it seems my RPMs are too high when driving on the freeway. which rear-end should i put in to bring the RPMs down. i don't have a tachometer, so i don't know what they are actually at it just sounds too high. i just dont understand axle ratios.
3:23-1 lower rpm and better mileage than a 3:91-1.. Less rpm at same speed... 4:10-1 is more rpm than 2:94-1.. Pulls harder from the start but less top speed and less mileage.. The numbers work as this: 4:10-1 the drive shaft will turn over four revolutions for every one revolution the axle turns... On a 3:09-1 the drive shaft turns three revolutions and axle turns one revolution.. So if you wanted a better top speed or (possibly) better mileage then install a smaller number gear... .
With a 3 speed transmission you should be turning around 3000rpm give or take a few hundred rpm at highway speeds. Are you sure it's shifting into high gear? There might be a tag on the axle or a vin plate with a code that can tell us what gears should be in there. We don't really know what transmission you have, I wondering if it's a 2 speed? OK I messed up and thought your car was a '53, so I edited this post out....
http://www.charlietranny.com/Fordomatic.htm Fordomatic also known as Mercomatic and Cruisomatic Was used 1951-68 in many Ford products. In 1953 for a three month period, they were used in Cadillacs after the Livonia, MI Hydramatic plant burnt to the ground. It was also used in some International and Dodge trucks and Checker Cabs. This was an hydraulically controlled rear wheel drive transmission. It had a cast iron case and either an aluminum or a cast iron bell housing. (I've included two explanations about how these transmissions worked. Both are by people that I highly respect for their knowledge of older units, but they do vary slightly.) 1. When Ford first came out with an automatic transmission, it was called a Ford-O-Matic. It was an iron case transmission. It started off in second gear and shifted to third in the D position. You could shift to L for first gear manually. In 1958, Ford started using a sprag in the planetary and called the transmission a Cruise-O-Matic. The D position next to neutral started off in second gear and made a shift to third, just like a Ford-O-Matic, and you still had manual L for first gear. But, using the sprag, there was another D position (green dot) that started off in low, shifted to second, and shifted to third, all automatically.
If your 1963 has a big V8, you could even get away with lower than 3.09:1, like a 2.73:1. The big HP V8 would guzzle gas in the city and in mountains, but she'd purr like a kitten on normal highways. Some big Ford/Mercuries had Positrack rear-ends at the lower ratios or really high ratios (4.10:1), and might be a fairly lowcost swap (whole rear axle). This might help for finding parts or tech articles: http://www.lovefords.org/ or here: http://home.bresnan.net/~dazed/clubs.html
And make sure your transmission fluid is good and topped off so that there isn't torque converter slippage.
This is a neat site. It shows the options and costs for 1962 Fords, and good details about the available tranny options, etc.: http://62ford.com/registry/options.asp
Yeah, there was a special cruising package. The old EBAY ad is gone, but his original Ad details the axle: Here, just below the Classified image: http://62ford.com/registry/classifieds_view.asp
Take a chalk. Mark the rear wheel (either side), as close to the treads as you can, and the driveshaft, so you can see from the same side. Raise the rear wheels off the ground, with the trans in Neutral, and count how many turns of the driveshaft to get ONE revolution of the tire. That should give you a rough Axle ratio. You could also read the Axle tag, if there is one, and then check it up on the LoveFords.org site. That Cruise 'gear' (mentioned in one of the articles) is probably about 70 or 80% of the Drive (third gear) ratio. What Andy said about fluid checks is a good Step One, though.
I had 3:42s in my Malibu with a 3 speed TH 350. It turned about 2600 RPM @ 60 mph. My Challenger had 3:55s and turned about 3000 @ 60 mph. My GMC truck supposedly has 3.06 gears and turns 2000 A 60 MPH.
The attached excel spreadsheet shows the impact of gearing and wheel/tire changes. It's very helpful when you are evaluating potential changes or - as in this case - when determining the existing details when you don't know all of the configuration details. Enter your vehicle information in the cells with the blue text (final drive/rear axle ratio, tire size and transmission ratios), then modify individual items to see the impact of your planned revisions. It will accommodate up to 6-speed transmissions. All you need to do is add the proper gear ratios to switch from a 3-speed w/o overdrive to a 4, 5 or 6 speed with overdrive ratios. I entered the 3.06 axle ratio and a top gear ratio of 1:1 (no overdrive). Then I adjusted with the tire size until I got approximately 2000 RPM at 60mph. To get those results, I had to use a tire diameter of about 30.16". To be turning 2000RPM at 60MPH with a 3.06 axle, your current tire diameter must be about 30.25". If that diameter matches what is on the truck, you can be confident that it is a 3.06 gear (or very close to that; I think 3.07 was the "economy" axle ratio for 1963 Chevy/GMC trucks). If your tire diameter is NOT around 30", you probably don't have a 3.06 rear end. I downloaded this from a website several years ago and use it frequently. Can't remember where I got it, but it is VERY handy.
Sorry, I think I got the vehicles mixed up...are we talking about the Ford or the GMC truck? With a 27.7" diameter tire, a 2.73 rear gear will turn approximately 1988 RPM at 60 MPH. If the Ford wagon is turning only 2000 RPM at 60 MPH, it probably has a 2.73 axle. Best way to be sure is to count driveshaft rotations per 1 tire revolution (as described by stormin norman) or count the ring & pinion teeth. Divide the number of teeth on the ring by the number of teeth on the pinion and that's the ratio.
My GMC truck has the 27.7 diameter tires. I know the best way to find out is to drop the cover off the rear end. Just haven't done that yet. Not my favorite "messy" job.
