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bullrun

1941 Cadillac Automatic Trans fluid and service

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Just brought a 41 Cadillac out of a 25 year slumber. Auto transmission was full to top of dipstick and no leaks evident. Car shifts thru all 4 forward gears-not as smooth as a Turbo 400. I have put about 300 miles on it and it drives better each time I take it out. It sometimes clunks when it down shifts from 4th to 3rd. I also have to place it in drive-wait for the trans to lurch and then quickly drop it in revese or else it grinds. If you just try to drop it in reverse it always grinds. I want to change the fluid-does anyone know if our "Dexron" of today is what I should use? Also a source for a filter kit. I'm ordering a transmission repair manual. Can the bands in these transmissions be adjusted with ordinary tools? Any help or suggestions are appreciated

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The way your transmission acts when trying to shift into reverse is 100% the way it was when it was new. On the early hydramatics, when shifting into reverse, you have to put it "low," then wait a second, and then lurch it into reverse for it to go smoothly. You might want to try www.cadillaclasalleclub.org under the forums tech section there's several guys on there who know a lot about hyrdamatics and they can answer any other questions you might have.

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If you just try to drop it in reverse it always grinds.

You're doing it wrong.

1941 Hydramatic Performance

On either the prewar transmissions or the postwar models, the shifts should all be positive, with no hesitation. The prewar models did not have clutch plates with lining, and the shifts will be a bit soft, but positive.

Postwar transmissions had lined clutch plates, and shifts were strong, and positive, but not harsh.

Reverse selection in the prewar models was tricky. In all Hydra-Matics through 1950, the rer wheels must be at an absolute stop. In the prewar transmissions, it was necessary to go from neutral, if that was desired, to "LO", and wait (less than one second, as a rule) and when the transmission is felt to engage, then, bring the lever into reverse. It is possible on the prewar models, to pull the lever directly into reverse, and do a lot of damage to the transmission.

On the 1946-1950 model,, there is a "reverse blocker" feature in the trans, that prevents selecting reverse before the transmission engages. However, in all cases, Hydra-Matic transmissions require the rear wheels to be completely stopped to get reverse.

In both prewar and postwar transmissions, through 1955, with the engine turned off, and transmission in reverse, the rear wheels are locked. This is the "Park" feature.

If a postwar transmission were to be installed in a 1941-42 car, the ideal model would be a 1951 Cadillac model. this one has a cone clutch reverse, and it is safe to yank it into reverse as soon as the engine fires, without damage, and the selector quadrant still matches the previous years.

1941 Hydramatic Shop Manual & other info: http://www.modifiedcadillac.org/documents/1940s/1941/

1941 Factory Shop Manual: http://www.modifiedcadillac.org/documents/Shop_Manuals_and_Illus_Catalogs/

Military Service Manual w/Specs for Cadillac Flathead: http://www.modifiedcadillac.org/documents/1940s/1944/

Edited by CarFreak (see edit history)

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Don't be surprised if your trans starts leaking. 25 years slumber is not good for transmission seals.

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I believe the early Hydramatics have only two seals, plus the pan gasket, so if it's not leaking, it probably won't. I just bought an all-original 1941 60-Special with 66,000 original miles and will probably be facing some of the same things you are, but the experts to whom I've spoken about it confirm the shifting sequence above, and I have used it on the 1941 Cadillac convertible we had in stock, which was definitely a grinder, and it eliminated the problem. You may also experience some harsh shifts, like a TH400 with a shift kit, and the 1-2 shift may give you a whack, but that's apparently normal as well. One fellow with whom I was speaking just yesterday who is our local Hydramatic guru says that if it doesn't leak, it probably won't start, and that the harsh shifts are pretty typical. You may also hear your pump moaning more audibly than you'd expect. But overall, they're indestructible transmissions that usually only need some fine-tuning to the shift linkage to work properly. Just don't expect modern levels of sophistication out of them--these were the first of their kind, and evolution happened quite rapidly in subsequent years.

Good luck and enjoy!

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Hi Bullrun,

Carfreak's advice is correct. Stop the car, put it in low range and then "smartly" but smoothly move the lever to reverse. When done correctly there is no grinding. Also don't expect the shift points to be all that smooth, there will be a lurch when the transmission shifts. It's norrmal, that's the way they were. I use Dexron 3 and it works just fine in my '41. You should check the fluid level fairly often since you probably will have at least a little leakage. Glad you are driving it regularly, they need it.

Bill

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