The Stovebolt Site Forums The Shop Area Driveline Open Vs Closed Driveline

Ive heard alot about having an open driveline or closed driveline.

What does this exactly mean? And whats the benefit of either?

'54 and older had the closed driveline. The actual driveshaft and u-joints were inside of a tube that ran from the transmission to the rearend. Starting in '55 the open driveline was used. It's what is used today with the driveshaft and u-joints exposed. Advantages are open to personal opinion, so here's mine. I hated closed driveline. Keeping a truck truly original is the only advantage in itthat I can see. With the open system you have the advantage of being easy to work with, but you lose originality. I guess it all boils down to what you (the only that really matters anyway) want to do with it.

Before 55 not all trucks wee closed driveline.
The 1 ton and bigger are all open.
There was somethinig fishy with 3/4 tons, what are the details on that?

Grigg

A closed driveline is just that closed. Old chevy trucks are closed. commonly known as a torque tube. these have limited gear ratio choices. stock- and patrick's 3:55.1 is about it. the U joynts are on the small size. thus stock rear ends limit a trucks drivability to 50's (miles per hour) on the freeway.

Open drive lines have no enclosure drive tube, both U joynts are exposed allowing them to be serviced when needed. the rear end has many different gear ratios available and there is a cover that can be removed for changing gears and maintainance work. 10 and 12 bolt 5 and 6 lug rear ends are a common switch for 3100's learn to do a search on this web site as there is tons of info.

good luck and welcome to this site.

I've not seen anything in writing about this but I believe the reason manufacturers produced the enclosed drive shaft was to protect the moving parts from the dirt roads that were so common back then. By the mid 50s most highly traveled roads were paved.

SO If i wanted to convert a 54' Chevy 3100 from closed to open driveline, where could I get a driveline that would match up?

I drive my 1954 1/2 tons at 60-65 mph with no problems. It will be even nicer with the 3.55 conversion.

There is only one u-joint in the enclosed driveshaft (called a torque-tube) and they last OK (as long as the bell contains lubricant).

"Longbed" 3/4 tons (and 1/2 ton longbed GMCs) had an open driveshaft but had a small enclosed link/shaft between the transmission and the open driveshaft (47-54).

Torque Tubes from ChevyTrucks.org

Closed Driveshafts Forever is a Tech Tip on Jim Carter's Site (Tech Tips, 1947-55, Mechanical, Closed Drive Shafts)

Since the 1955.1 series is basically a 1954 and earlier design, does this mean that it has an enclosed drive line too?

All sizes of 1955-1st series trucks had open drive shafts.

TCLEDERMAN,

MY 1953 GMC 1/2 TON LONG BED HAS AN ENCLOSED DRIVE SHAFT SYSTEM. I BELIEVE THE OPEN SYSTEM WAS FOUND ON THE 3/4 TON AND ABOVE.

From what I have seen on the 3/4 & up trucks, the driveline is closed to about halfway to the rear end, then it is a regular open drive shaft that goes to the rear axle. It looks confusing.

FIRST Learn to do searches ..................

do a search in the driveline section on rear ends

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=013343;p=1#000002

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=013386#000000

The closed drive line with torque tube driveshaft cover was quite common in most cars and light trucks from the beginning (early 1900's) until the '40's and '50's, most manufacturers changed to the open drive system in the early '50's, F**D changed in 1949 but Chevrolet hung on until 1955. There are advantages and disadvantages to both systems. All cars and trucks are now equipped with open drive lines, so if you plan to use a late model drive train you will use open drive. I used to drag race Chevrolets in the '50's and enjoyed the closed drive line because you could floor the gas pedal and then step off the clutch for a great launch. In order to do that type of launch you have to spend a lot of time and money preparing an open drive line to accept the shock forces generated. Such things as 4 bar suspensions, anti spring wrap up bars, etc. were products of overcoming the problems with the Hotchkiss suspension, that is mainly spring wrap up and rear end squat.

Nope, it's open.

A little more. Some manufacturers continued using torque tubes into the 60's. Look under an early 60's Rambler as an example.

And in the 80's GM started using a variation of that approach in performance oriented rear-drive cars. Look under a Firebird or Camaro of the era, or all Corvettes starting in '84.

