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It's in Vol 29, No 8.

They don't call it Dexron - sorry for the misrepresentation - I should have called it a Dexron type.

The fluid recommended has "anti-friction properties" to improve clutch life.

Since then there have been iterations of Dexron, but to me the implication is clear that they preferred an additive containing friction modifiers.

Maybe they were groping for a solution given all of the problems they were addressing with the transmission.

The question here is whether the ultimate clamping force is the same using the Dexron or Type F.

For example I have driven Ultramatics that had occasional direct clutch chatter and I know were filled with Dexron. When I suggested testing Type F the response was disinterest because the car went down the road. Also, they thought perhaps the problem might be exacerbated by a "grabbier" oil.

As to those owners who remedied chatter by switching to Type F, I absolutely agree but not neccesarily because of removing friction modifiers. Line pressures under Type F may be higher.

"For example I have driven Ultramatics that had occasional direct clutch chatter "

Chatter or groan??? Maybe my interpretation or diction is lacking but to me a chatter is something that would indicate a vibration coupled with a aound that would resemeble something like a repetitive small hammer strikes on a piece of wood.

A groan is a continuos moaning sound and only a sound.

I've never known of chatter described for the ultramatic. Only groan.

My point is that maybe we are talking about two different symptoms. One that occurs for some transmissions while not for others????

I believe that groan and chatter may be two distinctly different problems. I've experienced chatter with high-mileage and well-worn Ultramatics, but never with Twins or GearStarts.

I suspect groan is a direct drive clutch symptom and chatter is a high range clutch symptom. Just guessing, no real evidence.

"When I suggested testing Type F the response was disinterest because the car went down the road"

Maybe that IS a good reason not to switch to F. Perhaps some fear that the cure for "chatter" (groan?) would cause problems far worse than just an annoyance.

Again, the real problem we are faced with here is how does one determine the kind of materials CURRENTLY in ANY tranmission in order to choose the correct fluid??? Especialy in view of the fact that we are buying MODERN produced fluids.

For all we know, any trans of unknown history may have had a variety of differnt fluids installed over the years thus changing the friction materials characteristics.

Thanks Owen for the chatter/groan explanation..

Edit: That jars my memmory. On only 3 or 4 occasions some 10 years ago my 1956 TwinUltra would have a rather severe chatter. But it would occur at very low speeds of 5 to 15 mph, very cold weather. Hasn;t happened in years since. Note that i rarely if ever use "D". Alway "H". So very likely the chatter i heard was the high range clutch pack (not DD clutch). But again, it has not occured anymore in recent years.

The trouble-shooting section of the 55/56 shop manual has several categories for "chatter" all of which identify high range clutches as a possibility, but also note dragging bands as a possible cause.

Ross -

Good info, as always.

I try to keep notes on your tips-n-tricks and plan to implement them when it comes time to rebuild any of the Twin Ultras in my cars, which I hope to do with my own two hands.

The very characteristic that you cited for Type F make it even more attractive to me.

GM seems to have has a real hard on for undetectable shifts. While I don't want the transmission banging into the next gear, the feel of a shift lets me know the transmission is working.

Tim Cole -

Thanks for the specific reference. I've made a cut-n-paste of the article, attached below, for the benefit of the general viewing audience.

I was aware of that article (and it's listed in the Service Index), but no where does it mention Dexron - only a new type of fluid, AQ-ATF, but WITH friction modifiers that you noted.

Curiously, the stated application is for the Twin Ultramatic (which would include the Gear Start edition), but nothing about its use in the original Ultramatic; perhaps the focus was the Low/High shift.

Further reading, online, shows that AQ-ATF was a precursor to Dexron, which didn't come on the scene until the late 1960s. However, Dexron is supposed to be backwardly-compatible with AQ-ATF and Type A.

Yet, I have to wonder about the effectiveness of later formulations of Dexron, made without whale oil, in these old transmissions.

I've since enhanced the topic description in the Service Index, and I'll try to work some of this new info into my FAQ this weekend.

Attach file:

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In view of post #28 above it seems to me that all of this research keeps pointing toward Dex-MErc as a modern replacement. Not F.

Research shows that the original Dexron was backwardly-compatible.

Later formulations of Dexron are billed as being backwardly-compatible with previous versions, but be careful. I've read that GM recommends AGAINST using Dexron VI in NON-GM transmissions where Dexron III was previously specified.

Dexron III can be used in place of Mercon V and earlier formulations thereof.

Yet, I digress...

Personally, I'll stick with Type F, as recommended by Ross and others for Ultramatics with OE or factory replacement friction material.