Why a 2 piece driveshaft?

[WIDESIDE72]

Originally Posted by pritch

I thought about converting to a one-piece, but then I decided, why re-invent the wheel? It seems to me if I had to get a larger diameter, I would maybe run into clearance issues where it passes through the member that the trailing arms are connected to.

But I've always had one nagging question about two (or more) piece shafts. Does the carrier bearing(s) ever interfere with the movement of the yoke in the transmission? It looks to me like the carrier bearing is solid, I mean, not intended to have any give, so as the rear end travels up and down, forcing front and back movement onto the driveshaft, does it bind up at the carrier bearing?

I have not looked at a 2 pc shaft in a while, but isnt the splined part of the front section that goes into the carrier bearing supposed to slide in and out with rear axle movement?

[70blackfish]

my 70 chevy swb had a 2 piece with a stock 350 and turbo 400 trans.

it would shift hard, I replaced that center support all the time. (hated it!)

my 69 gmc swb 6 cyl. has a 1 piece...

[Shyguy]

Here is another reason for a two piece drive shaft, if you have a SM-420 or SM-465 transmission they do not have a slip joint so the two piece is necessary to take up for the movement of the driveshaft when the suspension flexes.

Just another bit of info.

[long67]

Not all carrier bearings are splined. Mine is solid. the bearing is pressed on the drive shaft behind the yoke that connects the two shafts. really does not allow for much movement.

[brad_man_72]

Originally Posted by long67

Not all carrier bearings are splined. Mine is solid. the bearing is pressed on the drive shaft behind the yoke that connects the two shafts. really does not allow for much movement.

I build driveshafts for a living.

The carrier bearing you are talking about allows for plenty of movement, trailing arm trucks Don't need much slip as the rear end doesn't move straight up and down, it swings in an arc very simmilar to the driveshaft.

I build one piece driveshafts for swb and lwb trucks like ours pretty frequently and have never had an issue. I would never attempt modifying a shaft at home especially the way the guys on hot rod tv did it.

Remember to have your driveshafts ballanced guys and gals. Its a lot cheaper than a new trans tailhousing.
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[ERASER5]

My '71 Chevy has the tear "drop" type of carrier like most people talk about.

My '70 GMC has a differnent carrier. The bearing is just a standard bearing like you could get at any bearing supply house. there is a rubber doughnut that goes over the bearing. There are 2 large clam shells the encase the bearing/doughnut. This thing is stout. I should get some pictures of it as I have never seen another one, but surely there are out there.

[brad_man_72]

Originally Posted by ERASER5

My '71 Chevy has the tear "drop" type of carrier like most people talk about.

My '70 GMC has a differnent carrier. The bearing is just a standard bearing like you could get at any bearing supply house. there is a rubber doughnut that goes over the bearing. There are 2 large clam shells the encase the bearing/doughnut. This thing is stout. I should get some pictures of it as I have never seen another one, but surely there are out there.

Those are pretty uncommon, may have been a 3/4+ ton thing or a leaf spring truck thing. I know I've only seen a half dozen or so in the last 5 years.

A lot of prople think the car style or teardrop style carrier bearings are weak. Carrier bearings don't just fail, our 2 piece driveshafts can very easily be reassembled incorrectly, changing the timing of the bolt on yoke or putting the rear shaft in 180* out or even backwards will cause a vibration. Many people just think old trucks are supposed to have some vibrations and are completely unaware of why ther carrier bearing fails 3 times a year, some even go out and buy one of those fancy billet/poly supports instead of fixing the real problem, an out of phase and or ballance issue.
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[pritch]

Originally Posted by brad_man_72

I build driveshafts for a living.

The carrier bearing you are talking about allows for plenty of movement, trailing arm trucks Don't need much slip as the rear end doesn't move straight up and down, it swings in an arc very simmilar to the driveshaft.

I build one piece driveshafts for swb and lwb trucks like ours pretty frequently and have never had an issue. I would never attempt modifying a shaft at home especially the way the guys on hot rod tv did it.

Remember to have your driveshafts ballanced guys and gals. Its a lot cheaper than a new trans tailhousing.
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That certainly makes sense.

[long67]

Originally Posted by brad_man_72
I build driveshafts for a living.

The carrier bearing you are talking about allows for plenty of movement, trailing arm trucks Don't need much slip as the rear end doesn't move straight up and down, it swings in an arc very simmilar to the driveshaft.

I build one piece driveshafts for swb and lwb trucks like ours pretty frequently and have never had an issue. I would never attempt modifying a shaft at home especially the way the guys on hot rod tv did it.

