1946-1949 Early Hydra-Matic Transmission Fluid

[Michael Brittan CLC #2750]

About ten ears ago my '48's original Hydra-Matic was rebuilt.  Prior to the rebuild, the transmission had the characteristic hard 2-3 shift when cold but the shift smoothed out as the car warmed up.  After the rebuild the hard shift persists, even when warm.  I don't know what fluid is currently in the transmission.  Could the change in behavior be due to transmission fluid viscosity differences when the fluid was replaced at the time of the rebuild?  The original fluid had been in the transmission for decades prior to the rebuild.

I've had the transmission adjusted, including varying the length of the throttle rod, but the hard 2-3 shift remains.  Since the transmission once had a smooth 2-3 shift when warmed up, I thought that perhaps replacing the fluid might be worth trying to see if something with more appropriate viscosity-temperature characteristics helps.  Any suggestions as to what might be the recommended fluid to use?
Any and all advice appreciated.

[PHIL WHYTE CLC 14192]

I believe you can still buy older (unlicensed) versions of Dexron transmission fluid. It is worth a try. I would also take the car on a drive and stop and make very small adjustments to the throttle rod, as little as a quarter turn can make the difference. The harsh 2-3 shift happens because it is the point where the power switches from the 1st clutch drum to the 2nd and involves perfect timing between the bands and clutches. If it persists maybe a band adjustment might help. I rebuilt my 54 transmission many years ago with the help of an expert on these. He set my clutch packs up with a graded plain plate to give uniform clearance (I failed to note the spec, sorry). He told me that would give a smooth shift in all gears and it did.

[Lexi]

Fairly certain that my local lubricants supplier still has Dexron (think it is #3). I bought a couple of pails of it 2 or 3 years back. Yes, it is available in bulk. I am in Canada so the supplier probably is of no use to you. Will provide if you want that info. Clay/Lexi

[Jeff Rosansky CLC #28373]

I run Dexmerc in our 55. It hasn't been rebuilt. Smooth 2-3 shift. However it leaks so much that it is constantly being refreshed.

[signart]

I run Dexmerc in our 55. It hasn't been rebuilt. Smooth 2-3 shift. However it leaks so much that it is constantly being refreshed.

You can reseal it, without rebuilding it, which is what I did in my '53. No regrets, no hard shifting.
You would have to remove to seal completely, however.

[toybox]

The first generation Hydramatic's were known for their clunk like shifting in2nd and third. When the 2nd generation came out in the early  1950's this characteristic almost gone completely. However  if yours is shifting at inappropriate speed and RPMs causing it to shift hard it can be adjusted if you have the manual and it's easy. Tim

[Jon S]

I believe your transmission came with Type A which contained whale oil which has since been banned. Type A without whale oil is still available. Not sure if the friction coefficient is the same.

[Michael Brittan CLC #2750]

Thank you one and all for taking the time to provide input to this issue.  About a year ago I took the car to a transmission 'expert' whose shop was quite a way from my house.  I had to leave the car there in his small shop where he and a coworker worked on several oldies.  This did not appeal to me since my car, which has an immaculate paint job, had obviously to be moved in and out frequently since there was only one lift in the confined space.  To cut a long story short, they made some adjustments, I took the car (now caked with dust and dirt) away, but the 2-3 shift was no better.

More recently, I took it to a mechanic and we did what Phil suggested - he shortened the throttle rod incrementally and I would test drive the car in between each adjustment (why pay a shop manhours to do that?!).  We left it one full turn shorter, but now I have lost the throttle kickdown from 4th to 3rd.  I suspect that the transmission shop did the same, adjusting the rod just short enough to retain the kickdown.  I will probably have the rod reset back one turn to get the kickdown back and then try to scrounge some Dexron III or equivalent as proposed and do the fluid transfusion.  If I'm not successful in finding an appropriate fluid I might revert to you, Clay, for the name of the supplier north of the border.  Failing that I can see resetting the clutch packs (per Phil's post) as the only real solution but would have to hunt to find this expertise here in the Denver area.

