drive gears. The cost of the new gears themselves is cheap but the cost of fitting is expensive.

Q:   What is the change in ratio offered 

A:     In the case of a Series Land Rover it is 31%. In a Defender it is 15% or less .

Q:  If I put a HRTC in my Series what will it be like to drive 

A:     If you have a standard Land Rover engine you will find that the altered ratio makes it possible to drive in fourth gear on the flat with reduced RPM (similar in effect to driving with an overdrive engaged).  However, on even a slight incline you will find you have to drop back into third gear.  There is no splitter gear available between third and fourth, as there is with an overdrive fitted.  If your vehicle is loaded you will also find that it is difficult to pull off on a hill without starting in low range.

If you like to use your vehicle off road you will find that you have to drop down into low range to climb obstacles that could easily be surmounted in high range before the HRTC modification was made.

Q:   If I put a HRTC in my Defender what will it be like to drive 

A     You will notice that engine RPM drops somewhat on the highway making the vehicle quieter. However the 15% or less drop in RPM has nothing like the effect of an overdrive which drops the engine RPM by 28%.  You may notice that your ability to pull off on hills has been compromised.  If you like to use your vehicle off road you will find that you have to drop down into low range to climb obstacles that could easily be surmounted in high range before the modification was made.

Recognizing the limitations of a 15% HRTC, manufacturers now offer a HRTC with a RPM drop of 9%.? This compromise has the effect of making it possible to pull off on hills with less slipping of the clutch, but the higher ratio is negligible on a highway and has nothing like the effect of fitting a ROAMERDRIVE overdrive that drops RPM by 28%.

Q:   Is it easy to take a HRTC out of my vehicle 

A:     No. You have to remove and refit the transfer case with the original gearing. This is time consuming and expensive. Compare this to a GLOBAL ROAMER OVERDRIVE that can be removed (and refitted into another vehicle) with ease.

Q:   Can a case be made where a HRTC has advantages over a GLOBAL ROAMER OVERDRIVE 

A:     No. Manufacturers of the HRTC emphasize the simplicity and reliability of their modification but the GLOBAL ROAMER OVERDRIVE is a robust well-proven design that offers multiple advantages to the owner without compromising vehicle performance.

You can take the GLOBAL ROAMER OVERDRIVE anywhere with confidence!