VCU Life

The Mad Hat Man said:

Looking at the temperature hysteresis curve for gaylander VCUs, I would suggest that anywhere between 10C and 85C should be fine and 10C above ambient shows that the VCU is actually working. The VCU locks up at about 100C. I would be concerned about a larger increase at Motorway speeds as the VCU should be working at its easiest, as there is the minimum difference between front and rear road speeds, compared to lots of roundabouts and bends....

If temp of VCU is either too hot to touch or at ambient, those are the times to be concerned.

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Been testing ma vcu quite a bit recently and it's the reason for the tyre change. I've found on both new and previous tyres the vcu gets hotter at 60mph constant as opposed to 30mph constant, over the same distance. Logically you would think it's the oppersite. Previous tyres could heat up the vcu much quicker than the new tyres. Peeps won't believe me when I tell em why, and how amazed I was to find out... by mistake... the debate will start LZ style. I will write up whats been going on at hippo towers from the start and why changing my vcu for the fault I found would have been pointless. Trunip Test is the answer to all our problems, I finks.

Singvogel said:

...Hippo will too - as I'm sure he likes to play with his infra-red thermometers.

...Singvogel.

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Yup. Drove 80 miles yerterday at 60mph whilst stopping at intervals to check ma vcu's temp. Lets just say I is now a happy hippo, with a happy hippo.

[smile]Turnip Test Rules[/smile]

Hippo said:

Been testing ma vcu quite a bit recently and it's the reason for the tyre change. I've found on both new and previous tyres the vcu gets hotter at 60mph constant as opposed to 30mph constant, over the same distance. Logically you would think it's the oppersite. Previous tyres could heat up the vcu much quicker than the new tyres. Peeps won't believe me when I tell em why, and how amazed I was to find out... by mistake... the debate will start LZ style. I will write up whats been going on at hippo towers from the start and why changing my vcu for the fault I found would have been pointless. Trunip Test is the answer to all our problems, I finks.

Yup. Drove 80 miles yerterday at 60mph whilst stopping at intervals to check ma vcu's temp. Lets just say I is now a happy hippo, with a happy hippo.

[smile]Turnip Test Rules[/smile]

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Have you been checking the rear diff temp to? This will give an indication of the torque being transferred.

Nodge68 said:

Have you been checking the rear diff temp to? This will give an indication of the torque being transferred.

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Nope. I forgot. :doh: It was dark though. Will do it again sometime and make sure I have me torch.

Turns out my VCU has gone at 58k. Thought something was up with rear diff, getting weird creaking noises on tight turns and the odd knock. Removed the prop shaft and VCU today and it cured the noises... also feels a lot better to drive now. Have to decide whether to replace the VCU and put the prop shaft back in... I was told it would be around 500 quid? sound right?

ballyligboy said:

Turns out my VCU has gone at 58k. Thought something was up with rear diff, getting weird creaking noises on tight turns and the odd knock. Removed the prop shaft and VCU today and it cured the noises... also feels a lot better to drive now. Have to decide whether to replace the VCU and put the prop shaft back in... I was told it would be around 500 quid? sound right?

Click to expand...

No chance - a re-con exchange VCU from Bell Eng is £200 and a pair of GKN bearings from Foundry4X4 is around £30

£500 for a garage to do the change over maybe - but if you're savvy enough to take the props off you'll be able to do the refit yourself I should think.

Singvogel.

Nodge68 said:

Have you been checking the rear diff temp to? This will give an indication of the torque being transferred.

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Went on a 140 mile trip today. Took loads of measurements at different intervals. These are the results of my trip. 2001 v6 with new Pirelli Scorpion STR 215R65/16 98H tyres. Short story is:

120 miles at 60mph + 20miles mixed speed of 30/40/50mph (some at beginning, middle and end of trip).

8 = ambient temp
10 = average road temp
22 = max rear tyre temp
23 = max front tyre temp
41 = max vcu temp (measured circumference side of vcu) (7.8 at start)
46 = max rear diff temp (measured underside outer case) (7.8 at start)
75 = max ird temp (measured ird filler plug)

All values in degrees. I got 28mpg.

