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caseyl
Samba Member
Joined: September 28, 2016
Posts: 60
Location: VT
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 Posted: Wed Jul 23, 2025 3:15 pm Post subject: Question for the CV Joint Gurus - Help Identify Failure Mode |
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Hey Samba People!
I have a good question for all the CV joint guru's out there.
What causes this failure? I can't seem to figure this out.
I have had this occur a few times on my Syncro Vanagon, which I assumed was my fault for some reason because I do the assembly.
But this time it happened on my Q5, on an axle I replaced as an assembly. This is a new GKN assembly from FCP euro. Seems to have lasted about a year.
When I have taken a similarly failed joint apart from my vanagon, I was surprised to see the star balls and cage intact. I initially thought I exploded the joint, but that doesn't seem to be the case. |
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MarkWard
Samba Member
Joined: February 09, 2005
Posts: 18828
Location: Retired South Florida
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| Posted: Wed Jul 23, 2025 5:50 pm Post subject: Re: Question for the CV Joint Gurus - Help Identify Failure Mode |
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| On the Racecar I’d run no small clamps. I believe it has to do with temp differential. Expansion and contraction. One try is to slip a small section of wd40 straw between the boot and the shaft to allow for equalization. When the boots were of good quality the small clamp wasn’t really required. Recently I had 4 Lobro cv boots split on the seam starting at the small end. |
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ALIKA T3
Samba Member
Joined: July 30, 2009
Posts: 7216
Location: Honolulu,Hawaii and France
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MarkWard
Samba Member
Joined: February 09, 2005
Posts: 18828
Location: Retired South Florida
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| Posted: Thu Jul 24, 2025 5:13 am Post subject: Re: Question for the CV Joint Gurus - Help Identify Failure Mode |
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| I should have added I’m not a Guru. Is the problem the boot or did the joint fail? Are you driving some altitude changes? |
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ALIKA T3
Samba Member
Joined: July 30, 2009
Posts: 7216
Location: Honolulu,Hawaii and France
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| Posted: Thu Jul 24, 2025 5:39 pm Post subject: Re: Question for the CV Joint Gurus - Help Identify Failure Mode |
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| MarkWard wrote: |
| I should have added I’m not a Guru. Is the problem the boot or did the joint fail? Are you driving some altitude changes? |
The CV is broken, look at the boot, it twisted, by about 90* judging by the mold seam, while the ends haven't budged. I had the same on my Syncro, can't believe I got home and boot was still good 
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget |
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dobryan
Samba Member
Joined: March 24, 2006
Posts: 17176
Location: Brookeville, MD
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ALIKA T3
Samba Member
Joined: July 30, 2009
Posts: 7216
Location: Honolulu,Hawaii and France
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| Posted: Wed Jul 30, 2025 10:19 am Post subject: Re: Question for the CV Joint Gurus - Help Identify Failure Mode |
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| dobryan wrote: |
| Johnny had that happen at Syncro Solstice. Broke the cage. |
There's a famous picture a good decade ago at the crazy steep hill at Hollister, of a Syncro that broke the front outer cage and subsequentally rolled on its side.
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget |
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Sodo
Samba Member
Joined: July 06, 2007
Posts: 10673
Location: Western WA
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| Posted: Wed Jul 30, 2025 12:31 pm Post subject: Re: Question for the CV Joint Gurus - Help Identify Failure Mode |
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Yeah that gives me the Willies wrt relying upon granny on a steep slope. I just don’t have a lot of faith in the strength of the drivetrain. One CV failure and you’re now a 2WD inserted into a dangerous situation.
I’m not a CV guru either but I have been denigrated for statements aligning me with “clocking deniers”. 
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Thats a curious failure!
The star can rotate only after the 6th ball has fallen out. I have a hard time believing it would rotate just 1/6 turn.
And where are the balls - on the inside?
I don’t see stripping the spline. They’re real strong. Possibly the spline pulled out & reinserted? 
_________________
'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb |
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MarkWard
Samba Member
Joined: February 09, 2005
Posts: 18828
Location: Retired South Florida
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| Posted: Wed Jul 30, 2025 1:38 pm Post subject: Re: Question for the CV Joint Gurus - Help Identify Failure Mode |
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| It’s hard to imagine the outer cv failing in the above photo and not destroy the boot completely with a free wheeling shaft. The original poster hasn’t been back, so we are guessing at this point. |
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ALIKA T3
Samba Member
Joined: July 30, 2009
Posts: 7216
Location: Honolulu,Hawaii and France
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| Posted: Wed Jul 30, 2025 11:11 pm Post subject: Re: Question for the CV Joint Gurus - Help Identify Failure Mode |
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| MarkWard wrote: |
| It’s hard to imagine the outer cv failing in the above photo and not destroy the boot completely with a free wheeling shaft. The original poster hasn’t been back, so we are guessing at this point. |
I shattered a 16"cv cage as well, the boot held up til I got home, no twist. I couldn't believe it. I did decouple though, so it was only passive anyway, open diff too.
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget |
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SyncroTrev
Samba Member
Joined: August 06, 2021
Posts: 50
Location: Bend, OR
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| Posted: Thu Jul 31, 2025 10:15 am Post subject: Re: Question for the CV Joint Gurus - Help Identify Failure Mode |
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I am by no means a CV guru either.... but I do service mine often. (Syncro with TDI ALH swap running 930 cvs everywhere but the front outers, those are the 16" Burly upgrades.)
To answer the original question.... why do they break:
1) Cheap parts. Try and buy the nicest you can.
2) Vehicle mods that increase horse power / torque. (if you're running more power than stock and are still running stock CV's it can be a weak spot.
3) Driving certain ways that are known to be hard on CV's. Applying lots of power with the wheels turned as sharp as possible for example. Or spinning wheels on ice then catching dry pavement with lots of power down.
4) Also lift kits... the extreme angle will wear them out faster.
Judging by your picture... you look stock with no lift. So likely just bad luck with cheap parts. Or maybe you have a teenager your letting drive the car... they could break a military tank those kids... haha
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1989 Vanagon Syncro
Adventurewagen Hightop
Westy Cab Interior
1.9 TDI ALH
Bend, OR |
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