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Gear Ratios for:
Pick the best combination of gear ratios to match your engine's power specs to how and where you wish to drive your Land Rover. The gearbox used in series Land Rovers was first used by Rover in 1932. In general the Series gearbox is considered to be strong enough for about 120 HP, 160lbft is about the limit on torque. If you install an engine with more HP or torque consider updating the gearbox. The LT77 is not much stronger than the Series gearbox. It will work fine for a LR 2.5dt but is a little weak for the tdis or V8s. The later Land Rover 5 speed gearboxes would be a good match for the newer Land Rover 4 cylinder engines and the 3.5L aluminium V8. The last of the 5 speeds, the R380 should be able to handle up through the Aluminium 4.6L engine in stock form. If you are installing a higher power engine, especially a high torque diesel, you are better off looking at options other than pre 2007 Land Rover gearboxes. When making drive train upgrades it is generally a good idea to pick components that fit without special adapters whenever possible - less engineering involved; you get components proven to work together and have fewer replacement problems should something break. Different engines have different needs. Smaller petrol or turbo diesel engines often rely upon higher RPM's for power. Larger engines usually put out a lot of power and get their best fuel economy at lower RPM's Your choices in drive train components define how your Land Rover will handle, so the more homework you do before locking yourself into specific drive train components the better your chances of ending up with a vehicle that meets your needs and is a pleasure to drive. The first thing you need to do is honestly define what the vehicle will actually be used for. A vehicle used mostly on the freeway with off road travel on maintained trails will have very different gearing requirements than a serious rock crawler or mug bogger that gets towed on the highway. A rule of thumb for picking a drive train to match a new engine is to pick a transfer case high range ratio and ring and pinion ratio that places the overall high range top gear ratio where you want it for optimum highway driving. Then pick the gearbox that will give you closest to your ideal low range first gear ratio using the transfer case and differential gears you picked for top gear. Tyre diameter can be used for fine tuning. Calculating the optimal highest and lowest ratio for the kinds of driving you intend to do is the best place to begin deciding which gearbox, transfer case and differential combination will work best for you. Be sure to calculate axle ratios for the size of tyre you intend to be using. Pick your target high range top overall ratio. You will be looking for a ring and pinion plus transfer case high range ratio the will get you as close as possible to that ratio in top gear. Stock Land Rover ratios are 4.7:1 and 3.54:1. Common aftermarket ratios are 4.75:1 (stronger R&P) and 4.1:1. If you need something different you might start looking at Toyota axle assemblies. Explore possible transfer case high range gears. This will give you a tentative transfer case and differential that will meet your driving needs. Next, pick your target low range first gear ratio, then recalculate that ratio for high range using the transfer case and ring and pinion you have tentatively chosen for high range top gear. This will be your target ratio for the gearbox's first gear. Then start looking at gearboxes that can come closest to your target ratio first gear ratio using the transfer case and ring and pinion ratios your have tentatively chosen for high range top gear. You may have to calculate ratios for several gearbox, transfer case & differential combinations to get closest to your target ratios. You can do a little fine tuning of the ratio buy going to a larger or smaller tyre diameter. Some thoughts about low range first gear ratio: I found the stock Series Land Rover low range first gear ratio (40.7:1) to be too tall for most rock crawling and many climbing situations. Having over 5 years experience with a 70:1 ratio I have found it to be too low for anything but the most technical rock crawling situations (with 33.3 inch dia tyre). At this time I'm leaning towards somewhere around 55:1 as being the best overall low range ratio for use in many different situations with 32 - 34 inch dia tyres. This target ratio is for an engine that has plenty of power off idle and a lot of torque in the 2000 RPM range. Smaller engines or diesels that need to wind up the turbo will often be better off with lower gearing to get those RPM's up. Deciding on a high range top gear: Here you need to target best fuel economy for the highway speeds you will most likely drive at. This is influenced by several factors, engine used, highway speed limits, driving style, vehicle weight and so on. This is where you look to see what top gear ratio the engine manufacturer used when placing the engine in a vehicle most like the Land Rover. What the manufacturer used is probably real close to what would be best for you to use on a Land Rover driven on the open highway for long distances. Most V6 and V8 engines do best cruising between 2200 and 2700 RPM. If the vehicle weight does not tax the engine, best fuel consumption usually occurs around 2200 to 2400 engine RPM. When calculating engine RPM ratios don't forget that tyre diameter plays a part too. Different diameter tyres are a good way to fine tune an overall ratio that isn't quite optimum. Putting it all together: With your low range first gear ratio and your high range top ratio chosen you can start looking at combinations that will get you to both places with usable steps in between. If you have an engine that has a wide torque band and is free revving, a four speed gearbox that gets you to both ends of your gear ratios is often the best choice. Engines with a narrow power band can often benefit from as many ratios as you can fit. A longer than stock gearbox or an engine that requires the gearbox and transfer case to be moved rearwards will place the front prop shaft closer to the bulkhead cross member. So will any kind of lift that moves the frame farther from the axles or any modification to the suspension that allows for increased upwards articulation. A half moon shaped divot in the leading edge of the bulkhead cross member should be added under any of those conditions. Model 88's have a very short rear prop shaft. When choosing components try not to reduce the spacing between the rear prop shaft mounting surfaces. This is just asking for expensive high tech rear prop shafts and decreased reliability. The best solution for a longer gearbox in an 88 may be to move the engine forward. Land Rover did this when they started using 5 speed gearboxes. The rear axle on a Series Land Rover sits 1-1/2 inches forward of the body rear wheel arch. You can move the rear axle assembly rearwards 1-1/2 inches using off set plates between the axle mounting pads and the springs and pick up 1-1/2 inch additional spacing for the drive train without negatively affecting the rear prop shaft geometry. And you get the benefit of better tyre to front of the wheel arch clearance . Stock Land Rover gearbox and transfer case ratio charts
Borg Warner T-18 :The Borg Warner T-18 transmission is a top loading four speed with granny first gear that was used in 1965-1985 Ford pickups, some Jeeps and IH Scouts. Ford used three different versions of this transmission. From 1966 until 1978, many T18s used a T98 shifter assembly. 1979-newer T18s used a three-fork shift cover assembly that shifts reverse gear directly. Earlier versions of the T-18 go into reverse by shifting to the right then up. Later versions shift to the right and down the same as a series gearbox. Parts are easiest to find and cheapest for the Ford versions of the T18. Off the shelf clutch & bell housings adapt the Ford T-18 to a small block Ford engine There are 12 versions of the Jeep T-18 transmission, most of which are close ratio gearboxes. Several parts for the close ratio Jeep T-18s are no longer available. The Jeep T18 is usually a direct bolt up to the Dana 18 transfer case There are adapters available to fit Chevy engines to the Jeep T18. International harvester only used the close ratio version of the T-18. Engine & transfer case adaptors can be hard to come by. The T18 gearbox has a cast iron housing and top plate . The PTO side plate is on the right side. The housing casting is 13-01.
housing length is 11.875".
Oil Note: Use a GL-4 rated oil instead of GL-5. GL-5 has a higher sulphur content that is mildly corrosive to the bronze alloy syncros used in this gearbox. StaLube and RedLine are brands to look for.
Borg Warner T-19 :The Borg Warner T-19 transmission is a top loading four speed with granny first gear that succeeded the T-18. The T-19, was used in '74-'88 Ford pickups and some IH trucks and Scouts. The T-19 appears identical to the T-18 except that the PTO side plate is on the left side and the housing casting is 13-09. Most T-19 transmissions used in Ford trucks used the close ratio gear set. The IH Scout T19 was available from 1975 to 1980 with both close and wide ratio options. As for the IH T18, they had a unique case and input shaft that makes adapters hard to find. housing length is 11.875".
Oil Note: Use a GL-4 rated oil instead of GL-5. GL-5 has a higher sulphur content that is mildly corrosive to the bronze alloy syncros used in this gearbox. StaLube and RedLine are brands to look for.
New Process NP-435:This is a four speed with an unsynchronised granny first gear. This strong and reliable transmission was installed on '67-'83 Ford pickups, as well as Jeeps, IH pickups and Scouts. The 2WD versions have a square tail-housing bolt pattern, while the 4WD version has a trapezoid pattern (lower bolts farther apart than top bolts). 4WD trucks that had a divorced transfer case also used the square tail housing bolt pattern. Different transfer case adaptors fit different tail bolt patterns. Be sure to verify that the gearbox will fit the adaptor for the transfer case you plan to use before handing over your money. The NP-435 has a cast iron housing with a PTO port on the right side and looks similar to a Borg Warner T-18. Unlike the T-18, it has an aluminium top cover which is usually stamped with 'NP' enclosed in a circle. Housing length is 10.875"
SM420The SM420 was used in ½, 3/4, 1 and 2 ton GM trucks from 1947 to 1967. Later versions had two horizontal ribs cast into the passenger side of the case. The "SM" in the transmission's designation stands for Syncrho-Mesh. The SM420 has a "H" shift pattern, with reverse being towards the left side and down. The a power-take-off (PTO) port is on the driver's side of the case Housing length is 10.7"
SM-465The SM465 was used in GM trucks from 1968 to 1991. They are found primarily in GM and Chevrolet trucks, Blazers, Suburbans and many other models falling under the 1/4-ton to 1-1/2-ton platforms. There are three versions of the SM465 each with about the same strength 1968 - 1978: There were both 2wd and 4wd versions. The 4wd version has a 10-spline output shaft and 4wd adapter housing. The 2wd version has a 35-spline output shaft compatible with a drive shaft yoke and 2wd style tail housing. Internally, they are identical to each with the exception of the output shaft and rear housing. Note: Unlike axles, the # of splines here has nothing to do with strength. 1979 - 1991: The short 10-spline, 4wd output shaft was replaced by a 32-spline 4wd output shaft and a different output housing to connect to the New Process 205 transfer case 1988-1991: The last years of SM465 had a 4th gear switch to signal cruise mode operation to the GM EFI Engine Control Module. This version had an aluminium top cover. housing length is 12.0"
NV4500The NV 4500 is a fully synchronized top loading five-speed transmission with a cast iron case, aluminium top cover and dual PTO ports. It is found in GM and Dodge trucks. The 1993, 1994 GM version has a different bellhousing pattern, a lower first gear ( 6.34:1) and an unsynchronised reverse gear than later units. 1995 and later NV4500's have a higher 5.61 low ratio and reverse gear synchronization. The NV4500 has a case length of 12.37" plus an extension housing length of 6.5". This housing contains fifth gear. 2wd style housings are longer. GM input shafts are 6-5/8" long . Dodge input shafts are 7-5/8" long.
