posi or open??

66StangGuy · 05-19-2002, 05:43 PM

im trying to find the gear ratio in my diff. is there anything different when trying to find the ration with a open or posi unit? iv tried to find it using the open method and it says i have a 1.5 gear ratio. that dosnt make sense so i was wondering if anyone out there knew what that means. if i raise the back end and turn one wheel the other one turns oppisite direction. meaning i have an open diff. but when i do a burnout i get both to spin eavenly. i asked my friend who is the son of the guy who was head of the mustang racing team way back when and he is also stumped. anyone know out there??

Rev · 05-19-2002, 06:00 PM

What you might have is a CURRIE TSD (torque sensing differential). They work by using the "side loading" that occurs in the spyder gears ,when you mash the gas , to put pressure on the clutches that equalize torque to both wheels. Without heavy torque to the differential, that just doesn't happen. This is supposed to deliver somewhat equal torque to both wheels when you nail the throttle.

Now, having said all that, I changed mine to a spring loaded Ford Traction-Lock because I found that the Currie TSD was not reliable all of the time. Sometimes the TSD seemed to not deliver enough traction to the low traction side.

I spent another $150 or so to correct that short coming at a local shop.

BTW, it sounds like you might have a 3.00/1 which is a very common ratio and very useful with an auto tranny.

Rev

66StangGuy · 05-20-2002, 01:02 AM

thanks rev. im glad someone knows. any way i can find out what gears i have for sure? i want to put in new gears and i would like to know how higer i would like to go according to whats already in there. also is this for a 8.8 or 9 inch ford? or is it for both? just trying to find out what rear i have also...thanks for the help.

Rev · 05-21-2002, 06:59 PM

Jack one rear wheel off the ground leaving the other one on the ground. Put the trans in neutral. Make a chalk mark on the tire that's off the ground and a chalk mark on the yolk or the drive shaft. Make exactly one turn of the wheel that's off the ground. If you have a 3.00/1 rear axle, then the yolk (drive shaft) will make exactly 6 revolutions. If it makes some other number of revolutions, then just divide that number in half. Eg, 5.6 revolutions would mean you have a 2.80/1 axle.

Rev

66StangGuy · 05-22-2002, 01:26 AM

ok...iv tried that and this will confuse the hell outta you like it has everyone else. i did that and i get 1.5 revolutions...?? any ideas ..im sure iv done it correctly and i even had a friend of mine who has worked on cars his whole life and he cant figure it out either. Any ideas? questions or comments welcome.

Rev · 05-23-2002, 04:48 PM

Are you doing it with both wheels off the ground? If you are turning one wheel and the other wheel is allowed to turn some in the opposite direction , then all bets are off.

There's something wrong somewhere as you just can't have a .75/1 rear axle ratio. With one wheel locked (on the ground) , one revolution of the wheel off the ground must produce more than 1.5 revolutions of the drive shaft. Usually it would be 5-7 revolutions. That equates to 2.50/1 to 3.50/1 as a rear axle ratio.

Rev

66StangGuy · 05-23-2002, 11:16 PM

yeah i know it dosnt make sense. And this is with one wheel off the ground. iv done it about 4 times now and i get the same answer every time. i get a lot of noise from the gears at any speed below 20 and i have a lot of play in the driveshaft so ill probably take the gears out and check everything over and find a rebuild kit for it and have my neighbor help me. if you have any more ideas or any more questions that can help solve this mystery dont hesatate to ask... thanks.

6T9PONY · 05-25-2002, 11:27 PM

You have 3.00:1 gears. I'll guarantee you of it. Your 1.5 revolution problem was the same one I had. Get some 3.70s or 3.89s! And get REAL posi! (ie Traction-Lock). You probably have some sloppy u-joints, that's why you have a lot of play in the driveshaft. I'd replace those, too.

05-19-2002, 05:43 PM	#1
66StangGuy Registered Member Join Date: Feb 2002 Location: Diamond Bar Posts: 258	posi or open?? im trying to find the gear ratio in my diff. is there anything different when trying to find the ration with a open or posi unit? iv tried to find it using the open method and it says i have a 1.5 gear ratio. that dosnt make sense so i was wondering if anyone out there knew what that means. if i raise the back end and turn one wheel the other one turns oppisite direction. meaning i have an open diff. but when i do a burnout i get both to spin eavenly. i asked my friend who is the son of the guy who was head of the mustang racing team way back when and he is also stumped. anyone know out there?? __________________ 66 mustang-292-Holley 4160-World Castings Windsor Sr.-Hooker super comp headers-MSD box & Coil.3.55 gears. B&M Z-Gate-Black leather racing seats with 4pt harnes.