To prolong the life of my vcu it comes off in April and goes back on around now.......

FREEL4NDY said:

To prolong the life of my vcu it comes off in April and goes back on around now.......

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Me too !!

Hippo said:

Went on a 140 mile trip today. Took loads of measurements at different intervals. These are the results of my trip. 2001 v6 with new Pirelli Scorpion STR 215R65/16 98H tyres. Short story is:

120 miles at 60mph + 20miles mixed speed of 30/40/50mph (some at beginning, middle and end of trip).

8 = ambient temp
10 = average road temp
22 = max rear tyre temp
23 = max front tyre temp
41 = max vcu temp (measured circumference side of vcu) (7.8 at start)
46 = max rear diff temp (measured underside outer case) (7.8 at start)
75 = max ird temp (measured ird filler plug)

All values in degrees. I got 28mpg.

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Great info Hippo. Nice one. Why don't you start a new thread for temperature testing, and copy this info over? my thermometer arrived today :clap2:. road temp? do you mean the temperature of the road surface itself?

seraphin said:

Great info Hippo. Nice one. Why don't you start a new thread for temperature testing, and copy this info over? my thermometer arrived today :clap2:. road temp? do you mean the temperature of the road surface itself?

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Hi.

Thanks. I will be writing up what I've been up to over the last few months, soon. Not in the right frame of mind to do it at the moment. It's vital to give an explanation of what I did, and why. It's a follow on from my wheel tracking thread when I was thinking about buying a trackace, which I did. I could start a new fred off but few peeps have done the original One Wheel up Test despite there being nearly 27000 views on you tube, with 1810 views from links direct from LZ. Few bother to give results so I guess peeps don't want to test. I have other more interesting projects to play with so vcu work will stop soon, other than ocasional checks.

Road temp is the road surface temp.

Good to see you've got a thermometer. Start measuring and keep some records. vcu tart temp from FL standing after being left overnight, vcu trip end temp, ambiant temp (use bodywork in shade) and the trip length + what sort of speeds. You'll soon realise why the Turnip Test is so important.

'A' road .. some 70mph d.c. .. mainly twisting / hilly s.c. .. 30/40/50/60 mph ..
aprox 35 miles each way ..

didn't measure ambient temp before setting out ..
weather page sais 6.4C

on destination arrival :
carpark tarmac temp. .. 5.4C
VCU temp 23.6C

on return arrival :
street cobble stones temp .. 0.2C
VCU temp .. 20C

~~~~~~~~~~~~~~~

conditions weren't exactly favourable to stop and measure temps
i.e. immediatly after the 70mph d.c. sections ..
.. and probably need a place to stop directly after the medium speed sections as well
as opposed to the few minutes of very low 'manouvering to park' speed ..
which no doubt gives the vcu time to cool ..

will have another go at it .. midweek .. dry day if possible ..
although .. info on the i.r. thermometer sais it won't operate below 0C/32F
.. if ambient be below freezing ..
guess i could wrap it in some thermals 'n hop out of the car right quick ..

~~~~
pic from mid-journey attached .. looks like a sprinkling of snow on yonder hill
( slightly altered due to zoom 'grain' .. de-noise filter )

Hippo said:

Went on a 140 mile trip today. Took loads of measurements at different intervals. These are the results of my trip. 2001 v6 with new Pirelli Scorpion STR 215R65/16 98H tyres. Short story is:

120 miles at 60mph + 20miles mixed speed of 30/40/50mph (some at beginning, middle and end of trip).

8 = ambient temp
10 = average road temp
22 = max rear tyre temp
23 = max front tyre temp
41 = max vcu temp (measured circumference side of vcu) (7.8 at start)
46 = max rear diff temp (measured underside outer case) (7.8 at start)
75 = max ird temp (measured ird filler plug)

All values in degrees. I got 28mpg.