Remember to have your driveshafts ballanced guys and gals. Its a lot cheaper than a new trans tailhousing.
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That makes sense, I have replaced it twice, last time because the housing broke. First time because of bearing.

[Builtbychevy]

Originally Posted by brad_man_72

I build driveshafts for a living.

The carrier bearing you are talking about allows for plenty of movement, trailing arm trucks Don't need much slip as the rear end doesn't move straight up and down, it swings in an arc very simmilar to the driveshaft.

I build one piece driveshafts for swb and lwb trucks like ours pretty frequently and have never had an issue. I would never attempt modifying a shaft at home especially the way the guys on hot rod tv did it.

Remember to have your driveshafts ballanced guys and gals. Its a lot cheaper than a new trans tailhousing.
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I have a stock height '71 LWB. I was looking to go to the 1 piece without modifying the crossmember and without lowering the truck. Do you recall any modifications or diameter etc?

[brad_man_72]

Originally Posted by Builtbychevy

I have a stock height '71 LWB. I was looking to go to the 1 piece without modifying the crossmember and without lowering the truck. Do you recall any modifications or diameter etc?

3.5" diameter tubing will fit through the crossmember. Id worry about the shaft hitting the bottom of the crossmember at stock ride height.

[69GWC]

Originally Posted by Shyguy

Here is another reason for a two piece drive shaft, if you have a SM-420 or SM-465 transmission they do not have a slip joint so the two piece is necessary to take up for the movement of the driveshaft when the suspension flexes.

Just another bit of info.

My 69 has a sm-465 wi5h a one piece shaft, but its a 4wd and the shaft has a built in slip joint.. . Just thought I would throw that info out there..
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[midniteblues]

I've never owned a lwb truck(except s10 and parts trucks) but I had swb's with both shafts and never understood why they came both ways either

[67chevemall]

67 stepside with stock one piece shaft. 6cly 3 on the tree....

[hardwaycooke]

Contemplated trying to get a 1 piece made for my 500hp longbed. After much discussion with reputable drive shaft shops and a couple my buddies who build high end pro stock engines for a living , I decided to keep my 2 piece, get it balanced, get new heavy duty u-joints and a new improved yoke to handle my needs. I love it. It does not wobble, rattle, shake, etc...oh, and a new carrier. Much cheaper than having one built ad probably much smarter.

[2009kvfd976]

i have a 68 lwb with a 350/th700. engine is bone stock crate goodwrench but will get vortec heads, xe268 or thumpr cam, headers, performer intake and 600 carb. trans will be swapped for a 700r4 and rear gears will have 3.42 and eaton tru trac locker. will i be able to have a 1pc drive shaft made? or a 1pc shaft from like a 90 gmc 2wd lwb? it currently has a 2 pc shaft...

[mike16]

engineers do things for a reason. may be they study the tea leaves or cat guts on the highway. long drive shafts can get whippy at speed. also remember that drive shaft angle can change based on loads. I dont know but i'm betty on the cat gut theory

[Mike_The_Grad]

Originally Posted by mike16

engineers do things for a reason. may be they study the tea leaves or cat guts on the highway. long drive shafts can get whippy at speed. also remember that drive shaft angle can change based on loads. I dont know but i'm betty on the cat gut theory

I had forgotten I was subbed to this thread, how strange I was notified of an update to this thread at the same time I'm facing a 2 piece driveshaft dilemma on my '72 custom/10 LWB with factory overload rear leaf suspension. I had removed the driveshaft a couple years ago to rebuild the 350 sbc, I had to remove the actual center bearing support bracket from the frame in order to remove the driveshaft. Now I can't remember which of the two 4-bolt bracket mounting locations (heightwise) is the correct one for my vehicle. I do have the factory assembly manual and it does not define which of the two is correct. It does differentiate between the two based on RPO#'s but only for 1968 vehicles, with no mention anywhere else in the entire book of any other production years.
Picture for reference and clarification on which holes I'm referring to.

[mike16]

Originally Posted by Mike_The_Grad

I had forgotten I was subbed to this thread, how strange I was notified of an update to this thread at the same time I'm facing a 2 piece driveshaft dilemma on my '72 custom/10 LWB with factory overload rear leaf suspension. I had removed the driveshaft a couple years ago to rebuild the 350 sbc, I had to remove the actual center bearing support bracket from the frame in order to remove the driveshaft. Now I can't remember which of the two 4-bolt bracket mounting locations (heightwise) is the correct one for my vehicle. I do have the factory assembly manual and it does not define which of the two is correct. It does differentiate between the two based on RPO#'s but only for 1968 vehicles, with no mention anywhere else in the entire book of any other production years.
Picture for reference and clarification on which holes I'm referring to.

all kidding aside. looking at your cross member it is covered with a lite suface rust except where the carrier bearing mounting brackets attach. the carrier bearing mounting brackets covered and protected the paint under the mounting brakets. That would be a clue as to where the brackets origonally mounted. Hpe that helps.

