|
Author
|
Topic: Speedo gear again?
|
bibbs68
Gearhead Posts: 1554
From: Jackson, TN
Registered: Sep 2000
|
posted 02-02-2004 12:42 PM
   
I checked the history files and have confused myself. Here is the skinny...I have a stock speedo gear that was hooked up to a stock 3spd. tranny. My rear gears are also stock 2.79 ratio. Tires are 215x70x14. I now have the T5 put in with the 3.35 first gear. I have not changed my speedo gear or rear gears. In order to make the speedometer read close to right I figured that I need a 17 tooth speedo gear. Am I right? ------------------
Jeremy
'68 Coupe
M&M Member #685
MCA Member #49134
Help make the world a better place, drive a Ford and race a slot car!
IP: Logged |
Fastymz
Moderator Posts: 18143
From: Reno Nv USA MEM#1240
Registered: Apr 2001
|
posted 02-02-2004 12:45 PM
Just do like I do,take it out on a long road and floor it when it stops going any faster thats your top speed.  
Sorry I don't know, but SteveL does.http://www.finer.com/Internet/pages/speedo.htm ------------------
SCOOP oddly obsessed with big scoops on little Mustangs 2.26 60'S
14.9 @ 90.86MPH 65 coupe,351w,C4,Big Boss 429 hood scoop,8" 3.40 TracLoc. My Pics [This message has been edited by Fastymz (edited 02-02-2004).]
IP: Logged |
bibbs68
Gearhead Posts: 1554
From: Jackson, TN
Registered: Sep 2000
|
posted 02-02-2004 12:50 PM
quote:
Originally posted by Fastymz:
Just do like I do,take it out on a long road and floor it when it stops going any faster thats your top speed.
Scoop, unfortunately with my 2.79 running gear I can't even use 5th gear. Well unless I wanna pay a big fine. I'm still in 4th gear at 70 mph with room to go. I imagine as it is right now, in 5th gear at top speed I would be going about 140-150 
IP: Logged |
Fastymz
Moderator Posts: 18143
From: Reno Nv USA MEM#1240
Registered: Apr 2001
|
posted 02-02-2004 12:55 PM
quote:
Originally posted by bibbs68:
Scoop, unfortunately with my 2.79 running gear I can't even use 5th gear. Well unless I wanna pay a big fine. I'm still in 4th gear at 70 mph with room to go. I imagine as it is right now, in 5th gear at top speed I would be going about 140-150
They have to catch you first.
Did you look at the link I posted. I think it'll help. 
------------------
SCOOP oddly obsessed with big scoops on little Mustangs 2.26 60'S
14.9 @ 90.86MPH 65 coupe,351w,C4,Big Boss 429 hood scoop,8" 3.40 TracLoc. My Pics
IP: Logged |
bibbs68
Gearhead Posts: 1554
From: Jackson, TN
Registered: Sep 2000
|
posted 02-02-2004 12:57 PM
quote:
Originally posted by Fastymz:
They have to catch you first.
Did you look at the link I posted. I think it'll help.
Geez! I didn't even see it. Thanks for the link. Another site said with the T5 to use an 8 tooth. Now I'm really confusededed! 
[This message has been edited by bibbs68 (edited 02-02-2004).]
IP: Logged |
indyphil
Gearhead Posts: 2255
From: Senoia, G.A. USA
Registered: Jul 2002
|
posted 02-02-2004 01:29 PM
Dont confuse your speedo gear with the driver gear thats in the transmission. Since you didnt change your rear end the only thing you need to know is what driver gears the transmissions had in them.So You need to find out what the driving gears are in your T5 and your 3 speed. Then multiply your speedo gear by the same RATIO. Example: lets say the 3 speed tranny has a 10 tooth driver gear in it, and the T5 has a 8 tooth driver gear. maybe you had a 20 tooth speedo gear for the speedo with the 3 speed. Now you would need to do 20x(8/10) = 16 so you would need a 16 tooth cog for the T5. Does that math make sense? Phil ------------------
'68 coupe 289 C code
66 heads, edel 600cfm carb, performer intake, dual exhaust http://www.geocities.com/ottouk_77/68mustang.htm
IP: Logged |
bibbs68
Gearhead Posts: 1554
From: Jackson, TN
Registered: Sep 2000
|
posted 02-02-2004 01:38 PM
quote:
Originally posted by indyphil:
Dont confuse your speedo gear with the driver gear thats in the transmission. Since you didnt change your rear end the only thing you need to know is what driver gears the transmissions had in them.So You need to find out what the driving gears are in your T5 and your 3 speed. Then multiply your speedo gear by the same RATIO. Example: lets say the 3 speed tranny has a 10 tooth driver gear in it, and the T5 has a 8 tooth driver gear. maybe you had a 20 tooth speedo gear for the speedo with the 3 speed. Now you would need to do 20x(8/10) = 16 so you would need a 16 tooth cog for the T5. Does that math make sense? Phil
Phil, the math actually does make sense. I do know the T5 drive gear is 8T. My original 3spd however, I don't know.