[TJ Hopland]

One note about Dexron fluids,  the current Dexron VI is the only version that still is officially licensed and approved by GM.  Anything else you buy isn't so its up to who ever is bottling it what they are putting in the bottle and on the label.  I'm not saying its bad just saying that you could buy 2 different brands and end up with a significantly different fluid.  Different in a good way?  Or a bad way?  Who knows.  Dex/Merc is how most brands market the kinda the 'universal' stuff now.

Its hard to tell if you are too slippery or too grippy, both could give you hard shifts but so could pressure problems that are not fluid related.  It could be that it slips and slips then suddenly grabs just as easy as it could be just grabbing when it should be slipping a bit. 

Don't these have hydraulic test ports and pressure settings?  If so seems like that would be where you would want to start to make sure the pressures are correct.  If they are then you could try blending in some Dex6 since that should be on the more slippery side.  If you think you need sticky then Type F (also no longer an official standard) or many of the 'shift improver' additives.   

[Michael Brittan CLC #2750]

TJ Hopland makes a very valid point.  In fact, two points.  One can't say for sure that the viscosity-temperature characteristics of the transmission fluid are at the heart of the problem, and, secondly, that any fluid other than that approved by GM has reliable specs.  At this pont I am inclined to try a transfusion with Dexron III which is apparently available through Napa, but the specs of which I can't speak to.  This may be a bit of a gamble, but might be an interesting experiment to conduct just to see what difference a fluid change might make.

Pressure is another intriguing angle raised by TJ.

[PHIL WHYTE CLC 14192]

Thank you one and all for taking the time to provide input to this issue.  About a year ago I took the car to a transmission 'expert' whose shop was quite a way from my house.  I had to leave the car there in his small shop where he and a coworker worked on several oldies.  This did not appeal to me since my car, which has an immaculate paint job, had obviously to be moved in and out frequently since there was only one lift in the confined space.  To cut a long story short, they made some adjustments, I took the car (now caked with dust and dirt) away, but the 2-3 shift was no better.

More recently, I took it to a mechanic and we did what Phil suggested - he shortened the throttle rod incrementally and I would test drive the car in between each adjustment (why pay a shop manhours to do that?!).  We left it one full turn shorter, but now I have lost the throttle kickdown from 4th to 3rd.  I suspect that the transmission shop did the same, adjusting the rod just short enough to retain the kickdown.  I will probably have the rod reset back one turn to get the kickdown back and then try to scrounge some Dexron III or equivalent as proposed and do the fluid transfusion.  If I'm not successful in finding an appropriate fluid I might revert to you, Clay, for the name of the supplier north of the border.  Failing that I can see resetting the clutch packs (per Phil's post) as the only real solution but would have to hunt to find this expertise here in the Denver area.

Michael, a band adjustment prior to stripping it down to do the clutch packs would be preferable. I've found on my 54 and on the 51 my wife used to own that the adjustment on the TV rod can be as small as a quarter turn to get it right. Try all the simple things first, including a fluid change.
Phil

[Michael Brittan CLC #2750]

Thanks Phil.  Sound advice.  I have tried the incremental throttle rod adjustment to no avail.  So my next step is the ATF transfusion.  To TJ Hopland's point on the uncertainty of the fluid specs, I will probably go with a branded Dex/Merc product such as Valvoline or Castrol for older vehicles supposedly meant for the Dexron III era, and which presumably are not synthetic.  This may have a higher viscosity at a given temperature than the current synthetics.  As I said, I don't known what fluid is currently in the transmission, but it would be 2014 vintage. 

[jwwseville60]

Im tired of the hard shifts on my 47 coupe.
Im wondering if a later Hydramatic would fit?

The last year for Hydramatic was 1963. Its VERY smooth.

[Lexi]

...Clay, for the name of the supplier north of the border.  Failing that I can see resetting the clutch packs (per Phil's post) as the only real solution but would have to hunt to find this expertise here in the Denver area.