05-19-2002, 06:00 PM	#2
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	What you might have is a CURRIE TSD (torque sensing differential). They work by using the "side loading" that occurs in the spyder gears ,when you mash the gas , to put pressure on the clutches that equalize torque to both wheels. Without heavy torque to the differential, that just doesn't happen. This is supposed to deliver somewhat equal torque to both wheels when you nail the throttle. Now, having said all that, I changed mine to a spring loaded Ford Traction-Lock because I found that the Currie TSD was not reliable all of the time. Sometimes the TSD seemed to not deliver enough traction to the low traction side. I spent another $150 or so to correct that short coming at a local shop. BTW, it sounds like you might have a 3.00/1 which is a very common ratio and very useful with an auto tranny. Rev __________________ '66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi. O.B.C. #2 '66 coupe Last edited by Rev; 05-19-2002 at 06:08 PM..

05-20-2002, 01:02 AM	#3
66StangGuy Registered Member Join Date: Feb 2002 Location: Diamond Bar Posts: 258	thanks rev. im glad someone knows. any way i can find out what gears i have for sure? i want to put in new gears and i would like to know how higer i would like to go according to whats already in there. also is this for a 8.8 or 9 inch ford? or is it for both? just trying to find out what rear i have also...thanks for the help. __________________ 66 mustang-292-Holley 4160-World Castings Windsor Sr.-Hooker super comp headers-MSD box & Coil.3.55 gears. B&M Z-Gate-Black leather racing seats with 4pt harnes.

05-21-2002, 06:59 PM	#4
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	Jack one rear wheel off the ground leaving the other one on the ground. Put the trans in neutral. Make a chalk mark on the tire that's off the ground and a chalk mark on the yolk or the drive shaft. Make exactly one turn of the wheel that's off the ground. If you have a 3.00/1 rear axle, then the yolk (drive shaft) will make exactly 6 revolutions. If it makes some other number of revolutions, then just divide that number in half. Eg, 5.6 revolutions would mean you have a 2.80/1 axle. Rev __________________ '66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi. O.B.C. #2 '66 coupe

05-22-2002, 01:26 AM	#5
66StangGuy Registered Member Join Date: Feb 2002 Location: Diamond Bar Posts: 258	ok...iv tried that and this will confuse the hell outta you like it has everyone else. i did that and i get 1.5 revolutions...?? any ideas ..im sure iv done it correctly and i even had a friend of mine who has worked on cars his whole life and he cant figure it out either. Any ideas? questions or comments welcome. __________________ 66 mustang-292-Holley 4160-World Castings Windsor Sr.-Hooker super comp headers-MSD box & Coil.3.55 gears. B&M Z-Gate-Black leather racing seats with 4pt harnes.

05-23-2002, 04:48 PM	#6
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	Are you doing it with both wheels off the ground? If you are turning one wheel and the other wheel is allowed to turn some in the opposite direction , then all bets are off. There's something wrong somewhere as you just can't have a .75/1 rear axle ratio. With one wheel locked (on the ground) , one revolution of the wheel off the ground must produce more than 1.5 revolutions of the drive shaft. Usually it would be 5-7 revolutions. That equates to 2.50/1 to 3.50/1 as a rear axle ratio. Rev __________________ '66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi. O.B.C. #2 '66 coupe Last edited by Rev; 05-23-2002 at 06:20 PM..

05-23-2002, 11:16 PM	#7
66StangGuy Registered Member Join Date: Feb 2002 Location: Diamond Bar Posts: 258	yeah i know it dosnt make sense. And this is with one wheel off the ground. iv done it about 4 times now and i get the same answer every time. i get a lot of noise from the gears at any speed below 20 and i have a lot of play in the driveshaft so ill probably take the gears out and check everything over and find a rebuild kit for it and have my neighbor help me. if you have any more ideas or any more questions that can help solve this mystery dont hesatate to ask... thanks. __________________ 66 mustang-292-Holley 4160-World Castings Windsor Sr.-Hooker super comp headers-MSD box & Coil.3.55 gears. B&M Z-Gate-Black leather racing seats with 4pt harnes.

05-25-2002, 11:27 PM	#8
6T9PONY All about the Windsor. Join Date: Feb 2000 Posts: 2,052	You have 3.00:1 gears. I'll guarantee you of it. Your 1.5 revolution problem was the same one I had. Get some 3.70s or 3.89s! And get REAL posi! (ie Traction-Lock). You probably have some sloppy u-joints, that's why you have a lot of play in the driveshaft. I'd replace those, too.

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