1 Piece versus 2 Piece Drive Shaft

Question

A guy on a Nissan forum asked why he should keep his 2 piece drive shaft in his truck instead of changing over to a 1 piece version.

This was the answer I gave him:

The 2 piece drive shaft (DS) is meant to prevent the drive shaft from pulling out under extreme axle movement.

The front of the DS slips into the transmission.

The rear of the DS bolts to the rear axle.

As the suspension travels, a conventional 1 piece DS slips in and out of the "slip sleeve" (my term) at the transmission.

If the "slip sleeve" is short, there is not much room for the axle to move ...or it will fall out.

A 2 piece DS fixes the shaft at a central point, preventing the "slip sleeve" from coming out as the rear axle moves around.

Also, a 2 piece DS will absorb some of the vibrations when a DS is out of alignment (due to dirt or getting bent).

That's all I see, anyway. There could be other reasons.

OK, now that I've satisfied that person, I want to know the actual reason why automotive manufacturers elect to use a 2-piece drive shaft as opposed to the "less expensive to manufacture" 1-piece drive shaft.

Can anyone tell me this?

Answer 1

I think it's more related to the angle of the driveshaft from the transmission to the differential. This way you could have more suspension travel without putting too much constraints on parts.

In fact, to answer your question, it may be related to the geometry of the truck/driveshaft that manufacturer will select one type over another one. If the truck is long, you don't want the drive shaft hanging under the truck which can be hit and break.

This is where I took my reference.

Image source

Answer 2

A two piece shaft is used to prevent the shaft from bending at high RPM. This is know as the whipping effect. As the shaft will not bend, therefore the transmission tunnel or floor above the shaft can be lower allowing more room for passengers or goods.

Answer 3

One piece designs necessitate a lighter material, such as aluminum, which requires a larger diameter shaft to achieve the same strength as the stock steel shafts. There are several issues with this approach:

1. A larger clearance is required to accommodate the shaft and its harmonics,
2. The shaft is more prone damage (due to angle and material),
3. This shaft is NOT significantly cheaper to produce, and
4. The critical speed limit is vastly reduced — most likely below what might seem reasonable for mass market (say 90mph for a 5" shaft diameter on an F150).

Making this same shaft out of steel for a street application would be too heavy overall, and would overly stress bearing, seals, etc.

Note: There are some benefits to one-piece aluminum, if doing so as an upgrade: lower maintenance due to fewer moving parts, and lighter weight (~50-65%); however, these are not necessarily appreciated as OEM.

Answer 4

Especially in 4x4 vehicles, a two piece Tail shaft is best. Most custom conversions to a one piece suffer when both rear wheels lift off the ground because the tail shaft usually hits the cross member because it is so long. This can happen easily over speed bumps & if a vehicle is bogged to the axle.

One piece tail shafts also get a flex wobble/vibration at high speeds too.You wont find one in a serious race car anymore either. But they do resolve vibrations caused by angle changes in the two piece tail shaft Uni-Joints after a suspension lift. Try to work out the correct working angles in your two piece using castor wedges under the rear springs and shims under the center bearing mount. IMO, Only get a one piece tail shaft if everything else you try fails.

Answer 5

I'm really not sure there is a single answer to this question. Some manufactures will claim they engineer a two piece drive shaft to eliminate vibrations and harmonics, but in reality, a one piece would have worked just fine. Personally, I believe that many manufacturers just use whichever shaft it can get the best deal on from their suppliers at that given time. Most european manufacturers use elaberate two piece drive shafts behind transmissions that have a rubber disk to absorb shock and no slip joint. These shafts are often not serviceable in the field at all. When center bearing or u joints wear out, the drive shaft must be completely remanufactured. While these methods may or may not provide a quiet and smooth ride, I personally believe they use them to increase the cost and complexity of the replacement part, therefore insuring future service business.

I would venture to say that just about any vehicle used for none offroad applications and with a slip joint front (transmission) yoke can be sucessfully converted to one piece, as long as the basic principles of laying out the shafts are followed and corners are not cut. There are plenty of websites that have all the information required to do it and its critical that every step is followed carefully.

As regarding cars and pickup trucks, I really don't believe that there is a magic number that becomes too long for a one piece drive shaft. As long as the shaft yokes have all been phased in properly, the shaft balanced correctly, and the proper shaft diameter and metal thinkness has been used to meet the application's critical speed formula, even a 70 plus inch shaft should perform well at or below highway speeds.

However, for most mass produced cars and light trucks, the parts required to replace high wear/mileage two piece drive shafts and the labor costs to install them are likely much less than the cost of a custom made or high performance one piece shalf, so the benefits of the one piece shaft may not justify the cost, especially for non high performance needs. Of course, this call it up to the individual.

I agree that if some shop it attempting to talk you out of the shaft you want, these are not the people you want doing the work on your shaft for you. Run, don't walk away from them. Do your homework on driveshafts so that you can make an informed choice as well as understand which shops are making sense when they are presenting you with options..or lack of opinions...and which can't or won't do the work you want.

Answer 6

When wheel base distance is between 3.4m to 4.8m then two piece drive shaft as far as L/D ratio concerns