Allison slow to come up to pressure

[egaito]

One of our trannies is trying to tell me something, but I'm not yet sure what.

When the engine is cold started, it takes about 30 seconds before the tranny comes up to pressure. It's not a slow rise, rather, a delay of about 30 before it shoots up to normal. The other side comes right up.

Oil is full, and clear. No issues running the boat.

Any ideas?

 

[SKYCHENEY]

Sending unit? Try swapping the gauge and/or the sending unit with the other side and see what happens.

 

[Pascal]

it's easy to see if it it the gauge or sender... put it in fwd gear after 5 or 10 seconds... if it engages then pressure is already up.

try with FWD gear... reverse will engage with much lower pressure...

 

[DAlter]

You may have some air in the system. Check all your hose connections and make sure they are tight. I changed my hoses last year and had the same thing happened. I just snugged up all the flare fittings and then everything worked fine.

 

[Nonchalant1]

I'm betting on the sender, but It could also be air getting into the suction side of the pump from the right angle elbow pipe at the intake side of the pump where the hose connects. They sometimes get a little loose and admit air into the pump, reducing your flow. When it's cold, it'll do it more easily. Put your hand on that right angle intake pipe at the pump and see if it'll turn any, even with the hose still connected to it. It should not turn at all (it's an NPT fitting). If it turns, take the hose off, tighten the elbow up tight and reclamp the hose onto the pipe.

Any loose fitting on the intake side between the three bolt flange and the pump housing could admit a little air. If it's a small leak, it may not affect it when it's up and operating, but it might let air in while it's not running and the let the oil run back down the intake hose into the gear. Then, when you start up, it will self prime but might take that 30 seconds to pump enough air out of the intake hose to prime itself with oil from the gear.

Doug Shuman

 

[Pascal]

also, have you cleaned the intake screen lately. If you dont' get a perfect seal there you will get some air and no pressure. or possibly issues with building pressure...

that happened to me once... i also think that if you get air in the pump, it will sound differently.

 

[egaito]

I have noted a change in engine sound when the pressure kicks in.....I'll start looking for potential air leaks.

 

[Genesis]

The most likely place for a leak is right on that 3-bolt flange where the suction strainer is.