Thread: Overdrive

no, or we'd all have one.

soon the renamed 'Roverdrive' to suit LT95 boxes will hopefully be available, just have to wait....


JC

Yes, I've got one but I think it's a doubtful blessing.

There is no doubt that it makes a huge difference to open road driving - I can cruise quite happily at 100k/hr (if I can stand the noise). It generates a fair whine but I'm sure this is because it's getting old. There is fretting and damage on some of the gears (see below). But my biggest concern is the fine drive spline between the output of the gearbox and the overdrive.

The LT95 is such a strong box and this spline looks like a significant weak point - I may be wrong but it doesn't fill me with confidence. So much so that I'm sourcing the standard drive gear and housing parts to take as a spare on a pending trip.

And, of course the LT95 overdrive is different from the standard Series III overdrive so they're pretty rare - with the up side that it gets continually refreshed with oil from the transfer box rather than relying on it's own small resevoir.

Here is a picture of the drive spline:-


And the wear/damage on the overdrive gear:-



I think it would be worth considering the higher ratio transfer gear set as an alternative (from the Range Rover I think) that would give the LT95 a bit more legs without compromising the strength.

That's my 2c worth....
Pete

I thought the 0.996 transfer that is standard on the Isuzu engined 110 was the highest available. With it, I find no problems cruising at 100 - 110. It is noisy, but at that speed a large proportion of the noise is wind noise.

I have thought about an overdrive in the almost twenty years that the 110 has been my main vehicle, but have come to the conclusion that it would be little advantage even if there was one that would stand it. If I had a turbocharger perhaps it would be a different situation.

John

I put a brand new Fairey behind the LT95/ 4BD1 back in the 80,s. Last year I put a turbo on it. Its got the 996 gears as well and its all still going strong. It shows some wear as the OD synchro clashes unless I double de clutch changing down but thats no problem. Changing up into OD is fine.
I am carefull with it and only use it for cruising on the flat. Coming to a steepish gradient I change back to direct.

Didiman

Yes the Isuzu tfr case if standard already has the .996 gears.

Over the years this topic has come up on AULRO a few times - some posters do not believe the O/d is up to the task behind the diesel but every now and then along comes someone who has one on their vehicle and it is running well and holding.

I suspect that if driven with caution it can last but get complacent and it can fail. I have a O/d behind my V8 and on longer trips I always take the bits I pulled out to put the O/D in, such as the bearings, gear, and cover plate because if the O/d fails you loose drive completely in the trf case and the ony way to fix it is to remove the O/d and return the tfr case back to original.

Garry

Yes, I should have qualified the transfer ratio. My LT95 is in a stage 1 with 1.34 hi ratio (I think) - the serial number of the box starts with 15C and the tooth counts on the high range transfer gears are 48 and 31 - does this stack up?

There is certainly no way I'd hit 100k/hr in 4th and it is more like an 80k/hr maximum, so the overdrive makes highway driving possible.

Next transfer rebuild its going to be out with the overdrive, .996 ratio and TRB. Until then I'll put up with the whine.

Originally Posted by captainslow

Yes, I should have qualified the transfer ratio. My LT95 is in a stage 1 with 1.34 hi ratio (I think)

As far as I am aware the V8 Stage 1 had a tfr ratio of 1.336:1 and the Isuzu Stage 1 was the same as the County Isuzu and later RR with .996:1.

I do not believe there is a ratio of 1.34:1 for the LT95.

As far as I am aware LT 95 ratios were
1.336 Stage 1 V8s and County V8s
1.174 Early RR and 101s
1.113 Late 70s/early 80s RRC
.996 All Isuzu engined Landies and 81-83 RRC.

Someone more knowledgeable than me might want to double check.

Garry

Originally Posted by captainslow

Yes, I should have qualified the transfer ratio. My LT95 is in a stage 1 with 1.34 hi ratio (I think) - the serial number of the ...

As Garrycol said. If your stage 1 is a genuine isuzu it would have left the factory with 0.996:1 gears.