Packard Forum Index » Post-War (1946-54)

Is the differential pumpkin interchangeable between the junior and senior cars. Assuming both have the automatic transmission. I have a line on one from a model 200 but need to know if the gear ratio is the same as the model 300.

I believe just carrier will bolt. The standard for Ultra was 3.54 in 52 on, but 3.9 in 51 200s. There were options available so standard not a given. If replacing entire rear axle, tread width narrower on 200.

The 24 & 2501 chassis also lists 2 different diameter drive shafts so the U joint may be different.

I show a gear ratio of 3.54-1 for the 51 as well. My knowledge of the correct terminology is lacking. I always referred to the assembly that is removed out the front of the differental housing as the pumpkin. Is that complete assembly (Ring and Pinion, Spider gears, all carrier bearings) called the carrier?

The part with all the gears & works is the carrier in Packard language and the tubing and housing is called case assy. You didn't mention what years you were looking at. I just noticed the case assy is same for all chassis except the XX13 in 51-52 but a different number in 53-54 as is the carrier different 53-54.

You're right! I didn't mention the year. I have a 51 model 300. The guy I found is parting out a 1951 model 200. SOme things are the same some are not. From what you've said I need a carrier from a 51 or 52 300. The 200 had a 3.9 rear end and I need a 3.54.

According to the specs page 51 200 had 3.9 for Ultras, but 3.54 was standard in 3 & 400s.

In the parts manual however, the 3.54 was listed for all Ultras and 3.9 was OD so it's a question as to what was actually done.

I've never looked for anything but don't recall ever reading that Packard had stamped a ratio anywhere. Anyone??

It's more complictaed than that I'm afraid.

The standard transmission models with overdrive had a different rear axle ratio than the ones without the overdrive. 4.1 versus 3.9, at least on the Model 200, according to the service manual. I hadn't checked the other models, but know the 200 info because that is the model I own.

Jim G

I had converted a 1952 250 to standard transmission and it lacked power to go up some Pa. hills without downshifting. I installed a 1953 OD tranny and the 4.1 rearend from the same donor car(Clipper) and it ran much better as I had the best of both worlds. I'm not sure of 55 and earlier but 56 has a tag on one of the rear-end bolts that gives the ring and pinion gear numbers, so you can determine gear ratio easily. Of course if you can see the ring and pinion it is an easy matter to determine the gear ratio.

Simple procedure for determining rear axle ratio: jack up the entire rear end of the car, so that both wheels are off the ground. (Making sure the car is out of gear and the front wheels are chocked so the car cannot move) Now, turn the rear wheel so the valve stem so it's on the bottom. This is where a helper will come in, take a piece of chalk and mark the driveshaft with a line that you can see easily. Have a friend turn the wheel ONE revolution forward, and watch the driveshaft, counting the turns. It will most certainly end up past 3 or 4 turns, so you'll have to do an "educated guess" here. If it turns 3 and a half times, you have a 3.54 gear ratio. If it turns a little over 4, it's a 4.10. A simple, but effective way of determining gear ratio. As always, be very careful while under a lifted car, as anything can happen at any moment.

This is all a "gear ratio" is, how many turns the driveshaft makes per one revolution of the wheel.

If I remember correctly, if it's an open differential (non-positrac) you only need ONE wheel off the ground.

G'day all, I normally only jack up one wheel, mark the top or bottom of the jacked wheel. Put a chalk mark from the tailshaft across to the carrier. Rotate the jacked wheel TWO revolutions forward and count the revs on the tailshaft. This will give you your final ratio. As Eric suggested you need a buddy as it is hard to turn the wheel yourself and watch the tailshaft at the same time. Best regards Peter Toet