RangeRovers.net Forum banner

1 - 9 of 9 Posts

·
Registered
1995-2002 Range Rover P38A
Joined
·
2 Posts
Discussion Starter #1
I have just bought my first Range Rover P38 HSE 4.00 LPG Year 2000

Just been for an MOT failed on front side lights and a drop link, No Trouble there.....

BUT The Mechanic said it is stuck in 4WD as he can't turn the wheels interdependently and had to set the brake tester to reverse one wheel when testing the other wheel

MY question, is this a correct state, I know some RR have a permanent 4WD Lock or is there a fault.

If there is how can I get it out of 4WD

Thanks in anticipation

MadBrit
 

·
Administrator
Joined
·
27,834 Posts
All P38s are full time four wheel drive. Yes this is correct. No there is nothing wrong with the four wheel drive system. You can let your "Mechanic" know that all Range Rover Classics, L322s and L320s are full time four wheel drive as well.

If he needs to place the transfer case in neutral he can simply follow the towing instructions in your owners manual.

I would urge a bit of caution with having inexperienced persons working on systems they do not understand. These are the kind of mechanics that may do more damage then repair.
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
2 Posts
Discussion Starter #3
Thank you very much, just had the brake pipe burst RIGHT ABOVE THE rear cross member, it will have to be re routed when mended I take it, as a mouse would have trouble getting in there, its the pipe that runs to the N/S wheel

Not my day

MadBrit
 

·
JACK'S GRANDAD
Joined
·
9,248 Posts
Search for the brake pipe, been covered numerous times.
And all Discovery's are also full time 4wd. If he didn't know that, take it elsewhere!!!!
 

·
Registered
Joined
·
78 Posts
Hi RR,
Perhaps you can explain for me why the differential between the front and rear wheels didn't allow the mechanic to turn the wheels independently ( this a real question not rhetoric;)
I totally agree about any mechanic not fully conversant with the idea of full time 4wd drive.
Regards
Al
 

·
Premium Member
2002-2005 Range Rover MkIII / L322
Joined
·
3,622 Posts
Hi RR,
Perhaps you can explain for me why the differential between the front and rear wheels didn't allow the mechanic to turn the wheels independently ( this a real question not rhetoric;)
I totally agree about any mechanic not fully conversant with the idea of full time 4wd drive.
Regards
Al
Because they are all locked together... only with open differentials when you spin the right rear, for instance, the left rear will spin the opposite direction and the fronts will do essentially the same thing also. The viscous coupler will mess with the fronts a little in this situation but in this scenario the fronts should still turn. Because of this and your mechanic being a fairy nancypants he didn't have the testicular fortitude to spin all 4 wheels at the same time.

:thumb:
 

·
LEGACY VENDOR
1995-2002 Range Rover P38A
Joined
·
4,225 Posts
In the UK, they shouldn't be putting it on a brake tester/rolling road, as these usually test an axle at a time - as he's tried doing...

Whenever I've taken mine for an MOT, because it is permanent 4WD, they do a different brake test on it with a G meter, which as far as I know - it's a handheld device, placed in the vehicle, and then they'll drive the vehicle up the road to a determined speed and then stamp on the brakes. The G meter will measure the force of deceleration due to braking, and if this is above whatever the limit is that is deemed required by law, then the vehicle passes.

I've had my P38 MOT'd at 3 different garages over the past 5 yrs, and they've all done the brake testing the same way.

I did have one try to fail it because the ABS light was on until I asked him if it went out when the vehicle was driven, and he said 'yes'... I told him it was supposed to operate like that as a wheel speed sensor check... and it's in the owners manual, if he cared to check!

If they can't do a proper brake check for a permanent 4wd vehicle, then I'd be taking it elsewhere to someone who knows!
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
121 Posts
It's not clear what your mechanic actually meant by "turn the wheels independently" but I agree with others that you should take it elsewhere.

The P38 has three differentials. One between each wheel on the front and rear axles and a third between the front and rear driveshafts. On a standard car the front and rear diffs are 'open' diffs i.e. there is nothing to restrict the relative speed of the two wheels. With an open diff any one of the 3 rotating elements (2 halfshafts plus 1 propshaft) can remain stationary while the other to turn. The centre diff is a viscus unit which resists and difference in speed between the front and rear propshafts.

So:
If you jack one wheel up and try to turn it, it will be almost impossible because the other halfshaft is held by the wheel on the ground and the propshaft is held by the viscus diff. If you jack up both wheels on an axle then turning one wheel will rotate the other in the opposite direction. (the propshaft is held still by the viscus diff).

If you jack up two wheels on the same side and rotate one wheel the the other will rotate in the same direction. Opposite wheels are held but the propshaft is now free to rotate.

So with open diffs you need traction on at least two wheels to go anywhere. This is why serious off-roaders use locking or limited slip diffs on each axle thereby allowing progress when only a single wheel has traction.

Open diffs aren't as bad as they may appear first because the brake system can sense a spinning wheel and apply the brake to that wheel alone. By locking (or at least applying torque) to the spinning wheel, an equal amount of torque is now applied to the opposite wheel so if that wheel can maintain traction, the vehicle will move.

The bottom line is that if you are stupid enough to put a P38 on a two wheel rolling road and spin both rollers in the same direction, then either it will drive off, or if you have really tied it down well then either the tyres will slip on the rollers or it will overheat the viscus clutch. Sounds like your mechanics rolling road can spin the rollers in opposite directions. In theory this is OK but any difference in speed between the rollers or indeed difference in tyre circumference, would put a torque into the viscus diff / rear wheels. I wouldn't let him do this to mine.

I agree with Marty, MoT testers should use a G Meter on 4WD cars. In the days before MoT stations had to have rolling roads all cars were tested this way. The downside of a G meter is that it can't tell how even the braking is across axles or what the front to rear balance is. You have to rely on the tester's judgement of it pulling under braking or locking the rears before the fronts.
 

·
Registered
1995-2002 Range Rover Classic
Joined
·
1,414 Posts
gosh darn, I am a certified Virginia state emissions inspector, we use a 2 wheel dynamometer roller and obd2 test depending on model and year of vehicle. I have to recertify my license every 3 yrs by taking a college mandated class.
in this class it is mentioned many times in no uncertain terms, that if you are presented a vehicle with full time awd or full time 4wd as stated on the vehicle's under hood specification sticker, you're not to test on the dyno rollers. there are other ways to further verify I/M dyno test as well.
if you do perform said dyno test, and the vehicle fails or breaks down due to mis-test, the test station operator is liable for repairs incurred by improper testing.
I cannot imagine other countries and specially test localities would deviate from afore mentioned procedure, oh well things happen.
I would have my vehicle tested somewhere else under proper procedures.

best of luck.
 
1 - 9 of 9 Posts
Top