Loading... Please wait...

Add to Wish List

Click the button below to add the Ashcroft Underdrive to your wish list.

You Recently Viewed...

Our Newsletter

Ashcroft Underdrive

  • Precision 'crawler' gear add-on to an LT230 transfer case
50.00 LBS
Calculated at checkout
* LT230 Serial Number (required) :

(Maximum Size: . Type: )

Sorry but this item is currently unavailable.

Please check back at a later stage.

This product is available for pre-order only

Product Description



The ultimate for hardcore Land Rover rock crawlers. Especially necessary when using large wheel and tire combinations, and doubly so when a manual transmission is installed.


This product has been brought back into production by popular demand. Ashcroft have made these in the past but stopped due to manufacturing and supply problems. These problems have now been overcome by re-engineering the unit so they can supply on an ongoing basis.

RoverWare do not generally stock these, as they are built to order. Typically they are available within 2-3 weeks.

For those that are not familiar with the unit, this is an additional reduction unit fitted to the LT 230, which bolts onto the Power Take Off (PTO) flange. By installing the underdrive, a four range transfer case is created. In addition to the stock high/low, an intermediate range and a super-low range are obtained. Typically the ratios could be 1.2/1.4/1.6 high, high x 2.69 intermediate, 3.32 stock low, 8.93 (2.69 x 3.32) super low. The intermediate range is a useful gear split between stock high and stock low. For a U.S. spec Discovery 1, Discovery 2, or Range Rover Classic (with LT230 retrofitted), some modification of the floor pan is necessary to fit the unit.

High and Low ratio will remain unchanged but when selected the underdrive will give an additional 2.69 reduction, this makes a low, low ratio of 8.93 (3.321 x 2.69). This gives the best of both worlds, high stays the same for road use, you have stock low for running about between sections and you have underdrive low for crawling over obstacles or winching.

The unit will only be supplied in the 26 tooth, suffix C onwards input gear format, if you have a 28 or 38 tooth input gear fitted you will also need to change the intermediate and the high range output gear (listed elsewhere).

Please note, although the underdrive will fit the Discovery LT230 transfer case it will foul the rear foot-well so the bodywork will have to be modified to clear.


Installation Information

In addition to the main unit, which has a 26 tooth input gear, you should receive : 6 x 10mm studs, nuts and washers 1 x stone guard 1 x LT230 input gear ‘bearing cone' 1x PTO gasket. Please note if this unit is to be used with a ZF auto gearbox you will need to use the longer splined coupling shaft (FTC5090), available separately if required.

Before fitting to the vehicle review the shifter possibilities, the shifter block is reversible i.e. it can be fitted to push/pull from the front or rear.

To change the set up, remove the yoke from the end of the selector rod, if fitted, then remove the seal housing (two M8 hex head to prevent damage to the seal as the selector rod is removed). Now remove the two detent screws, springs, balls. Next remove the top cover and loosen the 12mm clamping screw, it should now be possible to pull out the selector rod. Remove the block from the main body and assemble in other direction if required. The actual shift can be by cable or rod as preferred.

The underdrive is fitted to the LT230 at the PTO position and requires the removal of the input gear. Remove the PTO cover which will expose the bearing carrier, this is may be held in place by one or two countersunk screws.

Remove these screws then the bearing support plate, clean off any remaining gasket. It is now possible to remove the input gear, with the 1.4/1.6 ratio the gear will simply slide out, with the 1.2 ratio is will be necessary to rotate the intermediate gear to a position where the teeth on the middle and rear gear are in line.

Check the condition of the main shaft spline, do not fit the underdrive if it is worn/damaged and again confirm it is a 26 tooth gear. If it isn't the intermediate and high range output gears must be changed (order these separately). Split the underdrive, (note the main support plate to underdrive body has a gasket fitted be careful not to damage it) by removing the outer ring of 9 bolts remove the rear support plate and gearset. Note two holes are fitted with a short set screw, these are ‘jacking points’ use two 45mm long set screws, if necessary, to split the joint.

Put the rear plate and gear set on one side for now. You will note the selector detents are set ‘tight’ to reduce the possibility of the unit jumping out of gear!!!

You now have the output shaft and gear and the main casing to work with. Remove the PTO cover and bearing support plate from the LT230 and clean the joint face. Check the condition of the main shaft spline, a worn spline will cause premature wear on the underdrive input shaft.

Remove the handbrake drum and back plate.

Replace the inner input gear bearing cone using the new one supplied. Fit the 10mm studs into the LT230, using double nut, with the 15mm of thread into the 230. It would be advisable to remove the centre seat/plate if possible to facilitate access. The first step is to check the preload on the underdrive output shaft; it must be the same as the original LT230 input gear. Put the main box and transfer box in neutral and offer the shaft into the transfer case. Offer the underdrive main case to the transfer case, and fit the washer and nuts, (needs patience) tighten down evenly.

Double check that there is daylight between the end of the stud and the underdrive case, if not the stud has probably been fitted wrong and will prevent the underdrive from clamping down, causing leaks. Occasionally rotate the shaft, which can be gripped via the open end of the underdrive main case, to settle the bearings. If the shaft locks up stop tightening!

Note if fitting to an auto gearbox and the support plate assemble stops 10mm short, you probably have the wrong coupling shaft on the autobox, see earlier note (FTC 5090 must be used).

With the main gearbox and transfer box still in neutral rotate the underdrive output shaft, and check for end float and or excess pre-load, the pre-load was set on a test box with a gasket fitted but may vary from box to box. If it is necessary to reset the pre-load, change the shim behind the bearing cone. It was preset with gasket fitted and 2.5mm shim FTC 748 (thinner shim is FTC 746, thicker is FTC 750)

Reassemble the rear support plate and gear set to the main housing, using the gasket supplied plugging the ‘jacking’ holes with the short (25mm long) set screws. With the main assembly in place, but before re-fitting the handbrake drum, it is essential to grind/machine two flats, at 180deg, on the ridge at the front of the brake drum. (the second flat is to balance the drum). This will allow removal and refitting of the handbrake drum without disturbing the underdrive. Do not forget to fit the stone guard, essential to prevent small rocks falling into the natural trap between the drum and main casing. NOISE!!!

It is possible that this guard can vibrate at certain ‘harmonics’ sounding like a gear/bearing noise. If there is a noise issue remove the guard to check noise source. The selector is not supplied, we can advise you need a movement of 27mm of the selector rod from one range to the other.

The underdrive must be filled with same oil (EP 80/90) as the LT230 via the filler level plug, this is the higher of the two 3/8 square drive plugs. There is a small ‘well’ on the top lip of the main case where it enters the LT230, this catches oil from the LT230 and feeds it into the underdrive. be very careful not to block the feed with sealant. Oil will find its way out via the splined main shaft keeping the splines lubricated, or the max oil level hole. Once filled the underdrive will keep its own level, approx half full, feeding from the LT230.

Check the level after approx 50 miles to be sure the oil feed is working correctly.

When shifting ranges allow the vehicle to roll, slowly, to enable the drive dogs to engage, do not use excessive force on the lever to engage the gears. If using an auto-gearbox, you will have to get the car rolling then shift to neutral, to take the load off the drive dogs, then shift.


Write your own product review

Product Reviews

This product hasn't received any reviews yet. Be the first to review this product!