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1966 Mustang GT 4spd
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Discussion Starter #1
Good Afternoon to all my quarantined fellow Mustang enthusiasts!

I am going to be ordering a 9" from Quick Performance. To install it(it will have the large bearings) I need '67 Shock mounts and U-bolts correct? I currently have a 4 speed in the car and Im looking at 3.70 gears. Any thoughts on the ratio is welcomed. I currently have a 3.00 in the back. And at some point I will install a 5 speed.

Thank you for your input and comments or questions.

Chris
 

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Good Afternoon to all my quarantined fellow Mustang enthusiasts!

I am going to be ordering a 9" from Quick Performance. To install it(it will have the large bearings) I need '67 Shock mounts and U-bolts correct? I currently have a 4 speed in the car and Im looking at 3.70 gears. Any thoughts on the ratio is welcomed. I currently have a 3.00 in the back. And at some point I will install a 5 speed.

Thank you for your input and comments or questions.

Chris
Depends where you drive, city, country, suburban streets or freeway.

With a 3.70 I suspect 1st gear in a T5 will be pretty much useless.

In 289HP and BOSS 302 Mustangs, the standard transmission was a close-ratio 4-speed and 3.50 axle.
 

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Discussion Starter #4
Depends where you drive, city, country, suburban streets or freeway.

With a 3.70 I suspect 1st gear in a T5 will be pretty much useless.

In 289HP and BOSS 302 Mustangs, the standard transmission was a close-ratio 4-speed and 3.50 axle.
Thank you!! At some point I will go with the 2.95 1st gear T-5. But a 3.50 gear may still be perfect for both...

Chris
 

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What is the OD of the tubes QP uses? That will determine which U-bolts you need and the shock plate.

If you get a T5z with a 2.95 1st gear you will be fine with a 3.70 rear. I have an 8.8" 3.73 behind a T5z in my '65 along with a .80 5th gear. I wouldn't use the standard .63 5th gear. There's too much spread between 4th and 5th.
 

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1966 Mustang GT 4spd
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Discussion Starter #6
What is the OD of the tubes QP uses? That will determine which U-bolts you need and the shock plate.

If you get a T5z with a 2.95 1st gear you will be fine with a 3.70 rear. I have an 8.8" 3.73 behind a T5z in my '65 along with a .80 5th gear. I wouldn't use the standard .63 5th gear. There's too much spread between 4th and 5th.
3" tubes.

Thanks!! How do you like the combo? :)

Chris
 

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I've had both 3.50 and 3.73 in my '66 with a T-5z and both worked well. I do a lot of highway driving though so the 3.50 suits me just a bit better, but both match the transmission just fine.
 

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Thanks!! How do you like the combo? :)
I love it. All the young whippersnappers on this forum told me I was crazy for going .80 instead of .63 because my engine would be turning more than 2000 RPM at 70 MPH. Oh Lord, these kids don't know that a SBF loves to run at 3500-4000 RPM all day and won't blow up. With the .80 5th it's more like a true 5 speed than a 4 speed with OD.
 

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With a 3.70 I suspect 1st gear in a T5 will be pretty much useless.

In 289HP and BOSS 302 Mustangs, the standard transmission was a close-ratio 4-speed and 3.50 axle.
What he said. The T5 is a nice transmission when used with in it's limitations. It was designed as a compromise transmission for performance and fuel economy. As such it has a super low 3.35 1st gear to make a 2.73 axle ratio feel like a 3.50 axle ratio car. There is a big jump between 1&2 and 4&5. Go too low or too tall you end up with 4 really useful gears with 3 of them close and a big gap between the other. I've driven T5's with 2.73, 3.08, 3.27 and 3.40. I thought the 3.27 was a great communication with the 3.40 close behind.

Personally if I ran a T5 I wouldn't waste my money on a 9". The T5 will let go before a 8" blows apart. Save your money and buy a 8" with something like 3.25, 3.40, or 3.55
 

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1966 Mustang GT 4spd
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Discussion Starter #10
What he said. The T5 is a nice transmission when used with in it's limitations. It was designed as a compromise transmission for performance and fuel economy. As such it has a super low 3.35 1st gear to make a 2.73 axle ratio feel like a 3.50 axle ratio car. There is a big jump between 1&2 and 4&5. Go too low or too tall you end up with 4 really useful gears with 3 of them close and a big gap between the other. I've driven T5's with 2.73, 3.08, 3.27 and 3.40. I thought the 3.27 was a great communication with the 3.40 close behind.

Personally if I ran a T5 I wouldn't waste my money on a 9". The T5 will let go before a 8" blows apart. Save your money and buy a 8" with something like 3.25, 3.40, or 3.55
Thank you. Yes i will be looking at the T5Z with the 2.95 first gear(I'm thinking its a little steeper than my T-10 but I can't find any specs what my gear ratios are anywhere). I think 3.50s are probably the way to go considering how short of a tire I will be running most of the time(245/45/17).

