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12/02/2016 5:56 AM  #1


66 coupe with T5 what speedo drive ?

Hi Guys, 

I've been round in circles trying to find out which way to go with my Muzzy, It is a 66 coupe with a 80's 302 and T5 in it I don't know any more details than that really, are there different T5 boxes/ratios?? also I am assuming the rear axle is the standard ration 2.73?
anyway when accelerating is seems to run out of 1st gear real quick and so I'm grabbing for 2nd  almost straight away.
also the speedo is reading 25 mph when the car is really doing 30mph, any idea what colour speedo drive gear I should swap too, as there not so easy to get hold of here.
sorry for my lack of detail, but I don't really know any more of what I actually have..

cheers for any help

steve

 

12/02/2016 7:19 AM  #2


Re: 66 coupe with T5 what speedo drive ?

First, figure the rear ratio:  Jack one side of the axle, put a mark on the drive shaft and count how many turns you have to turn it to make the lifted rear wheel turn one full revolution.  Won't be exact but if you are careful and do a couple of repeats you'll get pretty close.  (USE A JACK STAND UNDER THAT AXLE BEFORE YOU CRAWL UNDER !!)

Use this calculator to determine the number of gear teeth you need on the driven gear. 
http://www.tciauto.com/tc/speedometer-gear-calculator/

I think Ford normally uses a 7 tooth drive gear in the trans but it might be eight in your case.  Since you have a T5, pulling the tail shaft housing to see the color of the drive gear really isn't easy.  You might be able to see the color of the drive gear by looking in the hole.  Otherwise, you can run the calculator with both and get both driven gears....use the one that gives the most most accurate speedo reading.  The  gears are not all that pricey. 

This subject was beat to death just a month or so ago so you may find lots more info here from people smarter than I by searching "Speedometer drive gear" or variants.

PS:  If it won't turn with one side jacked up, you have a track-loc and will need to jack both sides. 
It's going to be a 2.78, 3.00, 3.55, 3.73, or 4.11 so rough calculating the one you have should be fairly easy.  If you are running out of 1st gear that quickly, I'm betting you have a 3.55 or 3.73.

BB
 

Last edited by Bullet Bob (12/02/2016 7:31 AM)


"you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
 

12/02/2016 8:50 AM  #3


Re: 66 coupe with T5 what speedo drive ?

After you figure the rear ratio, per BB's instructions, move on to the trans.  If you are real fortunate, you may be able to find the borg/warner ID tag on the T5, and identification will be straight forward.  If your T5 came from a 4 cylinder 80's Mustang, you could have a 3.97 ratio on first gear, making a shift to second happen sooner.  Here's a link to the factory applications & gear ratios for the various T5's produced.

http://www.britishv8.org/articles/borg-warner-t5-id-tags.htm

Last edited by TimC (12/02/2016 8:52 AM)

 

12/02/2016 8:52 AM  #4


Re: 66 coupe with T5 what speedo drive ?

I believe that there are 2, maybe 3 different drive gears available on the T5, depending which model transmission you may have. You can pull the speedo gear out of the transmission and look inside and note the color of the drive gear to tell you the number of teeth and then determine the corresponding speedo gear based on gear ratio and tire size.

That said, what I do is take a baseline with the existing gear and then purchase the new gear to correct the recorded with actual measurements. You can either do this by comparing measured speed vs. actual speed or measured distance vs. actual distance. To me, the accuracy of the odometer is more important than the accuracy of the speedometer (in a perfect world there would be no deviation, but I have not found that to always be the case on these old gauges).

What I do is note the starting and ending mileage on a drive of known distance (longer is better). Use this ratio to determine the needed speedo gear:

needed gear teeth = (measured distance  / actual distance) x existing gear teeth

You can achieve similar results by substituting distance with velocity.


1965 Mustang 2+2 EFI
 

12/02/2016 10:13 PM  #5


Re: 66 coupe with T5 what speedo drive ?

When I swapped in my T-5 many moons ago I just used the speedo gear and cable from the 3-SPEED tranny that came in it.
Work good and was very accurate.
6s6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

12/04/2016 9:20 AM  #6


Re: 66 coupe with T5 what speedo drive ?

6sally6 wrote:

When I swapped in my T-5 many moons ago I just used the speedo gear and cable from the 3-SPEED tranny that came in it.
Work good and was very accurate.
6s6

 
I did the same with mine. I used the gear from the 66 C4 from the 66 fairlane donor. I'm running a 3:55 rear. Speedo is right on the money.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
 

12/05/2016 8:27 AM  #7


Re: 66 coupe with T5 what speedo drive ?

The info you need is at this location on FYIFORD Tips & How-To.

http://fyi.boardhost.com/viewtopic.php?pid=57167#p57167


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

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