Underdrive unit?

[alaskantinbender]

I see lots of info on overdrives or the roverdrive units but what about an underdrive?
I have a high ratio transfer case I'm not totally happy with and contemplating alternatives.

regards

Jim

[I Leak Oil]

I'm not aware of any that will bolt right into a series transfer case. I know Ray Wood (of Roverdrive fame) was talking about an over\under drive unit a few years back but I don't think anything ever came of it. I doubt it would work with a HR transfer case any way. The overdrives don't.

[ThePhotographer]

I'm not sure what there is for Series vehicles, but Ashcroft has an LT230 underdrive that's pretty well regarded. http://www.ashcroft-transmissions.co.uk/index.php?act=viewProd&productId=16

[o2batsea]

High Ratio transfer case has the same as stock low gear. You get a higher high gear with that for highway driving. No effect on low range. An underdrive would be the best option, but I don't know of anything made for the Series transfer case.
Are you running the winch off the back of the transfer case or from the crank?

[TeriAnn]

I see lots of info on overdrives or the roverdrive units but what about an underdrive?
I have a high ratio transfer case I'm not totally happy with and contemplating alternatives.


I too have the high ratio transfercase. It raises the high range gearing from a 1.15:1 ratio to a 0.87:1 overdrive while leaving the low range ratios stock (low first 40:1 at the axle)

The Ashcroft underdrive on the back of a US spec Defender will give a low, low first of about 70:1 at the axle.

You didn't say what your problem is that you are trying to solve. Do you want a lower low range ratio for technical off roading or is that 0.87:1 high range ratio too tall for your engine's power curve where you drive?

If your problem is your engine not being able to push the high range gears in some of the places you drive I think your best bet would be to go back to the stock transfercase and getting an overdrive.

If you are looking at the low range and want lower, your choices are limited and expensive with a LR Series engine.

What about your current set up doesn't work for you???

[alaskantinbender]

Thanx for the great replies.
My problem is 1st gear in high range being uncomfortably high. Being careful to not let the clutch slip
too much with the engine in low RPM for quick engagement is a skill I learned with my old unimog 404.
But I cant imagine towing a trailer or hauling much of a load with this high of a 1st gear. Starting out in 1st
gear on a hill is quite a trick. The clutch is just about gone after just 6,000 to 7,000 miles. Most of the
mile's where put on by the previous owner after installing the new ACR 2.8L engine.
The clutch engages right at the top of pedal travel and when worked hard in low range off road starts
to slip pretty good. The low range gearing is great and the engine powers the truck very well on the road at
speed's up to 65MPH. The winch is powered from the back of the transfer case which is why the high
ratio case was used in the first place.
I cant decide between trying to get used to it or going with a stock "T"case with an overdrive. Also going to a
warn 8274 or super winch husky 10 in place of the PTO winch. Still plenty of time to mull it over. I wont be able
to get to it until late April during my next break from work.
Either way it needs a new clutch soon.

Regards

Jim

[o2batsea]

There is just so little for options for you. I guess you could put a regular transfer case in it, but then your highway revs will be higher. I honestly think that you should think about a 110 with a Tdi. There's just way more available for gearing, suspension, etc. You really want the 5 speed. You have reached the zenith of modification possibilities on the Series. You may possibly be able to reduce the gearing to your liking with RRC diffs and those 4.75 Ring and pinion gears, and smaller tires. The only remaining way to go is off toward strangeness and shadetree engineering. SM 465 gearbox, divorced LT230, and stuff.

[TeriAnn]

Thanx for the great replies.
My problem is 1st gear in high range being uncomfortably high.

Humm, you have a '63. Any chance you have a A or B suffix gearbox?

A&B suffix gearbox first gear = 3.00:1
C and later suffix IIA & One ton first gear = 3.60:1
SIII gearbox first gear = 3.68:1

If you have a suffix A or B gearbox you might get some help with going to a newer box.

