On my Allison's over 22-years, I've seen a few problems...
The foamy, questionable level readings.
The slow shifting (like a 5 to 10 second delay) going into gear.
Even slipping badly at 2100 rpm .......... and overheating and blowing oil out of the filler cap
etc.
Finally, I removed the pump to see if I could find some issue ............ cleaned up the pressure regulator and components and then reset the pressure to 150 psi at 2100
THEN.......... found that for years someone prior to me had a totally incorrect shift cable setting. The trannie lever never went fully into gear and was skewed toward the reverse detent...... So, I found that moving the linkage to the next lower hole to get a lot more throw on that small shift lever made a huge difference.
After years of a worsening delay, I figured I had def. burned and scored the flywheel and clutch plate and hurt the large piston seal and made it hard and stiff or something ............ but, no, everything cleared up nicely over 10 or 20 hours of subsequent shifting.
My point to all of you .......... don't ever assume that great mechanic is infallable. Especially if the item you are checking is NOT easy for a "ONE MAN" look see. You run to the helm and put the gear in fwd and run back to the engine and see what that looks like on the lever ...... then DETACH the link and see whether you are in FULL FWD position on the lever and detent. Then go and repeat for the reverse position. Also, verify that the cable clamp is holding the shift cable firmly, with no slop.
Do, both engines while you are at it..... if the Admiral is willing, make her a cup of coffee, seat her at the helm (and if you have two cellphones for intercoms) and direct her to try fwd, reverse and maybe neutral on both stbd and port.
U should also send her to the bridge and do ditto. You may also have to adjust the cables at the helm controls to recenter and to make the handles even.
FINALLY, (the above was done with the engine off).... now it is time to judge the proper oil level on the stick(s)... I have found that there is a far easier way to judge things on an imperfect guesstimate of where full is ....
I have marked my sticks somewhere high above the full mark at the level shown when the properly filled trans is not running ..... I think it is approx. 1 to 1.5" above the full mark with the engine off.
With the engine warmed up, the trans picks up that temp via the oil cooler, and after shifting in and out of gear following the svc manual instr. I properly fill the beast ..... it is not important to know the stick inches vs qts or gallons .......... most of us are filling with a big funnel and the 5-gal oil drum and don't know if we dropped in a qt or 1.5 qts so every few seconds ......... check the stick with the eng running
If you overfill, big deal. Take the tube you use to change the oil and hook it to the dip stick tube and suck out a qt or two.
After all the above, I have had ZERO oil level issues ..... clearly the slippage caused by the incorrect linkage will overheat the oil immediately at the higher rpm's and cause foaming and overflow and low readings on the stick.
These Allisons are really forgiving ....... now,I ran a two hour run Thanksgiving over to Montauk and trying to beat the weather window ..... it was 50mph and 20-deg for two days prior ....... I ran at 2100 and 2200 rpm continuously with no issues.
So, get the svc and operating manuals and the xmission manual and follow EXACTLY what DD said.
Try my "cold, not running .... mark on the dip stick"
Check the linkage
Check the filter can/ gasket for leakage
ck the psi ............ 150 (max) seems to be OK for me.
