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

Hi guys,

I am trying to find out what gear ratio I have on my differential: 50 Deluxe 2 door, 288 cu. inch, 3 speed manual. I crawled underneath the car and looked at the 11 o'clock area on both the front of the pumpkin and rear and found no stamping at all. I was careful to clean it good and found one little spot on the front of the pumpkin and found a flat spot and couldn't find anything. Could someone please help me?
Due to the shortage of financing I am forced to replace my straight 8 with a Vee and won't be able to use my overdrive either. I am NOT using a SBC for replacement but a 472 Cad with an automatic and want to use my stock rear end if possible. I am not looking to race it or hot rod it, I am just trying to build a dependable driver. Are my axles strong enough to handle the torque if I'm not acting like an idiot?

I would be interested in buying your complete overdrive setup. Since I am local, there would be no shipping hassle.

Jim

I believe the gear ratio for the 1950 eluxe 8 with OD should be 390. The rear end should be strong enough to handle the horsepower, but I'm not sure if the brakes would be up to the task. Just my thought. Good luck on your project. May I ask what front suspension you will use? Thanks

This may be somewhat naive however I thought since the engine weight on the Cadillac is about 500 lbs. lighter I was considering using the stock suspension and replacing the knee action shocks with tube style shocks. Am I wrong in my thinking? The weight of a 472 Cad is only about 60 lbs. heavier than a SBC. Cadillac used a 2.92 rear end gear ratio in 1969 and the torque was approx. 500 lbs.@3000 rpm. Also they used drum brakes very similar to Cad. Any suggestions anyone might have is greatly appreciated.

Dear Tommycourt,
Some basic engineering information: torque breaks things, power does not (power overheats things). The Cadillac engine has about 60% more torque than the 288 Packard engine. If you drive the car using the available torque and use the stock transmission and rear end gears the stress on the rear axles will be about 60% higher than stock. They may or may not break immediately depending on how you drive, but the fatigue life will be shorter. The fatigue life is the number of load cycles it takes before small cracks form and eventually break the part.
You can bring the stress on the rear axles in high gear down to nearly the stock Packard level by using a 2.9 rear end ratio. You will need to change the entire rear axle housing probably since Packard never made such a gear ratio. That will also reduce the engine RPM and extend its life. Having less torque on the axles also means lower acceleration in high gear and less hill climbing ability. You can always downshift, but that increases the torque on the rear axles.
Before doing the engine swap you should consider all the costs and the many changes you need to make in the car to get a safe and reliable vehicle. The brakes and handling need to be considered too. In my opinion you would be better off financially buying a newer car rather than turning an old car into one.

I understand what you are saying Fred. I was considering using a Cad rear end also depending on the inner dimensions of the rear end (backing plate to backing plate measurements). Problem I am having is I love the old car and a Packard has been one that I have wanted for years. I want to use the car as a daily driver and not something to do any racing with. I want to keep it as quiet and smooth and maintain the Packard image. It's just one of those dreams I have always had and hate to think of changing cars, but I sure appreciate your input.

Tommycourt,
I may have misunderstood your motivation for the engine swap. Your first message mentioned lack of finance and that confused me. Building a proper resto-rod is a different motivation, but it will surely cost way more than just overhauling a Packard eight. Best of luck with your Packard.
Fred

Follow Freds advice on the axle.

However there are some questions that mite need to be asked relative to this analysis.

1. How much difference is there between the 54 rear axles and the 55 rear axle IN TERMS OF STREnGTH ???? Were they the same axles????
2. Then how much difference bewtween the 54 rear axle and the 50 rear axle????

My point here is to compare the transition of 54 streight 8 rear axle to 55 V8 rear axle. THEN compare the 54 to the 1950 rear axle.

I can not make the comparison because i am not familiar enuf with the 1950, 1954 rear axles.

Bottom line: IF the difference between 1950, 1954 and 1955 rear axles is very small then most likely the 1950 rear axle will hold up to the modern V8 just fine.

On a different note:
If u're trying to get the car on the road as quickly and cheaply as possible then why the 472 Cad engine???? Maybe u just so happen to have a good one laying around???? I certainly understand that concept completely.

But if u have to go buy an engine on the general market for conversion then your "budget constraint" is in direct contradiction of a 472 Cadillac engine.

I will further declare that ANY engine other than an SBC is a direct contridiction of any budget limitations.

The reason I am using the Cad motor is that I do have one available from a buddy of mine which he wants very little for. He had quite a few of old Caddies and has one with only 73K miles on it and it runs quite well. He is practically giving me the car as it's a donor car and he has no more use for it. He also has the complete driveline with a 2.92 rear end. Basically he just used the interior. In researching the Cadillac 472 they are a trustworthy engine with low torque capabilities and good longevity. A lot of guys here in Az are SBC believers and they feel that is the only engine to run. I want mine to be different. Their argument is if you break down you can go to any parts store and get parts; which is true. My theory is a big block geared correctly will fulfill my needs as I am not interested in horsepower as I am a lower torque and rpm running engine rather than having to wind the engine at a high rpm. I want a car that I can drive comfortably at 65-70 and not have to do it at a high rpm. Am I mistaken in my thinking?
Tommy

1. How much difference is there between the 54 rear axles and the 55 rear axle IN TERMS OF STREnGTH ???? Were they the same axles????

PackardV8, check the parts book, the 53,54 and 55 senior car rear axles are the same. I didn't check but the junior models may also be the same.

I must admit I can't see an alternative engine, be it a SBC or Caddy or whatever, as a necessity for cruising at modern speeds at 67-70 mph. Later prewar and all postwar Packards are quite capable of maintaining those speeds, especially when equipped with overdrive or Ultramatic, all hobbyists do it all the time. However, to each his own; just don't make that the excuse for an engine swap, do it because you want to, not because it's a necessity.