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syncro surf
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PostPosted: Fri Jun 30, 2017 12:12 pm    Post subject: Aggressive VC Reply with quote

Hi,

Getting my 87 Syncro back on the road after a long time in storage. I did the 2x4 VC test (cold) and in L or 1st I can't quite get it to idle without climbing the wood. The rear wheel spins until the clutch is 3/4 of the way out then over it goes.

Does driving with an aggressive VC do and harm to anything? and - is there a current source for VC fluid and seals so that I might attempt a rebuild?

Thanks
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ALIKA T3
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PostPosted: Fri Jun 30, 2017 3:57 pm    Post subject: Re: Aggressive VC Reply with quote

You might want to rebuild that unit, it is becoming too stiff, you can snap parts...

I sell the seals in the classifieds, all in viton, imported from Europe.
https://www.thesamba.com/vw/classifieds/search.php?username=ALIKA+T3

You can find silicone oil pretty cheap, I posted about it on one of the numerous threads somewhere.

This is a random link but you can choose your viscosity if you'd like

https://www.amazon.com/Silicone-High-Purity-000cst-500ml/dp/B00Z78H0CQ

Aloha!
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candyman
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PostPosted: Fri Jun 30, 2017 4:31 pm    Post subject: Re: Aggressive VC Reply with quote

syncro surf wrote:
Hi,

Getting my 87 Syncro back on the road after a long time in storage. I did the 2x4 VC test (cold) and in L or 1st I can't quite get it to idle without climbing the wood. The rear wheel spins until the clutch is 3/4 of the way out then over it goes.

Does driving with an aggressive VC do and harm to anything? and - is there a current source for VC fluid and seals so that I might attempt a rebuild?

Thanks


If its not super aggressive ie; extreme binding in turns, then you could always add a decoupler and get some life out of that vc. Mine failed the 2x4 test so I added a decoupler. That was 4 years ago and still rocking tha same vc. I couple when needed and the vc has not gotten any worse as far as aggressiveness goes. In fact other than the 2x4 test fail you would never know my vc has age to it
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Jon_slider
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PostPosted: Fri Jun 30, 2017 5:16 pm    Post subject: Re: Aggressive VC Reply with quote

syncro surf wrote:
Does driving with an aggressive VC do and harm to anything?


yes, it damages the ring and pinion in the transaxle. You can get some idea of the condition of your transaxle by checking the drain plug magnet. (Gotta be fast at getting your thumb over the hole so it does not dump all the fluid. It helps to have a spare drain plug ready. Or, maybe its time for a fluid change too..?)

This is what bad looks like
Christopher Schimke wrote:

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.


the solution is to remove the driveshaft until you either

add a decoupler, or install a less aggressive VC

It is not helping anything to drive it with an aggro VC on pavement. You will find the van handles very nicely without the drag of the VC.

Even with a brand new VC, it is easier to park decoupled, without the binding the VC causes.
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syncro surf
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PostPosted: Fri Jun 30, 2017 7:03 pm    Post subject: Re: Aggressive VC Reply with quote

Thanks - I'd rather not add a de-coupler so I'd like to end up with a VC soft enough to run on pavement.

Most of the VC rebuilding threads are quite old - has there been any consensus
on viscosity and volume of fluid to approach an original VC ?

I gather it's somewhere between 20,000 and 100,000 cst and 278-280 grams.

Is it that simple or is there still some black magic involved?
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gears
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PostPosted: Sat Jul 01, 2017 6:10 am    Post subject: Re: Aggressive VC Reply with quote

Tom Lengyel claims there is no R&P damage when running stiff VC or even a continually engaged solid shaft, so I have to question my own previous opinions on this subject ..
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tencentlife
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PostPosted: Sat Jul 01, 2017 7:50 am    Post subject: Re: Aggressive VC Reply with quote

Whatever torque is transmitted to the front driveline is torque NOT transmitted to the rear R&P, so a stiff VC will actually lessen stresses at the rear R&P (and proportionately increase them at the front R&P, of course).

