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Subject: "What can cause 4th gear to slip?"
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Archived thread - Read only
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vespatude
Member since Dec-12-05
90 posts |
Jun-20-06, 12:57 PM (EDT) |
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"What can cause 4th gear to slip?"
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In my continuing saga with my scooter, I had hoped to go last Saturday and have cphilip bead blast my gas tank. Unfortunately, I had other issues come up that had me trying to fix up some gearing. Hey, cphilip? Would you like to buy my engine?  Seriously, can you guys give me some insight on slipping gears? 4th gear keeps slipping into neutral. I have adjusted every-which-way and still it slips on me. IF it isn't my cable adjustments, could it be one of the following issues? 1. My selector box: could the spring not be strong enough to hold the roller bracket in place? Or could the rocker arm be worn down so that the roller bracket won't stay put? 2. My cruciform: I replaced the shifting cross when I rebuilt the engine (150 cc for a VBB). It hardly has any miles on it since then. However, I would assume the a worn one of these would cause problems - but wouldn't it also be a problem in the other gears? 3. The fourth gear: I put in new gears when I rebuilt the engine. They didn't appear to be a part of a complete set. They were sent to me by Scooter Parts Direct and came in several differently marked bags. My question is, is it possible that I don't have the gears lined up properly and the shifting cross is not able to completely engage the gear? I put the gears in so that there is proper spacing between them, but I wonder if it is possible to have mismatched gears? I have some parts coming in this week that I hope will give me some more confidence in the pieces I have. However, I'm about ready to just take the engine off and take it and the gas tank down to cphilip for him to tear into. I got a new vespatude.
http://www.vespatude.com |
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- RE: What can cause 4th gear to slip?,
AirborneVespa
 , Jun-20-06, 01:01 PM, (1)
- Update: What can cause 4th gear to slip?,
vespatude, Jun-21-06, 06:41 AM, (11)
- RE: What can cause 4th gear to slip?,
Rich toronto , Jun-21-06, 03:28 PM, (15)
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AirborneVespa
unregistered user
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Jun-20-06, 01:01 PM (EDT) |
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1. "RE: What can cause 4th gear to slip?"
In response to message #0
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I'm betting your fourth gear is facing the wrong way. I highly doubt that you are slipping from fourth to third to second to neutral. More than likely you are slipping into the space between third and fourth. Your cruciform usually acts up in 2d and 3d gears if it's worn, usually not fourth. |
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vespatude
Member since Dec-12-05
90 posts |
Jun-20-06, 01:03 PM (EDT) |
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2. "RE: What can cause 4th gear to slip?"
In response to message #1
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Correct, I am always calling that little crack between the gears "neutral." What I mean is it "slips out of gear into no-man's land" -- which, of course, makes it act like it is in neutral. Thanks for the correction. I got a new vespatude.
http://www.vespatude.com |
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AirborneVespa
unregistered user
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Jun-20-06, 01:17 PM (EDT) |
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3. "RE: What can cause 4th gear to slip?"
In response to message #2
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Are you sure that your cable isn't too tight? If it's too tight it can jerk the roller out of the divet (I make up terms too) but seems it would pull it into third... Hopefully someone who has experience with a backwards gear will chime in (I don't). If your cables are too tight that could be a problem, but you did say you adjusted them many times... |
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vespatude
Member since Dec-12-05
90 posts |
Jun-20-06, 01:35 PM (EDT) |
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4. "RE: What can cause 4th gear to slip?"
In response to message #3
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I have tried "just right" -- meaning putting the gears in neutral (the real neutral), pulling for equal and moderate tension of both cables, and then tightening the pinch bolts. I have tried tight. I have tried loose. Of course, with the last two options it is all bad (as you would expect), but the best I can get is a great 1st, 2nd, and 3rd with 4th working as long as I pull on the clutch lever to pull on the cable as much as I can. Even then, it will slip at times when I get up to speed. This isn't something that has just started happening. This has been an issue ever since I got the demented thing. I got a new vespatude.
http://www.vespatude.com |
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e
Member since Jun-3-02
7493 posts |
Jun-20-06, 03:48 PM (EDT) |
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5. "RE: What can cause 4th gear to slip?"