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Nice work Hippo.
My infrared thermometer is on order.
I will post results soonest,using your layout.

I for one think this test is more important than the wheel up test,as
if enough results come in on a regular basis it will give people a warning of a problem which may be about to occur and give time to sort it before VCU failure.
Or at least one would hope a reference point to test from.

webley2000 said:

Nice work Hippo.
My infrared thermometer is on order.
I will post results soonest,using your layout.

I for one think this test is more important than the wheel up test,as
if enough results come in on a regular basis it will give people a warning of a problem which may be about to occur and give time to sort it before VCU failure.
Or at least one would hope a reference point to test from.

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Well spotted. You can have a cookie.

Turnip test will tell peeps if:
their tyres are causing the vcu problems like mis-matched tyre size
vcu activating (seizing) sooner than the owner would hope
typical running temp of the vcu under different conditions, speed being one of them
if your vcu is seizing (activating) or running hotter so you can look for faults

One wheel up test gives an example of vcu performance as a comparison, if done from cold using the same length bar 1.2m and variuos weights, as a comparison for us to compare our results.

Just to bump this thread up a bit really.
I have been taking a few readings since my Infrared thermometer jobby arrived.

Weather is not a help.
Will have to pack a gardening kneeling mat or something for when dressed up,(best jeans)

I have also taken temp of the propshafts either side of the vcu beyond the joints.The front section does get hot(from the IRD) and probably effects the
VCU temp quite a bit.Longs runs more heat transmitted.I will include these in
the results.

I am off on hols this weekend so will post some results after I get back and have put a few more miles in.

Infrared thermometer well worth the £16 quid I paid and seems quite accurate when compared to wall mounted item..
Checking round the brake temps it shows the offside rear is 10 degrees down on the nearside,so another job rears its head.

Ambient temp = 30
Checked the following after 30 mile drive mostly at 80mph:

IRD = 95
Diff = 75
VCU = 56

Original VCU on 80000 miles.

seraphin said:

Ambient temp = 30
Checked the following after 30 mile drive mostly at 80mph:

IRD = 95
Diff = 75
VCU = 56

Original VCU on 80000 miles.

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Thanks. You can have a cookie.


Ambiant temp seems to have a lot to do with Turnip Test results. 30 degrees ambiant + 26 degrees gives the increased vcu temp after travelling mostly at 80mph for 30 miles.

200 mile journey at 85 mph in 35 degree (centigrade) climate. continuous motorway driving.

max temps:

vcu = 66
ird = 110
rear diff = 80


i have a td4 (2005) on 80000 miles, original vcu, newish identical tyres and no known drivetrain problems. sounds kinda hot, don't you think? :mad2:

Hard to say as been off and back on several times. Seems little point it being on during the summer but my problem is cant be arsed to re fit for winter. I believe, as do others, that the VCU is a crude, if effective device and none of us are completely sure what a fully working one is. I would not buy another vehicle where 4x4 used a VCU.

seraphin said:

200 mile journey at 85 mph in 35 degree (centigrade) climate. continuous motorway driving.

max temps:

vcu = 66
ird = 110
rear diff = 80


i have a td4 (2005) on 80000 miles, original vcu, newish identical tyres and no known drivetrain problems. sounds kinda hot, don't you think? :mad2:

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Thanks. You can have a cookie.

If your ambiant is 35 degrees and your vcu is 66 degrees then your vcu increased in temp by 66-35=31 degrees over a 200 mile distance. Thats not bad (I think). From what I've seen from playing with my vcu... it's temp increases by roughly the same amount, on the same trip of x miles at y speed. The difference in final vcu temp after the trip is offset by ambiant temp, roughly. If ambiant temp is hotter when you start then the vcu will be that much hotter when you finish.

Thats assuming your vcu was at ambiant temp when you started the trip.

The temp offset rough rules doesn't work as well when ambiant temp is very cold. But then the vcu doesn't get much of a chance to warm up if it's shivering too (I guess).

Just look how hot the diff gets, it's taking some serious load to run 45°above ambient!!