Adding OD to 1801 Packard 1940

Discussions related to engines, transmissions, rear axles, suspension & steering.
bobhattler
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Location: Sanford NC

Adding OD to 1801 Packard 1940

Post by bobhattler » Tue Dec 10, 2013 10:24 am

The 1801 has a final drive ratio of 4.09
The 1801 with factory overdrive has a final drive ratio of 4.36
Installing an OD in the 4.09 car gives additional speed but lessens pulling power.
Is the difference enough to cause problems, other than inaccurate speedometer readings?
Bobhattler
1940 Packard sedan conv.
9194992080

JWL115C
Posts: 196
Joined: Sat Jul 11, 2009 9:02 am

Re: Adding OD to 1801 Packard 1940

Post by JWL115C » Wed Dec 11, 2013 8:55 am

Bob - I would think the 4.09 ratio would handle an overdrive well. There may be some loss of pulling power on steep hills, but other than that it should make a nice cruising gear. Don't know about increased speed, but you will be able to enjoy faster speeds with more comfortable engine speed. Others here may have direct experience using an OD with this axle ratio and can better advise.

(o{}o)

saltydog
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Location: So.Cal.

Re: Adding OD to 1801 Packard 1940

Post by saltydog » Wed Dec 11, 2013 9:40 am

I've been running my 41 120 with OD and 4.09 rear end for over 20 years with no problems.

Saltydog

Adam
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Location: lincolnshire, uk

Re: Adding OD to 1801 Packard 1940

Post by Adam » Thu Dec 12, 2013 1:11 am

Running the OD ( and I do not know the step-up ratio of the OD unit you are going to use) with your 4.09 ratio, as opposed to the usual 4.36 ratio, will reduce your engine rpm by a further 6% over the reduction provided by the OD.

You could calculate your before and after engine rpm for any given speed, if you establish the tyre rolling radius.

Adam..
"Do not underestimate the English cousin.....they are not as stupid as they look!" - Signor Altabani in The Italian Job.

JWL115C
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Joined: Sat Jul 11, 2009 9:02 am

Re: Adding OD to 1801 Packard 1940

Post by JWL115C » Fri Dec 13, 2013 8:19 am

Bob - If the OD has a speed reduction of 30% then a 4.36 final drive would effectively be 3.05 with OD engaged and a 4.09 would be 2.9. Does this help?

(o{}o)

bobhattler
Posts: 381
Joined: Tue Feb 21, 2012 5:55 pm
Location: Sanford NC

Re: Adding OD to 1801 Packard 1940

Post by bobhattler » Fri Dec 13, 2013 1:50 pm

Thanks guys,
the OD steps up the propeller shaft speed by 38.5 %. This reduces engine speed by 27.8%
Multiplying the 4.09 by .722 gives 2.95 final drive ratio. compared to 4.36 X .722 = 3.15 final drive ratio.
.20 probably won't make much difference on the speedometer. I don't think the speedometer was a precise instrument to start with, so you can plead defective equipment to the judge.
My engine tear down showed a clean valve compartment. The oil rings were stuck to the pistons, but overall it was a beauty to behold. Estimated cost 2700-3000.
I'm glad to hear 20 years experience running Od with 4.09 was successful.
Again thanks for the input.
Bobhattler

Dave Czirr
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Re: Adding OD to 1801 Packard 1940

Post by Dave Czirr » Fri Dec 13, 2013 3:40 pm

Bob, there were factory gear sets for the speedometer drive pinion in the transmission corresponding to each of the final drive ratios, so speedometer error shouldn't be a problem if you can locate the parts.

bobhattler
Posts: 381
Joined: Tue Feb 21, 2012 5:55 pm
Location: Sanford NC

Re: Adding OD to 1801 Packard 1940

Post by bobhattler » Sat Dec 14, 2013 12:24 pm

salty dog had the answer live with it.
bob

bobhattler
Posts: 381
Joined: Tue Feb 21, 2012 5:55 pm
Location: Sanford NC

Re: Adding OD to 1801 Packard 1940

Post by bobhattler » Thu Jan 16, 2014 4:17 am

I have purchased an overdrive and need a few pointers. Where is the relay mounted on the dash and what do you recommend for replacing the dust cover on the governor switch? What size fuses are used on the switch wire. Wire 59 on the diagram page 41 of the manual.

Thanks
Bobhattler

I found it 30 amp
Bob
Last edited by bobhattler on Thu Jan 16, 2014 9:06 am, edited 1 time in total.

bobhattler
Posts: 381
Joined: Tue Feb 21, 2012 5:55 pm
Location: Sanford NC

Re: Adding OD to 1801 Packard 1940

Post by bobhattler » Thu Jan 16, 2014 9:04 am

OD relay has no marker numbers. Does anyone have a clue how to identify 1 thru 6?
Bobhattler

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