There are advantages to the torque tube approach, but for most of us with with old trucks its a trade off between originality and the ability to choose the rear gears and transmissions we want. The torque tube severly limits your choices.

A torque tube has the advantage of putting the driving thrust near the center of the car, instead of pushing it along with the rear springs or torque links as an open driveline does. Ford began using enclosed drivelines with the Model T, and continued the practice through the 1948 models, including Lincoln, Mercury, and at least some trucks. Chevy passenger cars and small pickups used closed drivelines until the mid-50's, as others have documented. American Motors used that system until 1965 or so, IMHO.
Jerry

Buick too!

Stuart

A '55 first is the perfect swap option for an AD. If you have the transmission, driveshaft, rear end and springs they will bolt right in with no other mods.

The only other advantage of an open driveshaft I can think of, apart from those already mentioned, is that of a theoretical ride improvement. Studies of mechanics have shown that the greater the ration of sprung weight to unsprung weight, the smoother the ride.
For the torque tube drive system, essentially all of the differential /torque tube/driveshaft assembly is unsprung weight. For the open driveshaft, the driveshaft contributes little if any to unsprung weight. I suppose the trailing arms contribute a small amount.
meansam

meansam,
I don't agree with your explanation of the difference between sprung and unsprung weight and torque tube or not.

Not all of the torque tube is unsprung weight, Actually only a portion of it is, and a portion of it is not, as it is nearly fixed. So to simplify things lets say that a certain % of the torque tube is unsprung weight.
The same thought applies to the springs, as part of the springs move with the axle, and part stay almost still, so a fraction of the spring weight is calculated with the unsprung weight. Clear right?

So, the drive shaft will follow the same rules, and part of the weight of the drive shaft can be added to the weight of the axle for unsprung weight, same as the torque tube. Thus, there is no advantage or disadvantage when it comes to sprung and unsprung weight and torque tube or open drive line. If the drive shaft weighed less than the torque tube it replaced then I suppose you could say drive shaft is better, but I think that the weights of each system are very close, so the supposed advantage is negligible.

Grigg

I hadn't thought of that aspect, but I think you'd need an engineer with a slide rule (showing my age!) to determine just how much of the torque tube was sprung versus not and how much of the driveshaft ends up as unsprung weight.

Unsprung weight also has a significant impact on handling and that would be another consideration.

And of course in the case of a IRS with a torque tube (C5 or C6 vette) you aren't going to have any unsprung weight from the driveshaft. There is one guy I know of who was talking about building a hot rod Task Force pickup on C5 stuff, so it does have some connection to old trucks. I don't know if he did it or not and I've not seen any pictures.

Grigg,

I have a 1940 1.5 ton with torque tube, so they were definitely not all
Open.

The 1940 Specifications Manual shows all sizes had a torqe-tube.

If I am reading that incorrectly, please let me know.

12 years later you point out a guy's error? No statute of limitations on the Stovebolt page!

Here is a pic of my torque tub axle currently under my 1940 1.5 ton. [img]https://www.stovebolt.com/ubbthread...B489F25-9B9B-40EE-9CFF-72FB29DE2A76.jpeg[/img]


For some reason I could only link to the pic I uploaded and not able to insert it.

I used the search function as is always recommends here. I don’t get a lot of results for converting a big bolt torque tube over to open driveshaft.

I have a 1979 nova rear end on my 1954 3100 but you will have to have a custom driveshaft made or get lucky like did. There are some other issues like the width of the springs, wider on newer cars and trucks. All are feasible with time and money. I believe it is worth it. I have 33,000 miles on the truck since being modified.

Hot Rod Lincoln explained it the best. The torque-tube is a different method of "driving" or propelling the vehicle. The enclosed drive shaft tube pushes against a bracket that's mounted to a crossmember in the truck frame at the rear of the transmission. The driving forces push against the vehicle near it's center, as Jerry wrote, rather than thru the springs. That's why the spring brackets have swivels on 3100s and Chevy cars. The enclosed front section of the drive shaft on 3/4-tons is a mystery. I think it was made this way so Chevy could use the same transmissions in 1/2-tons and 3/4-tons. Maybe not.