two piece or one piece drive shaft

[70CHEVYBB]

I have a lwb 70 and was wondering if I should just keep the two piece drive shaft or put in a one piece shaft. I don't really haul anything so clearance at the trailing arm member is no problem. I am reinstalling myhigh horse big block and have heard the carrier bearing is a week link. any thoughts on this would be great.

[brad_man_72]

People not having their driveshafts properly ballanced kills carrier bearings.

Theirs a dozen wrong ways to rebuild a driveshaft but even when everything is done right the shaft still needs to be ballanced.

A one piece shaft is far less sensitive to ballance issues, you can ruin 2 or 3 tailshafts before you figure out the driveshaft is the problem.

There's plenty of advantages to a 2 piece driveline, simplicity isn't one of them.

[bigmac73]

subscribing, and interested

[Oldtruckfanatic]

If I were running any horsepower I'd probably opt for a one piece driveline mainly for less rotating mass and because of the way you can move the joint around at the squishy stock style carrier bearing. I have been the demise of plenty of rear tires with a two piece driveline without any trouble either way but I would imagine with enough power and traction you could make the stock carrier isolator oscillate but that's just my opinion. I have never seen it happen.

[68shortfleet]

When I had a one piece driveline built for my SWB, I had to have tube with an extra thick wall for the length that I needed. The shop said I was right at the limit for length. Who know's if they were just playing it safe though, so as not to be a vibration/warranty problem in the future.

So, I am betting that a one piece is going to be too long for a 2wd lwb.

[tlcrz1972]

First off you can not run a one piece driveshaft on a longed with an unmodified bulkhead (trailing arm attach crossmember). The drive shaft will hit the lower portion of the bulkhead where the carrier bearing mounts. The reason for it hitting is that the bulkhead is further aft of the transmission (than what a shortbed is) and the line of sight from the trans output shaft to the pinion will allow it to hit the bottom of the bulkhead.

[Oldtruckfanatic]

In reply to 68 shortfleet that's weird. When I was looking for a driveline for my swb conversion I found several Chevy vans in the yard with long drivelines. Unfortunately every one of them was destroyed from being lifted by a forklift. I opted to just have the two piece shortened at that point but that's an interesting thing I'd like to know for my own builds. Also I watch street outlaws quite a bit and I'd love to know what the farmtruck has for a driveshaft.

[tlcrz1972]

I'm not an expert on vans but I believe those were all leaf springs rear suspensions.

Originally Posted by Oldtruckfanatic

In reply to 68 shortfleet that's weird. When I was looking for a driveline for my swb conversion I found several Chevy vans in the yard with long drivelines. Unfortunately every one of them was destroyed from being lifted by a forklift. I opted to just have the two piece shortened at that point but that's an interesting thing I'd like to know for my own builds. Also I watch street outlaws quite a bit and I'd love to know what the farmtruck has for a driveshaft.

[Oldtruckfanatic]

It doesn't matter leaf or trailing arm the truck still has the same crossmember it just doesn't have the trailing arm brackets on it. Even the holes for the brackets are still there so if it's a clearance problem it exists either way and if a certain length is too long for balance or strength issues it would apply either way. Shortfleet68 was simply stating that his driveline shop said the length he had made which I bet was about 59-60" center of the u joints was right at the limit for a one piece driveline. He didn't say at the limit for trailing arm or leaf springs. His 68 is likely trailing arm. The only difference I would think would matter as far as the two suspensions go is that without the shocks to limit the travel the trailing arms would allow more length change but with the shocks its about the same. I have built several trucks in both configurations and seen both kinds of drivelines in both wheelbases.at any rate not meaning to get off the topic. He just said the length was at the limit but I have seen plenty of longer one piece drivelines and I'm hoping that info.helps the original poster.

[70CHEVYBB]

I think I will install new u-joints (already have a new carrier bearing) and send it to get it balanced

[Keith Seymore]

This is why some trucks get a one piece shaft and a similar looking truck might have a two piece shaft:

Originally Posted by Keith Seymore

It has to do with propshaft (aka "driveshaft") critical speed.

What you guys might be missing is that propshaft critical speed not just based on wheelbase but is also based on trans type (length), rear axle ratio, tire size, and engine type (larger engines allowing a higher top speed) AND/OR any strange resonances in that particular combination (camping out on that resonance will break the trans/transfer case tailshaft housing).

