p38 viscous coupling

can some one please tell me is there any way of testing if the viscouse coupling is still working on my 1999 p38 4.0 also how the traction control works as i was off roading the other day trying to climb a steep hill and lost traction in the dust and the people who were watching said my front wheels were spinnig like mad but the rears were doing nothing thanks for any help

Lots of thread on the VCU. If your front wheels were spinning and the rears where not turning, for sure the VCU is not seized which is the usual problem. Jack one fromt wheel, it should with a lot of effort, be just possible to turn it. If it turns easily the VCU is bust, if it will not turn the VCU is seized.
Traction control was rear wheels only on early P38's, all 4 wheels on late models, your is around the changeover time.

A most concise answer. Good advice.

Hi friends,

Sorry to talk about "VCU" again.

First I must inform, that I have my complete Gearbox removed from the car.
(The well know "duo":the DMF and Clutch).

1) So I can not test the VCU like already reported (jack etc....)
Is there any way of testing it?

(Last MOT, it was the first time, (since i own the RR (5 years)), they put the car in dinamometer tester, and in the rear they have something to allow the 2 wheels from the rear spinning free.... (sorry guys language issues).
My rear wheels did not spin, and the RR get out off the test...)

It´s a VCU seized symptom? Right?

2.) I found this in the Internet (i think it came from RAVE)


Since I have TC in 4 wheel...., how I do the MOT?

3) Since a VCU isn´t cheap (+- 450€), remember that I have spend +- 1000€ recently, can I run 2 or 3 month with only RWD.

Thanks

If the rear wheels did not spin on the rollers, it's not a seized VCU, something more serious than that in the transfer box or the prop shaft is missing.

Datatek said:

Lots of thread on the VCU. If your front wheels were spinning and the rears where not turning, for sure the VCU is not seized which is the usual problem. Jack one fromt wheel, it should with a lot of effort, be just possible to turn it. If it turns easily the VCU is bust, if it will not turn the VCU is seized.
Traction control was rear wheels only on early P38's, all 4 wheels on late models, your is around the changeover time.

Click to expand...

Correct, the changeover point is very grey for 4.0s. The 4.0s soldiered on with rear wheel only traction control for up to half a year after the Thor 4.6 got all wheel TC standard. Land Rover "used up" their stock of GEMS FI systems on the 4.0 litre cars, so many were fitted with GEMS beyond the time when Motronic should have been standard, AFAIK all GEMS cars will only have two wheel TC. To confuse matters more, there are some early Thor (Motronic) 4.0s with two wheel TC as well! I don't know the reason for the latter setup - perhaps there was a glut of unused two pin diffs laying around so they were fitted to the front of 4.0s and four wheel TC disabled until they were used up? I wouldn't be surprised - sounds very Land Rover to me!

And yes Viscous Couplings Units usually seize rather than slip when they fail.

Datatek said:

If the rear wheels did not spin on the rollers, it's not a seized VCU, something more serious than that in the transfer box or the prop shaft is missing.

Click to expand...

I have the prop shaft.

If I manually move the front "axle", the rear move also or vice-versa.
If I have a problem in TB, it will no spin... right?
(remember that my Gearbox is on the floor, and language issue).

Could the cause of the problem be in the rear Diff?
And I am "going" in the VCU?

Thanks!!!

tomcatrr said:

I have the prop shaft.

If I manually move the front "axle", the rear move also or vice-versa.
If I have a problem in TB, it will no spin... right?
(remember that my Gearbox is on the floor, and language issue).

Could the cause of the problem be in the rear Diff?
And I am "going" in the VCU?

Thanks!!!

Click to expand...

The problem could be the rear diff, if the diff has failed it could have been caused by a seized VCU.

Re: Braking for MoT Test. The garages up here won't put any 4x4s on rollers to test the brakes. Instead they get up to 30MPH then brake. If the vehicle doesn't pull one way or t'other you pass.

I believe this is a standard practice for most if not all MoT Test Stations.

Bix said:

Re: Braking for MoT Test. The garages up here won't put any 4x4s on rollers to test the brakes. Instead they get up to 30MPH then brake. If the vehicle doesn't pull one way or t'other you pass.

I believe this is a standard practice for most if not all MoT Test Stations.

Click to expand...

Tis true...a Testing station should never use a Single Axle Brake Tester on a Range Rover...one place I went to tried with my P38, and before they set the thing in motion, I ran across and pulled the keys out of the ignition much to the Testers annoyance - told him not to be a #### and drove away!

I Have my RR, from 2008.
Take it to MOT in 2008,2009,2010,2011, and they never use Single Axle Brake, until 2012.
They use always a "machine" on the floor, then brake....

I will try today to check the rear diff and TB, and will inform...


Thanks for all infos!!!

Datatek said:

If the rear wheels did not spin on the rollers, it's not a seized VCU, something more serious than that in the transfer box or the prop shaft is missing.

Click to expand...

Or a busted half shaft.

I wonder what the most likely damage to a P38 would be by testing it on a single axle roller?

Blow the diff, halfshaft or transfer case. Really unlucky you could wind up the propshaft until it snaps. IIRC, they try to design the halfshaft to sacrifice itself as they are a bit easier to replace.

Ok,

1)
I check the rear diff. It will "spin" free: applying force in one wheel, and with other wheel "locked" and reverse.
Using a jack, manually spinning the "joint" (where the rear prop connects)in differential, both wheels move, if I block one wheel, the other continue the movement....
I think the rear diff is ok, right?

2)
Do the same in front, same results

3)
Try explaining to my friend (where the RR is, and who is helping me), the VCU "test", we try in the gearbox, locking one "shaft" and we apply force in the opposite "shaft"......... we can slowly move....but with some "force". we try in another direction, same thing.

(here came the photo that I took).


Remember, if I "spin" one "shaft" the other will spin freely.

What you guys think, about all that have tested.

Do I have or not a VCU problem???
Or it´s not conclusive??

What I sould do / test now, to check why my rear wheels did not "spin" in the mot?

Thanks

StuckAgainSteve said:

I wonder what the most likely damage to a P38 would be by testing it on a single axle roller?

Click to expand...

it would just come out of the rollers

Hi,

From my last post in April 30 th, any clue?

Thanks

tomcatrr said:

I have the prop shaft.

If I manually move the front "axle", the rear move also or vice-versa.
If I have a problem in TB, it will no spin... right?
(remember that my Gearbox is on the floor, and language issue).

Could the cause of the problem be in the rear Diff?
And I am "going" in the VCU?

Thanks!!!

Click to expand...

you can test vc by adjusting hand brake up until its locked on (or bar acroos the flange studs if brake removed),then use 30mm socket and bar on front output flange nut ,should turn slowly smoothly but stiffly ,if you jack up one wheel on each axle leaving the other side on the ground turning wheel that is jacked up should turn diff flange

Hi,

Gearbox in place, did the the "VCU test" and it´s fine!

Thanks