How to identify , drive and test any  4wd system?            

First, read the wiki,  see all those warnings for pavement.
Part time 4WD means full time in dirt, but part time on pavement , the word "part" means on ice/snow packed roads.
Part time 4WD, does not work, on dry pavement nor on just rain wet pavement. (it will wind up and cause damage.)
(rare exceptions exist on some Jeeps with a center slip clutch)

  1. Suzuki AWD from 2004 and newer ,offered the optional, "full time" system. ( except in 4-LOW)
  2. All Suzuki 1968 to 2003 are only PART TIME 4WD.  Just like many  Jeeps 1984 to 1995
  3. Why are my too big tires, giving me speeding tickets?
  4. What is my Sidekick® vehicle speed at 3000 RPM's , calc.'s and tables.
  5. End axle locking hubs?
  6. How to test the 1999 up front axle locker air pump and test it. or the same device on old Jeeps 84-95.
  7. How to shift in to 4wd safely (pre 2004)

1968 to 2003: Suzuki's: The Part time system.
Read the manual that came  with you new car, the operators guide (seen in the glove box it 1...)
The book, tells you ,what system you have and how to use it.
 1968 Jimny , Samurai , Sidekicks, Trackers and Sun Runners up through year 2003 are part time 4WD.
Factiod 1: ;
If the car came with no LSD  closed  opted axles (called OPEN axles), it is normal for the tires with the least traction  ,ot just spin  doing nothing on slippery ground.

The classic JEEP page: "STOP--- DRIVING ON ICE FREE  PAVEMENT, IN Part-time 4WD.  holds true on early Suzuki's

Suzuki had to make a TSB (tech.service bulletin) just to solve bind/wind up , and  recovery, (annotated)
Doing these  invalid actions: causes:
  • Can't shift in or out of 4WD? (or the main transmission will act up too)
  • Tires are Dragging, and steering feels very odd , binding up, like a  monster is attacking my front tires?
  • Horrid sounds from under car body !! (parts crying in pain !)
If this happens get one tire on ICE , or dirt/sand,gravel,grass and shift to 2H (edge over to side of road and shift out of 4wd)
Avoid sharp  turns, edge over easy, to avoid bindup, damage.

The Suzuki solution is here 2004+  Grand Vitara's .
I added Jeep to this mix, because there are zillions of Jeeps , and photos and drawings, and facts vastly more than any Suzuki.
Some cars, not Suzuki ! before 2004 Have special parts. to solve this issue.
The Jeep Select-Trac center diff looks like this.

(or a special  slip clutch seen some older Jeeps) See Jeep clutch here?

4WD  means 2 things,  the lever is in 4WD  and  the axle  locking devices up front, are locked, (auto locks/manual locks or motor actuator locked)
If the front axles is not locked, you will not wind up. But that is not 4wd, is it ? nop !
$1200 - 1600 new xfr. case.  The car is in great danger of skids in this condition, a great danger to you and others.

This was a Jeep Transfer case,  Same happens on Suzuki's
Two common exceptions for JEEP are:

(Select-Trac)- NV 242
Borg Warner QuadraTrac:  Some JEEPs, (RTM) can use low range 4LO to drive on dry pavement, slowly.   (dry means , no ice and hard pavement)
There are
many full time Jeep systems,  I'm not documenting them, but you can read it any time you want on wiki. (best place it is)

Suzuki Exceptions: Just one.
35 years later (making 4wd cars) Suzuki introduces, AWD; 2004 to Vitara, as an  OPTION!
Offered in single mode or 4 mode AWD, see here for how that works.
With single mode AWD, all of the wheels are driven all of the time, there is no low range and no center diff lock.
With four mode AWD, all of the wheels are driven all of the time ,EXCEPT when neutral is selected.
The four modes are H (high range), 4H (high range with locked center diff), 4L (Low range with locked center diff) & N (Neutral)
The four mode will shift in to 4H as needed and out ,to save fuel, on some models. (see link above for those rules)

Suzuki Grand Vitara/Escudo
-full-time 4WD using limited-slip center differential, off-road 4WD with selectable center differential lock and low range transfer case 4 mode (4h, 4h lock, 4l n), traction control and electronic stability control

Suzuki offered as an option AWD for Grand Vitara's starting, in 2004 (XL7 too)  In some cases 2006 is starting date.
Some Suzuki AWD you can not use lock on dry pavement, do read the operators guide carefully.  (dry means no ICE)

The 4H mode works on all surfaces. RTM, read the operators guide in the glove box with due care.

