Packard Forum Index » V-8 (1955-56)

I've been offered a NOS ring and pinion set for my car. Principal reason for installing would be to either cruise faster or get better mileage. It is a 2.92 rear end if I remembered correctly.

S0o what kind of job is this: quick and simple, or complex and precise?

I'd appreciate any thoughts on this....

This all depends on what ratio you have now and how you plan to drive the car. In the past you have mentioned poor mileage, and I am wondering what is the norm after you had the carb rebuilt.

I'll wager you will spend $1000 to have that ratio in the car to achieve a 1 mpg improvement on the open road--for example driving from Chicago to Denver. Less advantage , or even a disadvantage in traffic. The math is not promising.

When I drive a car so equipped around here on the back roads I find the performance dismal, especially on slow uphill corners where a kickdown becomes necessary because the engine is lugging or the direct drive starts to slip under the strain.

One of the most fun-to-drive Packards I ever had was a 56 400 with a 3.54 axle. It would leap off the line and regularly achieved 14/15 mpg in mixed rural/highway driving.

To your other point, a change from a 3.54 to the 2.87 saves only 400 rpm at 60mph.

I know 2 super axle guys in the Milwaukee area. Haul it up here.
Is yours a '55 or '56? The 56 might be cheaper as it uses common Dana/Spicer parts & you can add a limited slip @ the same time. Packard parts might be harder to source?
A 3.08 would be the best of both worlds if you drive a lot- reduced engine wear, heat & noise.

PS-Semi complex but definitely precise.

From his avatar, it looks like a 56 Pat, so 64Avanti is correct on the Dana parts. I also agree on the 3.08:1 gear.

To be more precise, here are the rpms at 60MPH with a 27IN tire and locked up converter:

3.54:1 is 2643RPM
3.08:1 is 2300RPM
2.87:1 is 2142RPM

So the RPM difference between 3.54 and 2.87 is 500 RPM and the 3.08 splits the difference at about 250RPM either way.

Craig

Dumb question, but why were so many different ratios offered?
https://www.packardinfo.com/xoops/html/downloads/partslist5556/12_Rear_Axle.pdf

Were some ratios better in certain parts of the country, hill/mountain regions, vs flat open areas?

I wonder how the factory decided which ratio went into each car, unless it knew which dealer the car was to go to.

Also don't forget about the trans if you change rear end ratios. The speedo gear for one and in the case of the 2.87, there were some complaints about the trans shift points occurring at a later speed than drivers preferred. That correction required a few shims to some valve springs.

Quote:

My guess is:

On 1955 and prior, Packard had been using that design for many years.

On 1956 Junior (Dana 45) and 1956 Senior (Dana53), the OEM supplier had those ratios available.

In all cases, they were listed in the parts book because of availability by the OEM supplier, not necessarily because a ratio was custom fitted by Packard factory for mountain driving or whatever.

Craig

HH56 Quote:

I would add to not forget about the carburetor power system either. The higher ratio (lower numerically, i.e., 3.54:1 to 2.87:1) will cause the throttle blades to be opened more at any given cruise speed resulting in a lower intake manifold vacuum resulting in the carb power system coming on earlier which causes a richer mixture which causes reduced gas mileage. This of course defeats your purpose of changing the ratio.

Since you are complaining about poor gas mileage with your present setup with rebuilt carb, what I would do is take your Pat to a high end tune up shop that has a chassis dyno and have them tune the carb that way. They can monitor the air/fuel ratio under all load conditions. They can also fine tune the spark advance. IMO, that's $$$ better spent than swapping out the rear gear.

Craig

While we're focused on rear end ratios, I crawled under my late production 56 and came up with a few more questions: First, seeing a bolt tag that says 46/13, I am presuming that means a final ratio of 3.54 if my math is correct. No complaints there. But I also noticed another tag that I had overlooked until the differential coved had been cleaned and polished. I also have a "T" tag on a cover bolt, on the other side, higher up. Does that indicate that I might have a Twin-Traction unit?

My second question involves another Packard mystery: After decades of making their own rear axles, why did the accountants let the engineers farm out rear axle production to an outside supplier (Dana-Spicer) in the final year of Detroit production? Given the fact that significant problems quickly arose in the first few months, requiring several recalls, I wonder why the decision was made. Were there reported problems with the home-grown units in 1955 and earlier? I also wonder if any "heads rolled" over that decision, either at East Grand or at Dana?

The reported supplier problems that seemed to plague the 1956 models must have made for interesting times and lots of gray hair in Packard management. But the sometimes unique and unexplained changes made for a special car in its curtain call.

Quote:
Yes. Tooth count is shown, for 56th Series, in the Specifications section of the factory shop manual. I believe that 3.54 was the standard gear for the Senior cars.

Quote:
Yes.

Quote:
I suspect there was some significant cost savings involved in making the change. Perhaps the old in-house axle was in need of costly retooling.

Also, it was not uncommon for the independent automakers to look to an outside supplier for the latest-n-greatest thing to distinguish themselves from the Big Three - like flanged rear axles shafts and limited-slip differentials.