- The advice given here
is derived from the author's own experience of a failed transfer
box which was stripped and rebuilt. This is how the author defines
looking after what is not the strongest transfer box in the market.
- No responsibility
is implied or accepted for this advice, but it does continue to
serve the author well.
Never apply the handbrake while driving the
- Under normal driving conditions the transfer
box is engaged, except while and only when the brakes are applied
over 16 mph.
- If the handbrake is applied, without the
foot brake, the stress applied to the viscous coupling and txb
clutch is anything up to enormous.
- In an emergency situation, try to have the
presence of mind to apply the foot brake as well as the handbrake
(disengages the txb), failing that pray you get out of the emergency
with or without a working txb.
- Don't start & drive the car immediately
- If the accumulator has lost any of it's pressure,
either by operation of the brake pedal with the ignition on or,
the car has been standing for more than a day, starting the engine
and immediately driving off can cause TXB clutch slippage, with
resultant wear. It is always good practise to start the engine
and wait 3-5 seconds on every occasion and then drive off. If
the accumulator is below pressure it is possible to detect a slight
increase in the tick over revs when the recharging is complete.
Then it is OK to go.
- Don't drive the car like a maniac.
- The txb will get you in the end.
- Don't run a lowered car without adjusting
the camber & toe angles
- Lowering the car without adjusting the camber
angles, effectively reduces the diameter of the rear wheels. This
is the same as running with more than 2mm tread depth difference
between the front & rear wheels. The result will be a damaged
txb (overheating) quite apart from the accelerated wear of the
tyres (inside edges). Camber bush kits are available
and the camber should be restored to GM's stated values.
- Don't fit the spare wheel without pulling fuse 19
- If you fit the spare wheel, as a roadside
emergency, you must remove fuse 19 to disable the transfer box.
In addition, the handbook tells you to not drive faster than 50
MPH. Fitting a wheel that is not part of the set should only be
considered as an emergency measure. The wear pattern will almost
certainly be different, which is the same as running the car with
more than 2mm tread difference between the front and rear wheels.
Failure to comply will almost certainly damage the txb. (See 'Tyres'
- Always fit tyres as a set of four
- It is essential to keep all four tyres very
close to the same diameter (within 2mm tread depth or 15mm running
circumference front to back) and with the same characteristics.
This means you change the whole set. If one tyre becomes defective
e.g. a blow out or damage, then the set of
four must be changed - (see the vehicle
handbook). They must also be of the same make and rating.
- Failure to keep all four tyres the same will strain the mechanics
of the txb, The txb clutch is put under additional strain to slip
and wear the lining material or, in extreme cases, to cause the
lining material to break up. (It's glued to the metal plates).
At the same time the viscous coupling is also under additional
strain, having to continuously respond to differences in diameter,
front to back. This will be a constant force causing the build
up of heat, which when hot enough will cause the txb to go over
temperature, and in extreme cases it all happens too quickly and
the box can go into 'meltdown'.
- A good indicator that all is far from well
is mysterious 'thumps' at certain times when driving.
- Txb £2500 off
the shelf - set of 'Z' rated tyres £300 - £500. QED
- Change wheels front to back every 1500 miles.
- It is quite reasonable to expect the front
and rear wheel sets to wear at different rates and in different
ways. The rear tyres tend to wear on the inside edge, easily missed
when conducting 'kick and look at what you can see' approach.
- The higher rated tyres are also directional.
(Arrow on the casing). Change the wheels front to back to maintain
the rotational requirements.
- BE RELIGIOUS about the wheel changing, it
is essential to maintain similar wear front to back (within 2mm).
Failure to achieve this will cause the txb to overheat with sometimes
- It is also reasonable to change the directional tyres on the
rims to even out the wear from the driven nearside tyres. ie.
Have the nearside tyres swopped out to the offside rims thus maintaining
- If the tyres do not have a directional arrow then complete wheels
can be changed from the nearside to offside.
- Regularly check tyre pressures
- Driving round on unevenly inflated tyres has
the same effect and accelerates wear.
|TRANSFER BOX OIL
- Change the txb oil annually
- GM recommend, for those vehicles using the synthetic oil, that
it is only necessary to top up the oil as required.
