P38A Viscous coupling

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Paul Coddington

Paul Coddington

Active Member
Posts
119
Location
Derbyshire
Afternoon All.
I've had a recent issue with a year 2000, P38 2.5 diesel fitted with a manual gearbox.
On the odd occasions it has started feeling like it's "skipping" almost as if the wheels are breaking contact. Daft description I know, but that's how it presents itself when you're driving it.
My first thought was the viscous coupling on the gearbox. I've done the test of gearbox in neutral, handbrake engaged, and jacking up a front wheel. I haven't got a cat in hells chance of turning the wheel by just grabbing the tyre but if I use a bar on a wheel nut it does turn slowly as described.
Can anyone shed any light on this, I'm wondering if the coupling is on the way out and presents as passing the test just because I'm using a bar to turn the wheel.
Thanks for any input.
Paul Coddington
 
Paul Coddington said:
Afternoon All.
I've had a recent issue with a year 2000, P38 2.5 diesel fitted with a manual gearbox.
On the odd occasions it has started feeling like it's "skipping" almost as if the wheels are breaking contact. Daft description I know, but that's how it presents itself when you're driving it.
My first thought was the viscous coupling on the gearbox. I've done the test of gearbox in neutral, handbrake engaged, and jacking up a front wheel. I haven't got a cat in hells chance of turning the wheel by just grabbing the tyre but if I use a bar on a wheel nut it does turn slowly as described.
Can anyone shed any light on this, I'm wondering if the coupling is on the way out and presents as passing the test just because I'm using a bar to turn the wheel.
Thanks for any input.
Paul Coddington
Click to expand...
If you can turn it at all, IMO the VCU is OK. How long was the bar? RAVE gives a definitive test.
Have you checked the UJ's?
 
Datatek said:
If you can turn it at all, IMO the VCU is OK. How long was the bar? RAVE gives a definitive test.
Have you checked the UJ's?
Click to expand...
UJ's checked recently, the bar was about
Datatek said:
If you can turn it at all, IMO the VCU is OK. How long was the bar? RAVE gives a definitive test.
Have you checked the UJ's?
Click to expand...
The UJ̌s were checked a couple or three months ago, the bar was 550 mm or so (2 piece improvisation) I will have a look at Rave later to have a look at how the professionals do it.
It only happens on the odd occasion, lasts a second or so and then disappears, generally when under acceleration.
Thanks for the reply.
Paul
 
Paul Coddington said:
UJ's checked recently, the bar was about

The UJ̌s were checked a couple or three months ago, the bar was 550 mm or so (2 piece improvisation) I will have a look at Rave later to have a look at how the professionals do it.
It only happens on the odd occasion, lasts a second or so and then disappears, generally when under acceleration.
Thanks for the reply.
Paul
Click to expand...
It sounds to me that the VCU is OK.
 
Paul Coddington said:
Afternoon All.
I've had a recent issue with a year 2000, P38 2.5 diesel fitted with a manual gearbox.
On the odd occasions it has started feeling like it's "skipping" almost as if the wheels are breaking contact. Daft description I know, but that's how it presents itself when you're driving it.
My first thought was the viscous coupling on the gearbox. I've done the test of gearbox in neutral, handbrake engaged, and jacking up a front wheel. I haven't got a cat in hells chance of turning the wheel by just grabbing the tyre but if I use a bar on a wheel nut it does turn slowly as described.
Can anyone shed any light on this, I'm wondering if the coupling is on the way out and presents as passing the test just because I'm using a bar to turn the wheel.
Thanks for any input.
Paul Coddington
Click to expand...

With a torque wrench on the 32 mm hub-nut you should be able to ease the wheel slowly round with about 110 nm. VCU failure also shows as scrubbing on outside edges of the tyres.
 
Bit of an update on this one. The problem became more noticeable, and felt like the vehicle was being held back all the brakes were checked for a binding caliper, they were all fine. A conversation with a chap, who breaks range rovers, gave a possible explanation. He experienced a similar problem, which eventually turned out to be a problem with the abs applying the brakes when driving over 20mph.
So that's the next thing to investigate.
 
Paul Coddington said:
Bit of an update on this one. The problem became more noticeable, and felt like the vehicle was being held back all the brakes were checked for a binding caliper, they were all fine. A conversation with a chap, who breaks range rovers, gave a possible explanation. He experienced a similar problem, which eventually turned out to be a problem with the abs applying the brakes when driving over 20mph.
So that's the next thing to investigate.
Click to expand...
I would expect the wheel(s) to get hot if that is the case.
 
Take your Range Rover to the nearest multi storey car park. One with a dry nicely painted concrete floor.
Drive it at a fast walking pace in a straight line. When up to speed take a full left or right turn with the gearbox in neutral. Ideally try to go in a circle.
If your viscous unit has failed you could notice two different things:
1. The vehicle grinds to a halt, meaning the VC is seizing up.
2. You hear a tyre screech from a wheel or two meaning your VC has already seized.
The main cause of failure of VC's in my experience is due to the wrong oil in the transfer case. They must use ATF. I have seen several units with failed VC's due to EP90 having been used. ATF is used as it transfers heat away from the VC.
 
Rangieman123 said:
Take your Range Rover to the nearest multi storey car park. One with a dry nicely painted concrete floor.
Drive it at a fast walking pace in a straight line. When up to speed take a full left or right turn with the gearbox in neutral. Ideally try to go in a circle.
If your viscous unit has failed you could notice two different things:
1. The vehicle grinds to a halt, meaning the VC is seizing up.
2. You hear a tyre screech from a wheel or two meaning your VC has already seized.
The main cause of failure of VC's in my experience is due to the wrong oil in the transfer case. They must use ATF. I have seen several units with failed VC's due to EP90 having been used. ATF is used as it transfers heat away from the VC.
Click to expand...
Thanks for the reply, unfortunately the nearest multi storey car park that I could do this in is about 10 miles away. I'm pretty much convinced that the VC is ok. I've performed the stationary test a couple of times on front and rear and they've all "passed"
 
Rangieman123 said:
Take your Range Rover to the nearest multi storey car park. One with a dry nicely painted concrete floor.
Drive it at a fast walking pace in a straight line. When up to speed take a full left or right turn with the gearbox in neutral. Ideally try to go in a circle.
If your viscous unit has failed you could notice two different things:
1. The vehicle grinds to a halt, meaning the VC is seizing up.
2. You hear a tyre screech from a wheel or two meaning your VC has already seized.
The main cause of failure of VC's in my experience is due to the wrong oil in the transfer case. They must use ATF. I have seen several units with failed VC's due to EP90 having been used. ATF is used as it transfers heat away from the VC.
Click to expand...
Landrovers don't have a great relationship with multistorey car parks 🤯😜
 
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