A Bad Rear End?????

Golden 68

Member

Dec 27, 2013

84

3

9

Hawley, Minnesota

Apr 21, 2014

#1

• Apr 21, 2014

• #1

Usually that is a beginning line to a joke, but not in this situation.

I have a 70 Boss clone that has a 347 stroker. The clutch is way shot so we pulled it and the tranny. We turned the wheels to get a guess on the rear end gears ...

279s ?? or so.

I am not very excited by that.

Can someone help me with this? Will this car be quick and fast? I am fearful it will be a dog at takeoff with those gears.

I am guessing I want like 355s?

Any and all thoughts, please.

My mechanic buddy said to drive it and see ...

Help?

 

horse sence

15 Year Member

Nov 29, 1999

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Wile Coyote's stunt double

Apr 21, 2014

#2

• Apr 21, 2014

• #2

Golden 68 said:

Usually that is a beginning line to a joke, but not in this situation.

I have a 70 Boss clone that has a 347 stroker. The clutch is way shot so we pulled it and the tranny. We turned the wheels to get a guess on the rear end gears ...

279s ?? or so.

I am not very excited by that.

Can someone help me with this? Will this car be quick and fast? I am fearful it will be a dog at takeoff with those gears.

I am guessing I want like 355s?

Any and all thoughts, please.

My mechanic buddy said to drive it and see ...

Help?

Click to expand...

With a 4 speed ,3.55 is a good gear ,2.79 would be good for freeway driving but would eat up a clutch driving in town just trying to get it rolling

 

Golden 68

Member

Dec 27, 2013

84

3

9

Hawley, Minnesota

Apr 22, 2014

#3

• Apr 22, 2014

• #3

Maybe that is why the first clutch was fried?

I just think it will be like trying to drive a fast car with the parking brake on?

 

Golden 68

Member

Dec 27, 2013

84

3

9

Hawley, Minnesota

Apr 22, 2014

#4

• Apr 22, 2014

• #4

Would you still try it first and see? Could we be off with our guess on gears?

 

Golden 68

Member

Dec 27, 2013

84

3

9

Hawley, Minnesota

Apr 22, 2014

#5

• Apr 22, 2014

• #5

I just checked the build sheet from matahari -- sp? and it says it was originally a 302 2v with 300 gears and a cruise o matic.

Does that say anything?

 

RacerJames

Active Member

Mar 21, 2014

165

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39

Kingman AZ

Apr 28, 2014

#6

• Apr 28, 2014

• #6

If it's an 8" rear end, (most likely with a 302 auto) then, to the best of my knowledge, the ratios Ford installed were 2.75, 3.00, 3.25, 3.50, and 4.10
A 2.75 ratio will give great highway mileage, and be doggy around town.
The 3.25 ratio I had in the '69 was great for all-around driving. I could run sub-14s in the quarter and get 19 mpg on the highway at 70 mph. That was with 23560R14 tires, a 351W 4v and FMX trans.

 

Golden 68

Member

Dec 27, 2013

84

3

9

Hawley, Minnesota

Apr 29, 2014

#7

• Apr 29, 2014

• #7

Thanks James -- can't wait to try it out!!!!

 

RacerJames

Active Member

Mar 21, 2014

165

23

39

Kingman AZ

Apr 29, 2014

#8

• Apr 29, 2014

• #8

More rear end tech courtesy Mustangsteve.com:

Rear End Ratio Selection
We are not talking economy here, just performance.
For a street car to be a strong performer, you need a torque multiplication ratio of at least 9:1. To figure this, multiply the transmission's first gear ratio by the rear end's ring & pinion ratio.
A C4 has a first gear ratio of 2.46:1.
An AOD has a first gear ratio of 2.40:1.
Example 1) 2.46 X 3.00 = 7.38:1 Torque multiplication ratio.
Example 2) 2.40 X 3.89 = 9.336 Torque multiplication ratio. (MUCH better!)
A Mustang with 26" tall tires, non-overdrive trans (1:1 in high gear), 3.00:1 rear end ratio, and travelling @ 60 MPH, will be turning roughly 2,326 RPM.
Given the same circumstances except for a AOD transmission change (.68:1 in overdrive), and 3.89:1 rear end gears, the same vehicle would be turning 2,051 RPM's! Rear end info provided by Steve Ainsworth - Thanks!

 

Golden 68

Member

Dec 27, 2013

84

3

9

Hawley, Minnesota

May 2, 2014

#9

• May 2, 2014

• #9

Wow! that is good information -- thanks!