- The author says a new txb costs £2500 off the shelf,
£800 rebuilt (with second hand parts) or up to £500
off the shelf second hand.
- 600 ml of synthetic oil costs about £7 - QED.
- In addition, it gives the user a chance to check what's in the
old oil. E.g. dirt, bits of txb clutch lining, metal swarf etc.
- The early boxes apparently used DEXTRON II ATF fluid. - Its
principally the same box - always use the synthetic oil.
- The author always uses the GM oil just in case something goes
wrong and GM became involved. (Good Luck!)
- If the box seizes in service, it will usually be because of
bearing failure or a gear tooth breaking. Either way a not too
big a piece of steel entering the gear train will, in extreme
cases, literally split the txb casing. Another good reason for
changing the oil regularly and closely inspecting what comes out,
if only to spot early signs of potential failure.
|BASIC FUNCTIONAL CHECK
- This is quite a good test, the difficulty
is that you do not necessarily know what a good box should sound
like when it is forced to disengage - 'the thump'. If you follow
the guidance in the workshop manual, and are only lightly accelerating
out of the corner the thump is heavy.
- The first time this happened to the author,
because the temperature sensor was intermittent, he thought he
had dropped a rear wheel into a manhole type hole with the lid
say, 3" - 5" below the surface, but without the body
- Change the ACCUMULATOR at 54k miles or
- If the accumulator bulb does not have a white
ring, clearly visible, then change the bulb immediately,
unless it is a Cav16 bulb with a plastic label attached. Original
accumulators without the markings are faulty and were a recall
item, which has now time expired. Accumulators with white dots
preceded the white ring model and are very likely time expired
and should also be changed.
- The accumulator bulb must be changed every 54k miles or six
years, which ever comes first. If you do not know the history
of your vehicle then follow the procedure in the workshop manual
for 'bleeding the hydraulic system' and check how many
'whooshes' its takes to empty the accumulator. GM calls it a pressure
vessel and it costs £99+vat. The instructions say the brake
pedal should be applied at least 25 times to empty the accumulator,
much less and the author recommends a change. It is still £116
against a potential £2500, or £800 etc etc etc.
- Experience with a new Accumulator has shown
that a cold engine run for a few minutes should achieve 25 whooshes
but the same accumulator after a run, and with a hot engine, will
return in excess of 30 whooshes.
- The Accumulator'
change procedure is available from the main menu above.
|POWER STEERING OIL
- Periodically and regularly check the Power
Steering Oil reservoir level
- This is a service requirement and must not
be overlooked. The oil is required to operate the transfer box,
as well as the steering. If the level falls too low air can enter
the system, requiring it to be bled, and/or the txb ceases to
function properly. The procedure for checking is in the workshop
- If the Power Steering Oil level suddenly
drops, investigate immediately.
- If the steering reservoir oil level drops
the power steering pump may start to whine and gurgle with the
engine running. Using the workshop manual procedure, check the
oil level in the reservoir. If it has dropped, say out of sight,
then follow the procedure to bleed and fill/top up the system.
- At the same time withdraw the txb mounting
bolt, used for oil level checking in the txb and check for the
box being over filled. If it is over filled, probably by the amount
you have used to top up the system then you have almost certainly
got terminal 'pressure plate (or ram) seal' failure. It is now
a case of removing fuse 19 to disable the system. The car can
still be driven, but it will be without 4WD and NO fluid pressure
is applied to the txb pressure plate resulting in further loss
of steering oil. (This should be considered an emergency procedure
because over a period of time the wrong type of tyre wear will
- Do carry a bottle of DEXTRON II in the
boot for such a failure away from base.
- The total and immediate failure of the seal
will result in a dashboard 4x4 tell tale and the loss of fluid.
Oil will be expelled from the txb breather/filler, behind the
water header tank. The roadside cure is the same, as above, but
without the txb oil level check, you know it is overfilled. (Fuse
19 must be removed to maintain power steering and the level replenished).
|January 15, 2004