VC test

Post by **Hacksawbob** » 09 Oct 2006, 10:25

I had the left side of the van jacked up the other day (rear up front just touching the ground), I forgot to loosen one of the wheel nuts before raising it so I had a quick go against the handbrake before I lowered it and did it 'proper". Needless so say the the HB didnt hold it and of course the wheel turned. But so did the front wheel, slightly. If the VC should allow some rotation before kicking in, surely the rear should have turned on its own? The VC shouldn't lock up, cold and with only 2 inches of rear movement should it? or does the VC need to be at operating temperature before it does its thing, if so could this be a static VC test?

Post by **toomanytoys** » 09 Oct 2006, 11:07

Hi Bob
If I get what you are saying correctly, it didnt slip (or did but very slowly) mine is the same if that is the case... there was talk of a certain amount of force required to turn, but its a subjective test... if it turns a bit with "X" force or turns a lot......

Does it scrub and slow the vehicle down in tight turns? especially after a run? Mine does.. so VC is tight... Gonna be looking at a refurb unit when the box is done..

Post by **Russel** » 09 Oct 2006, 12:19

It will be tight at low and high temp.It will give lowest drive at normal operating temp.

Post by **toomanytoys** » 09 Oct 2006, 12:48

Hi Russel
If it scubs and slows in tight turns its too tight then?

Does ambient temps have a big part to play? just wondering if the hot climate VC's are different to us temperate climate.!

Post by **Hacksawbob** » 09 Oct 2006, 17:25

mine scrubs at full lock esp with some gavel on the road as ther is outside my house, and its about a year old, always has from refurb.

It will be tight at low and high temp.It will give lowest drive at normal operating temp.

what is normal/low/high? and how is it measured?

Post by **HarryMann** » 09 Oct 2006, 17:35

They all scrub on full lock, for a start that full lock is a very tight lock anyway, so a FWD would feel a bit like its scrubbing when turning that tight

Don't worry is what Russel's saying I think, onl when warm but not at locking temp will it appear reasoanable at full lock

Yes, static torque when at ambient temp, due to seals (that have to stand up to 100 bar burst pressure) and residual fluid viscosity, somewhere between 30 and 50 Nm

Post by **Russel** » 10 Oct 2006, 05:27

If u look at the GRAAF

u would have received with the recon VC
u will see it is temp and taque related.At cold temp it will bind but loosening off at running temp and then binding again when very hot(when friction occures beetween plates)
At full lock there is a rotation speed difference big enough between ure
rear wheels and front to activate ure VC,this is nothing to wory about.
If u are concerened do a 2x4 test.This must also be done at normal operating temp.

Post by **toomanytoys** » 10 Oct 2006, 07:33

this old VC thing will always come up then... AIdan reckons one of his tight, but felt reasonable compared to mine... but then again was out off roading for 2 hours the other eve and it didnt feel as tight as in the summer... 4x2 test then....

Post by **Hacksawbob** » 10 Oct 2006, 11:28

Hi Russel, I'm not worried just trying to understand. What is the method used to measure the temperature of the VC? presumably it would need to be a reading of the fluid rather than an external reading? I am just curious as to how this is done in what would be a pretty hostile enviroment at hi pessures with plates whizzing around, not much clearance etc. and would need to be done with a sealed unit, with the correct ammount of air introduced. If it was an internal probe then this would need to be removed without altering the air/luiquid ratio. If an external reading were possible some monitoring equipment could maybe relay this info to the cab.....

Post by **toomanytoys** » 10 Oct 2006, 12:25

Bob.. think you are thinking too far out of the box....
Russel is saying, "warm" it up by goin for a drive (how far.. 20 mins?) then test it...
There has to be enough variance in the units to cope with winter/summer temps.. We got down to -18 last winter.. below -6 for six weeks even in the day...!!
This summer, saw 38-42 deg on a regular basis...

What temps are on the graphs?

Are there different "settings" for hot/cold climates?

Post by **Hacksawbob** » 10 Oct 2006, 15:18

Bob.. think you are thinking too far out of the box....

who says there should be a box!

would be a nice and not to superfluous a gadget to know when your VC is up to speed. I wonder if an IR probe could do the job externally? http://www.metrisinst.com/product_detai ... 0&ref=temp

A good point about the climates if you could potentially have 40 degs difference from temperate to equtorial. I dont suppose that SDP did make different units for different markets, does anyone know any different? Are they a different temperature spec in SA?

Post by **toomanytoys** » 10 Oct 2006, 16:32

Mmm... ok so there is no box....

Also what happens if you factor in the rad air... thats pretty warm too...

40 deg?? mine could easy be 55 deg... in a year...

Sensor would need mounting and then is it durable enough..

I feel we are prob thinking too hard... but prob good questions still..

I could do a full temp map of the system... I am mapping a cold room shortly, been doing steam sterilisations on equipment.. Easier to just use a hand held lazer temp reader..

Post by **HarryMann** » 10 Oct 2006, 18:47

Maybe read back and look at some of my posts on SyncroSA over the past two years or so.. on these very topics

Post by **Aidan** » 10 Oct 2006, 18:49

20-40 mile, mixed traffic with maybe rad fan on once will be a fair operating temp regardless of season.
If you can borrow a rolling brake tester for ten mins it's a lot safer and easier to repeat a few times.
The tight one on Beaker passes the carpark full lock in 1st at idle test but failed the rolling road three times and lays down rubber outside my house at less than 3/4 lock so I'd judge it a tad tight but acceptable. Be interesting to swap front diffs and see what the difference is, will do soon.

Post by **HarryMann** » 10 Oct 2006, 19:06

presumably it would need to be a reading of the fluid rather than an external reading?

Its an external reading Bob. Its done over a period of time (and thus rate of temperature increase which mirrors it) so that the casing temperature doesn't have much of a lag over internal temperatures.

In fact the calibration curves are just that, calibration curves. If they match up with the datum Torque ~Time (Temp) limits originally set, then that's all that matters.

These curves do not, nor are intended to fully describe the VC's characteristics as applied to on-road, in vehicle application usage. There is a whole set of different parameter plots needed to do that, and an understanding of how the thing works requires looking at several of them, together with interpretation between them.

If you would like a copy of Penske's original paper, I'll photocopy it and send it off. It's a remarkably good piece of work, but still didn't quite crack the nut of a full analytical explanaton of the mechanism behind torque locking, although it certainly laid out a subjective explanation good enough for the basic design to be modified to lock in the right range, for it to be made safe and durable and also for future scaling up and down of a datum design (often one of the most important things that comes out of a proper analytical model of engineering devices).

And lets not forget the guy that invented it - Tony Rolt, who I think still lives somewhere in the Cotswolds, one of the true designers of the Colditz Glider (allegedly), an escapee, and a Le Mans winner too... the VC wasn't the only invention to his credit either, by a long way. Unfortunately there's very little, if any history of the origins of the design, and its early applications. We know during the development of 4WD racing cars, Fergusons was one of the best and for a while used the VC in an early form - others were too heavy, or had horrendous problems.

GEC now hold all the original patents and development of servo locking VCs and other adaptations are still being developed for various markets.