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!959 Desoto (all Mopars) Automatic Transmission


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Posted: Feb 21, 2004 - 09:20 PM

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Got a question for all the transmission mechanics out there. On my Dad's '59 Firedome, when the tranmission fluid is hot, such as a trip on the interstate on a hot day, when the car is stopped, the transmission DOES NOT slide back to first gear. So when you take off again, it hesitates, and really SLAMS back into first gear. I believe it is an "o" ring or seal that has hardened or cracked somewhere, and it has lost the pressure needed to slide back to first gear. Works fine when cold. The car has only 26,000 miles on it.

What is the problem? And it it possible to get at it, without removing the transmission?

We have put additives in the fluid to TRY to give life to the old seals.

Lack of usage is probably one of the problems. We have driven the car to the National Meets at Dayton, Ohio and Rapid City, South Dakota, but it always acts up when it gets hot. I checked the automatic fluid cooling tubes, that run thru the radiator for blockage due to age, but they are clear, and the fluid is not getting over-heated. We would like to get this fixed so we can drive it to Akron this Summer to the Desoto National Meet. (from Wisconsin) I would think all Mopars used similar transmissions in '59.

Thanks!!

Mark Waite

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Instead of trying seal reconditioning additives, maybe you need to try a detergent additive? In the "old days" when trans additives were more "mouse milk" in many situations, it was somewhat common for service people to put a can of Berryman's B-12 (pourable can, not spray can) in the trans and drive the car for a while, going through all of the gears. After about 30 minutes, the fluid would be black as that lacquer thinner additive had cleaned up the guts of the valve body. Then, the car was brought in for an extended drip drain and then the fluid and filter changed. That usually fixed many valve body related issues where the shuttle valves might have gotten gunked up.

GM has an "Automatic Transmission Conditioner" additive that is detergent and seal conditioner. Note that any of these seal conditioners will only result in about a 5% "swell" of the old seal. The GM item will stay in for about 1000 miles before it should be changed, as the instructions state. If you do the B-12 operation, adding the GM item might be a good consideration.

Worst case scenario is that the valve body has some warpage and might allow some leakage between the various circuits. Hopefully not or that a new valve body gasket might take care of that problem if it exists.

Once, after I had the trans rebuilt on my '70 Monaco by the local dealership, I came to a stop after being on the Interstate. The car did not downshift, but stayed in 3rd when I took off. The explanation was that a piece of grit might have kept the shuttle valve from doing its thing. Their clean-up procedure might have left something to be desired, but I trusted them more than anyone else in town at that time.

The shuttle valves work on spring pressure resisting hydraulic pressure plus governor pressure modulating things too. Anything that interferes with their free operation can cause shift issues. Sludge/varnish or even weak/broken shuttle valve springs.

We've discussed the ATF issue in the Buick Club General Forum serveral times. Finding Type A fluid is still possible, but usually not a name brand as such. Chrysler superceded Type A to the original Dexron spec in 1968. The current Chrysler ATF specs are highly complicated to me so using a Chrysler/Mopar fluid might be a little risky. The current Dexron III specs are for a fluid that should be highly superior to anything that came before it, I suspect, but some insist on seeking out the Type A fluid at the grocery store or auto supply.

Hope this helps,

NTX5467

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Thanks for the reply. I have a gut feeling that wherever the shuttle moves, is not smooth due to varnish, sludge, or a ridge of some kind from standing. I just hate to take it in to a shop, usually it comes back worse. If I knew where the shuttle is, once the pan is removed, I probably can fix the problem myself. None of my repair manuals show an exploded view of the transmission. ANYONE HAVE AN EXPLODED VIEW THAT YOU CAN E-MAIL ME? I would be forever in your debt.Thanks!

Mark

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