Syncro front diff knock.

[Deadchemist]

Hi Guys,

I have a deep knocking coming from the middle front (as in between the front seats) of my 86 Syncro. I have taken the prop out for the moment as I'm working through a vibration issue with that.... but knock is still there. Seems to come and go but is especially knocking when for the first few miles (over small bumps) and then settles down.

Found a youtube video which shows the exact same knock but the gentleman who posted it gave no more information as to what the issue is/was or the fix.

Anyone have any ideas?

https://youtu.be/DAEzovBkt7g

[MarkWard]

Even though the drive shaft is removed, the cv shafts and ring and pinion are still turning. I’d start with looking at the CVs and draining the differential.
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[Deadchemist]

Do you think i should remove the whole diff or just drain it, fill back up and go from there. Is there anything especially i should be keeping an eye out regarding the CVs/ring and piston?

[MarkWard]

I would not pull the differential unless there was a lot of material on the magnet. Unfortunately you can’t easily drive the van with the CV shafts removed, but you’d look for a torn boot or maybe some cracking. CVs do need to be serviced. If you aren’t sure when they were done, it might be worth servicing them. Quite a few members have had good luck using a needle to work fresh grease into the cvs.
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[Sodo]

[WiboBusMan]

That sound is not normal but I've heard a clunk similar to the one in the video from a dry rear inner cv on a 2wd.
X2 on the warning to not move a Syncro without front shafts installed and properly torqued.
Page 36 of the following doc has a good exploded view of the components, but not a nice cut-away sodo provided - thanks for your artwork (I think you have the circlip on the wrong side) .
See page 36:
https://hans-wibo.asuscomm.com/index.php/s/tmNy8nNaSSaeyCG


W
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[MarkWard]

If it were me, I’d remove both CV shafts expecting to clean, inspect, new boots, etc. But with the shafts removed, I’d knock the outer joints off the shafts and temporarily reinstall in the hubs tightened to spec. This makes it safe to operate the van. If the noise is gone, you’ve isolated it some what.

The problem is for many folks, this is not an easy job. In fact I find it to be on my list of least favorite things. Syncro’s by their nature just require more effort and patience.
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[Deadchemist]

Thanks for the replies, i certainly won't be messing around trying to drive it without the shafts properly sorted. But for the moment it all feels ok par this knocking so I'm hoping that it's just a dry boot.

I'll check the inner cv boots for splits or what not tomorrow. Whats the suggestion with injecting grease with a needle? Anyone got any info on this regarding method/grease type etc etc?

*edit. Found a good post on the forum detailing needle info so please ignore.

[Sodo]

[tjet]

Does it have a front locker? That could also be a noise source if partially engaged.

Thanks for the great illustrations Sodo & Wibo!!

[Deadchemist]

Yes thanks for the fantastic drawings and illustrations, 10 out of 10 from me

No front locker, just rear! The noise really really sounds like the video i posted in the original post.

[The Believer]

Bringing this one back,

@deadchemist, were you able to figure out the noise? I'm having a very similar noise on my Syncro after driving it across country.

Just curious if it ended up being the cv's or not?

thanks
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90 Syncro, 2.3 4-spd

[4Gears4Tires]

[Sodo]

[The Believer]

Good thinking on keeping a spare CV stub around.

I've uploaded a video of my van driving and tried my best to record the knock, which is a very rhythmic grand father clock sound of sorts.

I pulled the drive shaft yesterday, just to eliminate that as a possible source, and noise stayed the same.

No shavings in the front diff oil. the front diff was just also rebuilt and I had no noise for about 3000 miles or so.

I'm leaning towards a CV?


Link

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90 Syncro, 2.3 4-spd

[The Believer]

Here is one more pertinent video. This is at a shop on a life with all wheels in the air, van in gear and moving ever so slightly.

It's very clear to see the front diff hop/bind.


Link

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90 Syncro, 2.3 4-spd

[MsTaboo]

It looks like at least one of the mounts is loose, the diff shouldn't be moving like that even with the problem.
Could still be CV, but because of the loose mount(s) it's showing as the diff.
Tighten down the mounts and try again.
If the diff had something clunking around enough to lift it like that there would be debris in the oil.

The sequence of the bump seems to be correlated with the rotation of the CV.
Put a mark on the CV and case, see if the bump happens at the same point each time the mark on the CV passes the mark on the case.
Any idea how old the CVs are?

Although it's possible the bolts on the ring could be loose. Who did the rebuild?
You can try to check, disconnect the inner CVs and wiggle/rotate the output flanges. Try to grab both flanges, it will be tight working space. There will be some backlash but not much if all's good and smooth.

But it's most likely CV. If the ring were loose then it stands to reason there would be more vibration rather than a single bump.
A broken tooth might do it, but wouldn't there be more junk in the oil?

Here's a pic of what's in there.

Best of luck
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[The Believer]

@MsTaboo Thanks for having a look and I appreciate your advice.

I've been wondering about the diff bushings. I did loosen them yesterday when I removed the driveshaft and they all seemed nice and tight. Could the bushings be totally blown, causing the excessive movement? I'm not against changing them.

The CV's look rather old and crusty, unsure of the actual age though. The boots are not torn and I don't notice any obvious fresh grease splatter.

The diff was rebuilt by Ron's Transaxles in San Pablo CA. a reputable VW shop. The magnetic drain plug didn't have anything on it after 3k of driving.
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90 Syncro, 2.3 4-spd

[skills@eurocarsplus]

a bad CV with a "knot" in it would cause what i see in your video. i say "knot" because so many folks think the only failure of a CV is that death click you hear on sharp turns

pull the axles and move them thru their range of motion. bet you find a stiff one, and bet its an inner (they seem to "knot" up more than an outer)
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[MsTaboo]