Housing length 18.9"
Transfer casesWhile Land Rover Transfer cases are among the most robust available, they are lacking after market adapters to allow them to be mated to other brands of gearboxes. Adapting a Land Rover transfer case usually takes two steps. One is modifying the gearbox main output shaft so that it fits the transfer case input gear. The other is creating an adaptor plate for mounting. Often it is easier to use a different transfer case than to have a gearbox rear output modified. Most Transfer cases have the rear output shaft in line with the gearbox. This allows the vehicle manufacturer to use a single rear axle assembly for both 2WD and 4WD versions of their vehicles. While this saves the manufacturer money it does make driving over obstacles more complicated and damage prone. Having the front and rear diffs in line allows the driver to take more difficult tracts through obstacles with less chance of damage. Only manufacturers of ground up designed four wheel drive vehicles go through the effort to line up the front and rear diffs. For American Land Rover owners this means only Land Rovers, pre-Chrysler Jeeps and Toyota Land Cruisers have transfer cases that can be sourced locally. Pre-Chrysler Jeeps use the Dana 18 transfer case Toyota uses their own designs. As near as I can tell the Series Land Rover transfer case is the most robust OEM transfer case available. Both the Dana 18 and the Toyota transfer cases have been upgraded over time for additional strength but people still break them while off roading with big tyres and big engines. The one advantage of these Transfer cases is that there are a lot of vehicles out there that use them and a lot of people swapping more powerful engines and stronger gearboxes into those vehicles. There are off the shelf adapter kits available to mate these Transfer cases to strong gearboxes making swaps a lot easier to accomplish. Recently Advanced adapters have addressed the need for a stronger transfer case with both output shafts inline by becoming the exclusive retail source for Orion brand Transfer cases This adds another choice for people modifying the drive train of Land Rovers who can not source a custom made Land Rover transfer case adapter. If you are willing to swap in a different rear axle assembly, you will be able to use Transfer cases with the rear output shaft lined up with the gearbox. Many of these are quite robust. Just be advised that what you gain in transfer case strength you also also gain in technical off road driving difficulty. Transfer cases and rear axle assemblies that line up with the gear box are not addressed in this web site. Dana 18 Transfer case (Jeep 1941 - 1971)The Dana D18 ratios are 1:1 high range, 2.46:1 low range (slightly lower than Suffix C series low range). Why do I mention the D18? Because the series LR Transfer case design is based upon the early version of this transfer case and both share the same prop shaft offset allowing them both to be used with Land Rover front and rear axle assemblies. This is the only American made transfer case with the correct offset for Land Rover axle assemblies. 1966 and later D18 transfer cases can stand up to American small block engines and adaptors are readily available to mount a D18 transfer case behind a Borg Warner T18 or T-19 gearbox and the New Process NP435 gearbox. Pre 1966 versions of the Dana 18 will stand up to a stock 2.5L Land Rover engine but are not strong enough for most engine conversions. Early Dana 18 transfer cases had twin sticks and later designs used a single shifter stick. There were numerous factory and aftermarket add-ons for the Dana 18, including a PTO and overdrives made by Warn, Husky and Dual-Matic. Some of these overdrives had a PTO adapter available. Dana 18 rebuild parts & overdrive source From an email:
Orion Transfer caseAdvance adapters is the exclusive distributors for the Orion transfer case. As of Late 2006 they have an assembled heavy duty version that has the same offset as used by Land Rover, early Jeeps and Land Cruisers. I expect that adaptors will be available to fit commonly used gearboxes. Advanced Adapters offer a number of different gear sets for Land Cruiser transfer cases used behind GM SM420 and SM465 gearboxes. The Orion transfer case uses a cast iron housing and has the same mounting dimensions as the Toyota Land Cruiser Transfer cases The advantage is that it is a stronger units with better low range gearing options available (3.0:1 or 4.0:1 low range).
ToyotaToyota Land Cruisers, at least earlier models, had the same transfer case offset as the Land Rover and earlier Jeeps (Dana 18). If you are exploring drive train swaps it is worth exploring Land Cruiser drive trains. 3 speed, 10 spline 1963 to 1973 4 speed, 16 spline, 1974 to July 1980 4 speed 19 spline Aug 1980 to 1990 split case
Adaptor company web sites
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