P38A About that VCU thingy.

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DanClarke

DanClarke

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If both Freelander's AND P38's "benefit" from VCU's, how come I don't see large numbers of posts about seized P38 VCU's or One Wheel Up tests for P38's?

Is it that the VCU plays a MAJOR part in a Freelander and a MINOR part in a P38?

Not trying to be an AR5E, just not understanding the difference and why its critical to one and hardly mentioned in the other as a failing component.

Can someone enlighten me please?
 
DanClarke said:
If both Freelander's AND P38's "benefit" from VCU's, how come I don't see large numbers of posts about seized P38 VCU's or One Wheel Up tests for P38's?

Is it that the VCU plays a MAJOR part in a Freelander and a MINOR part in a P38?

Not trying to be an AR5E, just not understanding the difference and why its critical to one and hardly mentioned in the other as a failing component.

Can someone enlighten me please?
Click to expand...
range rovers like defenders and discos are equal front and rear drive,freelanders arent ,front wheels are driven slightly faster as we were told by lr at the time to give front wheel drive feel as the customer base was expected to be familiar to that,consequently the vc doesnt last as long before effectively seizing this then buggers the ird and or rear diff , not only is the transmission under strain cornering it is when going straight too, transmission is driving front and back at different speeds
range rover classic or p38 do have issues with vcu seizing but it takes longer and when seized often isnt noticed unless in full lock etc, but it will knacker a diff eventually usually front but rears not unkown and ive seen a front diff replaced as drive was lost due to rear failing earlier but wasnt noticed, i test rrc or p38s with one wheel up as a matter of course when they are bought to me for whatever reason, it was lrs preferred in vehicle test back in the 90s
 
Last edited:
jamesmartin said:
range rovers like defenders and discos are equal front and rear drive,freelanders arent ,front wheels are driven slightly faster as we were told by lr at the time to give front wheel drive feel s customer base was expected to be used to that,consequently the vc doesnt last as long before effectively seizing this then buggers the ird and or rear diff , not only is the transmission under strain cornering it is when going straight too, transmission is driving front and back at different speeds
range rover classic or p38 do have issues with vcu seizing but it takes longer and when seized often isnt noticed unless in full lock etc, but it will knacker a diff eventually usually front but rears not unkown and ive seen a front diff replaced as drive was lost due to rear failing earlier but wasnt noticed, i test rrc or p38s with one wheel up as a matter of course when they are bought tyo me for whatever reason, it was lrs preferred in vehicle test back in the 90s
Click to expand...
Thank you @jamesmartin that explains it very well. For the Freelander a Time to travel a certain number of degrees is crucial, is there a specific documented test for the P38? Will I find it in RAVE?
 
jamesmartin said:
range rovers like defenders and discos are equal front and rear drive,freelanders arent ,front wheels are driven slightly faster as we were told by lr at the time to give front wheel drive feel s customer base was expected to be used to that,consequently the vc doesnt last as long before effectively seizing this then buggers the ird and or rear diff , not only is the transmission under strain cornering it is when going straight too, transmission is driving front and back at different speeds
range rover classic or p38 do have issues with vcu seizing but it takes longer and when seized often isnt noticed unless in full lock etc, but it will knacker a diff eventually usually front but rears not unkown and ive seen a front diff replaced as drive was lost due to rear failing earlier but wasnt noticed, i test rrc or p38s with one wheel up as a matter of course when they are bought tyo me for whatever reason, it was lrs preferred in vehicle test back in the 90s
Click to expand...

So its just a breaker bar on the axle nut and the tranny in neutral?

or is it more complicated?
 
In the case of the Classic & P38 I believe even minor differences in the rolling radius of tyres between the front & back axles can accelerate wear, even the number of changes of direction the vehicle makes during the life of a VCU.
My last three RRC's haven't had one & I don't miss them in the slightest ;)
 
DanClarke said:
Thank you @jamesmartin that explains it very well. For the Freelander a Time to travel a certain number of degrees is crucial, is there a specific documented test for the P38? Will I find it in RAVE?
Click to expand...
you might, i just know by feel ,and obviously you cant be in park, when the p38 came out borg warner refused to service any of the earlier classic units ftc1564s money i suppose, so the firm i worked got to build new or recon any lr needed with BWs permission also led to doing the p38 unit too, the figures we had were supplied by BW and i long forgot the exact figures, interestingly enough i visited BW a few times down near port talbot picking up the old unit tooling and getting build instruction, whilst there they showed us the p38 box line nearly all automated except the 2 halves were siliconed together before final assembly by a woman with a caulking gun
 
Henry_b said:
So its just a breaker bar on the axle nut and the tranny in neutral, or is it more complicated?
Click to expand...