[TeriAnn]

The only remaining way to go is off toward strangeness and shadetree engineering. SM 465 gearbox, divorced LT230, and stuff.

That means a custom adapter between the engine & gearbox.

An expensive option would be a 300 tdi flywheel housing, short bell housing R380 and an Ashcroft adapter that allows a Series transfercase to sit behind the R380.

The only problem is that the R380 first gear ratios are lower than Series A & B suffix gearboxes but higher than the C suffix and later gearboxes. So it is no solution to the existing problem.

The pre 1993 LT77 five speed first gear ratio is essentially the same as a C suffix & later Series gearbox. The later LT77 has an even taller first gear.

The LR five speed boxes would only help with the stock Series transfercase. But it is a big $ conversion.

[alaskantinbender]

Humm, you have a '63. Any chance you have a A or B suffix gearbox?

A&B suffix gearbox first gear = 3.00:1
C and later suffix IIA & One ton first gear = 3.60:1
SIII gearbox first gear = 3.68:1

If you have a suffix A or B gearbox you might get some help with going to a newer box.

Thank you TerryAnn, you have certainly done your homework.
Your web site is a tremendous wealth of info as well.
The previous owner told me I do have a s3 tranny. At the time I thought the reason was for the syncro
gearing but now I realize there was more to it. Makes me think I just need to change the clutch and
keep it as is for awhile and just see how it all works out.
What has your experience been with your high ratio transfer case?
In 1st gear my truck is moving along at about 10 MPH.

Jim

[TeriAnn]

.
What has your experience been with your high ratio transfer case?
In 1st gear my truck is moving along at about 10 MPH.


I'm the wrong person to ask.

Engine = Ford 5.0L with EFI
gearbox = NP435 (first gear = 4.9:1, yours about 3.6:1)
Transfercase = Series high ratio
Diffs = 4.75:1

The engine has more torque coming off idle than the stock 2.25L does at peak and my first gear ratio is a lot lower then the LR gearboxes.

On the other hand with 33.3 inch dia tyres the engine turns under 2600 RPM at 65 MPH

My guess is your best bet for driving happiness is a stock Series transfercase and a Roverdrive.

[ArlowCT]

My guess is your best bet for driving happiness is a stock Series transfercase and a Roverdrive.

I have driven trucks with the high ratio box and trucks with and without over drives and I would agree with Teriann. Stock case with the roverdrive is the perfect setup for a stock to almost stock engine. I like splitting gears and being in the "perfect" gear at all times. This I felt was impossible with the high ratio box. Plus it's just cool driving a truck with 30 different gear combinations!

[TeriAnn]

I have driven trucks with the high ratio box and trucks with and without over drives and I would agree with Teriann. Stock case with the roverdrive is the perfect setup for a stock to almost stock engine. I like splitting gears and being in the "perfect" gear at all times. This I felt was impossible with the high ratio box.

I have come to believe that Ashcroft offers that box for people with serious engine swap upgrades and not for the 2.25L or 2.5L petrol folks. There are lots of Rover V8 swaps into Series rigs in the UK, making the high ratio box the perfect accessory. The high ratio box is also popular with North Americans doing engine swaps. Advance Adapters offers a family of adapters to go between popular US top loader gearboxes and the Series transfercase (Call and ask for Matt). These adapters make it easy to build an American V8 to American top loader gearbox to high ratio Series transfercase combination.

Unless you get an old Santana or new Heystee Automotive (http://www.heystee-automotive.com/) overdrive, an overdrive is just not up to the power of an American V8. Timm Cooper's Monster V8 powered Series I has a Santana overdrive in it. Anything that can stand up to Timm's driving has got to be very strong and reliable.

Back in ancient times when I had a 2.25L engine in my Dormobile and an overdrive, third over was my best friend in the mountains. But with the 5.0 V8 in there, I have yet to drive a paved mountain road where I needed to gear down because the engine was running out of oomph.