Thread: LT95 Overdrive

Originally Posted by kaa45

The way i drive, it (the overdrive) would only be engaged in 4th gear at highway speed to reduce rpm and noise. Be nice to have a conversation without yelling.

Picked one up recently for $100 , and fitted it for use on a recent trip to Darwin.

Found out pretty quickly that towing, or even driving with a load was useless, noise reduction was minimal, and was even noisier as the oil level slowly dropped over the course of the journey. (yet another reason to replace my TC seals)

Originally Posted by Larns

Just remember they move the army's 6x6 GMV fleet along alright and they can weigh in excess of 6.5 Tonne

no they dont, they cant... the GVM of the vehicle isnt that high....

no-one would ever overload a landrover........

the PB ive seen was 9.3T which upset me somewhat as I had to re rig the crane twice to lift the bloody thing.

the first was easy, just add one more line to the block but nooooo still ran past 110% on the winch and that had run me out of sheaves so I had to put that sheeve block back on the crane and rig up the next one.

Originally Posted by Larns

Ya reckon?

Check the spec's for the N/A and turboed, I think you'd be suprised.
There is a reason they kill R380's, and it ain't just because there ugly!
My first R380 suffered a snaped mainshaft, did that idleing off from the lights.

On the overdrives, Dave is spot on, the thing is in constant mesh. You break the OD you get " no drive for you", have personal expearience here, very embaressing in traffic let me tell you

Good luck though

FWIW

4BD1T torque figures from manual 320nm (236 ft lbs) @1800 rpm early engine
or 314 (230 ft lbs) @ 2200 rpm late engine. Turn the wick up a bit and you probably add 10-15% to these figures - 271 lbs ft (368 nm). The R380 is rated for 380 nm (279 ft lbs input torque).

I have heard of early R380s breaking main shafts - stree riser on the main shaft is the cause of the problem. My R380 is a very late one with big layshaft bearings.

Thanks though Larns for your input

Christopher

Originally Posted by isuzurover

Good point - might be worth starting a database of what has worked and what hasn't. A lot seems to be down to how gently you drive it.

Off the top of my head:
Justin C (4BD1T/RR) - 2 ZFs Destroyed
Sam/Def90 (4BD1T/90) - LT77S holding up fine, engine and box now belongs to DaveS.
Chuck(not on forum - 4BD1T/RR) - LT77 (ex VM) and about 6 R380s destroyed
CHT (4BD1(T?)/110?) - R380, holding up fine
Me (4BD1/county) - LT85 - rebuild at 240k km by Mal Story. Now 340k km and holding up fine.

According to Dave Ashcroft, the late model R380s are as strong or stronger than an LT85.

Isuzurover

Great idea - it would be helpful to idnetifiy which suffix box has been used eg mine is a late box with the big layshaft bearings. The boys at KLR have R380s behind turbo Isuzus apparently without any problems. add to the list a 4BD!T Rangie that I thought about buying - LT77S with big miles and no problems - how about starting a thread on the subject?

Christopher

Originally Posted by JDNSW

Actually, the discussion about tooth type is fairly academic, since tooth failure in gearboxes is relatively rare compared to broken shafts and failed bearings, not to mention worn splines, disintegrated synchro assemblies and various other failure mechanisms.

Same thing applies to the discussion about hypoid vs. spiral differentials - although here tooth failure is probably more common, my impression is that again, other failure modes still predominate - certainly in my experience.

John

Dead right, JD. Tooth failure in automotive transmissions is nowadays rarely seen except in the now uncommon unsynchronised gearsets with sliding gears. Nowadays, with constant mesh gearing in even non-synchro boxes (Road Rangers, Spicers etc.) you hardly ever see a damaged gear with a tooth or three missing. The dog clutches and synchros now take the hammering.

Originally Posted by Brian Hjelm

Theory vs. practice raises its ugly head again and again in engineering problems. Spur gears last better and longer in rough use. Helical gears are quieter hence their use in road going vehicles particularly passenger carrying vehicles.

Not in LR boxes - I have pulled plenty of IIA boxes apart where 1st gear is stuffed (worn/pitted/broken), but the rest of the gears are like new.

9.3T!!!!


That's impressive, can't say Ive ever weighed one that heavy.

Bet the turbo whistled on that one!

Originally Posted by isuzurover

Not in LR boxes - I have pulled plenty of IIA boxes apart where 1st gear is stuffed (worn/pitted/broken), but the rest of the gears are like new.

The reason S1/2/2a boxes tend to have stuffed first gear is the same reason that the first gear is a spur gear - unlike all the others (except reverse, which uses the same gear) - is that first and reverse are not constant mesh - they are sliding in and out of mesh. You cannot do this with helical gears, which is why they are straight or spur gears. And the reason they are stuffed is that subject to mishandling, they can have very high loads imposed on the leading edge of a single tooth as they are engaged. (in a constant mesh gear set, the shock load is taken directly by the leading edge of all the dogs at the same time, and the shock is transferred to the entire tooth on the constant mesh gear, not just the leading edge.

The difference is nothing to do with the fact that one is spur and the other helical - it is to do with whether the gears are constant mesh or not.

John