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View Full Version : Why won't an Overdrive work with a Hi Ratio Xfer Case???



KingSlug
02-14-2007, 04:55 PM
Why won't an overdrive work with a hi ratio Xfer case??? I remember reading this somewhere, but cant remember why.

Thanks

Tim Smith
02-14-2007, 05:18 PM
My guess is that they are getting the "high ratio" out of the input gear which (if memory serves) is where your fairey or roverdrive pops into the works. That would mean that the connecting overdrive gear wouldn't mate up any more.

Just a guess though...

KevinNY
02-14-2007, 07:13 PM
Regardless you would get unuseably high gears.

jp-
02-14-2007, 09:11 PM
Regardless you would get unuseably high gears.

But... But... It might go 100mph!

It would be Land Rover history!

TeriAnn
02-14-2007, 11:22 PM
Why won't an overdrive work with a hi ratio Xfer case??? I remember reading this somewhere, but cant remember why.


The high ratio kit comes with a new set of gears with different numbers of teeth than stock. An overdive gear will not match teeth with high ratio gears.

My Land Rover has a high ratio xfer case, stock R&P and 33.3" dia tyres. I just ran the numbers, and my engine would turn 4,126 RPM @ 100 MPH.

The same LR with stock transfer case would be going 75.7 MPH at the same RPM. With stock 109 tyre dia & stock xfercase the LR would be going 72.7 MPH @ 4,126 RPM. 100 MPH would be 5,675 RPM

If you run the numers, you get almost identical ratio with an overdrive and 3.54 R&P as you would with a high ratio transfer case and overdive.

So get some RR Classic diffs, a Rover drive and knock yourself out.

yorker
02-15-2007, 07:39 AM
So get some RR Classic diffs, a Rover drive and knock yourself out.

I don't think that will work- Jared wants to crawl too.

Jared you still want to use the MB diesel don't you? You'll need higher gears but not by a lot. 4.11's would be good.

KingSlug
02-15-2007, 12:11 PM
I am looking at a Cummins 4BTA/NP435/Series Xfercase/Toy Diffs. The 4BTA has a cruising RPM of 1800, so having a 4th/OD would be advantageous. With the NP435, an "B" low gear and the grunt of the 4BTA I should be able to creep along, but I wont be rock crawling.

yorker
02-15-2007, 07:34 PM
Sounds like a good choice with the Cummins. I'm looking at that possibility as well for my 109,w/ Toyota Axles and possibly SM420/465, I'm not sure which transfer case I want to use yet. I have a NP200 on the way and may use it to make a passenger offset NP205. Actually I'd like to use a 203 reduction unit with it but that would be overkill especially with a diesel. 116:1:eek: Decisions decisions...

What size tires are you planning to use?

roverolls
02-19-2007, 07:34 PM
I suspect there is an unspoken, unwritten law of physics, that the only time a series rover will go 100 mph or more, is going straight down hill, (like over the edge at Dead Horse Point), but your next of kin would be stuck with the EIS, and cost of cleaning the smudge from the slickrock.
Or possibly following ignition of your Genuine Parts brand JATO pod.
I rebuilt my 2.5 L 4 cyl engine in 1996, with pistons .030 over, planed
the head for increased compression ratio, added the 2 bbl webber carb, electronic ignition, Detroit soft locker, heavier axles, all of which gave the truck the ability to keep up at 65-75 mph, without straining the engine. I have had a Fairey overdrive since 1981, which added top speed, decreased engine strain. I have to use 88-91 octane, to prevent pre- ignition.
The 4 cyl Rover engine works very well for climbing, driving, etc., except for being a little slow. The original equip. trans, trans. case, function well with regular care, maintenance. Original equipment is very easily rebuilt, and easily repaired, with all parts still available for series 2 vehicles.
Considering the cost, and changes required to install a very powerful engine like a Cummins, someone might save some money purchasing a new truck, like a diesel Discovery, or Defender 90 or 110.

leafsprung
02-20-2007, 10:10 AM
someone might save some money purchasing a new truck, like a diesel Discovery, or Defender 90 or 110

Saving money by buying a NEW diesel land rover? What kind of conversion costs 35-50K :eek:


There are several series rigs out there that will pull 100mph with relative ease. Luckily Ive only been clocked going 90 . . .:D

A high ratio overdrive could be made from a normal fairey and a ashcroft input gear. The fairey input gear would have to be cut off, the ashcroft gear bored out and then welded to the fairey.