design - Land Rover section

 

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Drive train rebuild of Summer, 2007,
     or how a change can have unintended consequences

 

Did you ever have a project you did to improve things come back to bit you in the trail?  Or guess wrong but end up doing the right thing for the wrong reason?  I have.

Back in 1996, with the help of a friend I converted my 109 from a Rover Rear axle to a Salisbury (Dana 60 built by Land Rover under license).  The salisbury is a big beastie that is both longer and sits lower than the Land Rover rear axle.  But the axles are a lot stronger and I had recently broken my sixth rear 10 spline Land Rover axle.  Salisbury's are standard fitment to Series III 109s so a stock Series III rear propshaft is just the right length for fitting between the transfer case and the longer salisbury.  To compensate for the increased depth of the Salisbury I fitted military 109 long shackles and taller tyres.  Everything was bolt on and worked fine.  What I forgot to note is the the increase in ride height meant the transfer case and differential sat slightly farther apart so that at rest both the front and rear propshaft slip joints were a little more extended than stock.

In 1998 I replaced my leaf springs. Before they went on I rebuilt the rear set with UHMW (ultra-high molecular weight) Polyethylene plastic sheets between each leaf.  This plastic provides a low friction surface, similar to Teflon tape, but with a much higher abrasion and puncture resistance.  The goal was to eliminate leaf to leaf friction so that the springs were freer to move with the terrain. This worked quite well softening the ride and allowing for greater spring articulation.  Since everything was apart I went ahead and replaced the poor condition stock frame bushings and new spring bushings with poly bushings. Poly bushings allow the shackles to move more freely and respond better to spring movements.  I didn't have enough plastic to convert the front springs so decided to postpone  the front spring plastic upgrade.

One thing I didn't know at the time is that Series Land Rovers use a short prop shaft slip joint.   The stock suspension doesn't articulate well so longer slip joints are not needed and who knows, maybe the factory saved a a little money by specifying a short slip joint.  Or maybe some factory engineer ran the numbers and decided that was the length needed for a stock Series Land rover.  I didn't think about slip joint travel length when I modified my springs to articulate better and wouldn't be surprised if people who convert to parabolic springs don't think about it either.   This might be a problem only when both wheels on an axle are at or near full lower articulation at the same time. Not a condition Land Rovers driven on the street or on mild trails encounter.

In 1999 Timm Cooper converted my Land Rover to a V8.  The transfercase stayed in the same front to rear location but moved to the right to allow the engine to be centered within the frame. The engine mounts were raised a little to allow the Ford oil pan more clearance over the front differential.  The transfer case mounts stayed in the stock vertical location.   This slightly decreased the angles on the rear prop shaft and increased the angle on the front, slightly increasing the distance between the front prop shaft mounting flanges. Timm decided that a slightly longer front propshaft was needed to re-center the slip joint travel. We took my front prop shaft to a specialist along with the static distance between the mounting flanges for a slip joint replacement. At that time I specified that the next longer slip joint be used.  Since the rear prop shaft fitted OK, and was only 3 years old no one gave a thought to how far the slip joint was extended.

I soon noticed a clicking sound from the front when I was off roading in 4WD.  I traced the click to the front U joints binding and took a die grinder to them to increase clearances. I should have ordered higher angle yolks as well as a longer slip joint. on the front prop shaft.

During 2001 I finally got around to rebuilding the front leaf springs with UHMW plastic sheets so the front springs would have increased articulation. I also had taller 33.4" diameter tyres installed.  I noticed that the larger diameter tyres cleaned off the dirt on the back of my built in water tank during my more technical off road excursions. The water tank sits in front of the left rear wheel.   For some unknown reason, Land Rover mounted the axle an inch and a half forward of the centre of the body rear wheel arch.  I decided to solve the rubbing problem by moving the rear axle assembly rearwards 1-1/2 inches.  It centres the wheel in the wheel arch providing additional clearance and decreases rear body overhang.  I accomplished this by using a locating pin offset plate between the leaf springs and the axle housing.  The spring pack has a locating pin and the axle housing has a hole for the pin.  This keeps the axle assembly from moving about on the springs.  An offset plate has a hole for the leaf spring pin and a pin located elsewhere for the axle housing.   I installed the plates one at a time by removing the U bolts, rising the body slightly, installing the offset plate, rolling the axle housing back a little, lowering the body and reinstalling the U bolts.  I didn't need to remove the rear propshaft to accomplish this. 

I had extended the distance between the rear prop shaft mounting flanges when I installed longer shackles then again when I moved the rear axle assembly 1-1/2 inches to the rear.  I just forgot to account for how any change can adversely affect other things.  Slip joints make prop shafts adjustable length items, right?  I forgot the Land Rover slip joint was short.  In reality I have used up virtually all the rear prop shaft's slip joint extension with the vehicle sitting static.

During 2002 I was climbing in loose rock, loosing traction and the vehicle started bouncing up and down on the springs.  The nut holding the prop shaft flange to the pinion gear stripped off leaving my front propshaft end on the ground.   After I got home I tried a simple fix by replacing the stripped pinion nut.When I tried to drive in four wheel drive I quickly discovered that the front ring gear had a couple broken teeth .   I replaced the ring & pinion gears.  I also noticed a shiny ring around the front prop shaft just below the edge of the bellhousing.  The increased front articulation from eliminating leaf to leaf friction allowed the front propshaft to strike the bellhousing at full downward articulation and possibly exceeded the prop shaft slip joint movement at full lower articulation when the vehicle was bouncing on the springs.  I decided to address the body hopping on the springs in a future shock upgrade and  meanwhile try not to get into a situation where the body bounces causing the springs to flex between full upward and full downward articulation.  A future shock upgrade would include moving the shock mounts farther apart and installing stiffer, longer shocks.  Possibly dual shocks since the sprung weight is high.

