[Bryan Jensen]

Picking up my rebuilt rear end today!!! So excited . It originally had 3.36 gears with Safe-T Track, but I swapped them out for an Eaton Posi Carrier, 3.55 gears, Rear Disc Brakes, and Moser axles. The rumor I've been getting is that since I changed the gear ratio, I'm going to have overheating problems if I take it on the highway. Would a heavy duty radiator do the trick? I'm a long ways off from driving it, just don't want any surprises when I take it out for the first time.

[meanolgoat]

Did you have an over heating problem before you swapped the rear gears?

If you did not, why would now?

Changing the rear gear ratio from 3.36 to 3.55 ( if you have not changed the tire size) will increase engine RPM less then 200 RPM.

So if the engine was turning @ 3,000 rpm at 70 MPH with the 3.36 rear. The engine will be turning @ 3,182 rpm at 70 MPH with the 3.55 rear.

Yeah the engine is working a little harder, But you are not going to notice it much. Especially if it was all in good working order to start with.

[Cardo]

And i have been thinking about going to a 3:36 from my 3:55's so i could drop my highway rpm. If that's all you get maybe i should go to a 3:23.

[Phil Goat Nelson]

Originally Posted by meanolgoat

Changing the rear gear ratio from 3.36 to 3.55 ( if you have not changed the tire size) will increase engine RPM less then 200 RPM.

So if the engine was turning @ 3,000 rpm at 70 MPH with the 3.36 rear. The engine will be turning @ 3,182 rpm at 70 MPH with the 3.55 rear.

How did you figure this? Since my car turns about 3500 rpm at 70 mph, I must have some pretty tall gears.....how do I figure out what they are?

[meanolgoat]

I used a Calculator on Richmond Gears Website. As I did not know all the specifics, I Fudged the numbers a little (i.e Tire Size) But the results are accurate enough to get the idea.

Check out this link
http://www.richmondgear.com/101032.html

If that does not work, go to Richmond Gears website, and scroll down the left side you will see a link to "Gear & Transmission Calculators"

[merlotgoat]

Or you can do it the fun way--Jack up the back of the car (both wheels). Put the car in neutral and have someone turn the tire/wheel exactly one complete revolution while you lie under the safely supported car and count how many times the drive shaft turns completely around (put a chalk mark on it as a reference). If it turns 3 and a third times, you have the 3.36 gears. 3 and a half times and you have 3.55, and so on. If both wheels turn in the same direction, you know you have Safe-T-Trac (posi). If they turn in opposite directions, you have an open rear end. 3500 rpm at 70 sounds like you might have a 3.90 gears (just short of 4 complete drive shaft revolutions).

[Bryan Jensen]

Originally Posted by Cardo

And i have been thinking about going to a 3:36 from my 3:55's so i could drop my highway rpm. If that's all you get maybe i should go to a 3:23.

Hey Cardo...if you're interested in the 3.36 gears, I put them up in a box and are ready for sale if you'd like them. Absolutely no wear on them whatsoever.

[ER]

Originally Posted by Bryan Jensen

Hey Cardo...if you're interested in the 3.36 gears, I put them up in a box and are ready for sale if you'd like them. Absolutely no wear on them whatsoever.

If Cardo is not interested in the gears I am. You can PM me with an amount if you still have them. Thanks.

ER

[Phil Goat Nelson]

Originally Posted by meanolgoat

I used a Calculator on Richmond Gears Website. As I did not know all the specifics, I Fudged the numbers a little (i.e Tire Size) But the results are accurate enough to get the idea.

Check out this link
http://www.richmondgear.com/101032.html

If that does not work, go to Richmond Gears website, and scroll down the left side you will see a link to "Gear & Transmission Calculators"

The problem with that website calculator is that it doesn't reflect the transmission gearing......it must "assume" that the engine/transmission is running at a 1:1 ratio??? I think my TH400 in the drive gear is running at .7 to one.....if it had an overdrive (which I'm considering), then it would be running around 1:1, but without factoring that in the equation, this calculator gives very misleading results.

[merlotgoat]

The THM40 runs 1:1 in third gear. All transmissions in '67 (manual and auto) run 1:1 in high gear. The only thing that the calculator can't figure is converter slip, which is negligible at sustained speeds on level ground.

Here are the gear ratio stats for our transmissions -->http://ultimategto.com/cgi-bin/stats...967&f1=dttrans

[Phil Goat Nelson]

I don't know what I was thinking there.....actually, it must have been that if I installed the overdrive, THEN it would be down to a .7 to 1 ratio, somehow I got that confused with the standard gearing ratio

So, that calculator says I'm running about 3.87 instead of the 3.36 it had originally.....that explains a lot, I didn't think those cars turned that high when new!

[Cardo]

Yes Bryan, I'm interested. Gotta run out the door to work right now, send me an e-mail or if i don't hear from you, i'll get in touch with you tomorrow.