View Full Version : Installing a High Ratio Transfer case

12-28-2006, 06:25 PM
So what is the minimum work needed to install a High Ratio Transfer case into a IIA with a welded in cross member?

Can you leave the main gearbox in and unbolt the xfer case?
Do you lift it out through the cab? Do you have to take out the seat base?
What, if anything gets taken off of the stock xfer case?
Any special tools needed?

This will be my first time tearing out part of drivetrain and I'll be trying to get this done in one day. Thanks for any advice.

12-28-2006, 07:40 PM
Not really very hard to do. It's also a good time to install a fresh set of parking brake shoes to replace the old oil soaked ones that don't hold on a hill. Remove the floors, tunnel, and seatbox. unbolt both driveshafts. Disconnect the parking brake and remove the whole assembly, backing plate and all. Then remove the speedo cable. Drain the gearbox and transfer case oil and while you're down there drop the transfer case pan. Remove the securing nut from the back of the transfer case and slide out the shaft while catching the gear and shims in your free hand. Don't tilt the gear or the bearings will fall out. Remove the 4 nuts from inside the transfer case then support the transmission with a jack. Remove the mounts from the transfer case. Remove the remaining attaching bolts/nuts from above and lift it out over the frame. It,s not that tough but it is time consuming. Figure 2 days for your first time. You may need some whitworth spanners and/or sockets. 5/16 and 3/8 if I recall. Remember to have some gaskets and seals in stock. Best of luck, Mark

12-28-2006, 07:47 PM
Remember you will now have a 2.35 to 1 lo range VS the 2.88 lo you have now. You should be able to sell your tcase for a few bucks though to help pay for the new one.

12-28-2006, 09:04 PM
So what is the minimum work needed to install a High Ratio Transfer case into a IIA with a welded in cross member?

Changing the subject just a tad:

What engine are you running and what is your vehicle weight?

Installing the high ratio transfercase is virtually identical to installing a 3.54 R&P in your vehicle for the high range. 2.25L engines can have a REAL hard time pushing those ratios. If you have a 2.25L engine you might consider 4.1 R&P gears or a Roverdrive instead.

I have an Ashcroft high ratio transfercase conversion in my Land Rover and love it. But my Land Rover is powered by a Ford 302 V8 that has more torque at idle than a 2.25 has at peak.

The choice is yours of course, but I suggest thinking twice about a high ratio transfercase unless you have a stronger than stock engine.

Just a suggestion,


12-29-2006, 11:34 AM
If you are taking out the seat base and taking the transmission apart it is a two day job, unless there are two of you who know what you are doing and are willing to work about 12+h!! Believe me, I have done it five times in the last year. All those nuts and bolts take ages to undo! Some of them longer than others if it is 30 y since they were last turned.
Why a transfer case? An overdrive offers the advantages of a high ratio t-case (28% vs 32% increase in roadspeed) without having to tear into the bowels of the transmission. It takes about 2 h to fit and provides sufficent speed for most in a Series truck that does not have upgraded brakes! Also the transfer case will leave you without power in a 2.25 l when you do come to inclines or drive into the wind, but an OD you can shift out of and have the original gearing.
I have used both Roverdrive and Fairey and both are good units if well maintained.

12-29-2006, 04:43 PM
I've been thinking about the same conversion.

I have a Toro overdrive unit now, and I'm not sure how many miles it has on it or whether the oil level has been maintained (it leaked like crazy when I got it, and was a bit low.) As near as I can tell, there are no parts available from Bearmach if a rebuild is necessary. I could replace it with a Fairey or Roverdrive, but the transfer case would also need to be gone through, as it leaks, and I don't know anything about its history either.

The argument for the the High Ratio T-case for me is that it might run quieter and cooler than the overdrive.

The power question is something I could use some advice on. I have a 2.5 L GM engine, which is supposed to have more hp, though I don't know at what RPM. Also don't know about the torque curve. This might be marginal power (or not) on a lightly loaded 109 with a High Ratio. Any opinions?

12-29-2006, 11:32 PM
I think the the hi ratio conversion would be ideal with the GM 2.5 conversion.

12-30-2006, 09:25 AM
Thankfully, you DO NOT have to remove the entire floor if all you want to remove is the transfer box. (Yes, even with a welded in cross member as I have)

It is a bit of a job, but I had the low range gear sieze onto the high range gear/shaft assembly (which meant I had full high-range, but no low range because both gears mesh and one spins on the other [normally] in low range as you all well know)

SO, here's the procedure:
1) drain the transfer box and remove the bottom pan and the O/D-PTO cover from the rear.
2) Remove the drive shafts, entire brake assembly from the back of the box, speedo cable, linkages etc... Everything attached to the outside of the transfer box as normal. The flat floor pieces MAY have to come out to help with this (and they may not).
3) place a floor jack under the gear box and lift it slightly
4) remove the mounts from the frame (and possibly from the transfer box as well- I'm not 100% on this as it has been a while) for clearance
5) and here's the real trick to it... Remove the fixing bolt/plate which holds the interediate shaft in the center of the transfer box. It slides out the back; then remove the intermediate gear itself to allow access to the "impossible" bolts which hold the transfer box to the gear box. (there is no critical shimming of this gear or tricky set-up, so even if you re-install the original, just replace all the parts as they were. AND if you DO re-use the old parts, check that shaft itself- if worn, replace it.)
6) remove the rest of the bolts (now that you can get to them all) and wrastle that sucker out... It goes rearward, and then must be rotated, tipped and then crash down on your chest, which should knock the wind out of you. If the wind is not knocked out of you, replace the unit and try again. Liberal use of profanity is encouraged, and may actually help the process...

I developed this technique out of desperation, and it worked gret for me. And my cross member is welded in place. Unless you need to do clutch work, there is no need to remove the transmission and seat box (or shifter, or clutch slave etc...).

I have personally done this, so it's no myth. This not "easy"; however it should be much less time than removing the floor and seat box, which, if it has not been removed recently, you will find can take the better part of a day on its own.

Obviously, re-instalation of the new box requires you to remove that intermediate gear assembly from the box to bolt it back in, so don't forget to order a new pan gasket (and PTO gasket if this is installed on the new box).

PS: replace the transmission output seal while it is staring you in the face. This is why your 'tranny is always lowon oil, and the transfer box is always over-filled with oil, which is why your parking brake gets soaked with oil, which is why the parking brake won't work.

Have fun!