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11/16/2017 9:28 AM  #1


5 speed conversion

I have a 1966 mustang coupe with h 289 A code with top loader 4 speed with a 3:00 rear 8 inch gear .I want to convert to a T5 5 Speed trans and leave 3:00 rear gear will it work ok with out changing to a different rear gear?? Thanks any help would be appreciated

 

11/16/2017 11:20 AM  #2


Re: 5 speed conversion

With the 3.0 gear the standard T-5 will probably be fine.  The Fox's came with 2.72 gears and that seems to have worked.  With any lower (higher ratio) gears you'll probably find that 1st gear is about useless so what you have should be fine.  If you ever decide to get better off line performance and go to a 3.55 or 3.73 gear you'll probably want to change to the Z spec T-5 gear-set which has taller (lower ratio) 1st and 2nd gear and a .63 OD rather than the .68 of the standard T-5.

BB
 


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

11/16/2017 11:28 AM  #3


Re: 5 speed conversion

It depends on what your intended use is.  ??

I use a 2.95 1st gear with the 5 th being .63 over drive.     Some trannys  are 3.31 1st with a .84 over drive.  better out of the hole and with 3.0 rear ring is about the same rpm  (60 mph) as my 3.55 rear ring gear.     there are some on line calculators that can compare these numbers




http://www.jegs.com/i/Ford-Performance/397/M-7003-Z/10002/-1

 

11/16/2017 1:12 PM  #4


Re: 5 speed conversion

Bullet Bob wrote:

With the 3.0 gear the standard T-5 will probably be fine.  The Fox's came with 2.72 gears and that seems to have worked.  With any lower (higher ratio) gears you'll probably find that 1st gear is about useless so what you have should be fine.  If you ever decide to get better off line performance and go to a 3.55 or 3.73 gear you'll probably want to change to the Z spec T-5 gear-set which has taller (lower ratio) 1st and 2nd gear and a .63 OD rather than the .68 of the standard T-5.

BB
 

Thank You for a your input

     Thread Starter
 

11/16/2017 1:16 PM  #5


Re: 5 speed conversion

Thank You’s for the input it’s just going to be a daily driver not to worried about getting out of the hole in a hurry

     Thread Starter
 

11/16/2017 2:27 PM  #6


Re: 5 speed conversion

gotstang wrote:

I have a 1966 mustang coupe with h 289 A code with top loader 4 speed with a 3:00 rear 8 inch gear .I want to convert to a T5 5 Speed trans and leave 3:00 rear gear will it work ok with out changing to a different rear gear?? Thanks any help would be appreciated

​I have a T5 with a 3.00 rear end.  It works fine.  Particularly for a daily driver.  I go into 5th at around 50mph.  4 speeds are used in the street only.  No need to use 5th down low.


Original owner - 351w,T-5, 4whl disks, power R&P
 

11/16/2017 3:47 PM  #7


Re: 5 speed conversion

The 3.0 is fine as long as you have a camshaft that is close to stock.  If you have a lopey cam, the fifth gear will bog you down terribly under 75 mph.
Stock cam is best with that combo, or accept the fact you have a four speed with overdrive for high speed highway use only.

This is based on my personal experience with a cammed up 400hp 351w in my 66. With a 3.0:1 gear, it was useless in fifth gear under 70 mph.  Changed to 3.70:1 rear and the car came alive.


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

11/16/2017 4:30 PM  #8


Re: 5 speed conversion

Yes the engine is a stock 289 4V (A) code engine stock cam

     Thread Starter
 

11/17/2017 10:34 AM  #9


Re: 5 speed conversion

The big question is which T5 is it?  If its from a Fox V8 then the rear gear will be fine.  The Fox T5s used a 3.35 first gear, because they knew it would be paired with a numerically low rear gear (most were 2.73).  This gave the car decent off the line performance and good mileage on the highway.

Problem was, hot rodders wanted more.  One of the first swaps a lot of guys made was the rear gears.  2.73 just doesn't sound sexy when bench racing, and it was an easy way to cut 1/4 mile times without having to mess with that computer controlled engine they didn't understand.  A lot of guys went right to 4.10s and quickly found out that they had you shifting at or before the 60' mark, ruining your launch and hurting your ET.  With a stock trans 3.55s were a better choice.  Great off the line, a shorter first gear, but not absurdly so.

Then, Ford Motorsports tasked Borg/Warner (builder of the T5, prior to selling the design to Tremec) with building a stronger T5 with improved gear ratios that they could sell as a Ford Motorsports part.  Realizing that one of the first changes a lot of guys were making was a gear swap BW lowered the 1st gear ratio to 2.95 so running a typical performance rear gear ratio no longer resulted in an almost immediate 1-2 shift.  This trans became known as the Z spec, and is still sold today.  The strength gain is marginal, and mostly from that I've seen a marketing gimmick, but the gear ratios are better than a Fox T5 for sure.  Aftermarket gear makers like G-Force used the Z spec ratios instead of the Fox ones.

