|
Author
|
Topic: speedometer is wrong now...
|
68 Coop
Gearhead Posts: 5847
From: Mesquite, NV. 89027
Registered: Oct 2004
|
posted 05-14-2006 10:57 PM
 
that I have my new rear gears, and I was wondering what to do to correct it? I'm not totally sure, but I think it's off around 10mph now, and it seems to be fast. Thanks for any suggestions.------------------
William
The easiest way to find something lost, is to buy a replacement. 68 Coupe
289
C4
3:55's/Trac-Lok
|
68mustang351w
Gearhead Posts: 558
From: San Jose, Ca
Registered: Sep 2004
|
posted 05-14-2006 11:20 PM
Check this link The drive gear should stay at 7 (if the original rear end ratio was between 2.70 and 3.50 OR 6 if ratio was between 3.50 and 4.30*) and you are solving for driven gear... David F.* according to NPD catalog edit to add statement above [This message has been edited by 68mustang351w (edited 05-14-2006).]
|
68 Coop
Gearhead Posts: 5847
From: Mesquite, NV. 89027
Registered: Oct 2004
|
posted 05-15-2006 12:23 AM
Thank you, that's very informative. I didn't realize it was that much to it.
|
zieber
Gearhead Posts: 172
From: Central Coast, CA, USA
Registered: Mar 2006
|
posted 05-15-2006 01:24 AM
I don't know for sure if this calculator works but it is simpler.http://www.428cobrajet.com/speedo-calc.html
|
68 Coop
Gearhead Posts: 5847
From: Mesquite, NV. 89027
Registered: Oct 2004
|
posted 05-15-2006 01:41 AM
That one says I need an 8 with the 295 tires, so I'll just wait till I get my new tires and see what it says then. Thanks for the time and info.------------------
William
The easiest way to find something lost, is to buy a replacement. 68 Coupe
289
C4
3:55's/Trac-Lok
|
68mustang351w
Gearhead Posts: 558
From: San Jose, Ca
Registered: Sep 2004
|
posted 05-15-2006 01:42 AM
quote:
Originally posted by zieber:
I don't know for sure if this calculator works but it is simpler.link
Just checked it and the calculator works but it assumes you have a 6 tooth drive gear. In order for it to be accurate, William (or anyone else with a 7 tooth drive gear would have to change both gears (drive & driven)... David F.
|
68 Coop
Gearhead Posts: 5847
From: Mesquite, NV. 89027
Registered: Oct 2004
|
posted 05-15-2006 08:06 AM
 Thanks David, I just want to get it right the first time, and do the easiest way possible. 
|
68 S-code GT
Gearhead Posts: 3835
From: Sayreville, NJ, US
Registered: Mar 2000
|
posted 05-16-2006 08:06 AM
This will help some with your RPMs. http://www.ringpinion.com/content/calculators/RPM.asp I know this has come up in the past (cause I asked about it once ) and there are a few formulas here somewhere but you have to find out what the outside diameter of your tires are. ------------------
Ed S. 68 S-code FB GT 4spd(now C6)/3.25 PS PDB
68 J-code(now 289) Cp Sprint"B" C4/3L00-9" PDB PS AC Bla-Bla-Bla
99 F150 XLT Ext/cab, 4X4, 5.4L, 3L55
|
68 Coop
Gearhead Posts: 5847
From: Mesquite, NV. 89027
Registered: Oct 2004
|
posted 05-16-2006 09:18 PM
Thanks Ed.I have 26.5 OD(P295/50R 15) on my back tires, and they are bigger than the front, so I take it I go with the biggest tire??? [This message has been edited by 68 Coop (edited 05-16-2006).]
|
68mustang351w
Gearhead Posts: 558
From: San Jose, Ca
Registered: Sep 2004
|
posted 05-16-2006 09:27 PM
You always go with the rears because those are the ones that are doing the pushing of the car... David F.
|
68 Coop
Gearhead Posts: 5847
From: Mesquite, NV. 89027
Registered: Oct 2004
|
posted 05-16-2006 09:47 PM
 Thanks David, just wanna be sure about this .
|
68mustang351w
Gearhead Posts: 558
From: San Jose, Ca
Registered: Sep 2004
|
posted 05-17-2006 01:16 AM
No problem, thats what we are here for.... David F.
|
83j20
Gearhead Posts: 304
From:
Registered: Jul 2002
|
posted 05-21-2006 08:39 AM
Here's another good calculator:
http://www.hanlonmotorsports.com/t5speedo.asp
|
cynot65
Gearhead Posts: 1258
From: New York
Registered: Apr 2000
|
posted 05-28-2006 10:22 AM
junes issue of mustang monthly has an article on how to calibrate a speedometer.------------------
65 Convertible, Vintage Burgandy/Standard Black Interior, 289, 4spd
M&M Member#450
It ain't done yet, but it'll be done right!!
|
68 Coop
Gearhead Posts: 5847
From: Mesquite, NV. 89027
Registered: Oct 2004
|
posted 05-28-2006 03:24 PM
I have that issue too ! Thanks, I'll take it to work tonight and read up on it.------------------
William
The easiest way to find something lost, is to buy a replacement. 68 Coupe
289
C4
3:55's/Trac-Lok
|
DidgeyTrucker
Gearhead Posts: 1813
From: Greenbrier, TN USA
Registered: Oct 99
|
posted 05-28-2006 04:48 PM
quote:
Originally posted by 68mustang351w:
You always go with the rears because those are the ones that are doing the pushing of the car... David F.
(It's sing-a-long time)
The rear tire's connected to the rear wheel
the rear wheels's connected to the rear axle
the rear axle's connected to the ring gear
the ring gear's turned by the pinion gear
the pinion gear's connected to the driveshaft
the driveshaft's connected to the output shaft
the output shaft's connected to the speedometer drive gear
the speedometer drive gear turns the speedometer driven gear
the speedometer driven gear's connected to the speedomoter cable
the speedometer cable turns the speedometer
....and that's why you use the rear tire size in the formula. Tracy
|
