Clutch cone slipping

[Radams89]

Hi everyone, I am new to the forum but I'm looking for some advice on a transmission issue. I have a PRM80 transmission hooked up to a westerbeke 3c engine. The whole setup is fairly newly installed in 2019 but before I purchased the boat. Last year I had an issue that I could not get the gears to engage properly. Reverse worked but fwd would slowly rotate before finally fully engaging or refusing to engage at all. I had read that this can be common with a clutch cone transmission and often simply lapping the cone in the gears can solve it. So over the winter I pulled it out and tore it down. There was no obvious issues. The gear/cone connection was definitely smooth and after lapping the cone it felt like it had much more bite. With everything re installed it seemed to fix the issue. Now after about 20 hours of cruising the issue has returned.

When I put everything back together I made sure that the shift cable was properly engaging the shift arm as well. So now my only thought is that I'll try to flush the fluid (atf) and see if that helps.

I'm curious is anyone has a better insight to permanently fix this issue? The current cone is also an new replacement.

 

[colemj]

I'm not sure that is a common transmission on boats, so you might not get much specific expertise for it, but it uses a common clutch arrangement. I'm a bit confused about what cone is in there now, and whether that one is slipping. I see a picture with two cones in it, and you mention that the original clutch was slipping 20hrs after lapping, and said something about the current cone is a new one.

If there is a new cone in there now, is it slipping?

Before putting it back together, did you test the shifting to see if the cone fully fit in both directions? And that the dog was in the correct orientation? The dog is a bit tricky on many of these types of clutches because it appears at first glance to be symmetrical, but it needs to be installed in a specific orientation or it doesn't engage the cone well in one direction.

The other thought is that there is a thrust washer on each output gear. These washers can wear moving the gear away from the cone and not allowing the cone to seat properly. Since your issue is in forward gear, and that is the direction that the transmission would spend the most time in, it is possible that thrust washer has worn below minimum spec.

Mark

 

[kloudie1]

Any free play between the shift arm and the shift shaft? Could the shift arm have slipped a smidge on the shaft not allowing the shaft to rotate fully into the "forward" position? It sounds like the shift fork is not traveling far enough into forward detent to fully engage the cone.

 

[Radams89]

I'm not sure that is a common transmission on boats, so you might not get much specific expertise for it, but it uses a common clutch arrangement. I'm a bit confused about what cone is in there now, and whether that one is slipping. I see a picture with two cones in it, and you mention that the original clutch was slipping 20hrs after lapping, and said something about the current cone is a new one.



If there is a new cone in there now, is it slipping?



Before putting it back together, did you test the shifting to see if the cone fully fit in both directions? And that the dog was in the correct orientation? The dog is a bit tricky on many of these types of clutches because it appears at first glance to be symmetrical, but it needs to be installed in a specific orientation or it doesn't engage the cone well in one direction.



The other thought is that there is a thrust washer on each output gear. These washers can wear moving the gear away from the cone and not allowing the cone to seat properly. Since your issue is in forward gear, and that is the direction that the transmission would spend the most time in, it is possible that thrust washer has worn below minimum spec.



Mar
k

Yea sorry I didn't explain it very well. The original clutch was slipping but the transmission is new from 2019 and only had about 200 hours on it. Since it was a bit of effort to take it all apart I did replace the cone just in case but it probably wasn't necessary. I lapped the new one into the gears and it did all seem to bite fairly well when I put it back together. So now the NEW new cone is also slipping after about 20 hours. The rest of the washers are still the factory spec spacing, but nothing really showed excess wear when I had it apart. I did make sure the dog was the right orientation. I had the shop manual and it clearly showed an orientation with a small nub. I think maybe what kloudie is suggesting with the shift arm could be worth investigating next.

 

[Radams89]

Any free play between the shift arm and the shift shaft? Could the shift arm have slipped a smidge on the shaft not allowing the shaft to rotate fully into the "forward" position? It sounds like the shift fork is not traveling far enough into forward detent to fully engage the cone.

I think this could be a good thought to investigate next. It definitely seems weird that even when I physically shift it directly at the transmission it still doesn't seem to be enough to push it into gear.