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Understanding my syncro
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rctucker
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PostPosted: Wed Oct 14, 2020 4:14 pm    Post subject: Understanding my syncro Reply with quote

So, right after i bought my 87 syncro i drove about 300 miles and my rear drivers side cv/axle unbolted itself from the transaxle. (amazingly the bolts where all still there thanks to the cv boot) I have zilch (zero) knobs.

I went through all the gears reving the engine and there was no forward movement.

Does this say anything about my VC, I thought this ment that it was "stuck open"

based on this perspective... this disconnected axel should be detected as slippage and the other wheels should engage? if one of the rear wheels slips does the power get transferred to the other rear wheel or do both need to be slipping in order for the VC to heat and engage? this indicated to me that. all forward motion was driven through the rear drivers side wheel.

Obviously, I'm confused and don't understand the mechanics, if you can help me understand this better, next time in your town, ill buy ya a beer!

Thanks
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4Gears4Tires
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PostPosted: Wed Oct 14, 2020 4:46 pm    Post subject: Re: Understanding my syncro Reply with quote

Your VC is bad. I had the same thing happen to me when a terrible shade tree mechanic didn't torque the cv bolts to 33ftlbs. My van drove just fine with the cv shaft clanking around in the trailing arm. Laughing
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Sodo
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PostPosted: Wed Oct 14, 2020 5:10 pm    Post subject: Re: Understanding my syncro Reply with quote

4Gears4Tires wrote:
Your VC is bad.


- or you have no driveshaft
- or one front axle has also disconnected too Wink

Most likely your VC is dead.
They last long, unless abused somehow.

Heres a recent/decent VC thread: Blown Viscous Coupling?
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Wildthings
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PostPosted: Wed Oct 14, 2020 5:12 pm    Post subject: Re: Understanding my syncro Reply with quote

Assuming it was a rear CV that came undone, if you have a decoupler for the front and no form of locking differential in the rear, you are getting the expected results.

The torque on the CV bolt is supposed to be quite high and should be done with a torque wrench for best results. The torque is 33 ft*lbs and that is with moly grease on the bolt threads, though some will argue otherwise.
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4Gears4Tires
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PostPosted: Wed Oct 14, 2020 5:16 pm    Post subject: Re: Understanding my syncro Reply with quote

He said he has zero knobs.
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Sodo
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PostPosted: Wed Oct 14, 2020 6:42 pm    Post subject: Re: Understanding my syncro Reply with quote

4Gears4Tires wrote:
He said he has zero knobs.


Stranger things have happened.
One recent Samba member discovered that his new-to-him Syncro had different R&Ps.

Discovering a decoupler would be nice.
I’d look under with fingers crossed. 🤞
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....KTMs, GasGas, and a Stumpjumper
Gear oil is like underwear.
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rctucker
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PostPosted: Thu Oct 15, 2020 9:41 am    Post subject: Re: Understanding my syncro Reply with quote

To parse the responses.

with no knobs, and the driverside rear axle disconnected, getting no forward movement is expected?

to clarify my understanding of what has been said.
Unless i have a locking dif in my transaxle, power will not be transfered to the other rear wheel, both rear wheels need to be slipping in order for the VC to engage.

looks like i need to do the 2x4 test, just need some flat ground and a jack on wheels. Shocked
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Sodo
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PostPosted: Thu Oct 15, 2020 1:43 pm    Post subject: Re: Understanding my syncro Reply with quote

rctucker wrote:
to clarify my understanding of what has been said.
Unless i have a locking dif in my transaxle, power will not be transfered to the other rear wheel, both rear wheels need to be slipping in order for the VC to engage.


.....sort of. This is a step, but it's not clarity.

With one axle un-bolted, a proper VC would engage and the van would drive forward, you might not even notice the bolts had come out, except for clattering and banging. If the loose axle found a place to sit & spin you might not even know.

Lets start here:

1) Is there a driveshaft on the van?
2) Is there a Decoupler on the van? (yes i know there's no knob, wondering if someone put a decoupler, or a trans with a decoupler, on the van.

3) 3 wheels on the ground, and one front wheel lifted. Try to rotate the wheel. With a proper VC you can bearhug the lifted front wheel and rotate it very slowly with LOTS of effort. It should feel like it's stirring a pot of viscous bread dough = "the VC"

If it spins freely, look at the driveshaft, does turning the lifted front wheel rotate the driveshaft? Probably not (that's the “decoupler” possibility).

If the lifted front wheel (rotates and) does not turn the driveshaft, your VC is dead (freewheeling or open).

The 2X4 test is to measure “how good” a VC is.
There’s no need to qualify the performance of an freewheeling VC.

Wish for this: 🤞 The van has a decoupler thats “uncoupled” and the VC is good. And you can someday you can qualify it with the 2x4 test. 👍🏽🙏
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....KTMs, GasGas, and a Stumpjumper
Gear oil is like underwear.
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4Gears4Tires
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PostPosted: Fri Oct 16, 2020 6:03 am    Post subject: Re: Understanding my syncro Reply with quote

Sodo wrote:
With one axle un-bolted, a proper VC would engage and the van would drive forward, you might not even notice the bolts had come out, except for clattering and banging. If the loose axle found a place to sit & spin you might not even know.


