by Lorne Goldman
The LT77 gearbox (from the Rover SD1) has many different reputations. There were many versions made (A, B, C, D, and S) and the later ones became progressively more problem free. I have friends with rebuilt LT77s in a 290 HP cars that have given several years service with many track days and no problems. If you use an LT77 it is worth knowing the different variations. Some have stronger internals than the earlier 'boxes and are fitted with a higher 5th gear - 0.793 instead of 0.833. Morgans mate the box to a modified Sd1 bellhousing with and one of three Sd1 remote gear lever assemblies.
The LT77 was introduced to Morgans in 1976. It is the same box used with the Rover SD1. The early boxes are not great. A LT77 variation was introduced to Landrovers in 1983 with the suffix 'D' box (which was a big improvement) and was developed over the years to the suffix 'H' which was last used in 1994. This was improved upon with the suffix E which used a wider reverse gears. Then came the suffix F which used larger diameter laygear bearings. The suffix G was uprated with all the gears being widened. Then the last of the LT77 was the suffix H (also known as the LT77S( It used a dual synchro on 1st and 2nd gear. The best version is the last, the LT77S..or those with the G or H suffix. YOU NEED A SD1 VERSION.
The 'G' was further improved by all the gear teeth including the pinion getting approx 20% thicker. Also a much wider pump was used to increase the lubrication. The 'H' (termed the LT77S) was the same as the 'G' in terms of strength but used a different syncro set up called the'Double Syncro', (though in reality it didn't work much better.
The LT77 is quite particular about the oil that is used. Rover used to specify ATF (Ford Dextron 3) to overcome baulking when cold. That is very thin oil. There are those who use Redline MTL or Castrol SMX-S with reported success and much smoother shifting. There is a now synthetic oil specifically designed for this gearbox from a company called Difflock. The product is called Difflock Evolution 1 Fully Synthetic 5 speed Gear Oil - 1 litre. These oils are fully synthetic with friction properties designed especially for gear syncros. They reportedly make gear changes like a knife through butter and synchro engagement is really good.
The box is rated to 245bft. torque..but this reflects manufacturer caution and Morgans have a VERY light load and the later LT77s (post 1988) are likely stronger.
Borg Warner T5 Gearbox
The World Class T5 'box is rated at 300lbft of torque. (Other T-5s can be considerably weaker). This version is generally acknowledged to be a stronger 'box than the LT77 and is 12 pounds lighter. To fit this you can use a bellhousing for an automatic SD1. This is shorter than the manual bellhousings and can be fitted to the T5 with an adapter plate. The easiest way to operate the clutch is to use a concentric hydraulic release bearing that is attached to the gearbox front over the input shaft. Alternatively, you can buy an aftermarket specially cast bellhousing from John Eales Developments. The advantage with T-5 is easy accessibity of parts and a huge range of gearsets. In the UK, ask for the type used in the TVR. Note the proper gearlever placement
The R380 is a development made to replaced the LT77s. Same gear set as the LT77. It was fitted to the MG V8 and the latest Land Rovers from 1994 to 2002 but not in a Morgan configuration.
There is no need for extensive
chassis mods if replacing a Morgan LT77 with a Morgan R380. The bellhousing
and remote from the LT77 can be attached to the R380. A small part of the
chassis mounting plate for the LT77 will have to be ground away but the
new mounting postion arrives at the crossmember making the fitting easy.
The propshaft is same as the Morgan R380 is the same length as the Morgan
LT77. HOWEVER, the R380 used on the Morgan is a special version made for
Plus 8s, later Plus 4s, some TVR Chimaeras and Sherpa vans only. The oil
required is a MTF94, either castrol SMX-S, Texaco MTF-94 or Amsoil Synthetic
Manual Synchromesh Transmission Fluid (MTF) SAE 5W-30. The R380 corresponds
to its load rating in NM or 280 lbs/ft.
ASHCROFT TRANSMISSIONS has designed a strengthened (and Morgan friendly) gear set for the R380 which is a much better match for a Morgan. I For ultimate strength the gears are straight cut and 'close ratio' and manufactured from high strength 300M material. Complete with strengthened 300M mainshaft as these are a common failure point on high torque engines. It is designed to fit the later stronger suffix 'L' R380 with the bigger bearings.
Note due to the nature of straight cut gears they will be noisier than a normal R380.
Ratios are :
The ratios have been chosen to be ideal for racing and Morgans, ie higher 1st, 2nd and 3rd etc but still keep 5th as a reasonable overdrive ratio as this is often required for running between sections at lower engine RPM's. The gear kit includes the layshaft, Pinion, Mainshaft, 1st, 2nd, 3rd and both 5th gears.