Overdrive tranny in 1956 Cadillac?

I found this calculator on the 'net, and based on my calculations, my RPM at cruising HWY speed would be 1500RPM at 60MPH with a 700R4. Too low?? I figured to only use overdrive on the HWY, not in city streets. Which I drive less on.
http://www.angelfire.com/fl4/pontiacdude428/Hot.html

 

As far as I'm concerned, with a stock cam, you're going to get you best fuel economy right around where you have peak vacuum, which I'd guess in your Caddy would be right around 2100-2200 RPM. If you're gearing your Cad for highway driving, then you're going to want to pick a rear gear that when you're in OD, gets you to 70 mph at your RPM sweet spot. There you'd still be in your power band, but barely, so your Cad would still have enough power to maintain speed without really being under load, the fewest RPMs necessary given power/speed needs.

 

4l80's are electonically controlled, which means it's a paper weight, a very BIG paperweight at that, without the controller/harness. A stand alone controller is available but rather spendy. I believe that from '93 up, all 4l60's were electronically controlled, trucks may be the exception. I don't know when 4L80's were introduced, but they are NOT the same as a Turbo400. A 4l60E is a variation of the earlier 700R4.

You can get full manual valve bodies, but this wouldn't be very practical in a street driven barge like your Caddy. OK for mud-bogging or rock crawling, but would be a total pain.

You can very quickly ID whether GM transmissions are electronic or not by the wiring plug on the right hand side of the case. 4L60's and 4L80's have a large round plug with something like 20 pins. There are two VSS sensors on 4L80's, and only one on 4L60's, if you're shopping for a trans and don't know exactly what you're looking at. 4L80's are found mostly in 3/4 ton pickups, vans have 4L60's.

FYI the standard rear axle ratio for late model Chev/GMC pickups is something like 2.83's, they weigh 5,000 lbs, and the tires are much larger diameter than you're likely to be running, so I'm not sure that an OD trans wouldn't work for you. I just put an early 90's Roadmaster wagon Limited Slip in my '51, with something like 2.90's, it's much nicer to drive and gets WAY better mileage than the 3.75 stocker it replaced. It's got a 4.8L LS, so it's no torque monster.

Brian

either.

 

LOL, I don't think it'd be a GOOD swap either, I was just pointing out things to look for, if anybody IS thinking about a trans swap.

 

1955 the integral bell housing was removed, so 1956 up to 63 (dunno past then) does not have a cast in bell housing. Oldsmobile rockets up to 64 had the integral bell housing. Then they went to series two rocket engines without integral bell.

 

So how is the TH400 doing in the Bonnie?

 

Yes, the bell is coming in handy! Using on my project.

As far as the Dual coupling, well it has the same flow as the earlier dual range hydro, just done differently. The only element to slip in 4th is the controlled coupling, in third, main coupling. You have to remember that the main coupling is used in 1st and third, while in 2nd and 4th the controlled coupling byp***es the main coupling. (The engine is coupled to the front planetary, then it goes to the main coupling at a reduced speed. In 2nd and 4th the front planetary is locked to the main shaft via the controlled coupling. ( In the older versions, a multiple disc clutch does what the controlled coupling does.)

Conclusion, yes the DC has less slip than your 400, because of the converter. If you had a lockup clutch, then very little slippage.

 

What if I put a 350 4 bolt main from a pick-up in front of that 700R4? Same deal?
I know '93-96 Fleetwoods have a 2.93 axle ratio and weigh over 4500 lbs. and they have this set-up. (350 &700R4)

Lol! Sounds like I'm really determined to have OD,huh? Well...I am! You see, gas is well over $5.00 a US gallon up here, and since the drivetrain of my Caddy is gettin' tired, I may as well update it to be more efficient.
I'm planning to go to Viva Las Vegas with it next year.

 

Was that Roadmaster a station wagon?? My '92 Roadmaster sedan has a 2.56 rear gear. With less hp & torque than you have in the Cad it will deliver over 30 highway. It runs 75 all day at about 1800 rpm. 235/75 - 15 tires. If you put in a 700R4 use a 2.56 rear. Your engine will handle it easily. The TBI does have a lot to do with fuel economy.

 

An article I wrote about putting a 700R4 in our 59 Cadillac:
http://www.modifiedcadillac.org/articles/Cadillac_700R4/Cadillac700R4.html

Gary

 

This is odd...unless I did not do it right. I checked my rear axle ratio and it seems that it is around 1.52 to 1....is that possible? Cadillac offered only 3.07 and 3.36 ratios for '56. The diff looks original enough (only one wheel spins the diff)... I would think the car would rev too high on the freeway!
Any suggestions?

 

You certainly did not do it right.

 

That's what i'm figurin', but I did the check by spinning the wheel and observing the revolutions of the driveshaft and it spun 1.5 times per wheel revolution.

 

I work on many late model cars and trucks at the city and many hace tall gears and overdrive trans I say do it.I know many corvettes and camaros turn very low rpms and lots of mph.those cad motos have lots of low speed grunt. I have a 1991 v6 4.3 S10 blazer it weighs in at close to 4000 pounds it will pull overdrive at 1500 rpm.It wont speed up without kicking down but it will cruise there all day.

 

Spin the wheel then times 2 1.5x2=3.0 which is probally 3.07

 

Update.
I finally installed a 350 4 bolt main from a GMC, mated to a 700R4 transmission and stock torque converter. It turns out that the original rear gear ratio (3.07) of my '56 is compatible with this set-up. Car runs great, shifts fine! Overdrive kicks in no problem. Thanks everyone, for your feedback on this thread! It was very much appreciated!!

 

Update...I did a good run with the Cad on a 200 mile drive back & forth. No problems,none! And I was pleasantly surprised to notice that the car did over 20mpg on the hwy...on regular gas!! So, I booked a room at the Orleans Hotel in Vegas for next year's VLV. I'm drivin' down!
So note to all who have Cadillacs and want to swap a small block into it....DO IT! Car is not too heavy for the set-up.