Fwd Gear not always engaging- reverse fine

[moretonbaysails]

Hey all SBO,

I’m running a twin disc gearbox with a Kubota 21 hp little diesel inboard. Ive checked the linkages and tightened those, changed and topped up the fluid to the gearbox.. but still experiencing the same issue of forward gear not engaging.. so whats been happening is that after warming up engine - and pausing into fwd on gear selector, the output flange will spin, the prop shaft spns but then slows down , and there is no fwd propulsion.
this is not what happens when selecting reverse. ie, The prop spins but doesnt slow down and propulsion is gained.
before replacing the entire gearbox , which is no small physical feat ( the soace around the engine to the aft is tiny if non existent , let alone the cost. Im here to seek info from owners who experienced this issue , as stated, but found a different cause.
i have just dove the prop and cleaned the shaft at the hull entry .
Other info. The shaft, at the output flange, is run from a flexible coupling then to a PSS shaft seal, the aft to the through hull. Its a 9inch prop. And yes , its still there .

 

[moretonbaysails]

Typo - .. warming up engine and “PUSHing “ into Fwd.
The prop shaft is held in a P leg/bracket , and spins freely when manually spun .
The transmission type is conical cup and cone. With actuator. I don’t believe there are rings. But cant be sure(will speak with twin disc service tech again) .

my quandary is ; if there is a limitation on the shaft to allow it to push forward , when fwd gear select, either by poor alignment ,bio- foul on the prop shaft in water, or some other physical limitation. Wanting to know what else transmission owners of this type of gearbox, have tried/tested/ in the way of deductive logic parameters and did this solve the not always engaging fwd gear issue

 

[Project_Mayhem]

I would start out by securing the cable a bit better. Also check to see if it engages if you remove the cable and shift the lever on the trans by hand

 

[dLj]

Sounds like the linkage has slipped and it's not fully engaging in forward. I see @Project_Mayhem just suggested what I was going to say about manually engaging the shift lever. The linkage may need to be adjusted both at the connection near the shift lever on the tranny as well as the connection at the shifter.

How many hours are on your tranny/engine?

dj

 

[Ralph Johnstone]

output flange will spin, the prop shaft spns but then slows down , and there is no fwd propulsion.

For the sake of clarity, does the output flange continue to spin once the prop shaft slows down. I can see, but need to hear it from you.

 

[Ralph Johnstone]

The prop shaft is held in a P leg/bracket , and spins freely when manually spun

Am I correct in assuming the X-mission output flange also spins with the prop shaft and the X-mission is in neutral ?

"Why all the obvious questions" you ask ?

You'd be gob smacked at what is omitted and glossed over in these analyses and then shrugged off as unimportant. "Oh yeah man, like I forgot I had the engine rebuilt last week". There are likely enough people here with enough experience to solve your problem if you feed them all the info known on age, previous maintenance, and any other available details of this and related equipment.

before replacing the entire gearbox , which is no small physical feat ( the soace around the engine to the aft is tiny if non existent , let alone the cost. Im here to seek info from owners

With parts costs and chiropractic bills staring you in the face if you don't research this problem to the last cable connection, I'd be posting my underwear size and colour for all to see if I thought it would help .

 

[moretonbaysails]

I would start out by securing the cable a bit better. Also check to see if it engages if you remove the cable and shift the lever on the trans by hand

Thanks,
However.. as stated, have adjusted the lever arm cable, to as tight as possible. There was a little “play”
. Also did the removal if cable and manually shifted at the lever arm. Made no difference to prop shaft for fwd.

 

[moretonbaysails]

Am I correct in assuming the X-mission output flange also spins with the prop shaft and the X-mission is in neutral ?

"Why all the obvious questions" you ask ?

You'd be gob smacked at what is omitted and glossed over in these analyses and then shrugged off as unimportant. "Oh yeah man, like I forgot I had the engine rebuilt last week". There are likely enough people here with enough experience to solve your problem if you feed them all the info known on age, previous maintenance, and any other available details of this and related equipment.



With parts costs and chiropractic bills staring you in the face if you don't research this problem to the last cable connection, I'd be posting my underwear size and colour for all to see if I thought it would help .

No, the output flange doesnt spin in Neutral .

 

[dLj]

Thanks,
However.. as stated, have adjusted the lever arm cable, to as tight as possible. There was a little “play”
. Also did the removal if cable and manually shifted at the lever arm. Made no difference to prop shaft for fwd.

Well, it sounds like you need the tranny rebuilt.

dj

 

[Tally Ho]

I would have someone shift the tranny from N to F while you observe the transmission lever. The cable may be tight, but it could also be secured such that the inner cable cannot push or pull the transmission lever far enough.
So as Project Mayhem suggested, verify that the transmission lever is actually going all the way into FWD.

Greg

 

[Ralph Johnstone]

What fluid is in the x-mission now and when was it last changed ?

Did this problem occur in one fell swoop or has it been slowly deteriorating ?

How many hours are on your tranny/engine?

Refuse to answer this one on religious ............ or what grounds ?

 

[FastOlson]

What fluid is in the x-mission now and when was it last changed ?

Probably not the answer, but I do recall our mechanic saying that for the disc clutches to properly engage, the fluid has to be just a certain viscosity.
Our transmissions, both our former Hurth50 and present TMC40 (both Kubota blocks) has to be "ATF" and that some oils are more reliable than others. Has the fluid been changed and is the brand of fluid different?

Like I said, probably not the whole answer, but perhaps related?