[Guest]

I did a search, and found a lot of great advice on how to take out my 3 speed and put in a 4 speed tranny, but noone mentioned why the swap. It has been rolling around in my head for some time to swap to a 4 speed, but I don't know the advantages. So, what are the advantages, if any? Will I be running at less RPM at highway speeds, etc.? And, which 4 speed would drop right in without any changes other than a longer speedo cable and a possibly a different shifter?

 

[Huskinhano]

Much better spacing of gear ratios. Definately you'll need a new shifter.

You may also want to think about a T5 swap.

 

[dickson]

You can change your rear end gearing to a higher numerical gear, which will give you more punch off the line....at the same time that additional 4th gear will keep your revs down at higher speeds.

I'm with Tom - unless 100% originality is an issue, I'd drop in a 5 speed while I was at it. It's not as simple as a drop-in - IIRC you need a different crossmember and a cable clutch, but worth it. You can even get a shifter that appears stock until you look at the shift pattern on the ball. BTW, you might talk to Charlie Jones / "roadracer" as he's added a 5 speed to his '66 GT-350. Dickson

 

[Guest]

I'm pretty sure the final gear on 3, 4 or C4's is 1 to 1.

 

[Huskinhano]

You don't need a cable conversion, only if you want to go that way. You should be able to swap it out about the same as replacing the 3 speed with a 4 speed.

 

[SielkeD]

Charles Turner is right. On original transmissions the final gear is 1:1, the late model T-5 however is an overdrive gear, which would help at highway speeds. The improvement from the original 3 to 4 speed is in the lower ratios, not the final gear. Under regular street use you would see little improvement.

 

[craigh]

Actually, you will see quite an improvment in in-town driving. The extra gear makes it much more driveable. (I have both a 3 speed and 4 speed)

 

[pprince]

Unless you used a Granada/etc toploader you get direct drive in 4th.

This means the revs would stay the same. You need an overdrive tranny to reduce the revs.

 

[Art]

So, what are the advantages, if any?

If you have to ask, it's probably not for you! ::

 

[Stroked66]

I disagree with SeilkD........ (sorry, No offence )

Having a 4spd as opposed to a 3spd will give you quicker acceleration off the line and less wear & tear on the clutch. As other have posted the final drive ratio is 1-1 on both 3 & 4 spds so on the highway there is no advantage of one over the other, nor is there the need to change rear end gearing. The advantage of a 4spd. is in the lower gearing of 1-3 (You'll have to row through 3 gears and not just 2). If you change to a 4, you will need only to change those parts you mention and will see a noticeable difference in how the car accelerates.

T5 conversions are another good option, but will also require you to change your rear gear ratio and are much more costly than upgrading to a 4spd.

 

[Guest]

So, what are the advantages, if any?

If you have to ask, it's probably not for you! ::

Why would you say that?
OK, what was the last year Mustang used the 4 speed before they went to the T-5? And what other cars might they be in?
I need to go junk yard poking around so would need to know which cars to look for.
Thanks to all!

 

[66T2B331]

First, as mentioned, both the 3 and 4 have 1:1 final ratios so no diff there. The additional gear is really nice because it helps keep the engine in acceptable RPM ranges. ie w/a 3sp you end up with situations where you are either bogging the engine or winding it up.
If you were to change to a 5sp, you don't have to change the rear ratio. After all, 86-93 model t-5 5.0s used a 3.08 rear and autos used a 3.27. Don't get me wrong, 3.50s are a lot more fun, just not required.

 

[MattsMach69]

I also have had both and the 4 speed is just much more fun to drive. The 3.03 3-speed does, however, provide a little punch out of the hole but the 4 speed will provide better acceleration in the other gears.

 

[Stroked66]

Chances are he's got a 2.8 open rear ratio with that 3 spd. If he were to bolt a T5 to it the rpms would be too low in 5th gear and would require a gear change.

 

[Guest]

Chances are he's got a 2.8 open rear ratio with that 3 spd. If he were to bolt a T5 to it the rpms would be too low in 5th gear and would require a gear change.

Yes, I do have the 2.8 open differential, so you are right about the gear change in the rear. So, I may think on that one. If I did go the T5 route, what RPMs would I be pulling in 5th at 70 MPH with a 350 rear?
Again, what years of Fords used the 4 speed tranny that will bolt right in my 65 289 without changing the rear ratio?

 

[LMan]

Chances are he's got a 2.8 open rear ratio with that 3 spd. If he were to bolt a T5 to it the rpms would be too low in 5th gear and would require a gear change.

Yes, I do have the 2.8 open differential, so you are right about the gear change in the rear. So, I may think on that one. If I did go the T5 route, what RPMs would I be pulling in 5th at 70 MPH with a 350 rear?
Again, what years of Fords used the 4 speed tranny that will bolt right in my 65 289 without changing the rear ratio?

Stock 5.0 Mustangs came with 2.79 rears mated to the 3.35 First-gear T5 (like mine) and did OK. The torque of the 5.0 will pull the gear acceptably. The 3.08 rear was the "performance" option http://www.ls1.com/forums/images/smilies/wink.gif. Autos got the 3.27.

So, Glen can change the gear or not, it will still work. The O/D Fifth just makes it much more acceptable to have a DEEPER rear gear, it doesnt rule out keeping the 2.80.

 

[SielkeD]

I disagree with SeilkD........ (sorry, No offence )

Where's the disagreement? As I said; "The improvement from the original 3 to 4 speed is in the lower ratios, not the final gear." We really didn't disagree on what would improve, just how much that improvement is worth the change under normal driving conditions. If quiker acceleration is important to you, and posibly racing (keep it on the track now!), certainly make the change.

 

[Guest]

I disagree with SeilkD........ (sorry, No offence )

Where's the disagreement? As I said; "The improvement from the original 3 to 4 speed is in the lower ratios, not the final gear." We really didn't disagree on what would improve, just how much that improvement is worth the change under normal driving conditions. If quiker acceleration is important to you, and posibly racing (keep it on the track now!), certainly make the change.

No, I'm not into track racing with "Old Yeller." That's for my 03 Mach1. So, now I'm hearing that a 2.80 8" rear will be OK with a T-5 and my original 1965 289? Is that right?

 

[Huskinhano]

Maybe, maybe not. With a T5's 3.35 1st gear and a 2.80 axle, he'll have about the same torque multiplication or better then a 3 or 4 speed with a 3.25 axle ratio. Having owned a 85, 5.0 LX with a T5 and 2.73 gears, it had plenty of punch off the line and with that deep OD got some killer gas milage, like almost 26 mpg doing 80 mph with the air on :: IIRC, 70 mph the engine was loafing at about 1,700 rpm. Never had a problem with this.


IMO, with a mild 289/302, I'd definately recomend trying the 2.80's before changing them out. In my 66, I'm putting in a T5 witha 3.35 1st gear. The 2.80's are shot and howling, I have a 3.00 center that I'll put in. The 302 I'll be putting in will have a mild cam, headers and GT40P heads. I'm planning on using 3.25's for this.

 

[Huskinhano]

Glen, I'd think twice about the 3.50's with a T5 that has a 3.35 1st. 1st gear might be all but useless, too low. If you had a Motorsport T5 with a 2.95 1st, maybe.

With a mild engine and a 3.35 1st along with 3.50's, most likey you'd be starting off in 2nd most of the time. Keep it mild!