LT77 carnage – warning, content unsuitable for the faint hearted

mrtask

Well-Known Member
#1
I heard from my mechanic today, who had a preliminary diagnosis of why my gearbox had ceased to function. I'm sure he won't mind me sharing his informed opinion and XXX rated snapshots for your delectation. His initial impressions:
"Nothing visible without digging into the box. I’m nosey, so I did. Oil pump probably never worked, is my guess, and it has survived on splash fed oil until it said "No more". Oil pump gears broken up, gear drive looks to have punched through the gear it drives. The square drive has rounded corners now. It has all kept going until one of the bearings, which is bone dry, started screaming and subsequently broke up. This is why it was O.K. at first, until it got hot and bigger etc. It hasn’t done reverse gear much good either, but not so important."
Ooof!
I haven't got the faintest idea what I'm looking at, but I'm sure it isn't supposed to look like that.

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chrisw

Well-Known Member
#3
Wow. Now that's impressive!

What are your options? LT77s are getting hard to find.. drop an auto in for now, and look for something else down the line?
 

quattro

Administrator
Staff member
#5
That's your input shaft spigot bearing, a known weak point if you don't set up the tolerances correctly.

The bottom picture appears to be the reverse gear.

You can strip it down, wash all the parts then carefully inspect them. Replace what's necessary and rebuild it - kind of depends on the condition of the parts and how much you have to spend :hmm:
 

sdibbers

Well-Known Member
#6
This brings back memories! Bad ones. Years ago when I lived in London still I picked up my wife to be from Heathrow late at night. My TR7 started to get slower and slower on the M25 back. I called a tow truck when I got to Clackets lane services. Gearbox was locked up. On stripping it down the internals were welded together and the oil pump in bits. Same story.
 
#7
That is very ugly! Glad I checked my spare box for a functioning oil pump recently - pushed oil out the hole underneath readily, with the plug removed. Some LT77s out of landys are not so rare - I wonder if you can fit an SD1/TR8 primary pinion into one - will it mesh with the layshaft?
 

roverp480

Active Member
#9
I understand from when I worked at LR we had a number of LT77 box failures when people thought the recommended gear oil was "Too" thin and used heavy oil, which stripped the oil pump drive especially when very cold.
 

Demetris

Well-Known Member
#11
Not nice indeed, but it does happen from time to time if you trust unknown rebuilds.
I was lucky with my replacement engine, but not so with my gearbox. It was an early version with bronze sleeve bearings and whoever built it made it too tight for its own good. At the first 100-200 metres of the first test drive it locked itself solid in 1st gear. Thankfully it was still possible to drive normally just in 1st (with all the other gears selected the gearbox was locked) so i managed to limp it home. Later i rebuilt this box after replacing the 1st gear and associated bearings and i kept it as a spare.
I sincerely hope that you will find a reasonable solution soon with yours.
 

roverp480

Active Member
#12
I had a very stiff gearchange on a LT77 in my LR Discovery . Two dealers put it down to the gearshift & lubricated it with no improvement. Eventually went to one who's mechanic knew what he was doing. Within 100 yds driving he diagnosed too much preload on the mainshaft assembly . He said to me "do you notice selection of 5th is no trouble" , Vehicle was only a few months old and it had wrecked the mainshaft bearings and sundry other parts.
 

mrtask

Well-Known Member
#13
I can only add that my calamitous gearbox cost me something in the region of eight hundred smackers, allegedly fully reconditioned and warrantied for a year or 10,000 miles, whichever came first. It sat sulking on a pallet in the corner of my lock-up for five years before I finally got around to installing it. It has survived for a year and a half of my driving, apparently a miracle given it was basically dry inside. The chap I obtained it from seems to have ceased trading. Perhaps he was forced into liquidation by law suits from other aggrieved customers? Conjecture. You have to trust people, all I can say is it was shiny and clean when it arrived and my mechanic friend who put it in with me said it looked like a sensible purchase. Having never driven anything else with one of these boxes in, I had no bench mark for comparison. I did think it felt a bit stubborn before it warmed up, but was told to live with that. Three or four people who have driven plenty of "warmed up" V8 MGs took my car out for a spirited spin, and all said it felt good to them, so there's that. What can you do? You have to trust people.
Is around nine hundred bills for a similarly reconditioned R380, with a six month warranty, maybe a good choice? Followed the second link up above and saw that from the same vendor. Your thoughts, chaps?
 

sdibbers

Well-Known Member
#14
I understand from when I worked at LR we had a number of LT77 box failures when people thought the recommended gear oil was "Too" thin and used heavy oil, which stripped the oil pump drive especially when very cold.
I know on TR7’s early LT77’s used 20w engine oil (like P6 boxes). Later ones used ATF. I switched to ATF after the failure and have to say it much improved shifting quality.
 

quattro

Administrator
Staff member
#15
I use redline MTL and my LT77 is a right slick shifter. It was horrible when I first got it, with a shift akin to stirring a saucepan full of potatoes, but after a good clean out with white spirit and refill with the MTL, it just transformed it.

I did end up rebuilding it though :) - Sparky's winter/spring/summer/autumn work
 
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