Club 80-90 Forums

How's about this for the wiki:

Someone (or a few of us) with fresh/good VC's fitted do a tangental line pull test on their propshaft and post up the results to establish a benchmark/working range for testing installed VC's?

Could do the same for known tight and loose ones to improve the data set.

Simple enough: fix a cord to the prop yoke, wrap a few turns around the tube and attach a suitable spring balance (guessing around 30-50kg?), sit on ground and place feet on side of van then pull! Get an assistant to read off the constant load once the prop is turning.

Hard data rather than all the anecdotal stuff that relies on the approximately calibrated forearm...

Just a thought from an engineer who should be doing a proper machining job right now but has had too many callers today

I like the idea of a VC rating chart but, just thinking this through, the prop is connected direct to the rear diff pinion and therefore the back wheel(s) need to be off the ground to allow the prop to turn. That unfortunately means any brake drag or bearing stiffness also comes into play.

I think it would need the prop unbloting from the front diff and the rope wrapped around the collar of the diff flange. Sitting indoors I can't think how clear a route there would be for the rope to come out to the side of the van.

Garyd

Good point Gary, gearbox condition and bearing preload would affect the readings.
I had inadvertantly progressed from the premise of the anecdotal "using a 13mm spanner, you should just about be able to turn it" method.

Looking at ours right now, access to the front diff flange is unobstructed if the cord comes off the top. It is a tangental pull after all so a slight downward angle won't make any difference to the readings.

If the rear end is unbolted (5 minutes) and supported on an axle stand, the drag would be minimal with a dab of grease on the yoke of the stand.

Coming off the smaller diameter of the flange might mean it needs a hefty pull when compared to the diameter of the prop, though. Why not just unbolt the rear end but leave it plugged in so the cord could be wrapped around it?

Mine didnt work so I put a new one in.... It works now

jed

I recently had the opportunity to bench test 11 VCs that were in my possession, including a new refurb unit from Classic parts

Cold (less than 10 degrees celcius), on the bench, mounted on a fixed pinion shaft so output end fixed, and using an input shaft complete with flange to rotate the VC using a 27mm socket and a torque wrench

the obviously failed units - ie blocked oil holes on the seals with spirals of rubber seal coming out like worms and with silicon obviously leaked or present in the housing, generally ranged from 35-70 ft/lb force required to turn them
some others that were less obviously failed 70-120 ft/lb - the high end is higher than they should be according to the graph curve
we kept the 120 as that had no seal damage and came from a very late diff it should make a good tight one to go with a decoupler (for a while)
the rest went back to ClassicParts as core units for refurbishing

the refurbished one came out at.........................75 ft/lb

So test away to your heart content cos I think these figures show that it isn't possible to determine very much at all about the condition of a VC at a single temperature point, the real test is whether it humps correctly at between 100 and 120 degrees,

so I'd maintain that the spanner test, rotating wheel test, 4x2 test, brake tester test and car park full lock test, preferably all of them, will give you a pretty fair idea of the condition of the vc and dropping the oil and seeing if there's any silicon in there (it goes like the aqueous humour in the eye ball if you remember you biology dissection lessons and the smell is unmistakeable) will show if the VC has failing oil seals

it seems to be a case of once the silicon has gone through too many heat cycles you get a stiff one, that then blows the seals and becomes erratic in its behaviour like John's exhibited at the weekend and then fails open and you totally lose 4wd
A visual inspection of the VC in the hand will tell you whether the seals have gone - look in the oil holes that allow for lubrication of the seals, if they are blocked with rubber then you know the seals have blown, and I'd note that in this state I have seen a few with damaged internal spigot bearings caused by the rubber worm blocking the path of oil to the bearing so not good - worse case scenario can cause damage to the end of the pinion shaft, though this can be repaired

it seems to be a case of once the silicon has gone through too many heat cycles you get a stiff one,

This seems very much a thread for engineers and I'm a social worker (be interested to know if there are anymore in 80 90) but... is this a good argument for decouplers - to prolong the life of the VC??

mine lasted 300,000k i'm pretty happy with that lifespan

I'll sidestep the decoupler thing as it always starts a row

The important points to note are that no single test can tell you what's going on. Multiple tests are essential to get the full picture. That's why I kicked this one off.

Can I just nip in here and mention gearbox oil ........ I was going to mention de-couplers but someone beat me to it

I'll sidestep the decoupler thing as it always starts a row

Can I just nip in here and mention gearbox oil ........ I was going to mention de-couplers but someone beat me to it

Well thats two more things I've learnt about the forum...

What Aidan says regarding torque does nevertheless represent the beginnings of an additional test if an installed VC is in doubt.

Based on the refurbed one, it would seem that there is a median figure around 75 lb.ft (not including bearing and seal drag) and significant deviation from this value could indicate partial failure, regardless of it's performance at the critical temperature to initiate "hump" conditions for locking of the coupling.

If torque is too low, check the oil. If it's too high, combine with a 4x2 chock test.

What I am driving at is that with a robust set of installed torque figures for a range of ambient temperatures this could be a simple test that doesn't mean dismantling your front diff and could be part of your regular drivetrain checks.

P.S. I don't recall slicing up eyeballs as I took Physics and Chemistry

jed the spread wrote:Mine didnt work so I put a new one in.... It works now

jed

I ignored Jed's comment the first time

Experienced R&P failure due to VC, so re built Trans-axle, installed De-coupler and kept the aggressive VC

Syncro.org yahoo forum post

Still wondering whether stiff VCs really do rip boxes and diffs apart quite like this, or just used as an excuse


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Yes, Aidans probably right, takes several tests and specifically the time~temp dynamic calibration curve to really determine if the VC will perform properly when installed. The original VW ~ Steyr test rig that Dorfbrunnen use is obviously a well consdired 'quick check' for quality control purposes...not aboslute but 99/100, goo enough.

Ian, I think seal torque (static breakout) is in that 75 ft-lbf figure. I always quoted around 50~55 ft-lbf static torque. Would depend a lot on temperature and how long sitting ?

HarryMann wrote:I think seal torque (static breakout) is in that 75 ft-lbf figure. I always quoted around 50~55 ft-lbf static torque. Would depend a lot on temperature and how long sitting ?

That being the case, an installed torque test may simply not yeild useful results.

Nevertheless, if a few owners with fresh refurbs could all perform the same test it would give interested parties some firm data to go on.

The problem may also be that not enough people are really interested and default to "it's broken, I'll get another"