VCU Seizure

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Chaser

Chaser

New Member
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2,175
There are loads of threads on here about vcu failure and the impact that has on the rest of the transmission so I guess it must be the one thing all owners must dread.
Does anyone have any info on what actually physically seizes up in these units. Is it a progressive change in the condition of the silicon fluid or possibly a mechanical seizure of the casing/shafts?
I was thinking if there is anything we can do to help prevent the unit from failing?
Maybe someone has managed to get into an old unit, if so it would be interesting to know what had seized.

Any thoughts, Chaser..
 
Chaser said:
There are loads of threads on here about vcu failure and the impact that has on the rest of the transmission so I guess it must be the one thing all owners must dread.
Does anyone have any info on what actually physically seizes up in these units. Is it a progressive change in the condition of the silicon fluid or possibly a mechanical seizure of the casing/shafts?
I was thinking if there is anything we can do to help prevent the unit from failing?
Maybe someone has managed to get into an old unit, if so it would be interesting to know what had seized.

Any thoughts, Chaser..
Click to expand...
its old hat on this forum. . . .go into search. . . . .and no you cannot DIY it, new wun if its fooked :) :) :)
 
its old hat on this forum. . .I know . .go into search. . I have and didn't find an answer to my question. . .and no you cannot DIY it, new wun if its fooked . . .I know and it isn't..yet :p
 
Thanks mad hat man,
I have seen that write up before via google but hadn't found the thumbnail of the vcu you included. I still can't imagine exactly where the seizure occurs, the bearings shouldn't suffer too much wear given the speed differential between input and output. There may be a chance or water ingress around the input shaft.
I wonder if vcu,s are less likely to seize if worked hard occasionally instead of just normal straight line road use.

Chaser...
 
The VCU can fail in one of 2 modes.
a: seized solid
b: no drive

the reasons for failure are many but can usually be found to be either due to failure of the silicone liquid breaking down or failure of the plates inside the VCU. I believe that these have a rough toothed surface and can either friction weld together or just loose grip.
 
my vcu had the symtoms of potential faliure after testing .Drilled a6mm
hole in it got the silicone fluid out of it .Next put a grease niple in it and
filled it with grease .Put a air hole on the oppisite side .Removed the grease nipple sealed both holes.This is a basic outline of what i did
with out going into detail .Jacked the rear wheel up put the socket and bar on it and it turns with considerable pressure .Tyres wear evenly.
It worked for me
 
however if the viscosity and shear strength of the replacement fluid are not the same as the original - it will affect the operational characteristics of the VCU, sufficiently to make it a worthless exercise:eek:.:rolleyes:

why dint they use grease in the first place?
 
I wasn't aware that they sometimes fail with no drive. At least that scenario might cause less damage elsewhere.

Hugh's post seems to suggest there may be also some conical discs to give preload.
 
Internally, the same as found in limited slip diffs. Just thinking how Hugh at least had nominal drive after filling with grease...
 
hugh bathe said:
my vcu had the symtoms of potential faliure after testing .Drilled a6mm
hole in it got the silicone fluid out of it .Next put a grease niple in it and
filled it with grease .Put a air hole on the oppisite side .Removed the grease nipple sealed both holes.This is a basic outline of what i did
with out going into detail .Jacked the rear wheel up put the socket and bar on it and it turns with considerable pressure .Tyres wear evenly.
It worked for me
Click to expand...


have i missed summat - he drilled two holes, removed (some of) the silicone and repacked it with grease. Ignoring the out of balance effect of not drilling the holes exactly diametrically opposite, and the risk of knocking the nipples off again, with interesting results, where does it mention concave, convex or concubine?:rolleyes::confused:?
 
It doesn't, as I siad I was thinking how he at least had nominal drive afterwards. Just keeping an open mind as I have never seen one opened up.
 
there yar boys - as can be seen, it depends entirely on the viscosity of the fluid and its shear strength, combined with the hole/slot size to determine the amount of torque transmitted thro from one side to the other.

7646d1225880537-vcu-seizure-vcu.jpg
 

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So.....Does anyone have any info on what actually physically seizes up in these units. Is it a progressive change in the condition of the silicon fluid or possibly a mechanical seizure of the casing/shafts?
I was thinking if there is anything we can do to help prevent the unit from failing?
Maybe someone has managed to get into an old unit, if so it would be interesting to know what had seized.
 
Chaser said:
So.....
Does anyone have any info on what actually physically seizes up in these units. no
Is it a progressive change in the condition of the silicon fluid or possibly a mechanical seizure of the casing/shafts? possibly
I was thinking if there is anything we can do to help prevent the unit from failing? yes - go Mondo mode
Maybe someone has managed to get into an old unit, if so it would be interesting to know what had seized.
Click to expand...


best option is to go Mondo mode and remove one of the prop-shafts unless and when the driving conditions are poor - yu go offroading.

This problem has been discussed for years - so far the above is the best option.
 
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