|
Author
|
Topic: Speedometer Corrections
|
HHuggins
Gearhead Posts: 182
From: Laguna Niguel, CA
Registered: Feb 2001
|
posted 11-29-2001 09:24 PM
   
My 70 Mach I has an 8 in. rear instead of the standard 9. With the gearing it causes the speedometer to be off by about 12 mph. Is there anyway to correct this? ------------------
_ _____________________ _ Harley D. Huggins II
Laguna Niguel, CA 1970 Mach I
1998 GT Convertible
www.geocities.com/hh_machi/
IP: Logged |
HHuggins
Gearhead Posts: 182
From: Laguna Niguel, CA
Registered: Feb 2001
|
posted 11-29-2001 09:44 PM
I'll answer my own question. I did a search and it sounds like I need to find out the formula to figure out what gear I need in the speedo. Anyone know where to find it?------------------
_ _____________________ _ Harley D. Huggins II
Laguna Niguel, CA 1970 Mach I
1998 GT Convertible
www.geocities.com/hh_machi/
IP: Logged |
DidgeyTrucker
Gearhead Posts: 1060
From: Greenbrier, TN USA
Registered: Oct 99
|
posted 11-29-2001 11:34 PM
At higway speeds, one tooth (on the driven gear - on the cable end) is worth about 5 mph.
If your speedometer reads fast, you need a gear with two more teeth. That's the gear that goes on the cable end that goes in the transmission.
If your speedometer reads slow, you need a gear with two less teeth.Tracy ------------------
Tracy M&M #245
1956 F-100 Panel w/429
(3.50 9")
1966 F-100 SWB w/351C
(3.25 9" - 3.70 posi for Saturday nights)
Music City F-100's,
1965 GT-350 S/C
(2.78 1st & 3.70 TracLok 9")
Music City Mustang Club
Don't focus on the destination....make the JOURNEY the adventure
Visit my Web site: DidgeyTrucker's Website
IP: Logged |
JT
Gearhead Posts: 186
From: Pearland, Texas, USA
Registered: Oct 2000
|
posted 11-30-2001 09:23 AM
Harley, you can change the speedometer gear. The formula to figure out which one you need is in the NPD catalog in the speedometer section.------------------
JT
'68 Coupe w/351W
'01 Bullitt #3357, Dark Highland Green
IP: Logged |
SteveLaRiviere
Administrator Posts: 33988
From: Saco, Maine
Registered: May 99
|
posted 11-30-2001 07:42 PM
...and in our 'Articles' section:
https://mustangsandmore.com/ubb/speedogear.html------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC
My Photo Page
Christmas shopping? Why not use the Mustangsandmore.com Bookstore?
IP: Logged |
Doyle
Journeyman Posts: 38
From: Annapolis, Maryland
Registered: Oct 2000
|
posted 12-02-2001 08:44 AM
I am having a similiar problem with my
speedometer. I initially thought the
problem was in the trans but and was
going to have the trans guy check it out
this spring. Now you guys have me thinking
otherwise.How can I check to see what rear my
70 Boss has?
IP: Logged |
SteveLaRiviere
Administrator Posts: 33988
From: Saco, Maine
Registered: May 99
|
posted 12-02-2001 06:09 PM
Doyle, the most accurate way would be to put the rear on jack stands, mark the driveshaft and rear wheel, and count how many revolutions the driveshaft makes per wheel revolution. If the driveshaft turns 3.5 times per each rotation on the wheel, you have a 3.50 rear. ------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC
My Photo Page
Christmas shopping? Why not use the Mustangsandmore.com Bookstore?
IP: Logged |
Doyle
Journeyman Posts: 38
From: Annapolis, Maryland
Registered: Oct 2000
|
posted 12-02-2001 07:25 PM
Steve Thanks - I pulled the history rpt from
ford and it says I have a 3.91 - now
to confirm.
What does the size of the rear end, as
in the original post 8 vs 9 in, have
to do with the ratio?
IP: Logged |
SteveLaRiviere
Administrator Posts: 33988
From: Saco, Maine
Registered: May 99
|
posted 12-02-2001 07:30 PM
The 3.91 is your ratio. Your driveshaft should turn 3.91 times for every revolution of your wheels.------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC
My Photo Page
Christmas shopping? Why not use the Mustangsandmore.com Bookstore?
IP: Logged |
Mustangsandmore Forums
UBBFriend: Email This Page to Someone! 
