90 HP Yamaha new lower unit issue

Greetings, I repowered my ranger 690T 9 years ago with a Yamaha 90. While I could use a bit more power at times, have been very happy with adequately quick hole shot, and 35mph with two guys/gear.

I hit a stump awhile back at low trolling speed which killed the motor. Over time, the gears eventually started to severely 'grind'. I took to my Marina where was determined I needed a lower unit. Today was the first time out with it, and I could hardly get on plane with wife and kids which has never been an issue, with top speed reduced. No other setting was changed, and my prop wasn't damaged, as I was still getting same performance just after hitting the stump. The motor is very smooth, but just not seeing the power/take off/speed that I was before my old gear case went.

Is it possible that there is a different gear ratio in this new unit? It 'looks' the same as the old one sans the new paint. Just hoping to remedy this soon before my Canada trip.

Thanks much for any insight.

Jason Schillinger

While reading your post I was thinking you got a different lower case gear ratio (in this case higher) and prior to you asking the question about that.  I check that 1st.

The 90 two stroke has always been 2.0, but the four stroke is 2.27. Are you sure that you don't have a four stroke lower unit?

If you have a tach you will know if the gear ratio is different. Your peak rpm a top speed will be much lower if it's the gear ratio.

It's very likely that is the issue. You can also look at the part number of the replacement gearbox and have the dealer give you the ratio. You should be able to find the original ratio in the owners manual or on line for your model year.