Can someone please explain to me: Open drive vs Closed drive rear

I'm really showing my newbness with this here. I have no idea what the difference between open drive and closed drive rears are. Can someone enlighten me? The reason
I ask is because I'm putting a T5 into my 49 Chevy truck at some point and I know I need to switch to an open drive rear. But I have no idea why.


Thanks!

 

Hope this helps.

http://en.wikipedia.org/wiki/Drive_shaft

 

nope. not at all. it doesn't explain the difference between open and closed.

 

A closed driveshaft looks like this-the torque tube is a large, hollow tube that is attached (fixed-it doesn't move) to the rear end and the transmission-it physically ties them together. The drive shaft is a seperate piece, inside the torque tube. The torque tube does not rotate-it is instead a part of the rear suspension. Someone much smarter than me will tell us what it does. An open drive shaft is the most common-it serves no function other than to transfer power from the trans to the rear end and "floats" (slides) back and forth a little on the spline trans shaft as the rear end move up and down. Hope this helps. The reason to change is almost always due to the fact that old cars had high gear ratios and new transmissions are made to work with open drive shafts.

 

Your truck uses and enclosed driveline with a torque tube.
This means the driveline and balls from the transmission to the rear end are all enclosed in a "tube".

Open drivelines have a sealed gasket from the tranny to the u joint and the driveline is open with the same application at the rear to the diff.
Open drive lines make it very easy to switch out any of the components by seperating them at the u joint.

Closed drive lines, not so much...

 

belair,
We must have hit send at the same time.
Nice explanation.

 

This is a " CLOSED " driveline ...



The driveshaft runs inside the big tube ...

This is a " OPEN " driveline ...





The driveshaft does NOT run in a enclosed tube.

 

I am by no means an expert but I will take a shot at this. Closed drive rear refers to the drive-shaft configuration. The early Fords have a torque tube that surrounds the drive shaft which runs inside the torque tube. Because these Fords have buggy springs - the "push of the rear wheels is done thru the torque tube transmitting power thru the trans case - then the engine block - then to the frame up front via the motor mounts.

In an open drive - the power is transferred thru more modern parallel springs or other suspension/ rod arrangement to the frame at the rear - therefore the drive-shaft is "open" with no need for the tube arrangement.

Hope this helps - fellow HAMBERS feel free to trash my explanation.

 

Now I'm curious because I could swear my truck has a driveshaft that spins when the truck is on. Picture time. sit tight while I go snap some pics.

 

Hi synthsis. Belair pretty much explained it. Maybe I can add a thing or two. First thing is, don't confuse the word "open" with an open differential vs a limited-slip differential. You know...posi-traction...that is a GM term for limited-slip differential in the rear axle. The "open" type differential is not limited-slip, and only turns one tire at a time...generally, whichever turns easiest. OK, that outa the way. The "closed" driveshaft you refer to is commonly called a "torque-tube". As Belair stated, there is an outer heavy-duty tube that is solidly attached to both the tail-shaft of the trans, (the cast outer portion or "case" or "housing") and the rear axle housing...it does not spin. It is a major link that controls the movement of the rear axle. Inside of it, is an actual driveshaft similar to what you see on modern cars. It spins, and transfers the torque from the engine and trans to the rear differential and axle. Take a good look under your car, and you'll see that the trans and rear axle are solidly connected by the touque-tube. Because of this, you can't just drop the driveshaft to remove the trans as you would on a modern car. You have to either loosen the rear axle, and move it back, or more likely, pull the engine and trans together or the engine first, and then the trans. Good luck with your car!

 

ok, no pics needed, its definitely closed. There's no U-joint at the rear, just a tube going into it.

 

If your '49 Chevy truck has a driveshaft that you can see turn, it has already been modified. Good job, Deuce Roadster...pics help!

 

We have a winner!!! It all has to do with how the torque pushes the car down the road. As 39 says, The wheels are pushing the torque tube which is pushing the engine which is pushing the car.........
This is why a parrallel leaf spring is used when converting to open drive shaft.

 

This image from above explains everything. The two rods in the pic that are enclosed in the plastic bags run from the top of the differential to the frame of the car. They stop the differential from spinning back when the wheels put rubber on the road. You can understand, that when the real wheels spin, they will force the differential to "pop a wheely" like your kid does on his bicycle. In cars, it's the differential that pops a wheely. The torque tube's only job is to prevent the differential from popping a wheely and the Hotchkiss drive does it a different way, it bolts the rear axle to the leaf springs to stop the differential from popping a wheely. Now do you understand? Look at this pic at the 2 rods that stop the differential from popping a wheely. Because of them, you can use an open drive.

