Support

The GT-LT95 overdrive is designed to fit unmodified vehicles.

It goes without saying that you need to ensure that the oil level in the transfer case is correct and that the oil temperature remains within safe limits (we recommend below 110 degrees Celcius). To achieve this, we recommend fitting one of our finned transfer case covers, and it may be necessary to fit an oil cooler system which we can also advise you on. We will also have our own oil cooler kits available soon.

We do, however, recommend that you use a premium synthetic gear oil that can handle the higher loads and temperatures. We are lucky in Australia to be the home of Penrite, a specialist oil manufacturer that is owned and run by classic car enthusiasts. We love Penrite’s PRO GEAR GL-4 75W-90 oil. It’s a fully synthetic, full zinc gear oil specifically designed for gearboxes and transfer cases used in competition and heavy towing applications. If you can’t get this oil, hunt around for a similar spec oil, and remember, GL-4 so that it doesn’t damage the bronze synchromesh components of the overdrive.

When oil gets too hot, its viscosity reduces and they are not able to provide the high-pressure lubrication that is required in gearboxes. When this happens, friction between the sliding metal surfaces increases, often resulting in a runaway temperature condition. You may have seen components that have been subjected to a lack of lubrication where they are burnt and sometimes even welded together by the extreme heat generated. It is easy to tell if this has happened in a gearcase as the oil will have a distinctive burnt smell. 

The LT95 transfer case is well known to run at very temperatures, often in excess of 90 degrees Celsius. To assist with the added heat generated by the overdrive, we have designed a finned aluminium transfer case cover that doubles the heat rejection when compared to the standard cover. If you are operating at high speeds, high loads, in high ambient temperatures, you may need to fit an oil cooler to the transfer case. Our finned aluminium transfer case cover has two oil ports; one is used as the suction port for an oil cooler, and the other for an optional oil temperature switch to activate a circulation pump. The cooled return oil is directed back into a port at the top of the GT-LT95 Overdrive.

There is no special run-in procedure required for the GT-LT95 Overdrive.

However, like with all new gear sets, it will take some time for all of the mating surfaces to adapt evenly to each other. The time that this takes depends on a few factors including the wear on the existing intermediate transfer selector gear, and driving conditions; however, this should happen within the first 4,000kms. It is important to inspect the intermediate transfer selector gear properly during installation of the GT-LT95 overdrive, as excessive wear can result in increased gear noise and backlash. The oil should be changed after 4,000km to remove any fine metal particles created during the bedding-in period.

Slightly higher oil temperatures may also be experienced during the first 1,000kms.

The GT-LT95 Overdrive uses an epicyclic gearset along with CNC ground gears which results in near-silent operation. It is, however, important to inspect the intermediate transfer selector gear properly during installation of the GT-LT95 overdrive, as excessive wear can result in increased gear noise and backlash.

Depending on the application, a skilled automotive technician should be able to install the GT-LT95 Overdrive in less than four hours. The installation can take longer if other pre-existing problems such as oil leaks need to be rectified, or if the exhaust system proves difficult to remove and refit. 

The GT-LT95 Overdrive is easily installed using normal automotive hand tools and workshop consumables. Note that the LT95 gearbox and the GT-LT95 Overdrive both use metric fasteners, so metric spanners and sockets will be required. 

To enhance heat transfer between the GT-LT95 Overdrive and the LT95 transfer case, an ‘O’ ring seal is used in place of the standard paper gasket. This ‘O’ ring seals on the inside diameter of the LT95 transfer case PTO flange. Some epoxy ‘liquid metal’ (like Devcon) may be required should this area require patching. If the inside diameter of the PTO flange has casting flaws or is damaged and cannot be repaired, the standard PTO gasket can be used.

Depending on the vehicle, and whether you install the gearbox from below, you will require a jack and axle stands, ramps or a hoist.

Safety: The gearbox installation should only be undertaken by a suitably qualified technician or a person experienced in the repair and maintenance of off-road motor vehicles. It may involve lifting the vehicle which can be dangerous if proper equipment and procedures are not followed. The Installation Manual details the procedure for installing the GT-LT95 overdrive gearbox: however, procedures outlined in the Range Rover Repair Operations Manual 1970-1985 must be adhered to, especially as detailed in the section on General Fitting Instructions which contains Safety Precautions. It is the responsibility of the person installing this product to ensure that they are properly informed in relation to recognised workshop safety procedures. If you are unsure how to proceed, stop, and contact the support staff at Garage Therapy.