So - a long wheelbase truck with a low (numerical) rear axle ratio spins the shaft slower and might get a one piece, but an otherwise comparable truck with a high rear axle ratio might get a two piece.

One other comment - critical speed is not directly related to balance, but rigidity. When the shaft exceeds it's critical speed it begins to bow in the middle and swing like a jump rope. Hence the disturbance and durability concerns.

You can get around it by going to a larger diameter steel tube - or more expensive alternative materials like aluminum, carbon fiber or "metal matrix" (an aluminum/carbon wrap).

By the way, I hate the complexity and mass of a two piece setup and go out of my way to order my trucks such that they get a one piece shaft.

K

[brad_man_72]

Originally Posted by 68shortfleet

When I had a one piece driveline built for my SWB, I had to have tube with an extra thick wall for the length that I needed. The shop said I was right at the limit for length. Who know's if they were just playing it safe though, so as not to be a vibration/warranty problem in the future.

So, I am betting that a one piece is going to be too long for a 2wd lwb.

Extra thick would make the "jump rope" problem worse. You want a thin large diameter shaft for long lengths. This is why a lot of new trucks have 5" thin wall aluminum shafts that bend if you look at them wrong.

Rotating mass "polar moment of inertia" between a 2 piece shaft and one piece shaft would be nearly the same due to the larger diameter shaft required for a one piece shaft.

I've built dozens of 3.5" diameter one piece driveshafts for longbed 67-72s with no clearance issues. Most that I know of were lowered.

[Treetop839]

I was going to put a one piece shaft in my 70 lwb with a stock 1994 350/700R4 and stock stance. I have a friend that has three lwb trucks and runs a one piece shaft in them with no problems. He is using a steel shaft that has been cut down to the length needed, I don't know the diameter but they are a small diameter. I had a shaft out of a newer body style truck built and am going to go back to the 2piece. The new one is the aluminum and carbon fiber 4" shaft and it does not leave much room on side clearance through the cross member. With out the body on the frame I cannot bolt it to the rearend for it hitting the bottom of the crossmember. Drive shaft guy told me if the shaft hits the side of the crossmember it will cut it in two. There are a lot of people on here with more experience than me on this, just thought id let you know about my $150 lesson. Good luck!

[burnin oil]

5 foot is the theoetical max length for a drive shaft but that can be exceded without issue. U joint operating angle is the issue. Much more so than shaft balance! To much angle at one end will cause vibration and short joint and bearing life. There is nothing wrong with a thick tube driveshaft and rotational mass. A standard flywheel is around 44 pounds vs 5-10 for a flexplate. I know where you are going with this but steel wheels vs alum will have a bigger inertia difference. Search on roadranger.com for the Eaton driveline manual, around ten pages, and it will teach you more than you ever wanted to know about 1,2, 3, or four piece drive shafts, phasing, u joint angles, and shaft speed. A one piece shaft will fit on some trucks. I put a 1 piece in the rear of my 60 long bed without issues. If you need a 2 piece shaft to keep everything working correctly look into upgrading the carrier bearing. Medium duty trucks have 20 foot of driveshaft under them with alot more torque and low gears. How many of those do you see on the side of the road with the driveshafts hanging down. I have seen more pretzeled semi shafts from 2000 ftlbs of torque.

[burnin oil]

Originally Posted by Treetop839

I was going to put a one piece shaft in my 70 lwb with a stock 1994 350/700R4 and stock stance. I have a friend that has three lwb trucks and runs a one piece shaft in them with no problems. He is using a steel shaft that has been cut down to the length needed, I don't know the diameter but they are a small diameter. I had a shaft out of a newer body style truck built and am going to go back to the 2piece. The new one is the aluminum and carbon fiber 4" shaft and it does not leave much room on side clearance through the cross member. With out the body on the frame I cannot bolt it to the rearend for it hitting the bottom of the crossmember. Drive shaft guy told me if the shaft hits the side of the crossmember it will cut it in two. There are a lot of people on here with more experience than me on this, just thought id let you know about my $150 lesson. Good luck!

You could always just notch the bottom of the crossmember for clerence. If you think it needs support for rigidity some more metal could be added a little lower on the cross member. I love metal because of welders.

