Why? I'd personally keep the 4 speed and do a hydraulic clutch with it. I'd think that you would need a T56 for a 390 if you are dead set on changing it out.

 

I'm thinkin he wants an overdrive gear.
Another option would be to keep your original 4 speed and do a gear vendors overdrive swap, although it is also getting up close to $3,000.
T56 would be nice, although also expensive, but the main disadvantage would be having to cut the floor to make it fit.
I'm not sure if the T-5 would be a strong enough tranny behind your 390, you might want to look at a tremec, although it too requires some minor floor surgery.
David.

 

IMHO if you do the T-5 conversion behind a 390, better buy them by the dozen.

 

I agree with the other that a T5 will not hold up to a good running 390. I would look at a TKO600 if I were you. That is a tranny you should never be able to hurt.Some say it will work without cutting into your tunnel but you would have to check into that.

 

You are in dangerous territory here and while I never speak in absolutes the T5 will likely not hold up to a 390, there are adapters to do this swap though and these parts have gotten a lot easier to find lately.

I didn't go T5 because the parts were not available and it seemed like the weak link when I bought my toploader and I don't want the drive shaft angle issues or to cut my floor pans for a TKO600 so I am in the process of adding the Gear Vendors, while expensive it is next to bullet proof!

 

Not entirely true. It was just done without cutting the floor.

http://forums.vintage-mustang.com/showtopic.php?tid/1500607/

 

Not entirely true. It was just done without cutting the floor.

http://forums.vintage-mustang.com/showtopic.php?tid/1500607/

That was with a 302 so not apples to apples. We are all aware there are always cars that work better for certain mods way too many factors at play to say anything is certain.

 

Which is why I said not entirely true.

 

Hi guys and thanks for all the answers back and thoughts! My 4 speed seems hard to shift fast and reverse is horrible to get into. When on the highway at 70, I am at such a high rpm that I feel my brains are going to raddle out. (I have a 3.08 rear end)
If the T5 runs in most 5.0 mustangs with all the power they have, why won't it hold up to my 390?
Please let me know your suggestions as to what I should do. I don't have the $$$ for a tko.
Can I find a T56 somewhere for pretty cheap?
What gears ratios should I go with!?
I don't know anything about this stuff, I'm sure that's obvious. Haha

 

That is because the T5 you are referring to were/are built for the high HP cars that could handle it (aftermarket). Most T5 will handle a 302 no problem until the HP is at a certain level. I think everyone here will agree that a level of hp is vastly different from a 302 to a 390. You would be at the limit of a T5 for your 390. If you were dead set on a T5, then you would have to look for someone selling a G force or astro performance tranny. They were built to handle 600+hp or like a 4 speed with the overdrive. 2K for that rebuild job if you found a donor tranny.

Another idea would be to ask some of the more reputable toploader shops like the following for advise as to you issues and what can be done about it:

http://www.toploadertransmissions.com/
http://www.4speedtoploaders.com/

 

You are getting good advice here and now seeing why us 390 guys have it a little tougher to get overdrive.

Trust me for the money I have into my toploader and shifter linkage and Gear Vendors overdrive I could have had a sick 5 or 6 speed setup but its not just a money factor.

 

Everyone told me the T-5 wouldn't hold up behind my 351c, but it's been there almost 12 years with no problems. I'm sure that it's got a lot to do with driving habits, but they can live behind larger engines.

Joe

 

From this site:
390 c.i. V-8 4V Carburetor


C.R.
10.5:1

Horsepower
320@4800

Torque
[highlight]427@3200[/highlight]

From this site, Maximum torque for any factory T-5 is 330.
I wouldn't waste my time or money.