RE: [Chrysler300] RE: Teck question 1960 300f

["Richard Barber" <c300@xxxxxxx>]

Transmission Speedometer Pinion Charts show the proper driven gear as
dependent on tire size and differential ratio.  It seems a common goal was
to spin the speedo cable at 1,000 RPM at 60 MPH.  If these assumptions are
accurate, driveshaft speed at 60 MPH can be calculated as follows: 
RPM=(5,280 x 12 x R)/(Pi x D) where R is rear end ratio, Pi is 3.141592654,
and D is the OD of the rear tires (inches).  Simplified, driveshaft RPM at
60 MPH = (20,168 x R)/D.  

Gil Cunningham's table of tires at our website indicates the proper tire for
a 300 F is a 9.00 x 14.  The current Coker Tire catalog shows a 9.00 x 14
tire diameter as 28.68".  With a 2.93 axle, this would give RPM at 60
MPH=(20,168 x 2.93)/28.68=2,060 RPM.  This seems about right if Chrysler was
aiming for 2,000 RPM driveshaft speed at 60 MPH.

Now, the question is how many teeth are there on the driving gear (the worm
gear on the transmission output shaft)?  My 1955-58 Chrysler Parts Manual
has a table of Transmission Speedometer Pinions in section 21-85-0.
Plugging and grinding with some catalog tire OD's, it appears the driving
gear must have about 8 teeth.  If this is so, and if that nominal number
carried forward to 1960, the number of teeth on the driven (pinion)
speedometer gear of a 1960 300F is: 
N=(8x 20.168 x R)/d, or N= 161.34 x R/ D.  For D=28.68 and R= 2.93, N=16.48
or 16 teeth.  The Parts Manual specifies a 17-tooth pinion.

Anyone have a 1960 Service manual to check out these calcs?

BTW, there is a similar chart in the 1955 Chrysler Service Manual on page
442 which shows the correct pinions to have two less teeth for all tire
size/axle combo's.  Go figure.

See this website for a speedo pinion gear calculator:
http://www.bgsoflex.com/speedo1.html	 

It is entirely possible that the 1,000 Revs/mile speedo head specification
may vary and that the specification should be stamped or marked on each
head.

I hope you have as much fun with numbers as I have with this question.  As
always, corrections and constructive criticism is always welcome.  Using
this same math, and reviewing F engine specs showing HP peaks at 5,000-5,200
RPM, it is calculated that an F would be doing 145.6 to 151.5 MPH at the
peak HP RPM's.   How does that compare to actuals?  Pretty much uses up that
150 MPH speedometer!

Our 1955 C-300 with 29.08" OD 8.00 x 15's and  a 3.54 axle would be capable
of 129.3 MPH at its max HP RPM of 5,200.  VERY close to the actual speeds
achieved at Daytona.  I have no idea of what kind of torque converter
slippage might be occurring in the old PowerFlites and TorqueFlites at those
speeds.

And, finally, tire OD's do not exactly translate to distance travel due to
tread squirm and who-knows-what.  I have seen tables of revolutions per mile
at a specified speed for some tires and they vary by tire construction.
Also, that changing the driven speedometer gear by one tooth can change the
speedo readout by about 7%, therefore the selection of pinion gear might
result in 0-3.5% error, depending on how far off the computed number of
teeth is from an integer.  i.e.--you can't create a 14.4 tooth driven gear.
At 150 MPH, the basic error might be as much as 5 MPH!  Tell it to da judge.

Part number 1636406 for a 17 tooth pinion or 1732113 for a 16 tooth pinion
gear.  These part numbers may only be valid for the 1955-58 trannys, but I
suspect they will work on TorqueFlites into the '60's.  They are found in
section 21-85-0 Transmission Speedometer Pinion and come in 16-21 tooth
versions.

As a Christmas gift TO YOU , I have recreated the data in the Parts Manual
below.

Tire 		AXLE RATIOS
Size		2.93	3.07	3.15/3.18	3.31/3.36	3.54	3.73
3.90
8.00x15		17			18		19	20	21
8.20x15		17			18		19	20	21
8.90x15		17			17		18
7.50x14	17		19		20		21	21	21
8.00x14	17		19		20		21	21	21

8.50x14	17		18		19		20	21	21
9.00x14	17		18		19		20	21	21

9.50x14	16		18		19		20	21	21

11.00x14	16		17		17		ILLEGIBLE

Merry C-300'ly Christmas
Rich Barber (16 teeth, each jaw)
Brentwood, CA
1955 Chrysler C-300 (17 tooth pinion according to the 1955 Chrysler Service
Manual, 19-tooth according to 1955-58 Chrysler Parts Manual--ahh, Chrysler's
inconsistencies)
 
-----Original Message-----
From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On
Behalf Of LOUISENYLA@xxxxxxx
Sent: Saturday, December 19, 2009 7:44 AM
To: Chrysler300@xxxxxxxxxxxxxxx
Subject: [Chrysler300] RE: Teck question 1960 300f

Good Morning to all the members:
 
I know somewhere out there in 300 land someone knows the answer to  this:
 
What is the proper tooth number for the driven Speedo  gear in a 1960  300 
F  with a 2.93 rear?
 
I know someone out there has the answer thanks to all.
 
Teddy  
 


[Non-text portions of this message have been removed]



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