• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

T5 5 Speed or T56 6 Speed, Have both which should I use?

1

1965GTFB

Member
This is for my son's '67 we are building. I have both a new T5 World Class 5 speed .68 5th gear and a new T56 6 speed .80 5th & .62 6th gear. Looking for opinions and real world experience as to which to use on this build, which will also help me know which to sell. I'm wondering if the T56 is too much tranny for the engine setup we are planning(e.g. not enough hp or torque)?

Goal is to maximize MPG for a car that will be driven on a regular basis, probably 60/40 with the 40% being freeway. Shooting for 25 MPG or higher on the highway. My dead stock '65 with the 103,000 mile original 289 4v 4 speed with 3.00:1 rear gets 20mpg on the highway with a light foot so I think it should be possible with the way we are planning to set it up.

Engine & rear end will be:
289 4V Autolite 4100
Fresh rebuild .030 over balanced
Roller tip rockers maybe full roller conversion.(before it is said, don't want to go 5.0 EFI)
Heads will be ported
Shorty headers
3.00:1 non-limited slip
Rear tires probably 245 or 235/60/15 or 245 or 235/60/14(have the 14" Magnums but might go 15")

Car will be a full restoration and a driver, no racing, no burnouts(he's not a knuckle head 16 year old) but will have some fun driving it.

So which to use and which to sell? I've liked the idea of the T56 with the tall final drive since I already have it, but am wondering if we would need more motor for that tranny, which could kill the MPG goal.

Thanks for your feedback.
 
I have had both transmissions in my car. The T5 is a pretty simple and easy swap. I would do it if I were you. The t56 is much more involved. You will either need to buy/build engine mounts that will lower the engine and make a custom transmission crossmember. The T56 is larger and if you don't lower the engine it will require you to cut the transmission tunnel for clearance.

Now that I said that I love my T56 and was one of the first people to put one in a 67/68 without cutting the trans tunnel. I like the fact that you have 2 OD gears. One is like a road race tranny and the 6th gears is really only good for 70 mph or higher. The other thing I liked about the T56 was its first gear. With the t5 I had to shift out of first gear very quickly and it was a bit of a pain in the butt. My gearing is quite a bit lower than yours (3.70) so it would likely be more tolerable for you.
 
I knew from watching your swap(you are our role model for the T56) that I would need to use the lowering motor mounts with the T56.
If I go with the T5 is it still worth using the Lowering motor mounts to get an optimal driveline angle?
 
Not needed for a T5 and they may even create additional clearance issues with exhaust or other things.
 
I only used the lowering motor mounts for my blower to clear the hood. That is when I had the T5 in there . After I had the T56 in place they were required for the correct driveline angle.
 
I'm running a T5 with 3.00 out back. Perfectly happy with it. 1st gear is much more tolerable with the higher rear gear. I run about 1850 rpm at 70 mph. Never calculated the mileage but it seems like it's in the high teens low twenties.
 
I'm running a T5z with 3.5 gears and agree that first seems pretty low meaning I need to shift out of it pretty quickly. Wish I had a gear between 4th and 5th. Yes 5th is great for 70+ mph. Turning around 2000 rpm at 70.
 
From the feedback so far I'm thinking we'll be going with the T5 and selling the T56 to someone that has a setup more suited to it(e.g. more motor and shorter rear gears).
 
You must log in or register to reply here.
Back
Top