Old  (pre 2004)Suzuki's do not have this dial on the dash, nor the AWD transmission parts that make that work.

These drawings by Suzuki is not all that clear.  but the full text in the operators manual is clear.

end AWD:

Back to Jeeps better documentation, on subject:
I will now quote my 2008 Jeep Wrangler operators guide. Page 278 1st edition, USA spec car.    PART TIME SYSTEM IT IS.

"2WD is intended to be driven on normal street and highway conditions, such as HARD surfaced roads."
"4H & 4L positions are intended for loose slippery road surfaces only and not intended for normal driving"  (They assume paved streets are normal.)
"Driving in 4H or 4L positions on hard surfaces roads, will cause, increased tire wear, and damage to the drive line components." 
Unqual tire sizes, will do the same damage. "tire circumference mismatched"
Last: "do not attmpet to make a shift,  while only the front  or rear wheels are spinning" No transfer case synchronizer exists and damage will result." 
(kill the gear dogs, you will)
Virtual, LSD, Limited Slip Differenetial axles missing that option.
One more trick, say car has no LSD axle options ? so, if one/two tires slip ?, just drag the foot brakes, and presto, Free  LSD.   Braking will cause all 4 wheels to pull as one.  Try it on ice or mud,etc.
LSD is not hippy drugs, it's Limited Slip Differentials.

My 2008 Jeep JK wranger uses ABS brake controls, to do my drag brake trick above, automatically , it's called virtural LSD.
What it does in software, is drag the tire that slips (ABS), forcing torque to the non slipping tires. (like magic)
End how to use 4WD:

Manual hubs (locks seen  on both front wheels)
The Number 1 failure of  4wd is not cleaning and lubing the front locking hubs.
CLEANING THEM, those locking HUBS.

I will not try to cover all cars, 1968 to 2004 here (Suzuki or Jeep) Just 1989-98 first.
The dash light in 4wd means little to nothing, I totally ignore the lamp, I only pay attention to 4WD actually working.

Manual locking Hubs:
  (I will never attempt to test autolocking hubs , I don't know how, other than driving on ice and watching tire actions)
 (OEM axles , no after market LSD or closed axle modifications)  OEM is an OPEN AXLE. Part time system.
(Engine OFF, parked , rear wheels chocked and hand brake on. )
Transmission is in park or 5th gear (A/T or M/T stick transmission)
1: Put XFR case in 4wd , , this locks the front axle pinion  to tranny and the  engine , which shunts the rotational energy. (ergo can't' spin front prop shaft  front tires off ground )
2: Lock both hubs left and right side  ,see dial turn to "Lock".  The system is now locked, to the engine and the rear wheels. (and shunted by the dead engine)
2a: If the hub dial won't turn or all the way, then  the lockers are toast. (DOG corrosion most likely, but can also break up inside) (inspection time , solves this riddle)
3: Jack up the one left wheel, off ground. (not much ,just clear of mother earth.)
4: With both  hands, force left wheel to spin: (use plenty of force, you can't hurt it , in both directions try.) 
    if the tire spins round and round this is FAILURE.  (more later on bad diagnosis below)
    if it is locked , all  is good.  ( test is done, test offroad for 4wd proper actions, keep in mind the loosest tire in 4wd spins, Unlike LSD)
Was that not EASY?  No guessing at all.
Failure modes, for above: (NO LSD here)
There are 3 shafts to watch at #4 above.  left and right axles and front prop shaft.
The wheels are locked to the and the CV' axles must not turn (boht) and the front prop shaft must not turn. (3 shafts, that can spin and shouldn't !)
1 Left CV, 2 Right CV, 3 Front Prop shaft.
These no spin devices WILL TWITCH  CCW to CW a tad , at  the wheel, (by the fact of a little play in the system, mostly in the XFR case. )
FAIL ,  ( if left wheel spins and CV left does not ?, then left hub locker, is bad, (fails to LOCK).  [there can be more than one failure]
FAIL,  if left wheel spins and the right CV, spins in the opposite rotational direction, then the  right locker is failing. (front prop shaft is frozen, not moving now)
FAIL, if left wheel spins and  you  see  the front prop shaft spin, then XFR case, is at fault.  (only the left CV is spinning and front prop spins, in this case)
FAIL, the left axle spins, and the prop shaft is seen to spin , this is Transfer case failure. (or transmission not in park or 5th gear)
5: Drop the left tire to the ground.
6 :Repeat this on the right front.  ( this is not really needed, as you already know what is wrong, but is good practice!)
If both sides pass, you have working  4wd.  ( I test both sides just to see if there is excessive play or funny sounds from CV)