So, IMO, if you have a Fox T5 I'd leave your gears alone.  If its a Z spec it will be fine with the 3.00 gears, but you are leaving some acceleration on the table, and it would benefit from a 3.55-3.73 ratio with no real downside.

As a parting shot, tire size also make a difference.  If you've swapped to bigger wheels the tires have also likely gotten taller, reducing your effective gear ratio. 

 

11/17/2017 11:23 AM  #10


Re: 5 speed conversion

Hi , i have recently pass on t5 z spec from the 4 manual , have  listen some advice here and go with 3,89 .
I am very new with this so maybe in future i will change for 3,75 or 3,55 depends on feelings when i can run the car and have some miles.
After i can tell my feeling about 5th gear and 3,89  but i am happy to have an " overdive"

 

11/20/2017 4:03 PM  #11


Re: 5 speed conversion

I ran a T5 with a 2.79:1 rear gear for years in my '67 coupe and had no problems... but overdrive was only useful at about 65 and above.
I recently changed to a 3.25:1 rear gear and actually wish I had gone with a 3.55:1 gear instead.

Last edited by Michael H. (11/20/2017 4:04 PM)

 

11/20/2017 4:36 PM  #12


Re: 5 speed conversion

Will the top loader be available when you are done, I may be interested.


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

11/20/2017 5:54 PM  #13


Re: 5 speed conversion

Michael H. wrote:

I recently changed to a 3.25:1 rear gear and actually wish I had gone with a 3.55:1 gear instead.

Hey Michael........care to elaborate a little?!
Not much difference between the 3 and a quarter compared to the 2.79?
6sal6
 


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

11/21/2017 9:05 AM  #14


Re: 5 speed conversion

The 3.25:1 was a noticeable improvement over the 2.79:1 and definitely a worthwhile upgrade.  I just wish I'd gone for just a little bit more, and I think the 289 would be in the torque band better cruising at a slightly higher rpm... I can't prove that, but it just "feels" that way to me... whatever that means.

Having said that, I'm not sure I'd want to go lower than 3.55:1 because of the low first gear in the T5.

Last edited by Michael H. (11/21/2017 9:06 AM)

 

11/21/2017 9:33 AM  #15


Re: 5 speed conversion

Typically you need to go up a half point in gear to notice a difference, and a full point is VERY noticeable.  Going from say a 2.72-3.73 is a great swap.  It will feel like the car has another 100HP, and dragstrip times will bear that out, as typical reduction is a full second off your ET.  Coincidentally every 10HP added to an engine equates to a 0.10 reduction in ET, so adding 100HP equals a 1.00 reduction in ET.

With an OD trans the impact on cruising RPM is much less of a concern, but like I said, with a Fox sourced T5 and that 3.35 first gear it can make 1st gear too short.  In that combo I tend to think that a 3.55 rear gear is the best compromise.  But, with 3.25s I wouldn't be rushing out to swap gears for 1/4 point of gear.  There's something left on the table, but no enough to justify the expense in my opinion.  It would be cheaper and easier to add another 25HP to the engine and achieve the same end result. 

The 289 is a great engine, but it depends on how its configured.  The stock A and C code engines were cammed down to produce good low speed torque, and for the engine's size they did.  To make HP though you have to twist that little engine above 5,000, and you're not doing that with an A or C code cam.  The K code engines went solid lifter and got close to 1HP/cube in stock trim, and with the Shelby mods exceeded it.  But its a trade off for worse low speed manners and a loss of low speed torque.  That's when taller gears help because it gets the engine into its powerband sooner and bolsters that soggy bottom end.  With greater RPM potential the tall first gear isn't really an issue. 

 

11/21/2017 1:50 PM  #16


Re: 5 speed conversion

TKOPerformance wrote:

... with 3.25s I wouldn't be rushing out to swap gears for 1/4 point of gear.  There's something left on the table, but no enough to justify the expense in my opinion.  It would be cheaper and easier to add another 25HP to the engine and achieve the same end result...

I agree... that's why the 3.25's are still in there.

TKOPerformance wrote:

...
The 289 is a great engine, but it depends on how its configured.  The stock A and C code engines were cammed down to produce good low speed torque, and for the engine's size they did.  To make HP though you have to twist that little engine above 5,000, and you're not doing that with an A or C code cam...

I've put a small performance cam in my 289, but it still has the lower compression C-code pistons in it.  I know could swap to flat-top pistons, but it runs well and is very reliable so I hate to tear into it that deeply.

I'd love to put some aluminum heads on it, but 58cc is the smallest chamber I can find.  My understanding is that the stock 289 heads were 54cc, so going up to 58cc would mean losing even more compression.  I guess I could buy some aluminum heads and have them milled down to 54cc chambers, but that adds more expense to an already expensive endeavor.... plus, I'm not sure which ones have enough material to allow them to be milled that much.

 

11/21/2017 2:06 PM  #17


Re: 5 speed conversion

Michael H. wrote:

TKOPerformance wrote:

... with 3.25s I wouldn't be rushing out to swap gears for 1/4 point of gear.  There's something left on the table, but no enough to justify the expense in my opinion.  It would be cheaper and easier to add another 25HP to the engine and achieve the same end result...

