Trans Dip-Stick Tube Valley

[curtsprenger]

HTB-748 Allison Transmision -
The transmission dip-stick tube has a valley in it (holds fluid) making it most of the time difficult if not impossible to get a good reading on the dip-stick, either hot reading or cold. Suggestions appreciated. Is there a small plug that can be removed to validate hot-run level?

I drained the transmission oil and R&Rd the external filter. About 30 to 31 quarts of oil drained out. I refilled 30 quarts. Now can't get a good dip-stick reading because of the oil in the dip-stick tube.

[thomas_sorrentino]

Curt, did you ever get an answer to this? I have the same issue. My dipstick tube goes into the tranny horizontally. I always wondered how it could get a level reading like that. I wonder the same thing if there's a certain plug on the side of the pan that the correct level could be checked?

[curtsprenger]

Originally Posted by thomas_sorrentino

Curt, did you ever get an answer to this? I have the same issue. My dipstick tube goes into the tranny horizontally. I always wondered how it could get a level reading like that. I wonder the same thing if there's a certain plug on the side of the pan that the correct level could be checked?

Tom, no, no answers...my guess is most owners let the service co. service their transmission and they have not had to deal with checking oil level after oil change at home.

What I discovered...our coach sits almost level here in its parking place, ALMOST...but with residual oil in the dip-stick tube...could not get a good dip-stick reading at idle. Beyond ALMOST...I leveled the coach using the HWH system. Not a big level change but some. Now at idle the dip-stick reading shows cold-run level as it should be according to the Allison specs. I'm surprised...but using the leveling system to level the coach made the difference. HTH. After 11 years of ownership I'm still learning something new. I guess that's a good thing.

Once the coach was HWH LEVEL. Used a tape measure from tube to the ground. There is a SLIGHT downward to the transmission dip-stick tube. Otherwise the tube is level at best.

More Info. I used my Pela Extractor to extract 24 quarts of trans. fluid. Then removed the trans. pan drain plug and removed another 5 quarts. Then removed the external trans. filter. Approx. 30 or 31 quarts of oil removed in total. Put 30 quarts of new oil down the dip-stick tube. Checked oil at idle and all seems good.

[thomas_sorrentino]

Good info. Thanks Curt

[Randy Dupree]

the 755 has a 1/8th pipe plug in the side of the pan to check the level.
Not sure on any other model.

[jyclegg]

Curt The 748 also has a level plug. That is what I use, since the dipstick is useless. I get the engine running, remove the plug, and fill until I start to see it coming out the level plug hole. Put the plug back in, then shut the engine down.
It is a pain, but I know the level is good.

[96 Deluxe]

Some thoughts of mine on this old thread.
My dipstick tube is bent rendering it useless for checking the level.
The latest model cars have no dipstick! You fill them from below with a pump arrangement. The procedure reads like what an Engineer would use to find the correct level to calibrate a dipstick.
In servicing my HTB-748 for the first time here's what I have learned.
The internal filter is nothing more than a screen. If it's in known good shape it can be used forever. It's o-ring should be changed anytime you remove the filter.
The HTB-748 as fitted to my '86 PT-40 8V92 has no Lube Oil Pressure Switch. In stead it uses a Level Sensing Device. Aah! 1980s technology! It works but it's rather primitive. There is a procedure to calibrate the dipstick on page 3-1 of Service Manual SA 2004 B. It never mentions the 1/8th inch pipe plug on the side of the pan but I see no reason to ignore it. From my humble measurements the bottom of the plug is about 3.600 inches from the pan top surface. The "Hot Run" (160-200F) Band "ADD" level is 3.500 inches. The "FULL" level being an inch higher (2.500 inches)
The idea of crawling under a hot running bus to remove that plug doesn't have much appeal to me. I remembered that Model T Fords used two ball valves to check their oil. One for full and one for add. Supply shops sold an Oil Level Sight Gauge to be screwed into the bottom hole. A quick check of the Allison Parts Manual in the "Kits" section reveals a fancy "Closed Circuit" sight gauge P/N 23014640 which comes with instructions. It references SPI 65-TR-81. The measurements are 2.67 from the centerline of the dipstick port then 5.62 inches from the top surface for the bottom hole. .162 from the top surface to the top hole. Knowing what I know about Allison Dealer pricing this could be very expensive.
However, a person could use a "Vented Sight Gauge" ala Model T for around $30 such as MSC-Direct.com P/N 56447768. And you don't have to remove the pan. It will leak out the top if you overfill but that's the least of your worries if you do.

[96 Deluxe]

I got the sight gauge from MSC-Direct installed. I choose one much longer than required because it is vented at the top. If the coach rolls too far the fluid will leak out.
I had the dipstick tube out of the coach to inspect it and see if it could be straightened. When I put it back in I noticed there are two places on the water pump you can bolt it. I think the top position is better. Still I took the dipstick out and replaced it with a locking cap like the engine oil filler. (they make them in all sizes, a NAPA 703-1350 fits)
Here's what it looks like.
You don't have to get on you hands and knees to see it and you don't have to open the engine cover. My thoughts were the easier it is to check, the more you'll check it.