Now test it on loose ground,soil,sand,ice, snow. gravel, but never dry or only wet pavement in 4WD.

If you clean your hubs ,almost all 99.% of your 4WD locking problems will go away.

99% of all fails this forum this topic are, locking hub fails. (up to 1998)
Other posts are ,(clicking sounds from front axle in 4wd. Super common on all Auto locking hubs, I call them Lock and pray hubs.
(they too can be made to work, but do take TLC)
It's a 7.5k-15K mile inspection. in the FSM and the operators guide.

1999 and newer Suzuki (Vitara's and Trackers) ( I have an 04) PART TIME ONLY: All this is in the FSM book.
This uses a front locking device in the front center of the axles  and a pump actuator , my Jeep has vacuum actuator, they work near the same, part time.
Seen here.
If the pump can NOT pump air, it's bad or the hoses leak or the vent  line is plugged.
If pump tests  pass, then the  lock inside the front axle is bad. (remove carrier and test it)
Here is the 2004 test data for mine,:
Run test:
Engage 4wd key on, the pump runs. if not, the switch feeding this pump  is bad or fuse is blown,. (check for 12vdc here at the pump)
or if pump is silent with 12vdc you can also....
Hot wire the pump , if silent it's dead. New pump time!
LOCK test:
Using shop air, put 4.25 PSI  on the axle actuator port  at end of #29 (axle side hose off)  (hose 13/14 right drawing below)
Over 28 PSI is damage here, so do not use full shop air use a paint gun air regulator to keep pressure blow 10 PSI.
 At 4.25PSI the axle locks (tire off ground turn tests by hand) (open axles test with one front tire on ground for lockup, with LSD axles, test with both front tires off ground and 2 persons working tires by hand)

Pump  test:
To test the pump, use a 12vdc battery to hot wire  pump jack. pins 1 and 2.
Connent a pressure gauge 10  psi, on outlet. #30 below. Directly
Unplug pump electrical connector and hot wire pins 1 and 2, (3 is  switch)
The guage must read  (spec) 4.25PSI to 6.4 PSI for a good pump if not? th pump is bad or ( the  vent 27 clogged,  unplug  hose 27, pressure ok now, yes, then the hose  is clogged up.)
If the pump fails now, by self, that is hoses removed, it's  a bad pump.
Keep in mind , pumps fail lots of ways, (dead, leaks or is weak , or jams up)
If  all  pump test , run test and Lock test pass, then the 4wd is working. (must be loss of 12vdc to pump)
Keep in mind the pump may do ok in a shunt test, gauge to pump directly, but connected to the axle,  it fails ?(that is the part #18 (right drawing) in the axle bad, it leaks.)