Use your noggins, people.
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Jon_slider
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PostPosted: Sat Jul 01, 2017 12:30 pm    Post subject: Re: Aggressive VC Reply with quote

Because there is no center diff in a syncro, the front diff cannot turn faster than the rear. To get through a turn on pavement, the road pressure on the VC causes it to slip, because the front wheels turn too slow to get through the turn.

In this scenario, the front wheels act like brakes:

A syncro with aggressive VC, or coupled solid shaft, will stop rolling when steering into a parking spot.

That tells me the front wheels are braking, not pulling

Equal diff speeds front and rear, explain why the front wheels create drag, that stop a syncro from rolling, when turning into a parking space.

Equal diff speeds are all that the Syncro drivetrain can power, because there is no Center Diff to distribute more rotations to the front diff than to the back diff.

Some people do not yet understand that a center diff is required to power the front diff faster than the rear. And that therefore on dry pavement, a VC is not pulling the van, it is slowing it down.

Why do so many syncros need rebuilds more often than 2wd? Because the VC increases the pressure and wear inside the transaxle.

A VC only sends power forward when the rear diff spins faster than the front diff. This never happens on dry pavement. Therefore, decoupling on pavement protects the transaxle from pressure and wear.

some more magnet pics for the OP to compare to the one in his tranny
Image may have been reduced in size. Click image to view fullscreen.

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Sodo
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PostPosted: Sat Jul 01, 2017 8:58 pm    Post subject: Re: Aggressive VC Reply with quote

Jon_slider wrote:
Why do so many syncros need rebuilds more often than 2wd? Because the VC increases the pressure and wear inside the transaxle.



I don't think it's related to the VC. The VC, mile for mile, mostly "goes straight". And as such, mile for mile, it's "mostly" reducing the load on the rear R&P and the pinion bearing, extending their life. When the van is turning, and the VC is loading up, the RPMs are slow, and its for a short duration. Around town the oil might be cooler, thicker, more protective. I do not believe the VC can be detrimental to the trans.

If your VC is aggressive, then do your pavement maneuvers "more gently", slower, don't turn so tight if on grippy pavement (when possible). Look for gravel or sand patches. Take a wider line when you can. The Syncro is a short wheelbase vehicle (97 inches) the wheel paths aren't as divergent as an F250 pickup, for example (which could be about double, ~14 feet!). An aggressive VC is harder on your CV joints, but half of that is on the coast side.

Regarding why Syncro transaxles have more "trouble....."

==== <What Tom Lengyel says>======

The Syncro trans has the same size synchronizers as the 2WD, whereas the rotating mass of the additional gears & shafts in the low gear housing is MUCH heavier (big heavy granny and reverse, idlers + another shaft). All these gears and shafts spin all the time and the little 2WD synchros have to spin them all up. Anyone will notice a Syncro does NOT shift as nice as a 2WD. You have to shift slowly, or double-clutch to shift faster.

The Syncro synchros are too small for the weight they must spin up, therefore they (the synchros and the dogs on the gears) wear more. And then shifting gets a little harder. And it compounds.

Little abrasive chips come off these parts when the gears grind into engagement and contaminate trans fluid sooner than the 2WD. And "nobody" changes gear oil on Syncros or 2WD either, until their trans is already dead. Thats why EVERYBODY's magnet looks the same. It's not OK that your magnet looks like everyone elses, they're on a death spiral too. Contaminated gear oil begets more contamination, in a compounding death spiral as bearings wear out sooner and produce even more metal in your oil.

Gotta get that trash out of your oil - would you be OK with that trash in your engine? What if your rebuilder left that trash in your "new" trans? Trash in the oil is trans death.

And the Syncro is ~15% heavier, so there's a constant ~15% more load on the trans. And even more if your van is loaded to the gills. And more yet if you have a big engine. And drive fast.
====== <end Lengyel> ============

====== <a Sodo opinion> =======

Particles too small to be seen ('detectable' is somewhere around 3-6 microns) are still hundreds/thousands of times bigger than the oil film thickness. Your shafts/bearings/race surfaces, while looking real shiny, are a series of peaks and valleys. If 2 peaks pass by each other, and there happens to be a particle there, it will punch thru the EP protection, metal-to-metal, perhaps generating another steel particle. More trash in your oil and this "event" occurs more often, compounds, (gets worse and worse).