On that note, does anyone still know what U bolts and shock mounts I would need with a 3" tube?

Thanks again everyone and stay healthy and keep up the great work on your cars and here on the forum!! :)

Chris
 

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I'm using the 67 shock mounts and U bolts, my rear end came from a 67 cougar. think I got the mounts from NPD
 

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Discussion Starter #12
I'm using the 67 shock mounts and U bolts, my rear end came from a 67 cougar. think I got the mounts from NPD
Thank you Jedi!!

Chris
 

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Will the vent hole be in the same place? New brakes lines and all that system.
Think about your wheels and plans, you might want to tweak the width one way or another. Springs at the same time as the rear saves a lot of double work.

I'd do the T5 1st. it gives a whole new perspective to the 3:00 rear. My only complaint is slow speeds in 2nd gear. There is a huge gain from the 1st gear.
As said, a 9" is overkill at that point so a new pumpkin chunk and a half day later yore set for life.
 

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What he said. The T5 is a nice transmission when used with in it's limitations. It was designed as a compromise transmission for performance and fuel economy. As such it has a super low 3.35 1st gear to make a 2.73 axle ratio feel like a 3.50 axle ratio car. There is a big jump between 1&2 and 4&5. Go too low or too tall you end up with 4 really useful gears with 3 of them close and a big gap between the other. I've driven T5's with 2.73, 3.08, 3.27 and 3.40. I thought the 3.27 was a great communication with the 3.40 close behind.

Personally if I ran a T5 I wouldn't waste my money on a 9". The T5 will let go before a 8" blows apart. Save your money and buy a 8" with something like 3.25, 3.40, or 3.55
My 8 inch went first, however mine was one of the 65/66 carriers which I think are not nearly as strong as the later ones. The t5s can last quite a while if you don't shift without the clutch and you aren't launching with slicks all the time. From my research once you get enough power you will break them with the 2nd to 3rd shift when the case flexes too much.
The .63 is a big drop in rpm. However, for folks like me that want to run deep gears on the street it's great. I am at 2000 rpms at 55 mph in 5th gear.
 
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Couple of thoughts, first Husk is right, if your going T5, 8" might be a saner approach especially value per dollar. First a 9" eats a couple of HP due to the placement of the Pinion at the bottom. Its not much but hey, I've lost an autocross by 100th of a second ;o). 8: is lighter also. My car came with a 2" narrowed rear end gives me a deep dish look in the back which I personally love but its a PITA when you can't rotate tires front to rear and not all rims are available so to get a vintiques look, I would have to use 1" adapters on each side.

Since I track my car occasionally, I would rather have a .8 5 th gear as that big gap to .6 makes 5th a cruising gas-milage gear instead of a power gear. I tend to drive country roads here in Upstate so .8 would be perfect for 55-65 mph. However in Colorado at 75, maybe .6 would be better. That said, with 350s I can hit 120 in 4th at 6k and frankly I'm not so sure my car needs to be going any faster than that. It pulls hard to 120 but when I hit that .6 5th gear, the pull drops significantly, if I had a .8, I know I could get in real trouble. Frankly, I'm not sure I personally should be driving any faster - even on a track. I don't have the proper ground effects, she starts feeling floaty at 120 plus. I'm just a garage hack so from a Darwin point of view, 115-120 is likely more appropriate.
 

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With 3.70's and a T5, first gear will feel like low gear in a '74 F-250.... aka "Granny Gear". Your overall gear ratio in 1st will be 10.915:1... Many consider 10:1 as "ideal" for the street... that would put your rear axle ratio requirement at 3.389:1 or, most appropriately, a 3.25:1 9-inch gear set for a 2.95:1 T5. Note that the overall gear ratio for a HiPo car with a 3.50:1 rear gear was around 8.25:1 with both the 2.32 Toploader and 2.36 T-10 and why so many folks installed 3.89's.

Issue #2 for the T5 installation, in the majority of swap cases, is the need to even consider a 9 inch as you'll blow up the transmission before a 8 inch rear in good condition. While you CAN buy a "heavy duty" T5 that will put up with abuse for the money you may want to consider moving up to a TKO instead.

Issue #3 for the T5 is the gear spacing between 1-2 and 4-5. Since the SBF, even when stroked to 347, isn't known as a "torque monster", the rpm drop between 1-2 fails to keep the engine in the optimum power band and the 4-5 spacing means lots of 5-4, 4-5 shifts when cruising the 2-lanes to accommodate hills and curves.

If it were me.....