1984 to 1995 Jeeps  Command Trac models (part time) Seen on YJ Wrangler  jeeps and Comanche PU.  f
On other jeeps, the disconnect happens only in the transfer case.
Many have this vacuum servo below (called a motor) , that is very much  like the above pressure system, but is vacuum  on Jeeps.
On Jeeps it has a  vacuum servo and as such tests just like all such devices. 
Do  a vacuum hand tool leak down test on port 7,  it must hold say 15"(spec) inches vacuum for 1minute, if not?, the diaphragm is cracked. (bad servo)
Apply vacuum by hand at 15"HG and the rod most move and select  (engage) the DIFF. LOCK inside.
Keep in mind , servo actuators  fail lots of ways, (dead, leaks or is weak , or jams up) or the switch #5 is fibbing. (bad)
If the source vacuum is good to nipple 7 (4wd normal)  and the servo does it's job ,moving #4, and 4wd live action (tires to dirt) is still dead?,  then the problem is inside the axle.
if the diapharm leaks, air, a vacuum test with a Tee fitting at #7 will fail, do to this huge leak of air,
Front wheels off ground, in 4wd, engine stopped.
The inboard nipple removed, apply vaccum (fsm words) to this port, 15'"HG.vacuum.
Turn the left wheel by hand the axles must spin or the motor below is bad, or the internals jammed inside axle, (forks etc)
if the Axle locks the source vacuum must be bad, running.
The vacuum switch runs the motor in push pull style.  Both ports below most work pulling in for 4wd or out for 2wd.
Remove motor below, and see if #4 shaft moves freely , if not motor is bad.  if motor is  good , the axle forks are jammed.

end axle tests:

How to correct SPEEDO due to  having larger tires, than stock.

1994 stock is: P205/75R15  M+S   23 psi front and rear.  USA Tracker GM spec. (for sure not EU spec or other countries !)
To get accurate answers you need to find the:

True rolling radius ! 

Effect by , speed, pressure and maker of tire.  So only the maker of the tire can answer accurately.

But you could use this chart.

205 swapped for 235
you are going 69.25 mph , when speedo shows 65.  ( get a GPS and log speed )
45.64 less revolutions per mile !
6.5% error

85.16" versas 90.72 inches, that tire rolls  5.56 inches farther each and every revolution.

To get real accurate data, go to both the new and old tire manufacture and ask for the Rolling Radius.   ( or do Circumference differences in % between 2 tires)
I'm sure as heck not going to look all them up.


or answer questions to the modeling software .

81,000 HITS ON GOOGLE.  ( GOOGLE IS YOUR FRIEND ) Search "Part time 4WD"


My cheap OEM solution for mileage corrections:

Unsafe at any speed?  LOL !

Tires Size table1: metrics

Tires by BFG

Speed and RPM ?
Surely,  using a GPS to measure speed errors, is far more accurate than my calculations,  this page is only to show the scale of those errors.
Last but not least. my RPM / MPH Speed chart (table) Tire data from GoodYear. USA vehicles only.  Tire pressure 23psi  (some year show 26 on drivers door)
RPM 3000: top gear, clutch lock up.  USA spec tires. USA spec. kick
All information below assumes your Tacho reads accurately and the tires are not bald.  The below represents ,new tires (sizes), & a stock car.
Nor does it attempt to compensate for over 60mph centrifugal effects of  tire circumference changes.
That all 4 tires are the same size. All the below is useless for GPS Speed gage equipped cars.  (in a perfect world and noise free world)
Our stock tire is P205-75-R15   with 27.1" Diameter !
Stock tires can vary by style , passenger tire and off road types. same size. but.... 744/rev/mile  is the rule here.
EG: 27.1 Diameter times Pi  π  (3.14  {3.14159265}  ) is 85.1 circumference.
So, Tire rev per mile , is   5280 feet times 12" =  63360 inches per/ mile divided by 85.1" and you get 744 rev / mile .  (not hard math at all)   not moving.
I see many companies list 744.   (and will be less, as it wears down)  
My stock speedo (5sp 8v ) is tuned for 760/rev/per/mile , This is stamped on the front of speedo case  ! lens off !. 

