Thread: Overdrive??

I know next to nothing about this era of land rover. Isnt the lt85 a 5 speed? can it go in to replace the lt95?

Originally Posted by JDNSW

My 110 (same engine, gearing and tyre size as the army 4x4s) has been sitting comfortably on 110 without an overdrive for the last twenty years. As Mark points out, it is not revving all that fast at that speed.

John

Hmm, I've seen a few comments about 90-100kph being the maximum comfortable speed for a Perentie. Maybe those were referring to the realities of having a canvas back at those speeds as opposed to gearing?

Originally Posted by Mammalalien

How about changing the ratio of 4th gear, the transfer case or even at the axels as alternative to an overdrive? Just enough to allow comfortably sitting on 110kph would be ideal for SA.

Not sure what you mean about changing the ratio of 4th gear. In the LT95 4th is direct 1:1 engine to mainshaft and then 1:0.996 on the front/rear output shaft. (No 5th in a LT95)

Changing the diff ratios you would go backwards AFAIK there are no Rover Diff ratios higher than 3.54:1 so your limiting factor is the front diff ratio. Plenty of lower ratios.

Originally Posted by Landy Smurf

I know next to nothing about this era of land rover. Isnt the lt85 a 5 speed? can it go in to replace the lt95?

Yes, but, the Isuzu/LT85 bellhousing is different to the LT95 bellhousing, and since it was only made for the '86-'90ish period, they are somewhat uncommon, less common than LT95 bellhousings it seems.
Also, the LT85 uses the LT230 tranfser, so if the Perentie has a winch or third driven axle then it won't be compatible with the LT230.

Originally Posted by Lotz-A-Landies

Not sure what you mean about changing the ratio of 4th gear. In the LT95 4th is direct 1:1 engine to mainshaft and then 1:0.996 on the front/rear output shaft. (No 5th in a LT95)

Changing the diff ratios you would go backwards AFAIK there are no Rover Diff ratios higher than 3.54:1 so your limiting factor is the front diff ratio. Plenty of lower ratios.

Ah, yes. Thanks for pointing that out. I still have much to learn.

Actually I did come across that bit about 4th being direct drive after I posted. If you haven't seen it, there is a great YouTube channel with lots of how-to, tare-downs and useful advice on Landy maintenance.

Over the course of a few videos he opens up and compares the inner workings of LT77 and R380 boxes and even interviews people from Ashcrofts about common causes of failure.

Originally Posted by Mammalalien

Hmm, I've seen a few comments about 90-100kph being the maximum comfortable speed for a Perentie. Maybe those were referring to the realities of having a canvas back at those speeds as opposed to gearing?

I imagine that 110kph in one would be pretty noisy, wind noise, tyre noise, and flapping canvas mainly. Not sure what an overdrive would do about any that! Worth noting that the civilian 110 has a lot more soundproofing than has the Perentie, but even in it, the engine is not obtrusive at 110 - mainly wind and tyre noise.

John

Originally Posted by Mammalalien

How about changing the ratio of 4th gear, the transfer case or even at the axels as alternative to an overdrive? Just enough to allow comfortably sitting on 110kph would be ideal for SA.

Hi mate... I know this is an old post... but... can you expand on the type of work involved in re-gearing the diff or gear box for a better 4th gear at 100km/h?

Originally Posted by xxmaxx

Hi mate... I know this is an old post... but... can you expand on the type of work involved in re-gearing the diff or gear box for a better 4th gear at 100km/h?

As pointed out - there are no front diffs with a higher ratio, so you would need to get new gears designed and made. Probably cost more than the perentie. Rear diff is possibly simpler, as there are probably more ratios available.

As far as the gearbox goes, changing the ratio of fourth gear to anything other than 1:1 means a different gearbox, which means a different transfer case, as the transfer case is integral in the LT95. Possibly an Isuzu gearbox with an R230 transfer case, but as pointed out this means you can't use the PTOs designed for the LT95.

It should be pointed out that there are overdrives for the LT95, since they were fitted to the Rangerover for years. Whether they stand up to the Isuzu engine may be another matter - there seems to be mixed results on this. And there goes your PTOs again.

Can I suggest the simplest and easiest solution to the not very serious issue of engine rpm is to look at slightly larger diameter tyres.

John