toyota Tacoma. why 2-piece driveshaft?

[vash]

i am not a driveshaft expert..i grease zerk fittings and that is it. the rest is voodoo.

my carrier bearing squeaks when i jiggle the shaft/bearing..i think i found the mystery squeak plaguing me for about a year - two years. it is the junction where the two driveshaft segments meet..i dont even know if is called the "carrier bearing"..duh.

got me thinking? why not a single piece driveshaft..a stock tacoma isnt lifted that much.

[IROC]

Not sure. My '83 long bed had a one-piece driveshaft and my '84 long bed had a two-piece. The '83 drive shaft was really long, though. I also had to replace the center support/carrier bearing on the '84...

[pwd72s]

My guess is to reduce drivetrain vibration. My Mustang has a 2 piece driveshaft, and vibration reduction is the reason given. Lighter weight aluminum and carbon fiber one piece ones are offered in the aftermarket.

[BReif61]

Vash, you're a civil engineer, right? Picture the driveshaft as a bridge, with a single piece shaft being a bridge with no support under the span, whereas the two piece is a bridge with a central support. Now picture the deflection that each of those bridges would see.

That's why driveshafts are multi-pieced.

[cabmandone]

Is your truck an extended cab or crew cab by chance? If so, that should answer your question.

[wdfifteen]

Because that's the way GM does it and Toyota is still copying designs from GM.

[Bob Kontak]

I replaced a driveshaft in an '07 RAV 4. Joints were not serviceable. Not sure if the Tacoma is the same.

I bought used from LKQ for $200. New was pushing $1,000.

[cabmandone]

Now if you want to talk fun, certain year F150's have a split driveshaft with a carrier bearing. If the carrier goes out.... you replace the entire driveshaft! BRILLIANT
I discovered this when my dad's truck lost the carrier bearing. I told him "no problem... we'll just replace the carrier like I did on my F350"... I then called back and said "we have a problem". Ended up buying a split axle with a replaceable carrier from an axle company in Ft Wayne IN.

[vash]

Originally Posted by BReif61

Vash, you're a civil engineer, right? Picture the driveshaft as a bridge, with a single piece shaft being a bridge with no support under the span, whereas the two piece is a bridge with a central support. Now picture the deflection that each of those bridges would see.

That's why driveshafts are multi-pieced.

your example. that would be like a bridge that never sees any traffic load. a drive shaft sees an entirely different type of loading. my driveshaft isnt that long. not worth two extra u-joints and a squeeky mid bearing.

[john70t]

When you are cruising along at 120mph that long driveshaft is spinning pretty fast.
It must be perfectly straight and balanced, or the vibrations would bounce the tires off the pavement.
Shorter shafts are not as vulnerable to being unbalanced.
Vibrations only affect half of the drive train.

Also consider if you were using a 1/2 drive impact socket gun to drive a three foot 1/4 drive extension.
(not that you ever would of course).
The extension would twist up like a pretzel before any work was created.

A series of six inch extensions would have been much stronger. 1.2.3.4.5.6.
Shorter is mightier. Roman sword.

[vash]

Originally Posted by john70t

When you are cruising along at 120mph that long driveshaft is spinning pretty fast.
It must be perfectly straight and balanced, or the vibrations would bounce the tires off the pavement.
Shorter shafts are not as vulnerable to being unbalanced.
Vibrations only affect half of the drive train.

Also consider if you were using a 1/2 drive impact socket gun to drive a three foot 1/4 drive extension.
(not that you ever would of course).
The extension would twist up like a pretzel before any work was created.

A series of six inch extensions would have been much stronger. 1.2.3.4.5.6.
Shorter is mightier. Roman sword.

i can get behind this.. i'm just pissy cuz mine is making a racket, i suppose.

[john70t]

Just WAGes of course from an engineer groupie here. The big boys in the big three design departments are probably using harmonic algorithms in their CAD models of the frame and whatnot. Those guys discovered they can reduce the vibrations of of the starter motor by .05% by placing it under the intake manifold and using breakaway proprietary sockets. (sigh).

Another WAG:
Pretend you are driving a rally race hard.
The engine within it's soft rubber motor mounts is torquing left/right/forward/back while the driver hammers and lets off constantly. The rear axle and differential is bouncing around in every direction as well over rocks and stumps. Both of these units are moving around at their maximum travel abilities. Randomly and fast. These are normally supposed to be pointed almost straight at each other. IIRC, it's supposed to be a 2-4 degree deflection angle for universal joints to work properly and for a long time I think. But instead, both their output-center-lines are mostly pointing everywhere.
A normal axle would just have two universal joints and a slider.
A center carrier adds a second slider.

But while I was thinking about it, you do seem to have a good question: By shortening the driveshaft into two with placing a fixed pivot in the center, aren't the drive angle stresses increased?
(unless that center carrier point floats around which currently doesn't happen afaik)
Instead of a third bend 'around the corner', the carrier actually seems to be tightening the corner instead.

[javadog]

Driveshafts have to deal with a lot of vibrations, particularly torsional vibrations. They have what's known as a critical speed, above which Bad Things happen. Shorter shafts have higher critical speeds than longer shafts.

[vash]

holy chit..the placebo affect of this one is HUGE. my truck is glass smooth.

mechanic said i diagnosed the problem perfectly..it was the center bearing making the squeek.

money well spent i say.

[cabmandone]

Sounds like you got off easy. When my carrier went out in my F350 and when my dad's went out in his F150, you'd have sworn you broke a motor mount and the engine was going to jump out from under the hood.