I agree... that's why the 3.25's are still in there.

TKOPerformance wrote:

...
The 289 is a great engine, but it depends on how its configured.  The stock A and C code engines were cammed down to produce good low speed torque, and for the engine's size they did.  To make HP though you have to twist that little engine above 5,000, and you're not doing that with an A or C code cam...


I've put a small performance cam in my 289, but it still has the lower compression C-code pistons in it.  I know could swap to flat-top pistons, but it runs well and is very reliable so I hate to tear into it that deeply.

I'd love to put some aluminum heads on it, but 58cc is the smallest chamber I can find.  My understanding is that the stock 289 heads were 54cc, so going up to 58cc would mean losing even more compression.  I guess I could buy some aluminum heads and have them milled down to 54cc chambers, but that adds more expense to an already expensive endeavor.... plus, I'm not sure which ones have enough material to allow them to be milled that much.

You've got that right in both instances.
 


Original owner - 351w,T-5, 4whl disks, power R&P
 

11/21/2017 4:06 PM  #18


Re: 5 speed conversion

What gasket are you running?  You could swap to a steel shim head gasket and gain back some compression.  Its not going to be a ton, but its fairly cheap and not terribly hard, just a lot of labor. 

You could mill the iron heads too while they're off.

 

11/22/2017 6:05 AM  #19


Re: 5 speed conversion

I have the same combination in my 66 convertible.  I like it.  I also found that most of my driving didn't really benefit from the change (toploader to T5).  I sort of miss the toploader and may put it back in.  I won't say it was a waste of money but it has not really made a difference in terms of driving enjoyment or fuel economy. 

The worst part - I hacked up my original car to get the clutch stuff set up (I was utterly stupid and opted for one of the cable clutch setups - which was not very well engineered - rather than using the stock Z-bar) so it's going to be a huge pain to return everything to original.

Last edited by John Ha (11/22/2017 7:40 AM)


Founding Member of the Perpetually Bewildered Society
 

11/22/2017 8:42 AM  #20


Re: 5 speed conversion

You're only going to see fuel economy benefit on the highway.  Around town you aren't going to use OD much.  Constantly having to go from idle to speed to a stop and back is what kills economy.  The transmission in those situations doesn't even matter.  The only way to really improve around town economy is to have a smaller engine that uses less fuel. 

 

11/22/2017 10:13 AM  #21


Re: 5 speed conversion

TKOPerformance wrote:

What gasket are you running?  You could swap to a steel shim head gasket and gain back some compression.  Its not going to be a ton, but its fairly cheap and not terribly hard, just a lot of labor. 

You could mill the iron heads too while they're off.

A few years back I pulled the heads to do an exhaust port match and smooth out the thermactor bump castings.
I re-installed the heads with copper head gasket shims as gaskets, but when I was adjusting the valves (with the engine running) I noticed that the oil looked like chocolate milk and I knew I had coolant leaking into the oil.  So, I immediately assumed it was because the copper shims weren't sealing correctly.  I pulled the heads and re-installed with regular fel-pro head gaskets from my local autozone.  In hindsight I think that the leak probably was at the intake gaskets, because it occurred to me one day that I never re-torqued the intake manifold bolts before firing it up... oh well... you can bet that I re-torqued them the second time around though, and now I'll always remember to.
 

 

11/22/2017 10:32 AM  #22


Re: 5 speed conversion

Copper HGs sometimes require a sealer to be applied to them, but as always, follow the manufacturer's instructions.  We used to use this stuff called Smokey Seal (developed by Smokey Yunick) that worked great, but is sadly NLA.  Then I had good luck with various Permatex products, the best was almost like a spray form of Hylomar.  You could clean it right off a shim style gasket and reuse the gasket essentially forever. 

Intake leaks are somewhat common on SBFs I've found.  Another possible culprit is the timing cover developing corrosion and a hole forming between the oil and coolant areas.

 

11/22/2017 1:14 PM  #23


Re: 5 speed conversion

Yeah. I used permatex copper spray sealant... I'm pretty sure if I'd remembered to re-torque the intake manifold bolts I'd have been good to go.

I used the same copper gaskets and sealer on my father-in-law's 302, so if we ever get around to firing it up we'll see what results we get.

 

11/22/2017 3:18 PM  #24


Re: 5 speed conversion

For the normal car that is just street driven, I recommend using a good composite FelPro gasket rather than copper. You have alot better chance of everything sealing and never leaking with a normal type head gasket.  Rather than the “hope this works” approach.

Most folks will appreciate an engine that keeps on running alot more than an extra 1/10 of a horsepower at 6,000 rpm will be noticed.


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

11/22/2017 4:26 PM  #25


Re: 5 speed conversion

Agreed.  After I replaced the copper shims with FelPro gaskets they've taken me many miles worry-free (including 2 Mustang Steve Bashes)... which is why they're still in there. 

 

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