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woodoctr
Samba Member
Joined: June 01, 2013
Posts: 254
Location: Ohio
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 Posted: Sat Jun 01, 2013 10:20 pm Post subject: Input shaft let go....Hmmmm |
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My VW based kit car had a 2.8 v6 conversion for many years and ran great. About 14 years ago I decided to step up to a little more (ahem... about 300 h.p.) power and installed a supercharged 13 B rotary mated to a brand new build on a 72 transaxle by a great California transaxle guy. Both the motor and the tranny got the best stuff I could afford (motor- oil pan baffle, turbo bolts, street port, JDM seals, Camden supercharger, Holley 670 Street Avenger carb, etc.) and (tranny- welded 3 and 4th gears, hardened keyways, 3.44 heavy duty ring and pinion, etc.) The motor was actually broken in with a bench testing and tuning.
So I put about 20,000 miles on the car as my weekend driver covering about 7 states over thse 14 years. Fun car, plenty of power on demand and decent fuel economy.
About 4 months ago I start to notice more "whine" in my tranny. In fact rotaries are pretty quiet at cruise so I'm hearing my tranny OVER my motor. I'm figuring it's probably bearings ( not unexpected considering the power levels) throughout the transaxle that need to be replaced. So I pulled my engine and trans. and had another reputable California transaxle shop rebuild it. The bearings were replaced, we added a chrome moly pinion nut, a stronger 1st gear, replaced the reverse slider, and pretty much buttoned it up . Also did a new Stage 2 Kennedy pressure plate and a Daiken clutch with a new German throwout bearing. New German heavy duty mounts were installed along with a Mohr mid mount and a Fast Fab chrome moly rear truss. Whine competely gone, by the way.
So, I've driven the car about 500 miles now and one day it pops out of reverse. Then a day later it does that again. Next day and I'm getting ready to go the Carlisle show and NO REVERSE. There is no crucnchy sound, no nothing. Looks like it is going in gear at the rear inspection port but still no reverse.
Okay, checked all the obvious stuff, so lets' pull the motor... and when doing that my input shaft starts coming out away from the transaxle! The c clip is still on the front part of the shaft but it has come unthreaded from the other part of the shaft. This had allowed the reverse gear sleeve on that shaft to move back just far enough to not engage.
And my question here is... If this was some type of failure shouldn't that 7 mm stud have broken in there instead of just unscrewing itself? Since I've driven this car for so long without something like this happening I really am suspecting the rebuild process on that transaxle.
Yeah, I know, I'm running a lot of power but I'm no drag racer, so no clutch dumps, and I don't do more than 6 lbs. of boost and don't get into boost until the motor and tranny are warmed up.
Any thoughts? |
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Harleyelf
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Joined: April 23, 2009
Posts: 1572
Location: Appleton, WI
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| Posted: Sat Jun 01, 2013 10:44 pm Post subject: |
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Naw, they just sometimes unscrew themselves. You can take it apart and look for chunks if you want, but my guess is the stud is intact and attached to the propeller shaft. Threads expand with vibration and use and loctite doesn't always hold on a second torquing of a power-transmitting shaft end.
By all means, change the oil and look for chunks. But taking the transmission out is most likely a waste of time. |
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gears
Samba Member
Joined: October 28, 2002
Posts: 4391
Location: Tamarack, Bend, Kailua
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| Posted: Sun Jun 02, 2013 7:49 am Post subject: |
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Still scratching my head on that reply .. that 7mm stud doesn't use loctite, and the input shaft should never be "torqued". A sloppy input shaft is critical to the "Quill Shaft" design, which is considerably stronger than a 1-piece shaft. This is one of the coolest innovations ever arrived at by the VW engineers. If the shafts are torqued together, the result is almost always a snapped 7mm stud (and potentially other issues).
Some 7mm studs were poorly manufactured, and can screw too far one way or the other. It's extremely rare, but has happened. VW solved this once and for all when they upgraded this stud to have a bulge in the center. This new stud works with all aftermarket mainshafts, and cannot screw in too deeply in either direction. This is the same VW stud used in the 2-piece mainshafts of GT3 Porsche sequential racing transaxles.
But the stud probably isn't your issue. You may have split your reverse coupler (splined joining sleeve). There are choices when it comes to reverse couplers. Some are rather thin walled. These can split with a higher horsepower engine. The thicker walled reverse couplers rarely split.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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Dale M.
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Joined: April 12, 2006
Posts: 20378
Location: Just a tiny bit west of Yosemite Valley
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| Posted: Sun Jun 02, 2013 8:03 am Post subject: |
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They do not "sometimes" unscrew themselves unless they are not assembled properly....
THE REVERSE DRIVE GEAR is splined and it locks the input shaft to main shaft (through the splines) and does NOT allow threaded stud to unscrew.....
I believe if snap ring is still on input shaft and shaft has pulled out, you have broken the reverse drive gear (on main input shaft) and that has allowed stud to unscrew...