[Mike_The_Grad]

Originally Posted by mike16

all kidding aside. looking at your cross member it is covered with a lite suface rust except where the carrier bearing mounting brackets attach. the carrier bearing mounting brackets covered and protected the paint under the mounting brakets. That would be a clue as to where the brackets origonally mounted. Hpe that helps.

I agree. I had tried both mounting locations at one time with no noticeable difference. I think the difference comes into play as the suspension travels. I just don't want to pick the wrong one and have the rear of the transmission beat up or have my pinion bearing take a beating either. Does anyone know how to determine which location is correct?

[70STOVEBOLT]

Originally Posted by Mike_The_Grad

I had forgotten I was subbed to this thread, how strange I was notified of an update to this thread at the same time I'm facing a 2 piece driveshaft dilemma on my '72 custom/10 LWB with factory overload rear leaf suspension. I had removed the driveshaft a couple years ago to rebuild the 350 sbc, I had to remove the actual center bearing support bracket from the frame in order to remove the driveshaft. Now I can't remember which of the two 4-bolt bracket mounting locations (heightwise) is the correct one for my vehicle. I do have the factory assembly manual and it does not define which of the two is correct. It does differentiate between the two based on RPO#'s but only for 1968 vehicles, with no mention anywhere else in the entire book of any other production years.
Picture for reference and clarification on which holes I'm referring to.

Look on the other side of the crossmember. Can you see where the washers/nuts/bolts were on that side? I don't know how these mount up as I have never had one with a 2-pc shaft. I do know that my 70 came with a 250/3OTT from the factory, coil springs, one-piece driveshaft. I put a 402/TH400 in it and had a local driveline shop shorten and balance it, put new u-joints on it, and I have had it up to 100 mph - smooth as silk.

[Mike_The_Grad]

Originally Posted by 70STOVEBOLT

Look on the other side of the crossmember. Can you see where the washers/nuts/bolts were on that side? I don't know how these mount up as I have never had one with a 2-pc shaft. I do know that my 70 came with a 250/3OTT from the factory, coil springs, one-piece driveshaft. I put a 402/TH400 in it and had a local driveline shop shorten and balance it, put new u-joints on it, and I have had it up to 100 mph - smooth as silk.

I examined both locations pretty well,and was unable to get a distinct indication of where it was originally mounted,mostly because of all the old crud and oil built up on the frontside of the crossmember. But I went ahead and mounted it to the lower of the two mounting locations. I threw the u joint that is connected to the pinion of the differential back in December, which I believe was due to my failure to replace the spring clips over the end caps where the two straps secured the joint to the pinion. In addition to maybe not having the driveshaft in phase with the other components(180° out). So I replaced the joint and changed the driveshaft relation 180° installed the retaining clips,lol, and now I've got almost 10k miles on it,and had it up to about 115 m.p.h.!! My carrier bearing is shot though and I'm pretty sure the other u joints have seen better days. So as soon as I get the money,I'll be replacing all the u joints, the carrier bearing, and rebalancing the driveshaft at a local very reputable driveline shop. Coast Driveline out of Ventura, CA.

[Coley]

Wow, interesting thread.
In addition to the very important 'critical speed' issue is the ability to work around this speed....of which they are indeed ways.
For instance, if you went with a (less desireable) solid steel shaft you would very quickly find you couldn't rotate it as fast as you could a larger diameter hollow shaft due to its concentrated (central) mass wanting to initially bend at both rest conditions and at higher speeds.....and definitely quicker to approach this condition than the hollow one.
That is why you find most (all?) driveshafts, that are subject to high speeds, made of a hollow (larger diameter) tube material that is inherently stiffer over its length than a solid steel smaller diameter shaft over the same length.
Thus a great result of this is the ability for a large diameter tube to successfully deliver torque with a minimal amount of axial twist relative to its length....nice to have.
A lot of folks would really be surprised to see just how thin the material on a high hp driveshaft, or any typical driveshaft is....lol. Its actually, physically a fairly light part relative to its length and this is achieved by increasing the diameter which keeps it stiff while allowing excellent torque transmission characteristics.
If you want to have some fun....make a driveshaft out of solid 1-1/4"ø steel and wind up the vehicle on a hoist to say....4500 rpm, and watch the driveshaft....(from behind a screen or shield)...lol.
Interesting discussion....lets keep it going!
All Good
Coley