 

One or 2 slight corrections. A closed drive or torque tube drive, has one universal joint at the front of the drive shaft and a ball joint or trunion joint where the torque tube attaches to the frame crossmember. This is where the push is applied to the frame. With an open driveshaft the push goes through the leaf springs or in the case of coil sprung cars, through the links or rods attaching the rear axle to the frame.

And, if you can see the driveshaft spin, it's open drive. If the driveshaft is inside a tube it's closed.

To answer the original question - why do you need to change the rear axle if you change the transmission - nobody has used torque tube drive since 1960. All modern transmissions are open drive. To use one on an old car that came with torque tube drive you either have to change the rear axle, or adapt the back of the transmission to torque tube. Changing the rear axle is easier and cheaper, and has other advantages like more modern brakes and hiway friendly gear ratio.

 

Some of the earlier trucks did have an open driveshaft, that converged into a torquetube setup, but I thought that was on "bigger" trucks; somewhat like a two piece driveshaft with a support bearing in the middle (Chevette's are very similar). The good thing about having a truck, and not a passenger car of the same era, is trucks used the later style transmission-to-bellhousing mounting pattern; passenger cars used a smaller patter (until 1955 when they changed to the bigger pattern). So, you can bolt any newer 1955 on on manual transmission to the truck bellhousing (Muncie 318/319, Saginaw's, Muncie's, Borg-Warner G.M. T-10's); but, then an open driveshaft and rear end has to be used. As far as the T5 transmission goes, you may have to shorten the pilot bearing shaft, although I'm really not too familiar with that transmission. Post those pics so we know what you actually are working with. I am Butch/56sedandelivery.

 

before we start waiting for replies from the original poster, 9yr old thread and OP hasn't been on here since 2013

and here I was finding pictures of my closed rear!

 

Almost all AD trucks have an enclosed Drive shaft. I am not sure about the first gen '55 Chevrolet they still used an AD truck body.

The exception to this is the bigger AD trucks. The 3/4 ton up had a partially enclosed driveshaft. But that is fodder for a different discussion.

Basically if you don't see the drive shaft or the U joints it is an enclosed drive shaft.

If you are looking for an open rear the 10 bolt from a 90s Trans Am is nearly a bolt in and gives you the disc brake option.

 

This is true with 1/2 tons, the bigger trucks had open driveline from the factory. I don't know about 3/4 tons but the 1 tons and up did

 

'55 1st series AD has the open drive, Beaner. It's the major difference from the '54, the rest of the changes being mostly cosmetic.

 

Some three post dude answers a 9 year dead thread with his "wisdom" and sure stirs the pot up.

 

Makes me a bit grumpy. That's the second one I've seen today. I give myself the old palm slap to the forehead for not checking the dates.

 

Some people who have a question do a search first (good for them) and if they don't find the answer they need, add onto an old thread. So for them it is practically the same as a new thread. Besides, why not share your wisdom with others who read the thread besides the OP.

 

I'd say this time the poster of post 14 was searching throug the back pages and dug up the ancient post and decided to display his knowledge and maybe a photo he was proud of.

We have all seen the daily question posted on an old thread found on Google or by searching the archives that was usually already answered in the thread if the poster had read though the whole thread first.

 

You know I was not aware that "Wisdom" only came from the number of post any one has made on a internet forum, even one as good as the HAMB. If they were still alive and lets say came on the HAMB for the first time some one like Smokey Yunick, lets say, A guy who knew more about cars than most of us will ever in a couple of lifetimes be able to learn. And he made his 3rd post would that number alone be the reason for ridicule as to the low number of posts and his knowledge of cars? Looks like to me that the number of posts no matter it be (3) or ( 24,000) does not have one damn thing to do with the character or knowledge and certainly not the wisdom of the poster.

 

When I saw Deuce Roadster had replied, I KNEW this was an old thread.....

Randy was a good dude.

 

I read your response, and then your post count; it was 666/SIX-SIX-SIX!!! Just a little too spooky for me to continue further. Carry on. I am Butch/56sedandelivery.

 

I agree that the number of posts is not an absolute indication of the poster’s expertise. But invoking the reputation of Smokey Yunic as an illustration is a far reach. While the HAMB is blessed to have many members who are quite well informed, there is no shortage of inaccurate or incomplete responses. The post that inspired your comments really is not far off the mark in reference to newbie posts......most of which are questions, not answers.

 

I certainly did NOT invoke the reputation of any one, I used Smokey as an example of the ridiculousness of trying to compare the number of post a person has made with there wisdom on the subject of Hot Rods. That seems pretty clear and very simple.

So I guess I do not understand your statement "most of which are questions not answers" Are you saying that questions are no longer to be made or tolerated on the HAMB? That all new members here should only respond when they have an answer? Is that what you are referring in that statement?

 

Never had a closed drive line car. With only one u joint, doesn't the shaft speed up and slow down, or is the angle always kept nearly straight?