IP: Logged |
bibbs68
Gearhead Posts: 1554
From: Jackson, TN
Registered: Sep 2000
|
posted 03-19-2004 09:12 AM
Hey Phil or anyone else,Okay, here goes... My 3spd has an 18T speedo gear and a 7T driven gear. The T5 has an 8T driven gear. If I did the math correctly I need a 16T speedo gear. Now, where does the tire size(215x70x14) and rear gear ratio (2.79) come into play? [This message has been edited by bibbs68 (edited 03-19-2004).]
IP: Logged |
trashline
Gearhead Posts: 1217
From: Levittown, Pa
Registered: Dec 2003
|
posted 03-19-2004 12:23 PM
i think everybody had or has the same problem i did a bit of research. if you are positive about the drive gear being 8 teeth then you would need a 17 tooth driven gear. if the driven gear is 7 teeth then you would need a 15 tooth driven gear. tire size matters bc the bigger the tire the more rpm in the engine it takes to spin that tirethink of it as a bike. take a 20 inch bike and put a 10 inch wheel on the back youll be pedeling your ass off. so then you put a 26 inch tire on the back and it will take a bit longer to spin that tire one revolution. so your drivetrain no matter what spins at the same speed everytime unless you change gears . but it spins the same everytime.if you put 33 inch tires on the backthe drivetrain can only spin it a certain rpm bc its a bigger tire. 2.5 revolutions of the drive train may only spin the rear tires .75 times with the bigger tire. but 2.5 relolutions of the drivetrain will spin a 26 inch tire 1.25 times. i know imkinda rambling but i hope you can understand. do you know what size driven gear you have now?
p.s. the driven gear is the one on the speedo cable and the drive gear is inside the tranny also check this site i already did it for ya but they have alot of neat calulators http://www.bgsoflex.com/auto.html and i just re read your posts you have an 8 tooth drive gear so you would need an 17 tooth driven gear
------------------
1966 mustang coupe
200ci 3 speed tranny
msd 6a ignition, blaster 2 coil, 2 inch exhaust to a glass pac, stock rear,coming soon single out header,and cold air intake (homemade).
white w/ black interior[This message has been edited by trashline (edited 03-19-2004).] [This message has been edited by trashline (edited 03-19-2004).]
IP: Logged |
BornInAFord
Gearhead Posts: 456
From: Bend, OR, USA
Registered: Dec 2002
|
posted 03-19-2004 01:04 PM
I think the CJ Pony catalog lists what driven gear you would have. Here is another link in case you like to calculate things. The 815revs/mile on the site is based on the 26.5" diameter 5.0L tires, not the 25.5" the early years had, IIRC. http://ddperformance.com/speedo_gear_chart.htm I have a T5 from 1990 which was rebuilt by D&D as a 2.95, BUT the drive gear in the transmission is a 7T (yellow), not a 8T (green) as originally equipped. So, make sure to look what gear you have. For me, I have a 4spd with a 4.11 with a 20 tooth gear currently, but soon I will have a T5 with a 3.55. The 20 tooth driven gear should be the same. Lucky me.
Daniel
IP: Logged |
bibbs68
Gearhead Posts: 1554
From: Jackson, TN
Registered: Sep 2000
|
posted 03-19-2004 04:03 PM
Well, I went to the local Ford dealership to get my speedo gear today. They had the 17 R gear but the problem is that the square hole inside the gear that the cable goes in is smaller than my stock cable. Has anyone else ran into this problem?
IP: Logged |
Mustangsandmore Forums
UBBFriend: Email This Page to Someone! 
