design - Land Rover section

 

 

Demystifying the Series Land Rover Transfercase

 

The common Series transfercase found in Series II and newer 88 and 109 Land Rovers  comes with two sets of gear ratios, the early ratios found in suffix A & B transfercases and the ratios found in the suffix C and newer boxes. The high range is the same on both the early and later transfercases but the low range gears in the early transfercase are slightly lower. The later transfercases were strengthened by increasing the diameter of the intermediate gear shaft and using larger diameter intermediate gear bearings.  This increased the diameter of the gear requiring a different low range tooth count. In addition to the stock transfercases the Ashcroft high ratio transfercase is commonly found. I will explain the differences as I know them.

The gears and intermediate gear bearings used in the suffix A and B transfercases were discontinued decades ago and parts are very hard to locate. Some people still seek these out because they provide slightly lower low range ratios than the later transfercases.

It should be noted that the stock Series high range gearing is a 15% underdrive This is because the Land Rover engineers decided that their engines were not strong enough to push the common 1:1 transfercase high range ratio under all common driving conditions. Overdrives available for the Series transfercase boost the gearing to a 28% overdrive. This provides a higher gear ratio that can selectively be used under favorable highway conditions plus a third gear ratio between stock 3rd and 4th gears which is very useful during mountain driving. An overdrive adds a lot of flexibility for different driving conditions. The Ashcroft high ratio transfercase permanently replaces the high range ratio from a 15% underdrive to a 32% overdrive. If your engine can push this gearing it provides higher highway speeds for a given engine RPM. Many people with stock engines have found the new fourth gear ratio to be too high for many driving conditions. The Ashcroft high ratio transfercase is very useful for Land Rovers that have more powerful engines installed. I recommend against installing one to go behind a stock Series Land Rover engine. It should be noted that because the Ashcroft intermediate gear is relocated an Ashcroft high ratio transfercase cannot be used with an overdrive. It is either one or the other.

If you want to calculate the overall gear ratio at the axle you will need the gear ratio of the specific transmission gear, the ratio of the transfercase, and the ratio of the ring and pinion gear (4.7:1).

Stock transfercase
high range

Fairey
overdrive

Romerdrive
overdrive

Ashcroft
high ratio

1.15:1

0.78:1

0.8:1

0.87:1

To save you a calculation, the overall ratio of the stock transfercase high range plus the overdrive is 0.9 for the Fairey/Superwich overdrive and 0.92:1 with a Roamerdrive

 

 

The Ashcroft high ratio transfercase  assembly consists of a reworked transfercase housing minus the studs plus 3 gears, a new gearbox main shaft output gear, intermediate gear, and high range output gear. You reuse your low range output gear. You build up the new transfercase using parts from your old transfercase. The Ashcroft modified transfercase housing  can be identified  by the sleeves in the housing that relocates the intermediate gear shaft to compensate for the new gears.

Ashcroft transfercase

The Ashcroft high ratio case can be identified by the sleeve at the intermittent gear shaft hole which relocates the shaft for the new gears. The stock C suffix and newer cases share the same intermediate gear shaft hole size as the Ashcroft case, 1.72 inches, while the early A & B cases have a 1.14 inch diameter hole for the intermediate gear shaft. The hole size & presence or absence of a sleeve is a quick way to identify which case is which.

 

 

Tooth count for each gear
  Gearbox mains haft output
gear
Intermediate
gear
High range output
gear
Low range output
gear
Early stock

31

44/22**

31

40

Late stock

31

44/25

27

36*

Ashcroft Hi-Ratio

31

44/22***

31

36*

* Stock gear gets reused in Ashcroft high ratio transfercase
** Diameter of suffix A & B shaft/bearing hole in gear: 1-5/8 inches
*** Diameter of Ashcroft high ratio shaft bearing hole: 2-1/4 inches

 

 

Land Rover transfercase gears
Transfercase gear set: 
Left - gearbox main shaft output gear inside transfercase
Middle - intermediate gear
Right - assembled output shaft with high and low range gears

 

Land Rover transfercase gears
It is important to note that the high range gear (left) is not splined and rotates continuously without turning the transfercase output gear shaft. It is only when the low range gear is moved forward to cover the external splines on the side of the high range gear that the high range gear can turn the output shaft. The vehicle needs to be stopped and the clutch in before the spines can match up. The picture shows the gears in the low range position.

 

High range power flow


Land Rover transfercase gear location for high range
This is the power flow through the transfercase when the low range output gear is moved forward to engage the splines on the high range gear.

 

Low range power flow

Land Rover transfercase low range power
This is the power flow through the gears in low range. Note that the high range output gear is always engaged with the intermediate gear but since it is not splined to the output shaft it spins freely.

NOTE - In the neutral shit position the low range gear is moved forward enough to no longer ride against the
low range gear on the intermediate shaft but not far enough forward to engage the side teeth
on the high range gear.

 

Front nose assembly

The main transfercase section contains all the gears and can shift between high range and low range, providing power to the rear axle assembly. The front nose assembly contains the front output shaft that provides power to the front axle assembly, the linkage shafts that shift the high and low range gears in the main transfercase and shifts the collar that engages 4WD.

 

Front Series transfercase assembly
Inside the front nose assembly with everything assembled ready to be attached to the rear case.

 

Seriestransfercase front output shaft
Shows the front output shaft and the front bearing it rides in.
The gear at the near end of the shaft is what the collar engages when it is pushed forward into the 4WD position.
There is a bronze bushing in the centre hole. The nose of the rear output shaft fits into this hole aligning both
front and rear shafts.
Since GL-5 attacks bronze, this is why you want to use GL-4 gear oil in the transfercase.

 

4WD collar
Collar that engages the front axle assembly for 4WD.
In 2WD the collar rides against the front of the main case, spinning on the rear output shaft splines,
but not touching the gear on the front output shaft. When you shift into 4WD the collar moves forward
to engage the gear on the front shaft while still attached to the rear main output shaft splines.  This locks the 2 shafts together.

 

Series transfercase hi-Lo shift rod
The internal shift rod that selects high and low range
There is a spring loaded plunger that rides against the shaft and locks into the detents to hold the rod in position.
If a transfercase pops out of gear it is usually a symptom that the spring is too weak or the wrong
spring was fitted during a gearbox rebuild.

 

Series transfercase 2WD-4WD shift rod
The internal 2WD-4WD shift rod with collar mounted.
When the red knob shift lever is in 2WD the collar is back against the front wall of the main case.
When the internal shift rod is pulled into the low range position this rod gets moved forward causing
the collar forward to engage the front shaft gear.

When the high range 4WD rod (yellow knob) is pushed down a pin is lifted in the short centre rod that shifts the double fork which pulls the collar forward into the 4wd position without puling the low range gear into the low range position (moves one rod without moving the other)

 

 

 

 

Note to self: When reassembling the nose section to the main transfercase make sure the bronze shift fork remains in place on the collar that fits over the front of the transfercase shaft. It can easily slip out. The result is not being able to engage the front wheel drive.

There is an excellent pictorial guide to rebuilding a Series III gearbox and transfercase on a French web site. It is in French but it has excellent step by step pictures that speak for themselves.

 

 

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© 1997, 2001, 2017 TeriAnn Wakeman. All rights reserved.