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first gear slippage

Posted: Fri Jun 08, 2007 2:09 am
by big phil
hi all, have just returned from italy mugello moto gp and on the return journey my engine would 'slip' when accelerating in 1st gear.feels like some invisible hand has pulled in the clutch lever for a fraction of a second.there is no real crunching of gears and it only does it in 1st.could it be slipping dogs?i dont want to pull the crankcase apart AGAIN.
cheers ,phillip

Posted: Fri Jun 08, 2007 6:34 pm
by Rick F
Hi Phil,

The easiest one to check 1st is the selector box.

I had my 750 engine rebuilt a few years back now, but when I 1st got the engine back, installed it & rode it. I had the same problem.

A fullgearbox, & top end rebuild, and it was jumping out of 1st gear.

The engineers weren't happy, but took it back & rebuilt the gearbox a 2nd time.

Reinstalled the engine, same thing, jumping out of 1st.

Back to the mechanics, they were pissed!

This time, 2 of their mechanics went over it & eventually found the trouble.....

One of the springs in the selector box was broken, new spring installed (less than a dollar for the part) been running beautifully ever since

Not saying that is your problem, but it is a place to start!

Regards from oz

Posted: Mon Jun 11, 2007 3:38 am
by big phil
hey thanks rick.
so it seems i will be tearing it apart again.
you say your from murwillimbah.
i am moving to brisbane end august.might see you on the road.who do you take your bike to for parts repairs in queeny?
nice one,

Posted: Mon Jun 11, 2007 3:40 am
by big phil
did your bike slip straight back into gear or slip out and stay out?
mine always slips straight back into gear which is really weird.cheers mate

Posted: Tue Jun 19, 2007 4:35 pm
by Den
After you split the cases, before you do anything else, lay the left hand case (containing the transmission) down on some supports so the shafts are free. Spin the output shaft by hand while you turn the shift drum. Observe the transmission slipping into 1st gear. Look to see the 1st gear gear dogs level of engagement. You will probably notice that the gears could stand to be shimmed so they are closer together and the gear dogs are more fully engaged. You might notice the same thing with 4th gear too. Now you are well on your way to becoming an expert Ducati gearbox technician.

Posted: Sun Dec 09, 2007 4:45 am
by Steve Foster
Thought I'd recount my experience with a transmission problem on my 1974 750 GT. It has a happy ending.

Symptom: started to randomly jump out of first gear, resulting in engine revving alarmingly and a disconcerting lack of acceleration. Dangerous when taking off from the lights with traffic behind. It would also randomly get stuck in higher gears - 3rd, 4th, 5th - meaning a lot of clutch slipping if I had to get moving after having to come to a stop on the way home.

The fairly consistent advice about the jumping out of first gear issue was that this was a well known problem due to the dogs wearing on the original 6-dog type gearbox (e.g. See "Ducati Twins Restoration", Mick Walker, p.78). This was remedied in later models, from 1983 onwards, by using a 3 dog assembly, which can apparently be retro-fitted to earlier bevel twins.

Hence I was facing an expensive gearbox rebuild.

I decided to pull apart the selector box to give it a service as it hadn't had any attention since new (I've had the bike since 1975). Every piece was dissassembled and cleaned. I discovered that the small spring (part no. 0150.49.010) that pressed the detente ball against the circular selector plate to locate it into each hemishperical hole was broken into 3 pieces. No pressure was being applied to the detente ball - hence the selector plate was not being firmly located. Hence jumping out of gear. And the locking in higher gears was due to the circular selector plate being rotated slightly out of position due to friction as the selector fork/gear lever returned so that the selector fork was not positioned correctly to grip the pins to rotate it for the next gear change.

A few dollars and a new very small spring later the gears are now shifting without a problem. So, a similar experience to Rick F's in his post above.


gearbox woes

Posted: Sun Dec 09, 2007 10:25 pm
by Rick F
Hi Phil,

sorry I didn't get back to you. Have you moved to brissy yet?

Thanks Steve for a bit of back up on that story re the selector box. From your description, I now know exactly what they were talking about.

As far as duck mechanics up around here, I actually take my bike down to Arthur at Byron Bay, about an hour & a half south of brissy.
If you need contact details let me know.

How did you go with the gears poblem