Rear wheels chocked, one front wheel jacked up, tranny in neutral, handbrake ON & b/bar on a wheel nut. Should be able to turn the raised wheel slowly whilst feeling resistance. If it won't move (other than normal trans. slack) VCU is seized, if it turns easily then you have other trans. problems.
 
norseman said:
Rear wheels chocked, one front wheel jacked up, tranny in neutral, handbrake ON & b/bar on a wheel nut. Should be able to turn the raised wheel slowly whilst feeling resistance. If it won't move (other than normal trans. slack) VCU is seized, if it turns easily then you have other trans. problems.
Click to expand...

sounds like a thing even i can do!!!!

Cheers!

The tyres use to skip when on full lock, i'm pretty sure the VCU is goosed but want to be sure..

;)
 
brianp38dse said:
@Grrrrrr fitted a new TB and vcu recently and knows the figures iirc some thing like 70nm on hub nut.
Click to expand...

That's what I could turn the new one on. VERY SLOWLY. Transmission neutral, lift the from wheel, 32mm socket on the hub-nut. Set the torque wrench to 70nm and then try and tease the wheel round without it clicking. If you cannot move it without clicking then dial it up another 10nm. Once moving you should be able to just keep the pressure steady and it will very slowly rotate. The one I took off hadn't seized but it took 140nm to rotate and the car drove much smoother after I replaced it. Not that the missus noticed but I'm sure it made a difference!

If you do decide to do it then don't bother with those transmission jack cradles that fit to your trolley jack. Waste of time. Or if you really want you can borrow mine as it is just gathering dust in my shed now.
 
Grrrrrr said:
That's what I could turn the new one on. VERY SLOWLY. Transmission neutral, lift the from wheel, 32mm socket on the hub-nut. Set the torque wrench to 70nm and then try and tease the wheel round without it clicking. If you cannot move it without clicking then dial it up another 10nm. Once moving you should be able to just keep the pressure steady and it will very slowly rotate. The one I took off hadn't seized but it took 140nm to rotate and the car drove much smoother after I replaced it. Not that the missus noticed but I'm sure it made a difference!

If you do decide to do it then don't bother with those transmission jack cradles that fit to your trolley jack. Waste of time. Or if you really want you can borrow mine as it is just gathering dust in my shed now.
Click to expand...
No transmission jack needed to change the VCU, it's behind the front cover on the transfer box where the front prop connects.
 
norseman said:
In the case of the Classic & P38 I believe even minor differences in the rolling radius of tyres between the front & back axles can accelerate wear, even the number of changes of direction the vehicle makes during the life of a VCU.
My last three RRC's haven't had one & I don't miss them in the slightest ;)
Click to expand...

There is a built in differential between rolling radius front to rear on the Classic and P38 if the tyres are correctly inflated. Classic and P38 are classed as permanent four wheel drive equally divided front to rear. The Freelander is not permanent four wheel drive, but front wheel drive with four wheel drive capability. Therein lies it's greater VCU problems.
 
The thing about vcu lore that confuses me is, us freelander owners are constantly warned of the perils of having mismatched tyres, tyres with differing tread wear and tyres with different pressures. The reason being from what I gather is that unless the tyres are all the same diameter they will revolve at slightly different speeds and so goose the vcu. Well, it seems to me that most of my driving is not on straight roads, much more than 50% of my overall mileage is around town. So my tyres are revolving at different speeds relative to each other much of the time, so why doesn't that wreck the vcu?

Col
 
Colthebrummie said:
The thing about vcu lore that confuses me is, us freelander owners are constantly warned of the perils of having mismatched tyres, tyres with differing tread wear and tyres with different pressures. The reason being from what I gather is that unless the tyres are all the same diameter they will revolve at slightly different speeds and so goose the vcu. Well, it seems to me that most of my driving is not on straight roads, much more than 50% of my overall mileage is around town. So my tyres are revolving at different speeds relative to each other much of the time, so why doesn't that wreck the vcu?

Col
Click to expand...
It does.
 
Datatek said:
It does.
Click to expand...
Yes but it takes ages, about 70k miles on average, yet I've read that driving with a tyre more worn than its axle mate or a few lbs of pressure difference will cause harm within a couple of hundred miles. I know I'm not Einstein but the claim doesn't ring true.

Col
 
Colthebrummie said:
The thing about vcu lore that confuses me is, us freelander owners are constantly warned of the perils of having mismatched tyres, tyres with differing tread wear and tyres with different pressures. The reason being from what I gather is that unless the tyres are all the same diameter they will revolve at slightly different speeds and so goose the vcu. Well, it seems to me that most of my driving is not on straight roads, much more than 50% of my overall mileage is around town. So my tyres are revolving at different speeds relative to each other much of the time, so why doesn't that wreck the vcu?

Col
Click to expand...
as i said earlier the front and back are driven at slightly different speeds on a freelander so youve got that constant stress all the time as well as worn tyres effects and cornering etc range rove only gets that stress with worn tyres and cornering
 
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