Trim quits working

While the boat is out of the water, the trim works just fine. Even at low speeds while I on the water it will work just fine, but when I try to get up to speed it will fall all the way back down and will not come back up until I slow way back down. Therefore I can never get up to speed. The fastest I can probably get up to is maybe 10 mph before the trim fails and the motor come all the way back down. I have checked the fluid levels, wiring, ect. I don’t understand what is wrong. Please Help!!

My guess would be the seals / o-rings are bad.

What is the motor?

There are no leaks that I can find. The motor is a Johnson GT50 VROV6.

Guy Keeney wrote:

There are no leaks that I can find. The motor is a Johnson GT50 VROV6.

The fluid can leak past the piston in the cylinder without any external leak. I had a 40hp Evenrude in the ’90s that would drift down when parked and wouldn’t trim the motor up at higher RPMs. I had to have the cylinder rebuilt. I think the only parts were O-rings and teflon spacers.