Thread: Which is stronger LT85 (lightweight) or R380?

Thats funny , Perths top LR gearbox overhauler is swapping out his blown R380 for a LT85 HD based on the fact the LT85 is stronger where it counts .I suppose being a 85MM box as apposed to a 77MM box that the R380 is ,it makes sense . The R380 is no "stronger" (an ability to manage the Torque/Horsepower) than a LT77S . The R380 may have superior selectors/synchros and slightly better reliabiity , but it isnt "stronger"than a LT85 . I suppose its because he is putting 400-500HP through it using a real engine (417 Donovan ) that you would need some real Strength .
So it comes down to Horses for courses , and exactly what you mean when you say "Stronger"
(PS . you could say the same about the LT95 , versus the LT85 , then the woeful gear selection and modifications required to get it to mate to LT230 would make it not worth it )
(PSS Personally I would use a 4L80E with the "E" bit removed ,and fully manulised )

Originally Posted by 400HPONGAS

Thats funny , Perths top LR gearbox overhauler is swapping out his blown R380 for a LT85 HD based on the fact the LT85 is stronger where it counts .I suppose being a 85MM box as apposed to a 77MM box that the R380 is ,it makes sense . The R380 is no "stronger" (an ability to manage the Torque/Horsepower) than a LT77S . <snip>

Isn't the LT85 weakness in the the 5th gear set?

And where it counts in the 5th gear the R380 is significantly stronger than either LT77s, 30mm stronger in fact, or the LT85. More the R380 weaknesses are in the low oil volume which is compensated by the ability to run an oil cooler (standard) increasing oil volume and dissipating the generated heat.

I don't know about others, but on the highway where I travel the most kilometres, I use 5th gear.

You see Lotz-A-Landies , your confusing "Strength" with reliability . Each box has its own perculular reliability problems . Not many Racers , with high horsepower,high load applications ever go near 5th gear whilst in a competition mode.So its not a case of which is "stronger" , its which is most suitable for the intended application.

Originally Posted by Lotz-A-Landies

Spoke to KLR this afternoon and asked them the question. The answer was an emphatic yes to using an R380 over an LT85.

Once I get over the cost of the LT85->R380 bellhousing conversion and then converting my Disco R380 to Defender I'll need to sell the Defender!

Hi Diana,

On my Isuzu 110 I went down this path, with a late suffix R380 from a discovery. Initially I kept the 1:1 transfer but found it too high with 33s - so I went to a 1:1.2 from an early RR.

I'm extremely happy with the results. It was earth shatteringly expensive but 100000x nicer to drive. The ratios now are perfect (with 33's) and the gearbox is much quieter than the old LT85. I ran syntrans in the 85 and always had problems changing when cold, parts were extremely expensive to get and it was very worn out.

Shoot me a PM if you want any specifics of the conversion.

Originally Posted by 400HPONGAS

You see Lotz-A-Landies , your confusing "Strength" with reliability . <snip>

I take your point but I was using the word "strength" because that was the term you used in your previous comment.

If the LT85 has reliability problems when used in 5th gear for long periods, I would assume there is some sort of strength issue with 5th gear.

The intended use of the box is in 5th for highway speeds behind a 4BD1 in a 6X6 so I am assuming I'm not confusing strength with reliability under intended use.

Circa 150000ks now on My Isuzu 4BD1T + R380 conversion on my Defender and extremely happy with the result. The R380/1.2:1 transfer case are very well matched to the Isuzu - the ratios suit particulary well. The vehicle has crossed the Simpson 3 times (once across the Madigan Line), has done many tens of thousands of ks in the outback fully loaded and with a trailer without complaint from the gearbox

I spoke to ashcrofts before using the R380 - they said that the late suffix R380s were capable of handling at least 440nms of torque - and that th
ey were significantly stronger than any LT85

FWIW

C H T

Originally Posted by C H T

Circa 150000ks now on My Isuzu 4BD1T + R380 conversion on my Defender and extremely happy with the result. The R380/1.2:1 transfer case are very well matched to the Isuzu - the ratios suit particulary well. The vehicle has crossed the Simpson 3 times (once across the Madigan Line), has done many tens of thousands of ks in the outback fully loaded and with a trailer without complaint from the gearbox

I spoke to ashcrofts before using the R380 - they said that the late suffix R380s were capable of handling at least 440nms of torque - and that th
ey were significantly stronger than any LT85

FWIW

C H T

Thanks for the info Chris. However you may want to check the threads by P(ete)Simpson on his very late model R380 which failed. It is in a 90 TD5 - so not as stressed as if bolted to a 4BD1T one would assume.