When the ring and pinion was replaced, I discovered a twisted front axle that was close to breaking and replaced it. .  I had broken a front axle previously in 1998 while off roading on the Border to Border marathon run between Canada and Mexico.  So this was front axle #2.    I decided to put 24 spline front axles on my future upgrade list.  This upgrade was stalled because of the high cost of 24 spline front axles. I just stopped driving the more technical trails until I could get the shocks upgraded and figure how to handle the front prop shaft issues.

In 2005 I found myself on a loose dirt downhill slope and needed to back up.  The vehicle started to bounce on the springs again.  I minimized the bounce as much as I could to get out but noticed a new sound in four wheel drive.  I concluded that I had damaged the front ring and pinion gears again, put the vehicle into 2 wheel drive and unlocked the front hubs.  I decided to just drive in  two wheel drive until I could afford a diff and 24 spline upgrade.  This of course kept me off everything except pavement and well maintained trails.  This turns out to have been a good move, but for the wrong reason.

During the summer of 2007 I was given an almost new pair of used SeriesTrek 24 spline front axles making my front end upgrade affordable.  I commissioned Great Basin Rovers to build me a differential with a 24 spline Trutrac carrier and stronger than stock 4.75:1 ring and pinion gears.  I also ordered a custom front prop shaft that had a smaller diameter shaft where it passes by the bell housing, longer slip joint and high angle U joints.  Linus Tremain came by to help and do the heavy lifting in getting one diff out and the other in.  While dropping the front prop shaft he noticed that the transfercase was free to wiggle when the front prop shaft was wiggled.  We also found that the front ring and pinion gears were in good shape and not damaged as I had believed. Instead the transfer case had come loose from the gearbox!  Or more precisely the adapter plate that goes between the Borg Warner T-18 gearbox and the Series Land Rover transfer case came loose.  In four wheel drive the loose transfer case was causing symptoms that were like the ones I had with broken front ring and pinion gears. 

With the front axle upgrade completed the project moved to the middle of the vehicle and I removed the transfer case to find out why the adapter plate was loose on the gearbox.  As it turns out, all four mounting bolts had worked themselves back out.  I also discovered that the movement had destroyed the rear output shaft bearing, the thrust washers against which the bearing rested and damaged the rear of the main output shaft.  I wasn't sure why the mounting bolts backed out.  The hardened allan head bolts and the threads in the gearbox were fine.  I bolted the adaptor back in using loctite and likely more torque.  Before I used an 'L' shaped allan wrench to tighten them down.  This time I bought an allan head socket and used a socket wrench for additional torque.  I had a hard steel sleeve made up to repair the main output shaft where it rides against the rear bearing  and replaced the rear bearing.  When I went to replace the transfercase intermediate  gear I discovered a damaged thrust washer and replaced it.  I also went ahead and replaced a worn emergency brake expander unit, the rear output oil seal and  number of BSF nuts that got rounded off from using the wrong size wrenches.   Of course I assumed everything was in good reuseable condition and the project got stopped each time I discovered an out of spec part.  I really should have inspected everything before I started reassembly.  It would have saved me a lot of time.

Font end rebuilt, transfer case and adapter reassembled, new improved front prop shaft installed, all I needed to do was install the rear propshaft and ...

The rear prop shaft barely reached the rear diff at full extension.  Whenever rear downward articulation occurred the rear propshaft would pull on the transfer case with the force generated by several hundred pounds of moving salisbury axle assembly and those big 33.3 inch dia tyres.  No wonder the adaptor plate bolts worked themselves loose.  What I thought was a damaged front ring and pinion gear ended up being a too short rear propshaft pulling on everything!  All because I didn't think to measure the flange to flange distance when I did something to affect it.  And I've known since 1999 that Land rover slip joints are short.  It just didn't occur to me that I had run out of slip joint movement with the vehicle stationary.  I ordered an new custom rear prop shaft from Great Basin Rovers. This one the correct length got my rear flange to flange distance AND with a long slip joint. 

The lesson in this story is that any change made to your vehicle affects other parts of the vehicle, often in unanticipated negative ways.  It is important to think beyond the immediate scope of a project and try to understand how a change will affect each related part.  Increased articulation affects propshaft clearances, puts addition strain on shocks and increased extension of the propshaft slip joint.  Something that would be good for people converting to Parabolic springs to think about.   Moving prop shaft mounting flanges farther apart reduces the amount a prop shaft slip joint can expand before the diff and transfer case are pulling against one another. 

Of well, when all was said and done I did end up with a new 24 spline front axle conversion, correct length front and rear propshafts and a resealed partially rebuilt transfercase.   But I could have avoided 2/3rds the work and 3/4 the time if I had just remembered that moving the rear axle affects propshaft length years earlier.

Mid 2009 addendum:  Both the new propshafts that Great Basin Rovers sold me have twisted and need replacing 2 years from new.  I had Rover propshafts behind my 302 for the previous 7 years without any twisting.  And no, I have not done anything during the last 2 years that I hadn't been doing all along.  In fact 2009 has seen only one trip because of a lack of funds for fuel.

 

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