The more you lower Rev/mile , the lower the speedo reads,  falsely:  
Chart 1:  (factory stock RPMs and speeds with Stock speedo and speedo gear sets)
This chart shows all gear ratio's in the car , all years 89-98 and all speeds at 3000 engine RPM.  All speeds not corrected for squish factor.
1.6L only  and 1.8L red, uses 16v OD
Tire size
of tire. inches
Axle Ratio
 OD Ratio
16v / 8v
Total Ratio
top gear.
MPH @3k
4.1 / 4.41
OD is taller on 16v and @ .80 5th gear OD ratio
P205-75-R15 85.1
0.73 3.74
16v usually has this axle with a 4speed tranny.
P205-75-R15 85.1
4.30 /4.62
no OD.   4.62 8v  and 4.3 16v  (8v less power ,higher ratio)
As you can see the 3speed 8v valve motor spins the fasted and is even worse if the TCC fails. (slips).
My table does not account for squish factor or the high speed centrifigule expansion factor, but does show the vast differenences in speedo readings clearly.

Some Tires grow in diameter, as you drive faster than 60MPH ( centrifugal forces on the tire, can do that, on cheaper tires)
all Circumferences shown here are not with squish factor (  about 600 lbs on each tire)  Circum's. are acutally a tad less.  As are Rev./mile.

Chart 2  (  based on 5speed transmission and 8 valve engine witih OD ratio of .86)   Speedo tuned to 760 Rev/miles (stricker on the front of it)
 This is  the uncorrected error in your speedometer. ( cable gears are wrong !)
We call these ticket getting tires. Speedo reads way low. MPG will read way low (falsely)
revolution / mile
circumference "
percent error over stock p205  5sp 8valve 
indicated speed --> actual speed  ( USA gears in tranny and speedo)
P205-75-R15 744/760 85.1
0% (or -2% )  speedo is set to 760rev/mile, some stock tires can be  slow  by -2%
P225-75-R15 713 89.1 -4.1% (over 744)     59-->                       all errors are for 760 stock tires (basis)
P235-75-R15 698
59 --> 62.9
705 89.9 -5.6%
59 -- >62.3  MPH
677 93.6 -10.0%
59 -- > 64.9
656 96.6 -13.4%
59 -- >66.9
33x10.50R15/C  636 99.6 -16.9% 59 -->69
rev/mile to circum calcs:
(5280 ft  x12)  ÷ rev/mile  = circumference in inches to match my above metric and below equations (BFG uses rev/mile  in tire tables.)
or 63360  ÷ rev/mile  = circum

The Math for speed at RPM given.
MPH =  (((( RPM ÷ total ratio) X circum")  ÷ 12) x60)  ÷ 5280
12 converts to inches to feet.
60 converts minutes to hours.
5280 converts feet to miles.
Not that scary of an equation , no?

The correction for the SPEEDO, is mentioned here.

Photo's: (click an zoom)
This tool is pulling the bad bearing. The tool is not cheap , so rent them.

Best way to shift to 4WD is at 1/2 mile per hour, saving damage on part 29 big time. it's NO SYNCRO until 1999, so give it TLC and it will LAST.
The below Transfer case has no Center Differential.

 The below is a JEEP , you don't have THIS part 36 below in red circle , the Jeep Center Diff. allowing AWD to happen.

Suzuki G.Vitara case below, 2006 center diff.  See that small part below? at Red arrow #23 and the electric shifter #14 All the magic is there.

One more drawing of  the 05 Grand Cherokee SelectTrac 1, see part 16, that  to is the Center Diff.

CV constant velocity joints (those wiggly front axle things)
CW -clock wise rotation
CCW - counter Clock......
XFR  - Transfer case. and its shifter handle.
4WD - Four Wheel Drive.
RTM- Read the manual, in the glove box or get one for free from Suzuki. see some this  manuals page?

Rev. 9 ------------------ added more stuff,  12-1-2013  added 1999 and up data.