[brad_man_72]

Originally Posted by burnin oil

5 foot is the theoetical max length for a drive shaft but that can be exceded without issue. U joint operating angle is the issue. Much more so than shaft balance! To much angle at one end will cause vibration and short joint and bearing life. There is nothing wrong with a thick tube driveshaft and rotational mass. A standard flywheel is around 44 pounds vs 5-10 for a flexplate. I know where you are going with this but steel wheels vs alum will have a bigger inertia difference. Search on roadranger.com for the Eaton driveline manual, around ten pages, and it will teach you more than you ever wanted to know about 1,2, 3, or four piece drive shafts, phasing, u joint angles, and shaft speed. A one piece shaft will fit on some trucks. I put a 1 piece in the rear of my 60 long bed without issues. If you need a 2 piece shaft to keep everything working correctly look into upgrading the carrier bearing. Medium duty trucks have 20 foot of driveshaft under them with alot more torque and low gears. How many of those do you see on the side of the road with the driveshafts hanging down. I have seen more pretzeled semi shafts from 2000 ftlbs of torque.

A lot of what you said is true for large trucks, their driveshafts don't spin as fast as a passenger car. This is becoming less true with od transmissions, this is why we are seeing more rpl and spl style driveshafts that spin fast enough fo ballance to become an issue.

I've seen dozens of big truck shafts that weren't properly ballanced beat a carrier bearing to death very quickly.

I've built thousands of driveshafts, hundreds of them being for limos, so were talking 3,4,5 piece drivelines. Ballance is absolutly critical, driveline angles are very important also in a passenger car application.

I've seen people break 3 transfer cases, angle wasn't the problem, the shaft wasn't ballanced.

Dozens of cars with trashed tailhousings, again no angle problems, just ballance.

[slomotion]

You guys are talking way over my head, but I suspect GM thought out the drive shaft issue before they put millions of them together. I've never had to deal with a modified truck with so much torque that I was concerned with a two-piece shaft. I have installed heavier carrier bearings though just for peace of mind.
One thing I never did quite understand was why, if both shafts of a two-piece drive shaft was balanced independently was phasing so critical? I put a driveshaft together one time with the second shaft 180 deg. out, and it didn't take long to develop a vibration that rattled my teeth! I got home, dropped the shaft(s), re-phased the shafts, put it all back up, and everything was smooth as silk. Now I mark the yokes with a punch just to be sure, because chalk and crayon can and will come off!

[burnin oil]

Originally Posted by brad_man_72

A lot of what you said is true for large trucks, their driveshafts don't spin as fast as a passenger car. This is becoming less true with od transmissions, this is why we are seeing more rpl and spl style driveshafts that spin fast enough fo ballance to become an issue.

I've seen dozens of big truck shafts that weren't properly ballanced beat a carrier bearing to death very quickly.

I've built thousands of driveshafts, hundreds of them being for limos, so were talking 3,4,5 piece drivelines. Ballance is absolutly critical, driveline angles are very important also in a passenger car application.

I've seen people break 3 transfer cases, angle wasn't the problem, the shaft wasn't ballanced.

Dozens of cars with trashed tailhousings, again no angle problems, just ballance.

Even with tall tires I bet the medium duties are running similiar driveshaft speeds considering rear ratios in the 6 and 7s being normal. Some less and some more gearing.

If someone breaks 3 transfer cases I would be looking for more than a driveshaft balance issue. I can see it contributing to the problem but not enough to kill it. I have seen a few that were bad enough to feel like the truck was bouncing and not blow apart. I would suspect the shaft was to long, loose or bad/weak mount, or possibly a pinion angle issue under acceleration. The 2 biggest killers of tcases I have seen is the driveshaft bottoming out or excessive flex of the case from torque.

I am not doughting your expertise in driveshafts and think balancing is important but is only part of the equation

[burnin oil]

Originally Posted by slomotion

You guys are talking way over my head, but I suspect GM thought out the drive shaft issue before they put millions of them together. I've never had to deal with a modified truck with so much torque that I was concerned with a two-piece shaft. I have installed heavier carrier bearings though just for peace of mind.
One thing I never did quite understand was why, if both shafts of a two-piece drive shaft was balanced independently was phasing so critical? I put a driveshaft together one time with the second shaft 180 deg. out, and it didn't take long to develop a vibration that rattled my teeth! I got home, dropped the shaft(s), re-phased the shafts, put it all back up, and everything was smooth as silk. Now I mark the yokes with a punch just to be sure, because chalk and crayon can and will come off!