Michael I bought my pails of Dex III from Crescent Oil, a lubricants company in Hamilton, Ontario (Canada), that has been in business since 1905. Quite the place to visit. The retail and ordering area makes one feel like you are stepping back to near turn of the century. Located in a house that looks as old as the business. Here is a link to their transmission fluid page. Seems like what I bought may, perhaps, no longer be there but I see one product which seems to include Dexron III, so looks like it's equivalent is still available. When I go to my storage area I will check the pails for any identifying product numbers or other information. As I recall you can special order stuff that is not on display. Would they even mix specific blends? Not sure. You would have to contact them and make enquiries. Clay/Lexi


https://crescentoil.ca/category/transmission-fluid/

[Jon S]

Michael I bought my pails of Dex III from Crescent Oil, a lubricants company in Hamilton, Ontario (Canada), that has been in business since 1905. Quite the place to visit. The retail and ordering area makes one feel like you are stepping back to near turn of the century. Located in a house that looks as old as the business. Here is a link to their transmission fluid page. Seems like what I bought may, perhaps, no longer be there but I see one product which seems to include Dexron III, so looks like it's equivalent is still available. When I go to my storage area I will check the pails for any identifying product numbers or other information. As I recall you can special order stuff that is not on display. Would they even mix specific blends? Not sure. You would have to contact them and make enquiries. Clay/Lexi


https://crescentoil.ca/category/transmission-fluid/

Wonder if they make a "Type A" which was used through the late 1950's?

[TJ Hopland]

There are still a few brands that sell something called Type A.   Cam2 is the only 'bigish' name that seems to pop up.  The others are brands I have never heard of. 

What I always heard was if you had all original internals you were best to stick with as original of a fluid as possible.  Once it was rebuilt using more modern materials the Dex/Merc was what you should be using.   If you are running 70ish year old internals at this point I don't think the fluid is going to make much difference.  Those old soft parts are not going to be performing up to factory specs at this age so having the 'right' fluid isn't going to help get everything back to spec. Probably why people like Valvoline don't bother making a type A anymore.   

[Chopper1942]

Well, I guess I'll add my 2 cents worth. Usually 3-4 things cause harsh shifts or gear engagements.  Park or neutral into reverse or drive is usually caused by too high of engine rpm when shifting. Harsh shifts from gear to gear is usually caused by high line pressure or TV pressure issues, band release and clutch apply timing or its reverse, and fluid.

Dexron IV has more lubricity (slippery) than earlier GM fluids. This allows for softer clutch application.

High TV or line pressure increases the speed of the clutch application which cause a harsh shift. Next,I would check and adjust the TV pressure as outlined in the OE manual. If still to harsh, try backing it off until you lose your downshift. Then, turn it up until you get your downshift back.

If still to harsh, perform the 2 band adjustments. You can make slight adjustments to the OE setting to change the timing of the clutch and band. Make very small adjustments, 1/4 turn at a time to see if it improves. Just make sure you do not back it off so much that the band slips.

[Lexi]

Wonder if they make a "Type A" which was used through the late 1950's?

Did that have the whale oil additive? Thought that was discontinued many years ago. Next time I am there I will ask. But I thought I did see Type A on one of their 2 pages of transmission fluids offered. Clay/Lexi

[Michael Brittan CLC #2750]

Just by way of an update, as noted previously I tried the incremental throttle rod adjustment, but that did not improve the 2-3 shift.  The next step is the ATF transfusion.  Clay/Lexi and others have kindly provided further input on the fluid type.  Where I stand on that score is that next week I am scheduled to replace the transmission fluid with Valvoline Dex/Merc, which is readily available, if not ideal.  This at least accords with TJ Hopland's post for a rebuilt transmission with more modern materials.  This ATF transfusion is very much an experiment, with, in my humble opinion, a low probability of success.  But it is the next easy thing to do on the list.  If the Dex/Merc shows no improvement, then I would say it's unlikely that a fluid technically more appropriate for the early Hydra-Matic is going to be the answer.  I'll report back after the transfusion.  Hopefully it goes according to plan, and does not result in leaks to the extent that Jeff Rosansky reported!

[TJ Hopland]

Seems like a reasonable plan.   If you get some miles on it with the new fluid and there is some signs of change you could try more slippery it out with some synthetic like dex VI or more sticky like Type F or Lucas treatment.  That's all cheaper than hardware other than maybe a pressure check/adjustment.