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(1) 2 »

Speedometer Accuracy
#1
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Scott
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My '55 400 reads 6mph faster than actual. Any suggestions to correct it?

Posted on: 2023/3/28 18:27
1942 Clipper Club Sedan
1948 Custom Touring Sedan (22nd Series)
1955 Patrician Sedan
1955 400 Sedan
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Re: Speedometer Accuracy
#2
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BigKev
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Is that at all speed ranges?

They can be calibrated by a speedo shop.

http://www.bills-speedometer.com is owened by Patrick Mescher, a member of this website, and comes recommended.

Posted on: 2023/3/28 19:18
-BigKev


1954 Packard Clipper Deluxe Touring Sedan -> Registry | Project Blog

1937 Packard 115-C Convertible Coupe -> Registry | Project Blog
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Re: Speedometer Accuracy
#3
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Ross
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If your tires are about 26" diameter instead of the 28" the car was built for that will account for 4.7 mph difference changing 66mph to a little over 61.

Oh, and if you read old road tests of most any brand most all of them had errors of 4-7 mph at speed.

Posted on: 2023/3/28 19:29
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Re: Speedometer Accuracy
#4
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humanpotatohybrid
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My tripometer runs like 10% different than the actual distance.

Posted on: 2023/3/29 4:11
'55 400. Needs aesthetic parts put back on, and electrical system sorted.
'55 Clipper Deluxe. Engine is stuck-ish.
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Re: Speedometer Accuracy
#5
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BDC
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Mine is 100% accurate when standing still after that it goes downhill.

Posted on: 2023/3/29 8:19
I can explain it to you but I can't understand it for you

Bad company corrupts good character!

Farming: the art of losing money while working 100 hours a week to feed people who think you are trying to kill them
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Re: Speedometer Accuracy
#6
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HH56
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And if tires or a speedo shop cannot get it close enough there are some street rod type places that make a custom gear box that inserts in the drive cable to correct or fine tune the RPMs the speedo sees. As I recall the boxes are made primarily for those that mixed parts so a brand X speedo would work with a brand Y trans and brand Z rear end but the principle still holds.

Posted on: 2023/3/29 10:28
Howard
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Re: Speedometer Accuracy
#7
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BigKev
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To me, a 6 mph difference isn't worth the cost or time to correct since that is in the normal "error" range.

You just have to remember to do the math when looking at your speedo.

Posted on: 2023/3/29 10:41
-BigKev


1954 Packard Clipper Deluxe Touring Sedan -> Registry | Project Blog

1937 Packard 115-C Convertible Coupe -> Registry | Project Blog
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Re: Speedometer Accuracy
#8
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HH56
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And at least it is reading fast. Imagine the speeding tickets you could attract if it was reading 6 mph slow.

Posted on: 2023/3/29 10:45
Howard
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Re: Speedometer Accuracy
#9
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Scott
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The car is running 235/75R15 tires, which have a diameter of 28.9". The speedo reads high pretty much the same across the typical 25-60 driving range.

Do all Ultramatics have the same speedometer drive gear regardless of rear end ratio? I do know the previous owner rebuilt the transmission and had at his disposal a parts donor Clipper. (I had to remove the transmission due to an inoperative DD clutch and discovered a mismatched '55 pump and '56 plate, blocking the oil path.)

Posted on: 2023/3/31 10:48
1942 Clipper Club Sedan
1948 Custom Touring Sedan (22nd Series)
1955 Patrician Sedan
1955 400 Sedan
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Re: Speedometer Accuracy
#10
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HH56
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There were several different speedometer gears available for Packard rear ends but the parts book does not mention the number of teeth per ratio. Perhaps someone might have a chart with that information.

The Twin Ultra was also used by some 55 Nash and Hudson models and the 56 Stude Golden Hawk. No idea if any of their rear end ratios were different from Packards and if they had any other gear options.

Attach file:



jpg  speedo gear.jpg (206.60 KB)
209_642706e07d3db.jpg 1796X1252 px

Posted on: 2023/3/31 11:15
Howard
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