1956 400 Ultramatic Transmission Questions

Discussions related to engines, transmissions, rear axles, suspension & steering.
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Joined: Wed Feb 24, 2021 5:53 pm

1956 400 Ultramatic Transmission Questions

Post by AndrewM » Wed Feb 24, 2021 5:58 pm

I recently purchased a 1956 Packard 400. I've have several classic cars, but this is my first Packard. The car was restored in 2002-2003 and the engine and transmission were rebuilt as well. The previous owner of the car rebuilt a lot of Packard drivelines and cars over the years. According to the previous owner's notes on the car, the original transmission was taken out at the time of restoration and replaced with another Ultramatic. In 2009, the previous owner took out the transmission that was installed in 2003 and replaced it back with the original transmission out of the car in order for it to be all original. In 2011 the previous owner stopped driving the car due to health reasons. He passed away several years ago, and his son got the car. It was started and driven some since 2011, but not much.

I bought the car earlier this year and got it running again. It runs smooth and gets good oil pressure so far. It is a little below the half way mark when the engine is hot. Besides driving it up and down my driveway about one mile, it haven't driven the car much. I took it down the road about 3 miles yesterday, and noticed the transmission seems to be slipping. When driving, the car will accelerate to about 20 mph with no problem. Then after that it doesn't seem like it will go into any other gear. I put it in Low, Drive, and High, and it didn't seem to make any difference. It still won't go above about 15-20 mph according to the speedometer. It will pull fine at very light acceleration, but as soon as you start mashing the gas very much, it will slip.

The transmission doesn't have but maybe 500 miles on it at the most according to service records that the previous owner had. According to the previous owner's notes, when the transmission was rebuilt, the low range pivot shaft was replaced due to the old one being broken. Also according to the notes, the previous owner added what he called 5 updates to every Ultramatic he built.

They were:
1. Plug case side vent
2. Add vent from tail case
3. Put feed hole in rear check valve
4. enlarge passage from rear pump to reduction gear rear support bearing
5. Put hole at 12 o clock position on rear pump housing

If the transmission can't be fixed relatively easily I have two never installed rebuilt ones on the shelf I can trade out. I would rather fix the original though. I also have a rebuilt 374 engine on the shelf.

Here are some notes on the updates that he did in the transmissions he rebuilt:

Posts: 65
Joined: Tue Apr 27, 2010 5:28 am

Re: 1956 400 Ultramatic Transmission Questions

Post by mrpushbutton » Sun May 23, 2021 7:18 am

Ross should jump in here and give some ideas. I would start by verifying the pressures as outlined in the shop manual.

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