Note parts 1 & 2 & 3 and 12 & 13 in above diagram...
#12 (reverse drive gear) is the "lock" that keeps 1 & 2 from unscrewing off #3 (stud)
Pull drain plug and it should be magnetic and it will probably have some chunks on it ( depending on how gear broke - if it just split in half there may be no chunks), if no chunks, pull passenger side "side cover & bearing support" (If SA) off and the truth will be revealed!... IF later trans with single side plate you have to go in the more difficult way from left side...
Dale
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
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All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...
Last edited by Dale M. on Sun Jun 02, 2013 9:13 am; edited 1 time in total |
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bugguy076
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Joined: December 11, 2007
Posts: 1068
Location: Dover, PA.
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| Posted: Sun Jun 02, 2013 8:20 am Post subject: |
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| You can remove the side cover without removing tranny to make the repair. First, drain oil. Remove axles, grease seals, retainer clips, then the axle adapters. Remove nuts or bolts from left side cover. IF it has nuts, remove bottom two studs, then tap the cover free. the diff will be free to come out also. Now you have access to make the repair. |
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woodoctr
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Joined: June 01, 2013
Posts: 254
Location: Ohio
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| Posted: Sun Jun 02, 2013 12:16 pm Post subject: |
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Well guys, here is where I'm at. I wanted a really good look inside that tranny so I did indeed pull it so I could get it at face level for an inspection. Dumped and screened the oil, nothing.... checked the drain plug, I'd describe that as having a few minor particles of metal, not unexpected with breaking in the transmission... inspected the stud (yes, it had moved toward the front of the tranny but no cracks or chunks broken off and the threads looked fine (checked all this with a magnifying glass), threads chased clean on everything. Checked the sleeve/reverse gear (yes, mine is a thick one) and again no cracks.
So, it had to have come unscrewed, right? I am thinking this was an assembly problem and may also have been aggravated by increased vibration from my new mounts, truss, mid bar???? |
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gears
Samba Member
Joined: October 28, 2002
Posts: 4391
Location: Tamarack, Bend, Kailua
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| Posted: Sun Jun 02, 2013 12:36 pm Post subject: |
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Go to the dealer and purchase the improved version:
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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gears
Samba Member
Joined: October 28, 2002
Posts: 4391
Location: Tamarack, Bend, Kailua
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| Posted: Sun Jun 02, 2013 12:46 pm Post subject: |
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Oh .. I think we forgot to ask: Had the circlip come out of the groove, allowing the reverse joining sleeve to move on the shaft? Purchase a new circlip, too.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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woodoctr
Samba Member
Joined: June 01, 2013
Posts: 254
Location: Ohio
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| Posted: Sun Jun 02, 2013 9:21 pm Post subject: |
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| Nope, the c clip was still there. Nice bulge on the new stud style. Newer stud, and just to be safe, c clip on the shopping list. Thanks, guys, that should put me back in business. |
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Dale M.
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Joined: April 12, 2006
Posts: 20378
Location: Just a tiny bit west of Yosemite Valley
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| Posted: Mon Jun 03, 2013 7:16 am Post subject: |
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I'm with "Gears" on this...
Hard to understand how reverse gear moved and allowed shaft to unscrew off stud if "C" clip was in place..... Can only be "C" clip was not seated in its groove (originally), and allowed reverse gear to slide out of position and let shafts unscrew..... Only explanation for "C" clip being in groove upon disassemble was it was pulled back into groove as you pulled shaft out...
Only other scenario would have been a split reverse gear, which you state it was not...
Dale
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ... |
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gears
Samba Member
Joined: October 28, 2002
Posts: 4391
Location: Tamarack, Bend, Kailua
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| Posted: Mon Jun 03, 2013 8:24 am Post subject: |
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As I've stated, there is from time to time the rare instance of an over-machined stud on which the threading from both ends happens to meet up exactly in the middle. One of these, paired with a mainshaft that has been machined a bit deeper than average, can allow this problem to occur.
The first time this happened to one of our customers, I went through a bag of over 150 studs, and found that perhaps 3% were overmachined. Of these 20-odd studs, perhaps only 1 would have caused this problem, but I tossed them all. Shortly thereafter, we began using ONLY the late model stud. It's cheap insurance, and obviously VW felt the same way.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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Dale M.
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Joined: April 12, 2006
Posts: 20378
Location: Just a tiny bit west of Yosemite Valley
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| Posted: Mon Jun 03, 2013 5:26 pm Post subject: |
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| gears wrote: |
As I've stated, there is from time to time the rare instance of an over-machined stud on which the threading from both ends happens to meet up exactly in the middle. One of these, paired with a mainshaft that has been machined a bit deeper than average, can allow this problem to occur.
