Modern Vespa

In the continually receding horizon of getting my 1974 Primavera going again, I am at the stage of reattaching all of the cables at the business end.

I was trying to set up the gear shift cables and find that the smallest movement bumps the scooter into gear. Even after careful efforts lining up the neutral mark at the handlebar and taping it there while I tighten the pinchbolts, when I go to check my results, the neutral mark ceases to be accurate. I think that's a symptom of whatever is happening to allow it to go into gear.

Of course, I disconnected the clutch cable to see if that was the cause; it was not.

The backstory: I had the engine out to split the cases and replace seals. I replaced the clutch plates, spring, and brass bushing thing at the same time. Everything seemed to go back in just fine -- nothing seemed weird or confusing. Yes, I soaked the plates in 30w oil for a day or so before I reassembled the clutch.

The guts of the engine were in good shape -- the crank and shifting cross had been replaced just a couple years before I parked it.

I haven't started the engine yet (that was on my to do list for today) and I am chomping at the bit to see how it does with the VAPE kit.

Your insights gladly accepted -- also on the question of whether something else might be going such that I shouldn't try to start the engine until I have this problem resolved.

ETA I referred to a diagram somewhere on here that shows the routing of small frame cables opposite from large frame cables at the shifter.

Does it sound like I could have installed the brass plunger wrong? I tested it before I put the cover back on and it seemed right.

Could it be on the other side -- I put the gears back on wrong somehow? I didn't disassemble the whole shaft. I left the shaft in the case but took the gears off and checked the shim with feeler gauges.

Whatever the final result, I don't think it's going to be anything related to the clutch.

Do you just have the cables a little too tight? That can make it easy to bump the gears. That'd be my first guess.

I have also been told that the stock cruciform detente spring isn't quite stiff enough. I was advised to (and did) put a third ball bearing in my detente and it snaps into gear nicely. I wouldn't want it to be any less snappy.

Is it possible you screwed up the gears? Only you can say for sure, but if the slop is within tolerance and it finds all the gears when you check them, I suspect the stack is fine.

Thanks. I hope it's the gear changer cables, though I did try them in various levels of looseness. I will try again more systematically.

But it's weird that it will just bump into gear, no?

I am 99% sure I got the gears right. But not 100%. Funny that. I watched a video on youtube several times -- Old Nut's Garage, and thought it was a good idea when he tied the gears together in order as he disassembled the gearbox. I did that too. But later, when I reassembled, I idly untied them and didn't pay attention. Still, I turned them every way around and it seemed they could only go back together one way so as not to rub or be weirdly close.

Is there a way to put the gears back on that looks and feels right but is still wrong?

As for the detente -- I would say it was just fine before disassembly, and I didn't take off the cruciform and expose the ball bearings, so it should be the same as before.

I had to step away and get advice. You know how it is when something doesn't make sense and so suddenly there are 100 mysterious causes because you've overlooked something obvious. I hope it will be the cables in the light of a new day.

First off let's assume for a minute that things are ok inside and see if you can find all the gears and neutral. It sounds like you have the cables pretty tight, you need to have a tiny bit of rotary 'slop' at the handle bar end. It's supposed to be that way or you can wear out the shifter shaft bore in the case if they're always too tight.

I lay it over on an old mattress or cushions to do this, so much easier! No problem if not much gas, or siphon it down or seal the cap w/ plastic bag trick to avoid spilling gas.

At this point, I'd pull the plug(so motor turns free), and with the cables OUT of the batwing, I'd try hand shifting the batwing thru ALL the gears & neutral while slowly spinning the tire. If all seems good, then on to the next.

First set the two threaded adjusters about a third of the way out so later you can fine tune either way to match your neutral mark on the hand grip and get the tightness just right. Now find 1st or 4th and put your hand grip in the same(taping there is a good idea) then put on your pinch bolts, tight into the batwing while a helper is pulling both inners snug. Remove the tape and hand shift into neutral so wheel spins free

Now see how far your grip twists with nothing happening, you should now have too much slop. Is neutral mark near the middle of the slop? Start taking up on the adjusters until cables are snug but not too tight. You will be back soon doing this again as the cables seat in and stretch a little if all is well inside so don't obsess with perfect alignment to the mark yet

Get the bike upright, straddle it and without starting the motor or pulling clutch, can you walk it freely in neutral? If so, now walk it slow and shift to first with no clutch. It should clunk into gear and stop you now. Try the same thing for all the gears.

If all that works, or if it doesn't, report back to discuss your clutch, etc if need be. Good luck!

It's pretty easy to get a number of gear selection problems because of shift cable adjustments. My first time through, I had a hard time shifting into first, because one cable was too tight and there wasn't enough slack to shift into first. It was a lot of trial and error.

these guys hit it right on the head. too tight can cause it to jump gear, too weak of a spring or worn lands on the cross can cause it to bump as well. a little too much from either compounds the problem.

check the exterior first and hope you get lucky!

Thanks for talking me down, everyone.

I got half an hour out in the garage this evening, loosened everything and went back to the beginning. I reattached the cables with a good bit of slack and the problem went away.

I may be back with more questions as I dial it in, but it's super helpful to have eliminated literally everything from the clutch and cruciform to spirit possession or having done something particularly stupid (at least for now).