Foam O. Trans dip stick

[Chasemmc]

Allison m20 behind 8v92ti. Stbd oil level low mark when cold. Oil honey color. Idled the engine 1/2 hour periodically running to 1000 rpm. Oil level rose to 1/2 between full and low but foamy oil dip stick. Added 1 qt 40w, oil level at full foamy.I have read that if overfilled will cause foaming, but under filled? Temps: at brass fitting to trans oil filter 125 by infrared. Lower er gauge - 137. Lower helm - 150

 

[saltshaker]

Allison m20 behind 8v92ti. Stbd oil level low mark when cold. Oil honey color. Idled the engine 1/2 hour periodically running to 1000 rpm. Oil level rose to 1/2 between full and low but foamy oil dip stick. Added 1 qt 40w, oil level at full foamy.I have read that if overfilled will cause foaming, but under filled? Temps: at brass fitting to trans oil filter 125 by infrared. Lower er gauge - 137. Lower helm - 150

Could be getting air through the suction side, over filled or the gear is whipping up the oil. There’s a guard above one of the gears in the trans. If that has shifted this will happen but it’s rarely the issue.

 

[Chasemmc]

Do u think operating the transmission will damage it?

 

[saltshaker]

Typically no but can’t say without knowing what’s really going on

 

[Chasemmc]

The operating temp at the sea trail was 153 degrees. I'll monitor while operating. It shifts fine. Wasn't there a good Allison shop in Alabama mentioned in the forum. Maybe I can call them, anyone remember the name?

 

[MagnaBill]

The operating temp at the sea trail was 153 degrees. I'll monitor while operating. It shifts fine. Wasn't there a good Allison shop in Alabama mentioned in the forum. Maybe I can call them, anyone remember the name?

Acadian Marine Transmission ask for Brian. Broussard, Louisiana. His knowledge is amazing.

 

[Chasemmc]

Thank you, I will give him a call

 

[Chasemmc]

Brian was very helpful. I will repeat his knowledge for the benefit of the forum.Brian said that foam on the dipstick is due to an air leak on the suction side or low oil level. He said the reason the transmission first presents by not going into forward is that the oil has a more circuitous route than in reverse and pressure is bled off as it travels.He said temperature, while an indicator, is less important than pressure as low pressure allows the clutch plates to slip while underway. He said it should be between 135 - 150 psi. I think the temperature is monitored but not sure about the pressure. He said to add another qt. And see if that stops the foaming. The trans holds 5 qts plus whatever is in the lines and filter.

 

[Chasemmc]

Has anyone put pressure gauges on their Allison MH-20's and if so where? Where would I find?
mark

 

[saltshaker]

Has anyone put pressure gauges on their Allison MH-20's and if so where? Where would I find?
mark

Don’t you have them already?

 

[Chasemmc]

I have trans temp. I think oil pressure gauge is for engine.

 

[davidwigler]

All the boats I have seen have transmission pressure rather than temp. Including mine.

 

[Chasemmc]

I'll take a pix and post

 

[saltshaker]

Every Hatt I’ve seen had the trans pressure gauge. Temp is in addition to pressure. Never saw one with temp and no pressure gauge

 

[SKYCHENEY]

What about the seal at the screen? Could it be getting air there if not sealed well?

 

[llldks]

I have a 1972 8V71 TI with an allison M20 transmission which functions properly and maintains good pressure ( gauge reads 135 although Acadian Marine says they were set to 150 during a pump rebuild) but have developed foam in the transmission oil. I have checked the level of the oil after warm, at idle, after the foam dissipated and even tried varying the level to no effect. I've replaced the screen filter and gasket atop the transmission, replaced the large suction line from there to the Hydreco pump, and have rebuilt that pump ( Acadian Marine), replaced the spin on adapter and associated gasket for the oil filter, and replaced the filter. Additionally, have caulked all connections on the suction side and the pump to the oil filter. I still have foam.
So, I have three questions-
1- I am contemplating replacing the housing for the screen filter atop the transmission but am concerned that after 54 years the neck might break off. Has anyone had experience with this?
2. Is it possible to entrain air from the tachometer take off? I have a similar setup on the port engine but no foam there.
3. Any suggestions of anything else to do first, besides calling a real mechanic?

Seadation, Houston, Texas

 

[Captain Ralph]

How are you detecting foam? Any issues while running?
CF-2 oil in use?

 

[Pascal]

Same here. Every Hatt I ve run had pressure gauge for the gears. The seal at the screen is very easy damage which will cause air to come in and pressure loss. This will cause delays going in FWD or loss of FWD altogether.

Major PITA!

Sorry to hear Seaduction is having gear issues. I will never forget the first couple of days of that delivery with the transmission issues. And that was like 15 years ago! Glad you re still enjoying the boat though.

 

[llldks]

The only issue I have is foam noted when I check the level. Transmission works fine, good pressures, shifting , and color. Same oil as the engine which I’ve used for several years.

Same here. Every Hatt I ve run had pressure gauge for the gears. The seal at the screen is very easy damage which will cause air to come in and pressure loss. This will cause delays going in FWD or loss of FWD altogether.

Major PITA!

Sorry to hear Seaduction is having gear issues. I will never forget the first couple of days of that delivery with the transmission issues. And that was like 15 years ago! Glad you re still enjoying the boat though.

 

[llldks]

I remember the delivery because retrospectively , I’m amazed you made it- you help save a Hatteras.