You already have (most likely) the wide-ratio toploader with nicely-spaced gear ratios and a 2.78 first gear.... a 3.50:1 gear set would put you right at 9.73:1 overall... damn near perfect. Yeah, at 70 mph you might be turning 3,000 rpm versus 2,000 with a T5 and 3.70 gears.... unless you're daily driving with more than 50% of your time spent on the 4-lane, and your major concerns are fuel economy and engine wear then maybe an overdrive gear is warranted... although I still couldn't justify the need in my own mind. If you don't frequent the superhighway then do you really think you'll be spending that much time in 5th gear? That 2,000 rpm at 70 is now 1,400 rpm at 50.....

Anyway, that's my 3 cents worth...... I'd keep the Toploader.
 

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Discussion Starter #18
Couple of thoughts, first Husk is right, if your going T5, 8" might be a saner approach especially value per dollar. First a 9" eats a couple of HP due to the placement of the Pinion at the bottom. Its not much but hey, I've lost an autocross by 100th of a second ;o). 8: is lighter also. My car came with a 2" narrowed rear end gives me a deep dish look in the back which I personally love but its a PITA when you can't rotate tires front to rear and not all rims are available so to get a vintiques look, I would have to use 1" adapters on each side.

Since I track my car occasionally, I would rather have a .8 5 th gear as that big gap to .6 makes 5th a cruising gas-milage gear instead of a power gear. I tend to drive country roads here in Upstate so .8 would be perfect for 55-65 mph. However in Colorado at 75, maybe .6 would be better. That said, with 350s I can hit 120 in 4th at 6k and frankly I'm not so sure my car needs to be going any faster than that. It pulls hard to 120 but when I hit that .6 5th gear, the pull drops significantly, if I had a .8, I know I could get in real trouble. Frankly, I'm not sure I personally should be driving any faster - even on a track. I don't have the proper ground effects, she starts feeling floaty at 120 plus. I'm just a garage hack so from a Darwin point of view, 115-120 is likely more appropriate.
Thank you!! All great points. My 8" has 115k miles on it and after you buy a 8" third member and biggrt brakes etc, a new 9" assembled with the brakes isnt that much more...so Im torn..

I know you were looking at a TKO-600. Is that what you installed? Right now Modern Driveline is having a special through the end of the month and the price between the TKO and the T5Z is only about $700. Granted you have to move the bracing on the car back about 2" but it doesn't "sound" that hard and it sounds like they solved the 3rd gear shift issues.

With 3.70's and a T5, first gear will feel like low gear in a '74 F-250.... aka "Granny Gear". Your overall gear ratio in 1st will be 10.915:1... Many consider 10:1 as "ideal" for the street... that would put your rear axle ratio requirement at 3.389:1 or, most appropriately, a 3.25:1 9-inch gear set for a 2.95:1 T5. Note that the overall gear ratio for a HiPo car with a 3.50:1 rear gear was around 8.25:1 with both the 2.32 Toploader and 2.36 T-10 and why so many folks installed 3.89's.

Issue #2 for the T5 installation, in the majority of swap cases, is the need to even consider a 9 inch as you'll blow up the transmission before a 8 inch rear in good condition. While you CAN buy a "heavy duty" T5 that will put up with abuse for the money you may want to consider moving up to a TKO instead.

Issue #3 for the T5 is the gear spacing between 1-2 and 4-5. Since the SBF, even when stroked to 347, isn't known as a "torque monster", the rpm drop between 1-2 fails to keep the engine in the optimum power band and the 4-5 spacing means lots of 5-4, 4-5 shifts when cruising the 2-lanes to accommodate hills and curves.

If it were me.....

You already have (most likely) the wide-ratio toploader with nicely-spaced gear ratios and a 2.78 first gear.... a 3.50:1 gear set would put you right at 9.73:1 overall... damn near perfect. Yeah, at 70 mph you might be turning 3,000 rpm versus 2,000 with a T5 and 3.70 gears.... unless you're daily driving with more than 50% of your time spent on the 4-lane, and your major concerns are fuel economy and engine wear then maybe an overdrive gear is warranted... although I still couldn't justify the need in my own mind. If you don't frequent the superhighway then do you really think you'll be spending that much time in 5th gear? That 2,000 rpm at 70 is now 1,400 rpm at 50.....

Anyway, that's my 3 cents worth...... I'd keep the Toploader.
Thank you as well. You both have great points. Once the weather warms I drive my Mustang everyday and everywhere so I think I'd like the OD. My car is one of those that got the T-10 at the San Jose plant and honestly Im not sure what the ratios are but I know its not too bad with the 3.00 rear end I have in my car now.

So many things to think about and variables. I just want to do the right thing the first time and not have to redo it.

Thank you everyone for your input. Without a doubt i will be asking a ton of additional questions and opinions as time moves on, especially on lock down. :)

Chris
 

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Do the 9" conversion and do not look back. For just a little more money you will have a nicer set up and if you go with more power down the road it will be up to the task.
 

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Discussion Starter #20
Do the 9" conversion and do not look back. For just a little more money you will have a nicer set up and if you go with more power down the road it will be up to the task.
Thanks!!! Those are the little pushes that I need.

Chris
 
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