Decoupler not disengaging

[garbaldie]

I installed a decoupler (the one from Van Cafe) when I had the transaxle out during the restoration of my Doka. Since getting it back on the road last month I had been noticing that the decoupler would engage quickly, however when disengaging the switch, it would take a very long time to disengage, I could drive around 20-30 minutes with the knob in waiting for the light to out before it finally would disengage. I suspected a vacuum issue, but when checking the vacuum lines everything checked out. Even when using a Mity-Vac to manually try to disenage it still wouldn't decouple regularly when tried, though in time it would always release when it saw fit.

Fast forward to a couple days ago, when I tried the decoupler again, it engaged quickly, but not disengaging. In fact now it wouldn't disengage at all, drove around several days with the knob in and the light still on. So yesterday I decided to pull the driveshaft (was intending on doing that anyways to replace the worn internal bushings), and remove the whole decoupler. To my surprise, when all unbolted, it wouldn't come off. No natter how much a pulled, I could only separate the housing about a 1/4" from the rest of the transaxle. I had to stick a flat screwdriver up between the casings and pry the splined coupler piece off the output shaft.

Once I finally pried it off, I examined the decoupler and shaft, no damage, nothing else amiss. From what I can tell, it seems when coupled the 2 pieces created a strong vacuum between then and did not want to let go. I wanted to see if anyone has also experienced this? I've not seen any mention of it when searching.

[Sodo]

I’m not understanding this “vacuum” force of the coupler on the output spline.
The coupler is a sleeve, open on both ends, there is no way to involve vacuum.
Is there another way to describe the problem you’re seeing?
With pics maybe?

Of course the coupler should slide easily off the output spline.
If you had to pry it off with a screwdriver theres no hope that the little vacuum actuator could pull it off.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[garbaldie]

[candyman]

https://www.thesamba.com/vw/forum/viewtopic.php?t=638795&highlight=

Check this thread and seeif this helps at all. My issue was the indicator switch. They sometimes use a reverse light switch which requires like 6-9#s pressure to allow the shaft to move. The vacuum is only like 4#s pressure if i recall. I installed a proper syncro diff lock switch and it fixed my issue. U can loosen the switch and see if it will engage and disengage as a test. Your light will not work but you should be able to tell if the decoupler is working properly or not

[Sodo]

Also pry up/down side/side on the output spline, is there any slop in the output shaft bearing?

It's 3 bearings all in a line on one shaft (from the pinion of the R&P) to the output "splined sleeve".
The stiffness of the shaft will mightily resist slop!
This is a wild, un-educated inquiry but I would certainly pry on the spline while the decoupler's off.
Definitely something strange happening here.

This cutaway diagram of the 094 Syncro trans doesn't show the case connection between the decoupler (nosecone) and the "low gear housing".
it can be confusing. There's also the '3rd shaft' of the 'transfer case' that is not shown, so don't be surprised if it confuses you but it's all we've got.

It makes sense there would be a sucking sound as you pulled the decoupler shaft out of the coupling, because the pinion shaft is covering the hole.
But there shouldn't be any suction in sliding the coupler from one shaft over to the other because there is no "displacement".

Maybe I can get some input from SyncroShop if he's around.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[garbaldie]

No perceivable play in the output shaft.

Going to cleanup the output shaft splines and casings and put it back together, as nothing seems wrong with it. On the bench the decoupler works with very little vacuum needed, so the light switch isn't stopping it.

When I reassemble, I'm going to fill the bearing hole and sleeve with assembly lube, and coat the output splines as well, so no air can get trapped in it. I can't explain why the thing is sticking, other than some type of void creating suction, even if that seems implausible as a cause.

[Sodo]

[Sodo]

I chatted a little with Syncroshop and he said sometimes one or both of the alignment sleeves are missing.
The two sleeves ensure alignment of the shafts that you want the coupler to slide across.
They can be on the low-gear housing or the decoupler, it doesn’t matter.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[garbaldie]

Definitely no issues with mis-matched ring and pinons in the front and back. Tires are all new so that shouldn't be putting pressure on the driveline. Also both of the alignment sleeves are present on the low-gear housing, so when mounted it's in proper alignment.

Test fitted the decoupler back on the transaxle, it engaged/disengaged fine. So fully sealed everything back up. With the Mity-vac takes about 5 in-Hg to engage and disengage now. Whether or not it says that way in real operation is yet to be seen, still waiting on the new bushings for the driveshaft before putting that back in back in.

Though none of this still explains why it was stuck being engaged. Shouldn't had to have pried the sleeve off of the output shaft to remove it.

[Steve M.]

How was your sequence of tightening the cover bolts and torque method?
Just wondering if the cover may have flexed as it was tightened.
_________________
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[garbaldie]

[Sodo]

Does your Low gear housing show evidence of "repair" or stress?
People bust them by bump-starting in reverse, and if that has happened it might cause a shaft mis-alignment.
If you see any welding that would be a huge clue.

Another way low-gear housings get busted is if the synchronizer rivets come loose then go thru the gears.

Lugging a big diesel in granny pounds these rivets, loosening them, and they come out.
Some builders remove the granny synchronizer for big diesels.
But the rivets can come out with normal engines too.
Don't lug. It seems like bad form, but slipping your clutch on a Syncro is much better than adding fatigue cycles from lugging.
Clutches are very cheap in comparison to busting your low-gear housing (like $8-10,000 less!)

I have a friend who bought a Syncro that came with a welded lowgear housing.
Low gear housings are no longer manufactured, so all the cracked ones are coming out of the junk-bins and getting repaired.
He eventually located a low-gear housing from Europe.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[garbaldie]

[Sodo]

Ok so now it seems to disengage smoothly?
That’s good news.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb