'69 Fleetwood Now Has 3.21 Gears

[Fleet 500]

Well, I found an auto yard in North Carolina which had a '69 Cadillac Fleetwood Limo. I was interested in the 3.21:1 rear axle ratio which was standard on the limos.

I contacted the place and bought it via credit card. The rear differential carrier which includes the ring and pinion I want. I made sure it was the correct gearing- it can be identified by the number stamped on the outside of the carrier. A "1" means 3.21 and a "2" means 2.94. The rear carrier weighs 90 lbs, incidentally.

Anyway, the car was ready today and I drove it home and was comparing this ratio with the former 2.94s.
As expected, I did notice a difference in hill climbing. I drove it up a steep hill in my neighborhood. With the tall 2.94 gears, it is best to leave it in 2nd gear; with the 3.21s I noticed it was revving more than necessary so I shifted into 3rd about halfway up the hill and it felt okay. No strain or anything; I was going about 40 mph.

I did one 40-60 mph test. Actually, it does it so quick it's kind of hard to both drive, watch the speedometer and time it. With the 2.94s, 40-60 was right around 4.0 seconds; with the 3.21s I got about 3.7 (which is what Car & Driver got with a '64 Sedan de Ville with 429-cu-in engine and 3.21 gears).
The weather was not ideal for acceleration tests... it was hot and I noticed a slight pinging at full throttle so backed off just a bit. Next time I will try it at night when it cools off more.

For those who are interested, here is an article about gear ratios. I is from way back (Motor Life, July, 1958) but what is written would apply to most American cars from the 1960s and '70s.

[roosterjuicer]

nice work sir...i think youll really like the change

[Fleet 500]

nice work sir...i think youll really like the change

Thanks.
Yeah, the car won't feel as "held back" as with the former gears. I could sometimes tell the tall ratio was holding the car back; the engine is making ample power, but that high ratio (numerically low) keeping it from revving up to where it makes its maximum horsepower.

Keep in mind that 3.21s are hardly the ratio for drag racing (but certainly an improvement over 2.94s!). It could be worse, though, the '75-'76 Fleetwoods had a ridiculous 2.73:1 ratio and it went even higher by the early '80s (2.28:1).

[johnnynumfiv]

Did you get your speedometer calibrated?
I can't believe how numerically low those gears are. We use 6.00 or 6.10's in the race car. :P

[Fleet 500]

Did you get your speedometer calibrated?
I can't believe how numerically low those gears are. We use 6.00 or 6.10's in the race car. :P

Yeah, I'll probably have to get the speedo recalibrated. I know where there is one of the digital "current speed" things on a local street. I will drive by that and do a quick check that way.

I know... 2.28 gears are ridiculous. Just imagine how those would hold back a car going up a steep hill. Even in 1st gear.

I've heard of muscle cars using ratios like 4.88 and 5.38. Didn't know they went up into the 6s. Except for the '56-'57 Chrysler 300-C... an incredible 6.17:1 ratio was actually available at extra cost.

[johnnynumfiv]

The 6's are aftermarket racing gears, those are for a chevy rear in the stock car. My MG has 5.37's, which are just insane.

[Fleet 500]

The 6's are aftermarket racing gears, those are for a chevy rear in the stock car. My MG has 5.37's, which are just insane.

Yeah, 5.37s are really deep gears.

I drove by one of those speed check things (a solar-powered readout which shows the speed of cars going by).

At 50 mph, the readout said 42 mph. So the speedo is showing 8 mph faster than actual. Which is what I guessed; I figured it would read 8-10 mph high.
I did the 40-60 mph test allowing for error; I did 45-65 mph.

[digitalcraft]

Its usually off by a percent, not a static number, isn't it?

[Fleet 500]

Its usually off by a percent, not a static number, isn't it?

Yeah, I think so. I just tested it at one particular number (50 mph).

[f6fhellcat13]

in hignway crusing is it significantly louder? and how does it effect fuel economy?

I noticed a slight pinging at full throttle so backed off just a bit

i think that means the fuel you're using inst high enougnh octane, but im not sure.

[Fleet 500]

in hignway crusing is it significantly louder? and how does it effect fuel economy?

Not much different with noise. It is revving a little more. According to a Motor Trend test, with the 2.94:1 ratio, it does 98 mph at 3500 rpm. Another test of a '68 DeVille (same engine and axle ratio) shows 70 mph 2450 rpm. So with the 3.21s it is doing 70 mph at around 2600-2700. Certainly in a comfortable range.
As for fuel economy it will use slightly more with the lower ratio, mainly on the highway. I don't expect to see much of a change driving on the surface streets. I refuel once a month, on average of which I only put $25 to $30 worth... 6-8 gals. I keep meaning to do a check on mileage but when it's driven only once a week (sometimes twice a week) it's easy to forget. A few years ago, it was averaging 11 mpg.

i think that means the fuel you're using inst high enougnh octane, but im not sure.

Well, I am using premimum (91 octane), a lead substitute and octane boost. It works okay except on really hot days. The problem is that these cars were meant to run on 1960s premimum fuel, which back then meant about 98 octane. Back then, 91 octane was "regular" fuel!

[johnnynumfiv]

Lead substitute isn't worth putting in. We've been having a lot of street/strip cars at the track blowing motors because of junk gas. They have to run half premium/ half racing fuel now.

[Fleet 500]

Lead substitute isn't worth putting in. We've been having a lot of street/strip cars at the track blowing motors because of junk gas. They have to run half premium/ half racing fuel now.

I use lead substitute to keep the valve seals lubricated. The engine doesn't have hardened valve seals (that began in 1971).

[johnnynumfiv]

It still doesn't make a difference.

[Fleet 500]

It still doesn't make a difference.

Cheap insurance to have "just in case."