Yep. With one axle disconnected my van drove completely normal. Aside from the noise.
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rctucker
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PostPosted: Sat Oct 17, 2020 10:30 am    Post subject: Re: Understanding my syncro Reply with quote

ok, lets eliminate the VC for a second bc that is confusing people.

lets focus on just the rear transaxle with NO decoupler.

If one axle is disconnected from the transaxle (let's say its the driver's side, but probably doesn't matter)

There should be no forward motion bc the transmission will give all power to the drive shaft that spins the fastest? (the disconnected driver's side)

If there was a locker, I could then lock that and then forward motion would result bc the power would be transferred equal (but this is probably not recommended)

If I disconnected the passenger side axle from the transaxle (now neither rear axles are connected) this would then enage slippage bc there now a differential dtwn front and back. (the 2x4 test)

sorry if im ignorant, im having a hard time understanding these systems from a top level from the bentley manual.

where does a peliquin limited slip come into play here?

thanks for any thoughts!
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Wildthings
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PostPosted: Sat Oct 17, 2020 11:24 am    Post subject: Re: Understanding my syncro Reply with quote

rctucker wrote:
o
where does a peliquin limited slip come into play here?

thanks for any thoughts!


It is my understanding that a Peloquin requires some resistance on the spinning side for it to lock. With the CV bolts backed out this resistance would not be supplied

If you do not have a decoupler then the front driveshaft might plain be missing or there is something else wrong somewhere. Likely the VC but possibly something else.
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Sodo
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PostPosted: Sat Oct 17, 2020 5:39 pm    Post subject: Re: Understanding my syncro Reply with quote

Rtucker you are correct WRT the behavior of a rear differential and a locking differential.

A Peloquin would not drive the van forward if one rear CV was unbolted.
There is a locking Peloquin though.

3rd request for these 2 basic details that are relevant to whether or not power gets transferred to the front differential.

1) have you confirmed that your van has a (center) driveshaft installed?
2 ) you wrote that there’s no knobs but have you confirmed that your trans has no decoupler? Are there ANY vacuum actuators on your trans?

If you don’t know this (yet.....you will !), just post a pic of the forward end of the trans.
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EJ25, Peloquin diff, locker, transaxle oil cooler/filtration system
....KTMs, GasGas, and a Stumpjumper
Gear oil is like underwear.


Last edited by Sodo on Mon Oct 19, 2020 2:16 pm; edited 1 time in total
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Sodo
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PostPosted: Sat Oct 17, 2020 9:24 pm    Post subject: Re: Understanding my syncro Reply with quote

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


Here's an info-sheet pic I started working on a few months ago.
It seems on-topic for a thread titled "Understanding my syncro".
I don't remember why I started on it.
Just a Syncro-nut thing.

It's still in-work.
If anyone sees errors or omissions I'm interested.
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syncro surf
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PostPosted: Sun Oct 18, 2020 6:40 am    Post subject: Re: Understanding my syncro Reply with quote

Sodo wrote:


3rd request for these 2 basic details that are relevant to whether or not power gets transferred to the front differential.

1) have you confirmed that your van has a (center) driveshaft installed?
2 ) you wrote that there’s no knobs but have you confirmed that your trans has no decoupler? Are there ANY vacuum actuators on your trans?



If you've only owned the this van for 300 miles - you really do need to verify that the drive shaft is installed. These drivelines can develop vibrations and it's not that uncommon for someone to simply remove the drive shaft and drive as a 2wd van, rather than sort out (pay for) the problem.
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Yellow Rabbit
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PostPosted: Sun Oct 18, 2020 7:24 am    Post subject: Re: Understanding my syncro Reply with quote

Or worse, someone blew up the syncro transmission and stuck a 4 speed in there.
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MarkWard
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PostPosted: Sun Oct 18, 2020 7:33 am    Post subject: Re: Understanding my syncro Reply with quote

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


I think for many new syncro owners, the viscous coupling VC is difficult to understand or appreciate. Add multiple previous owners and 30 plus years it gets even more complicated to know for sure how it should work.

There’s also not an easy way to test it without setting up safe test conditions. That said, It’s a pretty cool piece of hardware.

I believe any new syncro owner can expect to go through the entire drivetrain at some point.
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4Gears4Tires
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PostPosted: Sun Oct 18, 2020 7:58 pm    Post subject: Re: Understanding my syncro Reply with quote

rctucker wrote:
ok, lets eliminate the VC for a second bc that is confusing people.

lets focus on just the rear transaxle with NO decoupler.

If one axle is disconnected from the transaxle (let's say its the driver's side, but probably doesn't matter)


No, you are confused. We are not confused.

You can't just focus on the rear transaxle w/ no decoupler because you have an additional driveshaft coming out of the transmission.There are 3 driveshafts, right? 2 at the back and 1 going to the front. The front is attached to a VC.

If any single one of those axles is missing, you are still going to get forward motion. If you don't, such as in your case, something is broken/missing/unconnected/etc.
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