The first time this happened to one of our customers, I went through a bag of over 150 studs, and found that perhaps 3% were overmachined. Of these 20-odd studs, perhaps only 1 would have caused this problem, but I tossed them all. Shortly thereafter, we began using ONLY the late model stud. It's cheap insurance, and obviously VW felt the same way. |
Yes but splines on main shafts and reverse gear should have locked shafts from unscrewing at stud..... IF input shaft did a straight pull out ( instead of unscrew) not only would I not trust threaded stud, but threads in the two shafts also....
Dale
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ... |
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gears
Samba Member
Joined: October 28, 2002
Posts: 4391
Location: Tamarack, Bend, Kailua
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| Posted: Mon Jun 03, 2013 9:00 pm Post subject: |
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The shafts aren't turning in respect to each other, Dale .. Only the stud is turning. The unthreaded section in the center of the stud is supposed to stop it from screwing too deep. But if this section is "missing", and if the female threaded section in the mainshaft is too deep .. these two factors come together and we get that 1 in 1,000.
One of my customers has had it happen (a professional race team that knows how to screw shafts together), and now I've seen it come up on Samba. So it obviously happens.
It would be nice to see a close up photo of the stud that did this. It should appear almost as though it isn't threaded from both ends, but rather has a continuous thread. Woodoctr should also find that his mainshaft is threaded abnormally deep.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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woodoctr
Samba Member
Joined: June 01, 2013
Posts: 254
Location: Ohio
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| Posted: Mon Jun 03, 2013 9:48 pm Post subject: |
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Well, lucky, lucky me on this. What Gears said there at the end seems accurate. I already ditched the stud, but you were correct, it looked almost like continuous threads. And yeah, the mainshaft could have some extra depth to it.
Man, I sure know more about VW trannys than I ever wanted to know. Great info. though and I'm really getting fast at dropping motors and trannys.  Again, thanks for the thinktank on this. |
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SRP1
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Posts: 4340
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| Posted: Mon Jun 03, 2013 10:10 pm Post subject: |
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| gears wrote: |
| Woodoctr should also find that his mainshaft is threaded abnormally deep. |
Not that is damn funny right there.   |
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SRP1
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| Posted: Mon Jun 03, 2013 10:18 pm Post subject: |
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...
Last edited by SRP1 on Tue Jun 04, 2013 8:38 pm; edited 1 time in total |
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gears
Samba Member
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Posts: 4391
Location: Tamarack, Bend, Kailua
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| Posted: Tue Jun 04, 2013 5:31 am Post subject: |
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When you consider the acceleration/deceleration + vibration the input shaft is subjected to, one can understand how the stud can screw itself forward.
Although a somewhat different scenario, the Hewland and Webster transmissions did this like clockwork (the two shafts separating) if care wasn't taken to secure the laybolt running down the center of the gundrilled mainshaft, to keep the laybolt from unscrewing itself out of the input shaft.
This should never happen in a stock VW because of how the stud is held captive. But if the two factors that hold the stud from threading too deep are gone, guess what? .. it will thread itself too deep.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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Dale M.
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Joined: April 12, 2006
Posts: 20378
Location: Just a tiny bit west of Yosemite Valley
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| Posted: Tue Jun 04, 2013 7:21 am Post subject: |
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| gears wrote: |
The shafts aren't turning in respect to each other, Dale .. Only the stud is turning. The unthreaded section in the center of the stud is supposed to stop it from screwing too deep. But if this section is "missing", and if the female threaded section in the mainshaft is too deep .. these two factors come together and we get that 1 in 1,000.
One of my customers has had it happen (a professional race team that knows how to screw shafts together), and now I've seen it come up on Samba. So it obviously happens.
It would be nice to see a close up photo of the stud that did this. It should appear almost as though it isn't threaded from both ends, but rather has a continuous thread. Woodoctr should also find that his mainshaft is threaded abnormally deep. |
What you are trying to say is even with the two shafts "locked " by reverse drive gear,, the stud may be turning inside shaft (by inertia?) and eventually it may screw its self in one direction far enough to completely unscrew its self from other shaft allowing them to seperate?.... Have I got that right?
Dale
_________________
“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ... |
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gears
Samba Member
Joined: October 28, 2002
Posts: 4391
Location: Tamarack, Bend, Kailua
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| Posted: Tue Jun 04, 2013 7:31 am Post subject: |
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If you've got to ask, I suppose I haven't been doing a very good job of it.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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bowtiebug
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Joined: March 17, 2013
Posts: 902
Location: North Texas
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| Posted: Tue Jun 04, 2013 7:42 am Post subject: |
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| Dale M. wrote: |
What you are trying to say is even with the two shafts "locked " by reverse drive gear,, the stud may be turning inside shaft (by inertia?) and eventually it may screw its self in one direction far enough to completely unscrew its self from other shaft allowing them to seperate?.... Have I got that right?
Dale |
Dale that is exactly what he is saying , without the center shoulder on the stud it can vibrate and screw its self in one direction and become separated .
I had this happen to me about 20 years ago on my Baja , everything was fine and in place except for the stud had worn off the small center shoulder or never had it ..
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