In response to message #4
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Did you replace the selector box? Is the selector box good? Loosen up your cables a little to make sure that the cable isn't pulling on the selector at all and pulling it out of 4th. >I have tried "just right" -- meaning putting the gears in
>neutral (the real neutral), pulling for equal and moderate
>tension of both cables, and then tightening the pinch bolts.
> I have tried tight. I have tried loose. Of course, with
>the last two options it is all bad (as you would expect),
>but the best I can get is a great 1st, 2nd, and 3rd with 4th
>working as long as I pull on the clutch lever to pull on the
>cable as much as I can. Even then, it will slip at times
>when I get up to speed.
>
>This isn't something that has just started happening. This
>has been an issue ever since I got the demented thing. "You want to cripple the bastard? Send him a 130-mph cafe-racer. And include some license plates, he'll think it's a streetbike. He's queer for anything fast." |
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vespatude
Member since Dec-12-05
90 posts |
Jun-20-06, 05:34 PM (EDT) |
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6. "RE: What can cause 4th gear to slip?"
In response to message #5
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Hey, e, that is what I am trying to do -- narrow down whether or not I have a problematic selector box. After getting your post here, I went home and removed the pinch bolts so that the rocker arm would be free. I then put the bike in 4th gear. Right in front of my house is a good-sized hill. I coasted the bike down the hill with the clutch in. Once I got some speed, I let out the clutch and let the bike start. I then took it up to speed to see what would happen. Sure enough, the gears started slipping. It isn't like it slipped out and stayed disconnected. Rather, it would slip out and then right back in. I wasn't shifting at all. There was no tension at all when I turned the gear selector on the headset. I assume this wasn't supposed to happen? Sure leads me to believe it issn't a cable adjustment issue. My next thing to check is the components of the selector... I got a new vespatude.
http://www.vespatude.com |
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e
Member since Jun-3-02
7493 posts |
Jun-20-06, 05:46 PM (EDT) |
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7. "RE: What can cause 4th gear to slip?"
In response to message #6
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Make sure that your selector box doesn't have any play in the arm.
You have the notched rocker peice on top, it has a shaft that goes down into the box, then an arm attaches to that shaft held in place by a tapered pin. There should be no play between the rocker/shaft/arm, they should be solid, no wiggling (the little bit on the end of the arm that locks into your selector shaft will of course wiggle a little). The roller/spring on top also need to be in good shape.>Hey, e, that is what I am trying to do -- narrow down
>whether or not I have a problematic selector box.
>
>After getting your post here, I went home and removed the
>pinch bolts so that the rocker arm would be free. I then
>put the bike in 4th gear. Right in front of my house is a
>good-sized hill. I coasted the bike down the hill with the
>clutch in. Once I got some speed, I let out the clutch and
>let the bike start.
>
>I then took it up to speed to see what would happen. Sure
>enough, the gears started slipping. It isn't like it
>slipped out and stayed disconnected. Rather, it would slip
>out and then right back in. I wasn't shifting at all.
>There was no tension at all when I turned the gear selector
>on the headset.
>
>I assume this wasn't supposed to happen? Sure leads me to
>believe it issn't a cable adjustment issue. My next thing
>to check is the components of the selector... "You want to cripple the bastard? Send him a 130-mph cafe-racer. And include some license plates, he'll think it's a streetbike. He's queer for anything fast." |
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vespatude
Member since Dec-12-05
90 posts |
Jun-20-06, 07:22 PM (EDT) |
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10. "RE: What can cause 4th gear to slip?"
