I have a 1963 with the original motor and transmission. The car sat for along time before i had it. Im planning on rebuilding the 390 this winter and I'm considering having the transmission rebuilt or swapping it with a 4 speed. I would prefer to keep the Original but I'm looking for cursing speeds around 70. and I'm not sure if the stock transmission rebuilt is going to give me that. Any advice or anyone done a 4 speed swap on a 390?

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I cruise my 63 on the freeway/highway all the time. It will easily  cruise at 70 mph, all day long. These cars were designed to hit the road and travel, I wouldn't worry about a stock 63 or 64 in good mechanical condition keeping up with todays highway traffic. The 63 has a 4 th gear ratio of 1:1.  Formula for drive shaft RPM which would be engine RPM in this case, MPH x 336 x Diff. Ratio divided by tire height = RPM of drive shaft.

My car has 225/75/15 Hankook tires. According to their web site, my tire is 28.3" in diameter. I have a 2.94 differential. RPM @ 70 MPH would be calculated; 70 x 336 x 2.94 / 28.5 = 2443.4204 RPM @ 70 MPH. That is close to the same RPM my pick up is running at 70.

David , 

Thanks for the info, I guess now i just need to find a trust worthly transmission shop. Should I look for a shop that specializes in cadillac transmissions? Or will any reputable shop be able to handle the task? 

These cars were built to run at 70 miles an hour all day long when they were new ,and for 80--100,000 miles in those days
Super reliable ,road machines
The question is how NEW is your Antique Cadillac ,to be used in that fashion on a constant basis
I have the good fortune to have a 64 convertible with he top down , turn the
key to go anywhere ,kind of thing
I really like a lot what my 64 is all about

Nic, As David pointed out the Hydramatic is a 4 speed transmission. Also, there is no indication of current condition of transmission. If it is shift fine thru the gears with fluid topped off, and it looks nice and pink red, and no brown or burn smell I would replace fluids, filters, and gaskets and seals if needed.  If transmission needs rebuilding you might reach to those other CLC members in WV area with similar transmission (I see 3 in the CLC directory) and see if any can recommend a good hydramatic rebuilder. Also, any other local GM brand car club members may be able to point you to a good rebuilder in your area.  

Thanks everyone for the feed back, Jason the car runs ok now it starts up every time i want to drive it. Although there is some indications that i feel its going to need a rebuild. The car has trouble shifting from first to second if its under load(my foots smashing the pedal). Im guessing that it also isn't shifting into fourth because when I'm doing 65-70mph its turning at high rpm. The engine has also developed a ticking that sounds like its coming from the heads. I'm pretty sure something is tapping the valve covers. i haven't removed the covers yet to see whats going on, but I've have the car for three years now and i think an over haul on the motor and transmission would be doing her a favor. Thanks again for all the help i love that i can get on here and so many people are willing to help and with advice. Ill keep progress posted

 

I agree that the stock tranny will hold up for todays travels. 

I did the math for my Hearse, with a 3.77 rear end  3111 rpm at 70. Gas mileage is going to be terrible, but the rpm is a doable range.

Nic, the transmission is commonly called a Jetaway by the transmission folks. Just be sure the shop you choose is familiar witht the Hydra-Matic or Jetaway transmission. Cadillac, Oldsmobile and Pontiac all used a version of this transmission for many years. There are several sources for rebuild kits and parts, FATSCO Transmission is one I have bought from.

Concerning your shift issue, you may need to adjust the TV rod to smooth out the shifting. First to second is noticable but smooth, the second to third will be more noticable and almost like a hesitation while third to fourth will be so smooth about all you'll be able to hear is a lowering of RPM. Light throttle, you'll be in 4 th gear by 35 MPH.

thanks ill check the adjustments first and see if that helps. 

These engines only turn RPM in the mid 4,000 range ,so they are never really turning out a lot of RPMS ,unless your foot is stuck in the carb ,and you are being very hard on the drive train
The drive shaft on these cars can be a problem if you are hard on it ,and getting difficult to find
If you drive the car hard ,best to do it from a 20 mile per hour roll
These cars with all there weight are very strong from 20 MPH and up
A dead stop launch ,can alway be very hard on any car ,but our weight factor counts here
I only had my foot to the floor ,from a roll once in 35 years ,to check for pinging of the gas
Reminds me that I raced a few of the local hot rods in my Dads 55 convertible, back in the day from a roll, and won

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