Tranny Question.

[Lobo'74]

I have a '79 Saginaw all syncro 3 speed on my '67. It drops about 700-800 rpm 1 to2 shift, and about 1500 rpm 2 to 3 shift. In town I am about 3000 - 3500 rpm at 35 - 40. Too many revs in 2nd, too few in 3rd. And at highway speed its too many revs and too much noise.

Which would be cheeper, going to a 4 speed or going to an automatic? For auto it seems like 700R4 would be the way to go. I have probably around 325 hp or so. I assume that means I would need a stall converter of 2500 or 2800 or so, right?

What abot overdrive units? Anything available to put on my 4:10 or 4:11 rear end to convert it to an overdrive rear while keeping the current 3 speed?

So much to learn and such a small brain housing group to store it in!

[walker]

A 4 speed won't solve all your problems as the final drive ratio is still 1:1. Overdrive units are available and cost about 2 grand, not worth it. I have a th400 with 4.11's in my '67 and have the same problem at highway speeds. 700r4 seems like the solution. Something else to think about are some minor changes, that I have been playing around with on the various calculators available, including gears and tires. Dropping to a set of 3.73's in the rear and increasing rear tire size. Right now I have tires that are 27.5" tall, by increasing to 30" I lose about 500 or 600 rpm. I get the same with the gear change yet still have a fairly tall set of gears.

[lukecp]

How much do you like banging through the gears?

You could put in a car 4-speed, but they are kind of hard to find these days. Lots of fun though.....with 4.11 rear gears, a close ratio box would proably fit your truck the best.

The truck 4-speeds are great for hauling massive loads, but they are impossible to speed shift, making them not ideal for a performance situation. I would stay away from them, the only real gain you will get is a very low first gear, and it will be stronger than a manual 3-speed.

An automatic would be the easiest way to go. A TH350/TH400 tranny will have very ideal gear spacings that will keep your engine in its powerband fairly well. They are cheap to rebuild, and are both pretty tough (although the TH400 is by far the strongest.)

An automatic OD is anouther, more expensive way to go. The two easiest retrofits would be a 700R4 or a 200R4 automatic. The main disadvantage of the 700R4 is that the gear spacing between 1st and 2nd is pretty large...about 50 percent. So if you are pulling 5000rpm in 1st, when you hit second you will be pulling 2500rpm. The 200R4 has better gear spacings. Either of the OD's can be built strong...but figure at least twice as much cost as building up a TH350/TH400.

[bpmcgee]

Lobo,

I don't know the drive ratios of your 3-speed. If you switched to a 4 speed, you'd probably go to the SM465, which has the following ratios:

1st 6.55
2nd 3.58
3rd 1.70
4th 1.00

Notice the granny first. Basically you drive the SM465 like a three speed (2-4).

Also, the 4th gear on this trans, and any non-overdrive trans, is only 1:1. Thus, the 4 speed wouldn't help your RPM problem at highway speeds. the 700r4, being an overdrive trans, would.

My opinion is that if you've got 325 HP and a similar amount of torque, you might get what you're looking for by dropping the gearing in your rear end. With a 1:1 gear ratio in the tranny, switching to 3.73s will drop your RPMs by about 10%, 3.42s would drop it by about 17%. From what I can gather here on the boad, people like 4.10s if they have a 6 cylinder, or if they mostly cruise.

Good luck,

Brian

[Lobo'74]

To move from my manual floor shift to a TH400 what is required?

Off the top of my head it looks like:
Appropriate stall converter Say $150 to $250 ($100 on ebay)
TH400 Transmission rebuilt for $400-$800 ($425 on ebay)
Auto column (tilt would be nice) $200 on ebay
TV cable unknown$

Anything else? How difficult is this to do? Would a long saturday with a couple of knowledgable buddys and a couple of six packs (AFTER the install is done) do it, or is this a "I'd take it to a shop, Dave" job?

[Lobo'74]

and a 3:73 rear end, if I could find one cheap.

[lukecp]

That list is pretty much it...except i personally wouldn't buy a tranny off ebay. Go to a local tranny shop and pick one up with a warranty. If the Ebay TH400 goes out...you are proably gonna be screwed. If one built by a local tranny shop goes out, they will usually fix it free of charge under warranty.

Also...you should be able to find a non-tilt automatic collum for $50 or even less if you look around some salvage yards in your area. Tilt collums go for $200 and up...but you always could put in a van tilt.

You will also need tranny cooler lines, and a radiator with a tranny fluid cooler in it if your radiator dosen't already have a cooler tank (if it has ever been replaced, it proably does).

[Lobo'74]

Got the cooler covered. Just put in a 2 5/8 in thick 4 core "desert cooler" radiator. Has the caps for the tranny lines in place. Just waiting for me to change over...