best gears?

[rowingone]

I have a SB 64 with a 4spd and 308 rear . . . what rear gear is best for all around driving . . how do I tell if I have posi and if I have a close ratio 4 spd and is 4th gear that much different between the close ratio and std tranny to affect my rear end choice? Can you quantify the difference for me between say the 308 and a 355 or 370 in terms of driveability and performance?

 

[rowingone]

Yeah that helps . . . I figure the most bang for the buck in terms of acceleration would be to change the rear end .. . I"m definately going to make the change but have no feel for whether the 3.36 or 3.55 would be better .. . at 75mph with the 3.55 what kind of rpms would I be turning?

 

[66427-450]

the keisler web site (see below) has a good RPM/Speed/Ratio calculator, just go to the address below and page down when you get there.



asking what gear is best is a loaded questions..... some guys are pulling 3.36's to go for 4.11's, others pulling 4.11's for 3.36's. I'm a 4.11 type guy all the way.

you say "all round driving"? the questions is do intend to do a lot of freeway driving? or do you truly value performance 0-120?

freeway = 3.08 or 3.36
performance = 4.11

the 3.55 and 3.70's with do both, but not optimum for either.


http://www.keislerauto.com/gm/transmissions/corvette_63-67.asp

 

[Ron Miller]

I have a SB 64 with a 4spd and 308 rear . . . . . how do I tell if I have posi

An alternate method is to jack up one rear wheel and with the transmission in neutral (and the emergency brake off), try to turn the rear wheel by hand. If it turns freely, no positraction. On the other hand, a wheel on a car with the positraction rear differential can be turned by hand, but it takes several foot-pounds of torque to do so. Make sure you're on level ground with the wheel on the ground chocked before you do this, for safety's sake.

rlm:cool

 

[allcoupedup]

Along those same lines...

If you turn one wheel and the opposite wheel turns in the opposite direction you have a non-posi or a broken posi. of one wheel stays put while you turn the other - same thing.

Take a look at the bottom of your differential - look for a code like this:

I have a '65 but the rear end numbers say is a '63 non-posi 3.36:1 which seems to be true.

This will tell you what was originally installed. Post the numbers and we can help you out. Keep in mind that just about anything can be in that case!

Another thing - you can determine your ratio by couting the ratio of driveshaft revolutions to tire revolutions. If you have a non-posi rear end, you will need to multiply the number of tire rotations by two.

Brian

 

[rowingone]

A O W(?) 064 There is a middle mark that I cant tell if its a "w" or what . . . I was told by the previous owner that the rear end gears had been changed to 3.08s and thats obviously not the stock rear end as the speedo is off quite a bit.

 

[rowingone]

I must have misread that . . . must be CA . . . which would be nonposi 3.36 right?

 

[rowingone]

How difficult is it to change the rear end gears?

 

[Tom Bryant]

In 1964 the 250 and 300 hp engines used the wide ratio. The 365 and 375 FI used the close ratio. Both M20 and 4th is always 1:1 in a 4 speed Muncie. A very popular combo in the day and still today for driver midyears is the 327/300, 4 speed and 3.36 rear. I had a '65 convert like this. With origional size tires you get 3000 rpms at 70 mph (both tach and speedo needles point straight up :cool ) plus it's easy to get going from a dead stop.

For a good selection of online calculators to figure most anything you need there is no reason to leave the CAC site. Go to the top of the page and click on "Tech Center". Then Click on "Tool Box". They are all there.

Tom.

 

[Tom Bryant]

How difficult is it to change the rear end gears?

If the pinion depth and ring gear backlash aren't set perfectly you can eat the gears in just a few short miles. I once had a self proclaimed "Pro" set up my rear end on the '59 and it lasted less than a week. It howled almost immediatly and when I took them back out the gear teeth were as sharp as razor blades.

I suggest that you have a real professional rear end shop or someone that is highly recommended set it up and use all new bearings while you are in there. Also never try to swap in a used gear set. It is impossible to duplicate the origional ware pattern and that spells disaster.

Tom

 

[rowingone]

Thanks Tom . . sounds like a job that dont want to mess with!!

 

[Gerry]

best rear gears

I have a 67 BB with 3.36 rear gears, M20 and 235x60x15 rear tires. 60 mph is approx. 2450 rpm. There is lots of torque in the BB so it moves but I will eventually pull the trans and install a kreisler 5 speed and get the best of both worlds. I recently drove a small block with the 4.11s and really liked it around town. However, driving on the highway at even 60 was abusive. So drop $3000 and put the 5ver in and enjoy. No one but you need know the truth.

Best regards,
Gerry

 

[magicv8]

I had 4.11s and a th400 in the car when I got it 17 years ago - switched to 3.36 rear with a 2.2:1 1st gear Muncie - for two years - poor gas mileage - and I don't like sleeping at WY and MT gas pumps waiting for the station to open.

I switched to 3.08 rear and 2.5:1 1st gear Muncie - with the result being like the 3.36 and 2.2 low setup in the first three gears - and 4th gear feels (and lack of noise sounds) like overdrive I have used that setup for the last 14 years

 

[Tom Bryant]

What kind of mileage do you pull with the 3.08s? I used to get 18-18.5 with the 300 horse and 3.36s. I had a friend with a '64 of the same combo and he did the same. This was back when Indiana interstates were 70mph and you could get leaded premium.

Tom

 

[magicv8]

On a highway, I normally average 75 mph and I get 19.5-20.5 depending on my right foot and head/tail winds.

Headed west where the limits are higher - around 19 - but up mountain and into a headwind with the A-C running it can drop to 16.5 at 80-85mph - which is normal for being headed west into the Rockies on a hot summer day in WY or MT. That speed and load will also tilt your temp guage - unless you have made serious cooling system alterations.

 

[396 RAT]

With your ratio 1st gear, I would say 3.36 or 3.50 Tops.
(any higher and your 1st gear would turn into a granny gear)
I am running 4.11's with a close ratio 4 spd. Lots of fun!
(But not for long trips) I dont want to go on long trips anyway.
But my ideal set up is the close ratio 1st with a 3.70 RR.
(like my last 65, 365hp had)
Its really a personal issue. But some combinations simply should be avoided based on your trans. Below 3.36 with a close ratio
4 spd turns 1st into a dog. Or over 3.50 RR with a wide ratio 4 spd
turns 1st into a granny gear.
Just my opinion.

 

[Islander]

So, assuming we keep the tire diameter around 26.5" (stock-like) and add a 5-speed Keisler tranny, which rear-end gear is not going to render 1st gear useless and at the same time not pierce my ears during highway cruising? I assume 3.08 and 4.11 are out.

I went to the Keisler site where they have the calculator but that does not give me feedback on actual practical performance. Any feedback from the users on this?