|LT77 IDENTIFICATION WATCHPOINT : Aside from the variants described below, along with distinguishing the later (1994ish to 2004) VERY different R380, the major watchpoint for Morgan owners with this box is to make sure that you only follow the advice from the 4 wheel drive community as THEIR "matching" versions are different when it comes to remptying and filling them. Though their innards might be the same, the method of filling them and the addition of a second drain plus filter for the 4 wheel drives confuses Sd1 gearbox owners. Sd1 boxes where VERY widely used and can be identified through either their Serial Numbers or the use of the Sd1 Remotes (which are also used by the 2wd Morgan R380s).|
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.
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 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.
|CRITICAL WATCHPOINT: The LT77 uses an unusual internal
oil/lubrication pump. It is not only very sensitive to oil
viscosity, which is the reason, after a plague of failures when it was
first used, they finally settled on Dextron 3, an automatic gearbox
fluid (!), for these units as the feeble little internal pump could
deal with it. Of course, the LT77s did become much stronger as
time went on, but the automatic fluid is always called for. 25 years
ago I damaged a LT77 sufficiently to require a full rebuild after
driving 10 kms with the wrong fluid. :( 2021! update Dextron fluids are no longer made. However, the world's largest and wisest re-manufacturer of these boxes (ASHCROFT) (I have no connection with his or any other company aside for admiration for their expertise.)
TOWING a LT77 vehicle with the rear wheels on the ground is also a BIG no-no for the same reason...the internal plastic pump. The R380 is a completely different unit..in fact, stronger than the conservative 380nm it is named for. (440nm or 325 ftlbs) However, there have been reports that 5th gear can be damaged by towing with the wheels on the ground. Use a tow truck that lifts the entire car (they are much safer for all cars) or, alternatively, lock the steering wheel and tow by lifting rear wheels off the ground.
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 fit to the Plus 8s and Plus 4s from 1994ish until 2004 for the former and 2000 for the latter.. Same gear ratios as the LT77 but all else is very different. The later Land Rovers from 1994 to 2002 but NOT in a Morgan useable configuration. The 4wd versions are very different from the 2wds. Un;like tne Sd1 Lt77s, the 2wd versions of the R380 are as rare as hen's teeth. I have a list as long as my arm of Moggers looking for a 2wd R380.
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 as the distance from propshaft ro engine ramins the same, theough theboxes are shaped differently. A small part of the chassis mounting plate for the LT77 will have to be ground away but the new rear mounting position arrives at the crossmember making the fitting easy and solid. 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. Consequently, its shift is much smoother than the LT77 that are forced to use ATF.CONVERSION COMPONENTS TO TOYOTA GEARBOXES (a company in New Zealand)