In response to message #7
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I removed the selector box. Everything was nice and crisp. Plenty of tension in the spring, no extra movement in the components, and good fit in the notches. I couldn't detect any problems there. Now when I put it back on I noticed what I believe is the problem -- though I don't know what the solution might be. What I saw was that the roller did not seat completely in the 4th gear notch. Try as I might, I could not get the roller all the way down in the notch. I hadn't noticed this before because it was so covered with grease. I found it was very easy to knock the roller out and in between 3rd and 4th -- or even all the way to 3rd. This was not the case when the selector cover was off. So, my guess is that the shaft coming from the gear tree is not going far enough back in the case. Even though the selector has the potential to work correctly, the shaft is not allowing it. The next question is, what could be causing that? Could the shifting cross be on backward or something? I got a new vespatude.
http://www.vespatude.com |
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guest
unregistered user
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Jun-20-06, 06:07 PM (EDT) |
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8. "RE: What can cause 4th gear to slip?"
In response to message #6
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Didn't you write somewhere that you had trouble with the cable ends after they thread thru the shifter - did you sort that - or is there a chance you have loose ends that could be pushing/catching on something when it's in 4th?
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vespatude
Member since Dec-12-05
90 posts |
Jun-20-06, 07:11 PM (EDT) |
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9. "RE: What can cause 4th gear to slip?"
In response to message #8
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vespatude
Member since Dec-12-05
90 posts |
Jun-21-06, 06:41 AM (EDT) |
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11. "Update: What can cause 4th gear to slip?"
In response to message #0
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Once again, I removed the selector box and checked the shaft that moves the shifting cross back and forth. I discovered that it was loose. I tightened it back up and tried my fouth gear without cables test. The results seemed to be the same. It is almost as if I had a thicker gasket between the case and the selector box that the roller would engage the rocker arm more securely. I only have to move the selector box a millimeter or less away from the case to get the rocker arm to seat properly. Is there a way to adjust the mechanisms that would allow me to move the cruciform shaft deeper into the case? I got a new vespatude.
http://www.vespatude.com |
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Scooterso
Member since Jul-20-04
131 posts |
Jun-21-06, 08:40 AM (EDT) |
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12. "RE: Update: What can cause 4th gear to slip?"
In response to message #11
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is this a an early PE model? did you put the washer back on the selecter shaft between it and the cruciform? do you have a PE cruciform? (PE and PX are different) did you reshim the gearbox? if you put in new gears you should really re-shim it
..just some thoughts...
Gene
www.scootersoriginali.com |
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vespatude
Member since Dec-12-05
90 posts |
Jun-21-06, 09:49 AM (EDT) |
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13. "RE: Update: What can cause 4th gear to slip?"
In response to message #12
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Gene, It is a VBB. I put in a brand new VBB type cruciform and the washer was in place. Forgive my ignorance - I am a newbie to Vespa engines - but what do you mean by "reshim the gearbox" - in my dad's woodworking shop a shim was a little piece of wood used to hold something in place... Thanks for the thoughts... I got a new vespatude.
http://www.vespatude.com |
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dirtyhandslopez
unregistered user
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Jun-21-06, 12:32 PM (EDT) |
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14. "RE: Update: What can cause 4th gear to slip?"
In response to message #13
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There are different length selelctor shafts(what the selector and cruciform connect to). sounds like you need a longer one I have had this happen before. The good thing is you don't need to open the cases to do it. REmember a new locking washer. Cheers D.LO |
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Rich toronto
unregistered user
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Jun-21-06, 03:28 PM (EDT) |
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15. "RE: What can cause 4th gear to slip?"
In response to message #0
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Stupid question but is your rear hub tight?
I had this happen to me before. |
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vespatude
Member since Dec-12-05
90 posts |
Jun-22-06, 09:07 AM (EDT) |
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16. "RE: What can cause 4th gear to slip?"
In response to message #15
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Yeah, it is snug. However, I'm curious, how would a loose hub cause the gears to slip? I got a new vespatude.
http://www.vespatude.com |
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Rich Toronto
unregistered user
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Jun-22-06, 09:15 AM (EDT) |
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17. "RE: What can cause 4th gear to slip?"
In response to message #16
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When the hub is loose it lets the axle move tis causes the selector to misalign making the gears slip.
I would guess that it is the gearbox shims being the problem as Gene stated. |
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