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

I could probably do the research, but I seem to be short on time of late and you lot seem to be of a helpful spirit, so I thought I'd (humble myself and) ask. I do have plenty of time to overthink things, however. It's part of my charm.


So, rear ends. I have '47 Clippers mostly. I would reckon that those are likely the same as the 22 and 23 series, too. Question: how about the 24s? In other words, would a set of high speed Ultramatic gears from a '51 fit the 21 series pumpkin?


I think that would be a slick mod, or am I in left field?

'51-'52 pumpkins will fit into Clipper junior axle housings, but not Supers. But that still only gives a 3.54.

With the usual 4.1 and overdrive you are running the equivalent of 2.95. Unless you drive exclusively on the great plains, you don't want anything taller than that.

So, at a reduction of about 72% for the o/d, with a 3.54, that would give a final ratio of approximately 2.55. And the things only have 15" wheels.


(2.95)/(4.1) = .7195 * 3.54 = 2.547


I'm still wondering.

Here's one way to look at it:

Let's say your car originally came with 8.00-15 tires. Use the Vintage Tire Size Conversion Chart:

tengtoolsusa.com/blogs/news/vintage-tire-size-conversion-chart

So let's say you have 225/75 R15 tires on there now. Use the tire size calculator:

tiresize.com/calculator/

Those tires are therefore 28.3" diameter, 713 Revs/Mile. Which means at 60 mph, the rear wheel will be spinning at 713 rpm.

Now you say you have an effective ratio of 2.55:1 including the diff ratio and the overdrive. So you get at 60 mph the engine is spinning at 2.55*713 = 1818 RPM

I don't know what the "best" engine speed at 60 mph would be for your engine, but that's only about 3 times idle speed - probably about right.

The Packard 300/400 in 1953 with the Ultramatic had 3.54 gears on there, so they would be spinning 2500 RPM, which is a bit high.

And at 65, it would be (65/60) * 2.55 * 713 = 1969 RPM.


At 70 MPH, it would be (70/60) * 2.55 * 713 = 2121 RPM


My truck turns just about 2K at 70 MPH, and it's the gutless 6 banger model. The big SUV does likewise. and the little SUV turns maybe 2.1K at 70. Not ideal in WV but pretty good in most of VA and KY and running the Eastern Seaboard (I-95), and so on.


I'm still thinking about a 6-speed Tremec for one of these critters, but that's way down the road and TBD. That would be with something much closer to a 4 in the third member.

Maybe this is a better option for you:

gearvendors.com/restorationclassic.html

Yeah . . . no . . . I don't know.


Good thing I don't have to figure this out this week.


The gears were cheap (I think). They'll be here in a few days.