Packard Forum Index » V-8 (1955-56)

Hi All,

Down here in Australia we have enjoyed our national Packard Rally in the Hawkesbury, NSW. It was a great rally and my 1955 Packard went very well with the 700r4 transmission. This is defiantly a much better gear box than the torqueflite 727.

The only issue I have at the moment with the car is a noisy differential. It whines quite loud so I will be looking at getting this sorted soon. When I purchased the my Caribbean it has a manual transmission in it. From what I recall the car currently has a 3.54 ratio diff in it. This was probably put in to work with the manual box. Considering I now have a new gearbox installed it might be worth putting in a higher ratio diff. I was wondering if others out there with the 700r4 conversion have made changes to their diff gearing, and if so what are you running and what would you recommend. Would it be beneficial to change to a 3.07 or go lower or higher?

Many thanks,
Mathew

I checked the ratios for your new trans and was surprised to see the spread: 3.06 in first, to 0.7 in fourth. The remaining piece of the puzzle would be the torque multiplication of the converter, but I have not found that.

That first gear ratio combined with the the convertor multiplication should give quite a zippy launch with a 3.54 rear. Cruising, you have an effective ratio of 2.48. That yields only 1830 rpm at 60 mph. I personally would not want it turning any slower than that for the sake of flexibility and to not pound out the main bearings. In fact, in the hilly country around here the car would need to downshift continually to cope with even a moderate incline at below highway speeds. So I guess I am voting for 3.54. Or you can really surprise folks at the lights and put a 4.1. Still only 2100 rpm at 60.

Believe when Bendtsen was doing the engineering on the adapter poster "Smith" was the test car and had a 700R4 installed in his 55 . I don't remember him mentioning any rear axle change so he probably still has the original 3.54 but might be worth a PM to check or see if he has any shiftdown issues.

Went for a ride in Mat's Caribbean during the Rally, plenty of get up and go, but here's a pic of it standing still.
And, to go a select group including Mat, the Flackmaster, Gary Osko, and Peter Toet visited the bodyshop where Noel's '41 160 Club Coupe is now being painted.

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I'll send Bendtsen a PM and see what he recommends. From the sounds of things 3.54 would be the way to go.

Noel's 41 is looking nice. Hoopefully won't be too much longer before we get to see another Packard on the roads of Aus.

G'day Matt, I too enjoyed the Hawksbury Nationals but had a bit further to go than you this time. My '56 Patrician is auto and has a 3.54 diff and I can't hear it at all. We from the southern states took our time travelling up to Hawksbury and back home, mostly at around 85 - 95 kph (approx 50 - 60 mph), and we covered nearly 2,000 Km's (approx 1,200 miles). I kept mileage records and averaged 19.8 mpg (16.4 mpg US) which I thought was great for such a heavy old girl. In my view, a higher diff ratio might have improved mileage a little when cruising, but maybe not so good on hilly areas which could have the tranny dropping out of lock-up or even down to first. Cheers, John

JP, that's pretty nice gas mileage! Just for comparison, on purely highway driving at 65 mph +/- and with 10% ethanol gasoline I get about 14.2 or thereabouts on my 56 Caribbean 374 with dual 4-bbls; that's the equivalent of about 15.4 with non-ethanol gasoline which I consider pretty good for an engine in very good tune but with nearly 100,000 miles on it. Premium (93 octane) of course. Rear axle is 3.54. I do have an NOS 3.31 ring and pinion but the benefit of installing it would be trivial and not worth the effort, IMO. And a 3.07 is really too tall for the types of driving I encounter - too tough on the main bearings.

That's quite good mileage. I'm not sure what mine gets yet, but I don't think its quite that good. It was good to see some new cars at the rally this year.

I removed my dual carb setup as I didn't have the original linkages and as it wasn't tuned correctly was using Alot of fuel so I'm back to using the single 4bbl.

I know my diff needs looking at, hopefully its nothing too major. From this discussion I think my best option would be to stick with the 3.54 and just get the diff quiet again. At the moment I'm putting new carpet in the car so once that's done I'll get the diff sorted.

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Very important point few appreciate. While the engine might pull a very tall gear, the main bearings don't like heavy loads at low RPMs.

Back in the day of three-speed trannnies, the small block Chevy never had main bearing problems. Once computers and lockup torque converters enabled pulling hard up hills at sub-2,000 RPMs, main bearing problems were the result.

jack vines

Jack, thanks for the emphasis added. You're right, too many folks seem perhaps blindly focused on taller rear axle ratios without thinking about the downside. It's expensive to learn the lesson the hard way.