Thread: suggestions for rear end gears

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Well the seal in the 55 rear end is leaking so I figured I will change the gears while I'm at it . Cruzin down the road at 65 mph and taching around 3000 has got to go , @ 2.00 a gallon its time for a change.
I'm not sure whats in it I'm guessing a set of 300's. Any recomondations? I'm not going to race it , I want to get a little bit better gas milage and still have a good street set up. 3:55 or 3:73 maybee?
What are you guys using and how do you like the set up?
Thanx
Cool

Originally posted by cool55belair
Well the seal in the 55 rear end is leaking so I figured I will change the gears while I'm at it . Cruzin down the road at 65 mph and taching around 3000 has got to go , @ 2.00 a gallon its time for a change.
I'm not sure whats in it I'm guessing a set of 300's. Any recomondations? I'm not going to race it , I want to get a little bit better gas milage and still have a good street set up. 3:55 or 3:73 maybee?
What are you guys using and how do you like the set up?
Thanx
Cool

Don't know what your tire size is, but I'm guessin' you have 4:11 gears @ that RPM/Speed? That's about what my 56' tacked out at with 4:11 in it. That's if it is the original rear. If it's a 10 bolt or 12 bolt upgrade it's problee' 4:10.

3:55 would be a good relpacement or maybe a little taller still if yer' not worried about low end performance.

Since I have a very stiff 2.79 8" rear gear in a roadster I have not run yet and you seem to think a 3.55 is a reasonable ratio. Can I just find a 3.55 "pumpkin", slide out the axels and replace the full pumpkin without rebuilding the ring and pinion (assuming a good 3.55 pumpkin)?

Don Shillady
Retired Scientist/teen rodder

Here's a chart that will help you figure out where you are, and where you might want to go.

http://www.metropartsmarket.com/rearend/ratio.html

That's why I like my 700R4 with 3.73's. Killer first gear - equivalent to 5.20's with a close ratio Muncie. Then cruzin at 2000 r's at 60 MPH, 2500 at 75. Overdrive rocks.

I have 2:89's in my '55. It's looking like 18mpg give or take and 60mph around 2000rpm. I can still fry them off extensively

I had 3:55's in the 72 goat a few years back and with 28" hoosiers on it it got decent milage and very liveable cruise RPM and still had great seat of the pants acceleration.That was with a muncie close ration 4-spd though,not sure what trans you are runnin.

Maybe something in the 3:23-3:31 range would suit you better if you have a 3 speed.

BG