1946 - 1949(ish) Hydra-Matic question

[Jeff Hansen]

Hello all,

This question regards checking the fluid level in post-WWII (at least through '49) Hydra-Matic transmissions.

The question - how do you check the fluid level?

The 1946 Shop Manual Supplement indicates running the engine for one minute, then stopping the engine, and checking the fluid level at that point.

The 1949 Shop Manual indicates one should run the engine in neutral at the equivalent of 20 MPH for 90 seconds, then check the fluid level while the gear selector is in Drive (!) with the engine idling (obvious need for safety here).  The '49 manual indicates the difference between "F"ull and "L"ow is 1.5 pints.

The owner's manuals for 1946 through 1949 Owner's Manuals do not touch on HOW to check fluid level.

I have a post-WWII Hydra-Matic in my 1942.  I don't know what year the transmission is from, the number plate on the side is long gone.  It is NOT a dual-range unit.

If I check the fluid level as described for the 1946 supplement, the fluid level is right at 'F'.  If I check the fluid level via the 1949 manual, I am just below the "L"ow mark on the dipstick.

Fluid level could be an issue for me as I am experiencing a situation in which I have no second gear in the transmission.  All other gears function normally.

How would you perceive the fluid level I am seeing in this case?  Would you add fluid to see if second gear begins to function?

Your thoughts are appreciated!

Thanks,
Jeff

[Bob Schuman]

Jeff,
I have seen the same discrepancy in Hydra-Matic fluid level checking procedures in various Cadillac service publications. My Oldsmobile manuals are generally much better than Cadillac, but my 1950-51 Olds Shop Manual says onlt to start engine, with engine idling shift to Lo, and check oil, which should show full. Not much help there

From some experience, starting with a nearly new 1948 Olds, I never heard of checking with the engine off, always with it idling. Some references say shift through all ranges, then check in Dr (some say N), with oil warm. What does warm mean, since recent GM transmissions require fluid checking within a specific temperature range.
On my 51 Cadillac, with a cold engine and transmission, I started the engine, shifted to Dr (brake on, wheels blocked) and immediately checked trans oil, it was at low mark on dipstick. Then let engine run in neutral for ten minutes, rechecked oil, now it was at full mark. Nowhere have I ever seen anything about how much to warm up a Hydra-Matic before checking its oil level. This does not specifically answer your question, but it may lessen the confusion.

Regarding the skipping second gear-are you sure your throttle pressure linkage is adjusted exactly per the shop manual procedure? A few years ago Terry Wenger completed restoration of a 41-60S that another local friend had started, with a new military engine and a NEW 1946 Hydra-Matic. After much linkage adjusting and band adjusting, and experimenting with non-spec band adjustments, it shifted very strangely, usually missing second gear. We carefully adjusted the linkage between the carburetor and transmission, and it immediately became one of the nicest shifting HMs I have ever experienced. The 1941-1948 Cadillac linkage is a complicated "Rube Goldberg" design, unlike the single rod used starting with the 1949 models.

[Joe Jensen]

You could drain the transmission and the torus and refill the system with the amount of oil your shop manual specifies then check it with all the different methods to see which one works best.  I use the procedure in the '49 shop manual and that works for my '49 Hydra-matic.

Good luck!
Joe

[TonyZappone #2624]

Please do not perceive me to be a technical expert, of any sort.  However, with the large amount of fluid that these transmissions, hold, is it necessary to be so precise in the measurement?

[Bob Schuman]

Simpler is usually better. I like Joe Jensen's suggestion.

[Rossoroo]

Motors Auto Repair Manual [1935-1953] states that the transmission oil should be at operational temperature, which means a short drive or perhaps a period of time idling in gear with car braked and blocked to let the fluid warm up. They are also suggesting the fluid be checked with the car in "Neutral"

[Jeff Hansen]

Gentlemen,

I appreciate all your responses.  Thank you for taking the time!

Immediately after a run of about three miles last evening, I added just over a pint of fluid to bring the level up to the "F"ull mark with the car running and in neutral.  Second gear has returned.  I am certain some adjustment can be made in the linkage as it has not been touched since the restoration was finished back in 2005.  That will be my next project.

Thanks again!
Jeff

[Caddy Wizard]

I seem to recall that for the early Hydramatics the Shop Manuals (up to about 1949 or so) suggested checking the fluid level while in Drive with the engine idling.  Later, they switched that to checking it in Neutral.  It is essentially the same transmission up to 1955, so my guess is that they found the level in Neutral to be the most reliable way to get good results.