Shift problems with DP-A1

[Skybreeze]

Have had the sternleg fully rebuilt with new gears and shift cone (after hitting something hard in the water). When run for the first time had problems getting it to shift back to neutral. Tried putting the old shift shoe in and it shifted really well. Service bulletins indicate that the old shift shoe should not be used with the new cone. When I used the boat for the first time on the water it seemed to shift really well untill I had taken it for a decent run and then I had problems shifting back to neutral. Then when shifting back into gear the engine would start to rev up before engageing into gear which would result in it engaging with a sudden thump. It seems to me that the shift shoe is jambing in the cone in some way when shifting back to neutral causing a mis-alignment between shoe and cone so that when forward is re-engaged the cone is not going all the way up to engage with the gear. The engine then starts to pick up revs and engages with a thump. Any ideas on how to fix this issue would be greatly appreciated.

 

[Don S]

Re: Shift problems with DP-A1

Look at the shift shoe and cone clutch now. There is a reason for not using the old shoe with the new cone.

 

[Skybreeze]

Re: Shift problems with DP-A1

Thanks for the response Don. We initially had the new shift shoe installed but when we ran it for the first time on muffs the shifting was a lot worse. The shift lever would jamb when trying to shift back to neutral and we would need to tap the props to unload them allowing the cone to release. We then tried the old shoe and it seemed to work fine. I took the boat away at the weekend and every now and again it would be hard to get back into neutral. Then when engaging forward again the engine would gain revs before engaging. I have read the service bulletin about not using the old shoe with the new cone but it worked better when we first tried it. Do you now the reason why the old shoe should not be used or better still why the new shoe did not work as it should.

 

[Don S]

Re: Shift problems with DP-A1

We initially had the new shift shoe installed but when we ran it for the first time on muffs the shifting was a lot worse.

Did you reshim the new shift shoe per the manual?

Do you now the reason why the old shoe should not be used

The old shoe is the wrong material for the new type cones. Which if used, will gall the shift cone and destroy it. Did you pull the shift mechanism and look at it?

 

[Skybreeze]

Re: Shift problems with DP-A1

Hi Don thanks again for your response. I am taking it back to the mechanic today to get the new shoe put back in and will check about the shimming.
I will start at the beginning and hopefully a correct diagnosis can be determined.
I am running a Volvo 431 with a DP-A1. Everything was running fine until I hit something. After the impact I noticed that when engaging forward the engine would pick up more revs than usual before drive would engage. When boat was put on trailer it was found 2 blades were missing off the props. At this stage thought the missing blades contributed to more engine revs before drive engaging (i.e. cavitation)
New props were put on and boat taken for test run. All worked fine but after running for a while noticed that when shifting to forward the engine would pick up more revs before engaging. When checked by the mechanic we found that when forward was selected the props could be turned quite a lot before they would lock up. Checked it in reverse and they locked virtually straight away. The conclusion that we came to was that perhaps when the impact occurred it spun the cone in the gear housing causing damage. Full strip down of the upper gear box revealed a smear of brass on one section of the gear housing from the cone. There was also a lot of pitting on the upper section of the shaft where the bearing ran and the bearings needed doing so it was decided to do a full rebuild of the upper box. New gears, cone clutch, and bearings. Due to the cost of the shaft we sleeved the upper section of the shaft with a hardened sleeve and machined it to the correct size. Also replaced uni?s. The proper Volvo oil was put in.
Once re assembled we ran it on muffs and tried gear shifting. It would not shift back into neutral without giving the props a kick to unload them. We then tried the old shift shoe and it shifted perfectly. I then took it away for the weekend and it shifted well most of the time although we ran a lot at idle as we were trawling. I noticed that after going for a long run on the plane I had to use a lot more force to get it back into neutral and then when re-engaging forward the engine would pick up revs before engaging resulting in a sudden thump when it did engage. It seems to be fine when just idling around so could temperature be an issue or perhaps after a long run the cone is wedged in so tight that it needs more force to disengage it. Or is there something else from the initial impact that we are missing that may be the cause.
Will check on the shimming as I was thinking the same thing after reading the manual.

 

[Skybreeze]

Re: Shift problems with DP-A1

Had a talk to the mechanic about the problems with shifting. Although very experienced he was unaware of the shimming process with the shift shoe. He also remembered that when he put the new shoe in the adjusting bolt was loose so he tightened it. I suspect that the loose bolt played a part in a lot of my initial shifting problems. The new shoe is now in, shimmed correctly and it shifts really well on land. Will test it at the weekend on the water. Thanks Don for your input its great to have someone here with so much knowledge and so willing to help others. It is a problem here in New Zealand finding mechanics that have the knowledge and have worked on some of this gear. Will let you know how the test on water goes.