1955 cadillac hydramatic transmission question

[bigbry13]

Hey all,
New  guy here and looking for some advice. I am looking to purchase a 1955 cadillac coupe deville. the car runs great, but while on a test drive I noticed that the transmission shifts hard between 1st and 2nd gear. very noticeably hard. the owner says that the transmission was rebuilt top to bottom in the last year and a half, so perhaps it just needs adjustment? or is it truly how these transmissions were? I would figure that a cadillac being a high dollar car would be a smoother ride than it was. Im also wondering if the fact that it sits most of the time is playing a factor in it. the car has been garaged for the most part. any advice would be appreciated. thanks a lot!
Bryan

[CadillacRob]

I can't guarantee you that the trans is perfect, but I can tell you this:

My 1950 shifts a little rough from 2-3, "rough" compared to modern autos, and yes this is normal.

Also, the roughness you were likely noticing was 2-3, not 1-2, as 1 is very short and shifts really quite early.

You can adjust the shift points with the kickdown rod that is connected from the carb to the trans.

Just my 2 cents

[Roger Zimmermann]

On early Hydramatic, the rod to the transmission has some influence how the transmission will shift; there are also 2 bands which must be adjusted correctly.

[Caddy Wizard]

Yes, the transmission shift points can be adjusted with the TV rod from carb to trans.  Follow the procedure in the Shop Manual to perfection -- easily done if you are careful.  Adjusting the bands takes a good mechanic or maybe even a transmission specialist.  If you decide to tackle this as an amatuer, again, follow the procedure in the book.  Also, make a note of how many turns you adjust the screw from its starting point -- so if you make things a lot worse, you can turn it back in the opposite direction and get it back to how you found it!

But before you do any of that, make sure that the ignition and carb are in perfect tune. PERFECT tune! Many times a poorly shifting HydraMatic is really the result of an engine that is not running right.  Pay special attention to the vacuum advance (vacuum control unit) on the distributor.  If that thing is failing, it will cause funky shifts (learned the hard way).

The HM transmission has two drum assemblies and the first one handles first and second gear and the other one is for third and fourth.  When the transmission shifts from second to third, it is changing planetary drums, so the shift is much harsher than from 1-2 or from 3-4.  Modern transmissions have smoothed this out completely.  But it is quite normal that the shift from 2-3 is more noticeable than the others.  It should not bang or be sloppy, however.  But it should be noticeable and firm.  I say this from the experience of having had 16 of these cars and having worked on another dozen or so...

[Bob Schuman]

Another possible cause of rough shifting is the wrong transmission fluid. Cadillac originally specified Type A Automatic Transmission Fluid, which is now an obsolete designation. The proper currently available fluid is Dexron III (do not use Dexron VI, that is for the latest GM transmissions) Dexron is not a brand, it is a fluid type marketed by many lubricant makers. If the transmission has been filled with Type F fluid, that fluid may well be the cause of your rough shifting. Type F is for some older Ford transmissions, not for GM cars. If the fluid is unknown, I suggest draining the transmission AND fluid coupling and refilling with Dexron III.
Bob Schuman

[CadillacRob]

For whatever it's worth, I use Dexron VI in my 1950 with no issues.  To my knowledge, all GM trans fluids are reverse compatible.  I even went to Cadillac to determine this, although they were of no help.  There's a service bulletin that shows this, and I wanted to ensure that with a mechanic.  I did have an older guy take me back in the shop to look into that, but we couldn't find it.

[Caddy Wizard]

I've used DEXRON VI also, with no issues, and my understanding that all versions of DEXRON are backwards compatible (but not forward compatible).  But transmission mechanics have told me the opposite.  I don't know what is correct...

[Roger Zimmermann]

This is the bulletin you are looking for:

Quote
General Motors DEXRON®-VI Global Service-Fill Specification

During early 2005 General Motors released a newly developed automatic transmission fluid (ATF) for the factory fill of all GM Powertrain stepped gear automatic transmissions. The new fluid provides significantly improved performance in terms of friction durability, viscosity stability, aeration and foam control and oxidation resistance. In addition, the fluid has the potential to enable improved fuel economy and extended drain intervals. Since the performance of the new fluid far exceeded that of the DEXRON®-III service-fill fluids available at the time it became necessary to upgrade the DEXRON® service-fill specification in order to ensure that similar fluids were available in the market for service situations.  This latest upgrade to the service- fill specification is designated DEXRON®-VI.
Since General Motors introduced the first ATF service-fill specification in 1949 it has been periodically necessary to upgrade the specification. This upgrading process ensures that available service fill fluids are of an appropriate quality for use in transmissions that have been designed around the factory fill fluid performance. It should be noted that, as with previous upgrades, DEXRON®-VI fluids are designed to be backward compatible with earlier transmission hardware. More importantly, earlier type fluids are not forward compatible with transmission hardware that was designed to use DEXRON®-VI fluid, i.e. DEXRON®-III is not compatible with the most recently designed transmissions, and the use of these earlier type fluids could result in transmission damage. All current calibrations and certification tests are now conducted with DEXRON®-VI ATF. DEXRON®-III fluids should not be used for these applications where the owners manual recommends the use of DEXRON®-VI. GM does not license or support obsolete ATF specifications or the use of fluids that are being marketed against cancelled specifications.
All DEXRON®-III licenses expire at the end of 2006 and will not be renewed. Beyond that date GM will only support the use of DEXRON®-VI fluids for use in Hydra-Matic transmissions. Fluids sold in the market after that date bearing claims such as “suitable for use in DEXRON®-III applications” or similar wording should be avoided. DEXRON®-VI licensed fluids are fully backward compatible and can be used in all applications covered by earlier GM ATF specifications. 
The use of unlicensed fluids and/or non GM approved aftermarket additives may prove detrimental to transmission performance and void warranty coverage.
There is a published list of GM-approved brands of DEXRON®-VI (see page two of this release).  This list represents the companies who have conducted the appropriate testing and received GM approval.  Company name, license number, and brand name are shown.  This list will be updated on a regular basis as more approved products are added.
Unquote

[signart]

The shift from 1 to 2 should be very early, but not too early so as to get the mass moving and not bog engine in 2nd. Adjust according to instructions, then fine tune. My '53 is barely noticeable in all shifts, never overhauled, I have sealed it with fluid change and tv rod adjustments only. As mentioned carb & engine must be in proper tune.