Thread: LT95 Overdrive

Originally Posted by Blknight.aus

just a thought. Brians gearbox is repairable with a new front bearing, lay and input shaft. have you tried asking him about his....

IMHO the lt85 should be stronger than an lt95 with an overdrive.

Then I have to source a new bellhousing, not a common item

Originally Posted by C H T

If I might offer my two bobs worth: try an overdrive behind an Isuzu and see how it goes. I have heard a lot of theories about the longevity or otherwise of various Landrover transmissions behind Isuzus eg an R380 won't last the distance - yet when I speak to people who are driving vehicles with the various transmissions fitted I find out that they have not had significant problems. So try an overdrive - in good condition - drive with a bit of mechanical sympathy and we might all be surprised at how long it lasts.

MyR380 seems to handling a 4BD1T without any problems (over 20000ks now - heaving towing - long distance fully loaded) - the torque rating of the box is significantly above the torque output of the engine.

Christopher

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.

Originally Posted by Blknight.aus

FWIW

the thing that lets the suzi eat a gearbox is its torque impulse at or near idle especially if loaded up and "chugging"

the rapid acceleration and deceleration of the shafts makes the helical cut gears change thrust loadings significantly which is sort of the equivelent of using a jack hammer on your bearings over time. If Ive still got them the piccy's of the dead box from brian hejlms county (lt85) provide a perfect illustration of this. I cut the front off of the fubar input shaft to make a clutch alignment tool but he might still have the bits and be able to take some more pics of exactly what turns to swarf behind the isuzu.

a short term solution to the problem is to up the idle speed of the suzi. of course a pure square cut box would be my long term solution, no thrust loading of the shafts then. (just woefull tooth contact to worry about)

I still have the box, untouched since returned. I have sold the trasfer off it though.

Straight cut, or correctly, spur gears would make so much noise you would not hear the 4BD1. Generally speaking spur gears are stronger (subject to material and other design criteria) and run cooler not having the sliding friction of helical gears. Long time ago I cut a few gearbox internals including cluster gears on milling machines. These were for vintage/veteran restorations where usable replacement gears were no longer to be found and cost therefore was no longer a factor. Milling gears using involute cutters and dividing head is a slow and high labour cost task.

Originally Posted by C H T

MyR380 seems to handling a 4BD1T without any problems (over 20000ks now - heaving towing - long distance fully loaded) - the torque rating of the box is significantly above the torque output of the engine.
Christopher

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

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

4BD1 is about 250Nm, 4BD1T is about 320Nm in standard spec. Probably wouldn't be hard to get one to produce more than 380Nm though.

So haow many boxes of what type have you broken Larns???

Is there an adaptor out there to match a lt95 bell housing to a R380?

The lt95 gearing is ok but the noise is louder than the motor. Lower highway revs would be better.

Originally Posted by Brian Hjelm

I still have the box, untouched since returned. I have sold the trasfer off it though.

Straight cut, or correctly, spur gears would make so much noise you would not hear the 4BD1. Generally speaking spur gears are stronger (subject to material and other design criteria) and run cooler not having the sliding friction of helical gears. Long time ago I cut a few gearbox internals including cluster gears on milling machines. These were for vintage/veteran restorations where usable replacement gears were no longer to be found and cost therefore was no longer a factor. Milling gears using involute cutters and dividing head is a slow and high labour cost task.

Given same number of teeth, same size (diametral pitch or module) teeth, same addendum modification factor, same material and heat treatment, helical gears have a considerably higher rating than spur gears.

As mating teeth move in and out of mesh, the point of contact changes. The further out toward the tip, the greater the stress created in the root fillet of that tooth (the load is applied on a longer lever). But, when the contact is near the tip, another tooth is coming in to mesh and the load is shared - this load sharing is much more effective for helical gears. So the helical gear can have higher tangential load for the same allowable stress in the root fillet.

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.