Download the tech guide from eaton I mentioned. It is written in simple terms for the average tech to use and will make it all clear as mud.

Think of a driveshaft as a balanced tire on a rim. If you take the tire off the rim and rotate it 180* what happened to the added wieghts? They all got moved around even though nothing has physically changed other than orientation. This is the reason that a good tire tech will break down a tire and rim and reasseble it if it takes to much wieght. Then again I had a guy balance a tire for my truck with over 14 ounces of wieght.

[slomotion]

Thank you Burnin, I understand the tire and wheel analogy, but theoretically, it seems if the wheel, and the tire were balanced separately then assembled without disturbing the balances, it shouldn't matter what the orientation of the assembly is. (Of course that whole theory thing gets blown away when it comes to driveshafts )

[Keith Seymore]

You guys are mixing metaphors.

Balance is a "first order of rotation" issue; meaning - you get one disturbance per rev of the drive shaft.

U joint issues (like phasing) are a "second order of rotation" issue; meaning you get an acceleration and a corresponding deceleration for each rotation of the shaft, or two "bumps" per rev. Phasing addresses the accel/decel pairing and causes them to cancel each other out rather than adding together and transmitting the disturbance into the shaft.

They are two separate failure opportunities that are resolved in two entirely different fashions, even though they reside on the same part.

The tire/wheel analogy is actually a pretty good one, in that the wheel and the tire are "balanced" seperately but then again as an assembly. We adopted that idea for vehicles that are especially sensitive to imbalance (vehicles with large interior volumes, like an SUV or an M/L van) and "system balance" the driveline. We assemble all the components, including the shafts to the rear axle and balance that as a unit. They are marked, dissassembled for shipment and then reassembled in the same orientation at the vehicle assembly plant in an attempt to control driveline related "boom" and/or drumming (low freqency noise). For vehicles that are not that sensitive, like pickup trucks, we do not go through all the additional effort, expense and complexity.

K

[brad_man_72]

Multiple piece drivelines must be ballanced as an assembly!
Yokes, ujoints, tubing and welds aren't centered, straight, or ballanced. The multiple piece driveline is very ballance sensitive beause the stub that goes through the carrier bearing locates the front of the rear shaft and must be straighter that say a weld yoke on the end of the shaft. If you start moving stuff around the ballance will change. Even if you mark everything just removal and reinstalition will upset the ballance.

How do you ballance a driveshaft attached to the axle? Seems like a lot of mass attached to the driveshaft.

We always just use a pinion yoke and make sure the ujoint is within a couple thousanths of being centered, ballance the yoke then the shaft. Which isn't perfect because the pinion being used in the vehicle isn't going to hold the joint that close to center or be ballanced. We also make sure the trans yoke is centered which is much easier.

[70CHEVYBB]

I just called the drive shaft shop, it's 80 bucks to balance a 2pc shaft. I will be pulling mine this weekend.

[Keith Seymore]

Originally Posted by brad_man_72

How do you ballance a driveshaft attached to the axle? Seems like a lot of mass attached to the driveshaft.

Shafts were manufactured by GM Parma and axle assemblies by Detroit Gear and Axle. The two components were shipped to Dynotech (Balance Engineering) in Troy, Michigan, where the axle was constrained in a fixture (like it would be in a vehicle), a shaft selected, mated to the axle and the whole assembly balanced. This would take into account any imbalance or dimensional variation in either the tube or the longitudinal portion of the axle assembly (like a slightly squashed tube, imperfectly welded tube end or rear axle pinion flange runout).

They were then marked, dissassembled and placed together in the dunnage, and shipped to GM Baltimore (or the respective assembly plant) for installation in a vehicle.

K

[brad_man_72]

I've ballanced a couple hundred driveshafts, the company I worked for actually builds their own driveshaft ballancers and being lighter always made them more sensitive.

It just seems like it would be quite difficult to ballance a 10lb chunk of spinning metal when its ridgidly attached to a stationary100lb chunk of metal.