Low transmission pressure
What Chris sees on the bench
- Scratches on the selector valve. One transmission came in with no pressure, and the scratches on the selector valve were the issue. That one was a quick fix.
- A rusted plunger. Sometimes if you get water in a transmission, the plunger gets rusted in on the bottom and it won't give you the pressure you need.
- The wrong spring. On one unit that had water in it, the selector valve had an old spring with white paint on it, going back to the 80s. On the test stand the pressure stayed the same in reverse, neutral and forward, so Chris knew the problem was probably the selector valve. We put in a black spring.
- Cross-feeding. A rebuilt 71C looked fine at first. After we ran it for about an hour, forward pressure started dropping, and fluid was cross-feeding across the entire selector valve.
Fix and prevention
Pull the selector valve and check it for scratches, and check the plunger for rust. When you reinstall it, here's a tip: line it up with the bolt on the bottom. That gives you neutral, so the ball lines right up and you don't have to fiddle with it and fight it when you put it all together.
On 5000-series units, if you find the old collared springs, they need to be replaced with the updated springs.
And don't judge a rebuild on a quick test. That cross-feed only showed up after about an hour, and that's why we run these transmissions as long as we do.
One more thing on low rpm: if you're doing a lot of trolling or idling, you're not getting a whole bunch of lubrication through the transmission.
When to call
If your transmission is showing low pressure, call (804) 333-3677, Monday through Friday 9 to 3 Eastern, or email sales@halemarine.com.
Related reading: creeping neutral and selector valve problems and how we rebuild a transmission.