not racing

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Mike Stevens

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At our morning 'lairs club' coffee meetings we discuss everything. I drove the 61 one day last week. The talk turned to my miles per gallon. The factory put a 3.77 rear end in the commercial chassis in 61. The NORMAL Cadillacs got 3.31 gears. The limos had I think a 3.53. I don't haul any weight other than suit cases and the gurney now. Several of our group think I could raise my mpg by installing a 3.31 or even lower number rear gear set. The questions none of them can answer is: Will a lower number gear set fit my present rear axle housing and axles? Would it really be worth the amount of time, work, and money to make the change? The coach only gets about 3500 miles per year. No winter driving for us here. Since I don't race the car I could get by without the almost neck snapping get away start I can get now. I mean this thing scales out at over 6300 pounds. How fast do I have to get away from a stop light or sign? With a numerically lower gear set I should still be able to run on the interstate and keep up. I am not sure I would see a big difference in the mpg here. 10-12 mpg seems to be all this thing will give up now. I an not sure an increase of one or two mpg would give me a return soon enough to be worth the trouble. So what are your opinions here?
Mike
 
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The limo differential is set up differently on the outside, and I don't know about the axles. The best way to know what will interchange is to get a Hollanders book and look it up. Personally, I don't think that it will make much of a difference, except for cruising comfort on the interstate. My Corvair Spyder turbo came with a 3.55 differential from the factory. At 65 MPH, the engine is screaming. I rode in one that had been converted to the 3.27 gear ratio, and it was noticeably different in the cruising noise at 65 MPH, but when you started off in 1st gear, it was a dog. The other downside, is that with the 3.27 gear set, the turbo doesn't kick in until you are at about 3600 RPM. Normally, it will kick in between 2800 and 3000 RPM. With the 3.27 gears, you might as well take the turbo off the car. I would have to believe that GM spec'd the gear set for maximum efficiency and power curve of the engine.
 
My 49 S&S has 4.27 gears (original) and is now running a 350 engine 350 trans, and screams down the highway. at 60 mph it runs right at 3,000 rpm. The fastest I have had the car up to is about 90 mph but never looked at the tach, but still had pedal to go. It gets about 12 mpg so changing yours, I dont think will make any difference.
 
i keep thinking about the old 59 I had that my buddy put the 4:10 in for me. we drove it back to calf from SD it turned 4 grand at 70 all the way.
if you hold the throttle down it will shift up at around 5 or above. for the mileage your driving if you got 5 more MPG how long would it take at 4 bucks a gal to recoup the money spent. your talking years. but you be lucky to get 3 and gas is 2.50. if I was going to try for milage I would go for one of the electric overdrives. you could put it on the front shaft behind the transmission. but it's still a 1000.00 bucks or better. they would give you a 11% drop in rpm let you keep the lower gears for power when you wanted it. and still be a easy trade back. but them 1000.00 bucks buys you about 400 gal of gas.
 
that sorta what I thought

Yeah, I think the better idea is to use the $$ on new paint. I hate to let go of the original finish but it is showing its 48 years. At least part of it is. I kept looking at the time and effort involved in the axle change and just could not get real excited about it.
Thanks,
Mike
 
I have seen some remarkable restoration of old paint with some of the new paint cleaning and polishing systems. Give it a try before deciding that it needs to be painted, unless there is surface rust showing. No polish will help this problem.
 
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