Many think that specialty oil can provide better protection when contaminated, so they buy better oil with "EP protection" (the buzzword). But extended "EP protection" occurs at the molecular level, it's like "one molecule thick". Compare this with particles of steel, that you can detect with your eye (by a sparkle or sheen). "Visible" particles are on the order of 3,000 - 4,000 times bigger - than the thickness of "EP protection". Protection just CAN'T work that way. As one fella said, "use your noggins people"! Old oil is __loaded__ with these metal fines.

So if you really want to benefit from the EP protection of specialty oil, you have to be ready to "change it" or "purify it"...... ----->often. Changing it can be very expensive, like $70-$100 per change. In my case I'm filtering it via my pumping system; but there are low cost, highly effective methods to purify expensive oil (of metal) that are "not very popular", mostly because very few owners will get under their vans. And the folks who will, don't enjoy trans oil changes. They should.

Purifying oil is pretty easy though (once its out of the van). Reusing it though, is kinda like eating leftovers- best done but in the privacy of your own home. You are doing a good thing, just don't tell anyone. Laughing You don't serve leftovers at a potluck etc. Wink. But if you're afraid (or tired) of rebuilds.....it's not that big of a deal to keep your trans oil clean**. Its much easier than transaxle R&R.

**unless you have a Smallcar bellhousing. Smallcar bellhousing oil drain is 1/2 inch above the floor of the trans, thus a bunch of heavy metals remains to contaminate your new oil, perhaps the worst of the old oil. Your big engine produces MORE metal in your trans oil, so this is not a great feature to have. If your engine or trans is ever "out", unbolt your bellhousing and fix the drainhole (its an easy fix!). The Smallcar bellhousing has been produced with this (easy-fix) flaw for ~8 years now, so MANY big-engine vans out there have this problem.

===================

But anyway.... to rebuild your VC? Or add a decoupler to "save what you have" is the dilemma. And save your trans too, it's crazy expensive to rebuild.
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Skid62
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PostPosted: Tue Dec 12, 2017 2:47 pm    Post subject: Re: Aggressive VC Reply with quote

syncro surf wrote:
Hi,

Getting my 87 Syncro back on the road after a long time in storage. I did the 2x4 VC test (cold) and in L or 1st I can't quite get it to idle without climbing the wood. The rear wheel spins until the clutch is 3/4 of the way out then over it goes.

Does driving with an aggressive VC do and harm to anything? and - is there a current source for VC fluid and seals so that I might attempt a rebuild?

Thanks

Hi,
I had an 86 synchro that sat a long time while working on it. Silicone leaked out and I tried a rebuild using what I thought was a close viscosity fluid, and new seals. It worked, but was too aggressive. I could feel it binding in tight turns on pavement. The test I was told to use was, jack up one front wheel off the ground, try to turn it by hand. If it will turn, even with a lot of resistance it's probably ok. If it won't turn at all it's too aggressive, (mine was). I ended up sending my VC to Ken at German Transaxel in Bend Ore. He did a rebuild (the most aggressive of three options), and I purchased an on the fly decoupler that allows me to choose when and where I put it into all wheel drive.
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gears
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PostPosted: Tue Dec 12, 2017 6:17 pm    Post subject: Re: Aggressive VC Reply with quote

By coincidence, I visited German Transaxle today and talked to Ken about his VC rebuilding program. They actually tested 14 new VCs for their baseline info, finding a variation of 10-15%. The silicone fluid they arrived at is a very specific mix. Straight silicone is far too aggressive (as they learned the hard way).
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PostPosted: Wed Dec 13, 2017 8:50 am    Post subject: Re: Aggressive VC Reply with quote

gears wrote:
Straight silicone is far too aggressive (as they learned the hard way).


That implies that they're blending a non-siloxane liquid with the PDMS, or do you mean they're just mixing viscosities?
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gears
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PostPosted: Wed Dec 13, 2017 10:05 am    Post subject: Re: Aggressive VC Reply with quote

I purposely didn't ask for specifics.
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PostPosted: Wed Dec 13, 2017 10:25 am    Post subject: Re: Aggressive VC Reply with quote

Fair enough, thanks.
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