SP-A locks into gear, won't shift

I have a SP-A upper with a 290DP lower that is getting stuck in gear and wont shift out into neutral.
The first time problem occurred, I could not shift from forward to neutral. After 30 minutes of playing with the shifter and restarting and cutting off the engine, all worked fine for the next few minutes and shifted through all gears fine until after about the 6th shift it stuck in reverse.
Ultimately I disconnected all shift linkage to the upper drive and had to use channel locks to turn shift lever to neutral. This should rule out the reverse lock since it was still locked up after the linkage was disconnected from the drive.
I put everything back together and all shifting worked fine on trip back to ramp and went through multiple gear changes to get on the trailer.
The next time I took the boat out, I checked shifting ability on the hard without engine on and all worked well. I then backed trailer in and tried forward and neutral under power before pulling off of the trailer. Of course it then failed again stuck in reverse after clearing the dock.
Any suggestions on where to start? I've looked at the repair manual and nothing jumps out with an AHA moment on what the problem is

With drive down overnight, check oil level is correct on dip stick, then drain about 1/2 cup oil out of drive. Color, residue ???
What kind of oil?

Drain the GL-5 gear oil.
Remove the clevis pin from the eccentric piston arm, and swing the linkage out of your way.
Remove the eccentric piston housing.
Examine the shift shoe and the shift shoe tension spring.

Post photos and info on what you see.

I will work on it this weekend. Thanks

Finally got a chance to pull the transimission off the drive and check things out.
The opil looks fine. No water or metal fragments. The shift shoe has a very slight wear mark on the lower side. It does not extend into the coating or metal below.

The unit stayed locked in reverse through the removal, transport 2 hours home and stayed locked up until I put the shift linkage back on the unit days later. It now shifts fine sitting on the bench however it has behaved this way in the past and locked up after repeated shifting.
What do I check next?

He will need to pull the main drive gear/bearing box out from the main gear case.
Remove the top cover and remove the left hand threaded nut.
This will allow you to remove the upper and lower “driven” gears from the main case, and expose the sliding sleeve and gear cups.
Look closely at the sliding sleeve’s oiling groves for metallic debris.
Look at the gear cups for signs of burnishing.

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I'm assuming the sleeve is steel. The only bronze looking metal I could see was the coating on the shift shoe.

I've looked at the repair manual and while it looks easy to take the upper apart, i'm not sure if I can get it all back together correctly.
Does anyone know of a qualified repair facility around Virginia? I've tried 3 different ones in the past and their repairs have all blown up within a few hours of use

tedm2 said:

I'm assuming the sleeve is steel. The only bronze looking metal I could see was the coating on the shift shoe.

I've looked at the repair manual and while it looks easy to take the upper apart, i'm not sure if I can get it all back together correctly.
Does anyone know of a qualified repair facility around Virginia? I've tried 3 different ones in the past and their repairs have all blown up within a few hours of use

Click to expand...

If the shift shoe has a bronze friction surface, then yes..... the sleeve will be steel.


The east coast is a tuff area to find any qualified AQ series techs, let alone anyone who wants to work on them.

The transmission can be disassembled and re-assembled without any issues.
Other than what we do as Techs if need be, no changes to any shim values are necessary.


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tedm2 said:

I've finally gotten some time to take the main drive apart.
When starting to remove the first bolt on the u-joint/bearing box I heard a click and then I could then freely spin the lower splined shaft in either direction.
Loosening one of the bearing box fasteners has to be coincidental..... IMO, I cannot see how doing that would affect the gear cup/sliding sleeve contact.

I've continued to completely dismantle the gears and cups. I don't really see any wear marks, discoloration or any debris. There is a very slight wear mark on the forward gear portion (lower side ) of the engagement sleeve.
That would be the Sliding Sleeve!

It looks more polished where the shift mechanism probably rests on it. There is not even enough color change to show up on photographs.
The engagement sleeve seems to move up and down freely.
As of yet nothing obvious looks to be causing any problem.
Not sure what else to look for.
I would still look for debris within the oiling groves, pick clean if need be, and would then lap the sleeve and cups.
If you do this, place one gear on the bench with the cup facing up.
Coat the cup evenly with your lapping compound.
As you press the respective end of the sleeve into the cup, rotate both gear and cup (each in opposite directions) while you turn the two against each other.
You'll be gaining about 90* of total rotation for both parts (45* for the cup and 45* for the sleeve)
You may end up doing this up to a dozen or more times.
This ensures that you get an even pressure around the cup/sleeve surfaces while lapping.

Do same for the the other cup and end of sleeve.

Clean all surfaces of any lapping compound.


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Click to expand...

I cannot see any debris in the oiling grooves but I ran a pick along them anyhow.
The insides of my cups have a black coating that looks unworn. Am I correct in assuming that these cannot be lapped?

Would it make any sense to replace or stretch the spring?

Could it be the oil type I have been using.
Amsoil full syn 75w-90. I believe the SP-A2 calls for full synthetic but something is knocking in the back of my head that said some units were having problems with synthetic. Don't remember if that was upper or lower units.

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tedm2 said:

I cannot see any debris in the oiling grooves but I ran a pick along them anyhow.
The insides of my cups have a black coating that looks unworn. Am I correct in assuming that these cannot be lapped?
If the sliding sleeve is steel (not bronze), and if the black substance is a gear cup coating.... correct, these should not be lapped.

Would it make any sense to replace or stretch the spring?
There are two! One that pushes the shift shoe FWD into the sleeve, and one that counters sliding sleeve gravity.
IMO, neither would be your issue!

Could it be the oil type I have been using.
If the sleeve and gear cup are not fully engaging..... yes.
But generally, not if the unit is locking into or staying in gear!

Amsoil full syn 75w-90. I believe the SP-A2 calls for full synthetic but something is knocking in the back of my head that said some units were having problems with synthetic. Don't remember if that was upper or lower units.

The s/p lower gear units use a die-cast impeller style slinger pump to push gear oil up to the transmission for cooling.
Heavy gear oil can cause a load on the slinger pump impeller that will occasionally shear the drive pin off.
This stops the pumping action, and can cause higher than desired temperature at the transmission.

Click to expand...