Overdrive vs. High Ratio Transfer Box

[roverX]

Originally Posted by WineryRover

Hey X, yep, I'll be doing the install myself. If the timing works out, we could do them both at the same time. One of those beer, hard booze, strippers and dancing midgets kind of weekends. Oops, that's a different weekend, my bad .

But seriously, no problem, we'll get yours installed.

BTW... the 2a has a III tranny in it.

[jimfoo]

Having had no OD when I first got my 88", then getting one later, I would
much rather have an OD than x-fer box. Of course I have mountains to go up,
so splitting gears helps a ton. Also I have suffix B low range gears in my D
x-fer case for much better low range. This can't be done in the Ashcroft box.
I have cruised at 80 mph(75 limit highway), and it is so much better than
winding out at 65-70. On the flat lands, especially with little off-road, I could
understand an ashcroft conversion.

[Muddy Oval]

I think the RM version is better than the Fairey too- My SIII 88 had an overdrive and although I didn't have a tach, I don't think the overdrive gave it more speed by much- but it did make it cruise much more comfortably at speed.
Overdrive is better than none- but if you really want to get more speed out of them using the overdrive, increasing the torque a bit (maybe a stage II cam or some other tweaks) will go a long way.

[p76rangie]

Why not just put 3.54 diff centres in. Cheapest way. 1st is too low in most series vehicles anyway.

[TerryS]

Many people have done that, Ian. (many being a relative term) The drawback, from an offroaders point would be that the low range is also altered. Doesn't the back side of the ring gear need to machined? I have a vague recollection that the Rangie gears are thicker.

[p76rangie]

Terry, my understanding is that you just change over the whole centre. Don't really know about just changing the C&P.

[onslow]

Originally Posted by p76rangie

Terry, my understanding is that you just change over the whole centre. Don't really know about just changing the C&P.

P76 is quite right it is just a straight swap no mods needed at all,diff swap is the easiest way to go,although as Terry states it does affect high and low ratios,overdrives can be a weak link in the driveline when off roading (I know not to engage it when in low box but the torque still passes through it),ive blown up a few and now dont bother fitting them at all.

[roverX]

Dang it people, now I am more confused than ever! What would you put in a 2.25 diesel to get more top end speed out of her without revving the engine too high?

[pickuprover]

Originally Posted by roverX

Dang it people, now I am more confused than ever! What would you put in a 2.25 diesel to get more top end speed out of her without revving the engine too high?

2.25 deisel and inreasing top end speed should never be in the same sentence.......

My personal views.... it is a Series truck, theywere only ever designed to do 50 mph, (55 for short bursts..) and I would not look at the engine as the limiting factor.... the limiting factors as far as I am concerned is the axles, brakes and steering... anything above those speeds and way too much stuff is spinning way too fast. These trucks have limitations, and one of the biggest is speed. I see the overdrive/high ratio tc as a way of slowing the engine rpm's at cruising speed, not to increase the speed of the truck... if you want the truck to cruise at North American interstae speeds, well there is an easy fix, it is called a trailer.. other than that, it is Rover time in getting where you want to go.... Keep saying this to yourself on the trips... "Your rice burner may go faster, but I go anywhere...." Just my $0.02....

[Shearpin]

I installed a Rocky Mountain ROverdrive in late '05 after 10 some odd years with my Series III SWB. I have 7 or 8 thousand trouble free miles on the overdrive unit - including a trip to Mex/Guat/Belize and back. Highly recommended.

During the 10 years I ran the Rover prior to the install "Eore" and I wheeled in Arizona, Utah, Colorado, New Mexico, California, Canada, Mexico, Belize, etc. Those days when you need to cover high mileage of washboard two track with the odd ruts, mud, or bull dust sections I found the Series high range 4wd ratios perfect. I chose the overdrive over the high-ratio T-case because it preserved them.

With overdrive engaged on long highway sections my cruise speed increased from 45mph to 55mph with a 200 or 300 rpm drop. At 45 mph prior to the overdrive the 2.25 would turn approx 2700 rpm. I considered this rpm the max for long trips in an effort to keep heat and wear down on all components. Non of it was designed for 7 hour days with fuel stop highway slogs.

For shorter commutes at approx. 3000 rpm, overdrive engaged, I can get over 60mph indicated on flats and mild inclines. On hills it follows the familiar Series driving experience - the speed drops quickly with RPM until you are back in the power band where she'll pull. As previously mentioned, splitting third with overdrive is effective. On the highway I normally shift with the gear lever and maintain overdrive.

For the most part I use the increased "speed" over the economy. When I installed the overdrive I also put in a Vacum gauge - which was worth the effort. The 2.25 works very hard on grades with the overdrive engaged which is clear on the vacum gauge. If the grade is long I'll often gear down in the interest of longevity.

Damn - long rant. Hope it's helpful making your decision....

Henry
www.4x4freedom.com

[acornhoek]

pickup's right.......on flat stretches I can push the 2.25 petrol in the Carawagon to give me as much as 70mph, but heaven forbid something force an immediate stop. It really isn't just the engine that should keep you from trying to push you aluminum box faster.

If it’s about RPMs, I have a Fairley and have never (knock on wood) had an issue, but I'm a maintenance freak. I'd rather have the choice of the OD than the no-choice of the HRTB or switching out the 3rd members. Put an OD in (preferably RM) and carry the spares necessary to put the Tcase back to stock just in case...........unless you're planning to put in something other than the 2.25



......my 2¢

[onslow]

Originally Posted by roverX

Dang it people, now I am more confused than ever! What would you put in a 2.25 diesel to get more top end speed out of her without revving the engine too high?

A V8 !!!!!!


but seriously,what about fitting some bigger diameter tyres,with a 2.25d there aint a lot you can do even rangie diffs may be too much for it to handle,one of these RM overdrives may do the job for you but in all honesty I have had no experience of them we mainly use faireys over here,but its always alot of money for the benefits you get from them.

[roverX]

My main objective was to squeeze out an additional 5 - 10 mph on long flat stretches while preserving additional wear on the engine from revving too high. If I can maintain 55, possibly 60 mph on long flat stretches, then that is just fine by me! I am not looking to make a speed demon out of her, just really not wanting to slow down my peers too much while they wait for me.

Hell, I guess those disco and rangie guys can just sit around and wait for me then! Thanks for the input and you are right, it's rover time when you get there.

[p76rangie]

If you want less than 10% extra, tyres is a good idea. Just keep them narrow so they will suck less power.

[Thor]

Originally Posted by roverX

Dang it people, now I am more confused than ever! What would you put in a 2.25 diesel to get more top end speed out of her without revving the engine too high?

Taller tires... but skinny.

oops alreay been said.