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Old 10-30-2009, 01:57 AM   #1 (permalink)
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Drive shaft mod save fuel.

If you have a RWD vehicle you might save some MPG by converting to a 3 or 4 piece drive line.

Was helping a buddy on a Salt Flat car and noticed he had a 7 piece drive line.
He said they found the drive line can cost you over 15 HP as you approach a hundred. They found that several differing length pieces stop harmonics in the drive line and it runs smoother. You just have to build the carrier bearing holder for them...


Always wondered why my BMW had a 2 piece drive line.... When it doesn't have to flex..

Dave..

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Old 10-30-2009, 02:26 AM   #2 (permalink)
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That sounds like SO expensive
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Old 10-30-2009, 03:06 AM   #3 (permalink)
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That sounds like so not working on the street!

Extra carrier bearings = more driveline friction; extra u-joints = more driveline friction; extra carrier bearings and u-joints AND slip joints = more driveline mass.

I went the other direction on a '74 Chev pickup. It had a 2-pc shaft, I replaced the u-joints and carrier bearing only to have vibration afterwards. Just by dumb luck I came across a 1-piece direct replacement about that time. Put it in there, things got smooth, and I never looked back.
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Old 10-30-2009, 04:13 AM   #4 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
That sounds like so not working on the street!

Extra carrier bearings = more driveline friction; extra u-joints = more driveline friction; extra carrier bearings and u-joints AND slip joints = more driveline mass.

I went the other direction on a '74 Chev pickup. It had a 2-pc shaft, I replaced the u-joints and carrier bearing only to have vibration afterwards. Just by dumb luck I came across a 1-piece direct replacement about that time. Put it in there, things got smooth, and I never looked back.
Compretery agree with Frank, here.

Adding rotating mass, bearings, slip-sections, and Universal/CV joints (depending on your driveline setup) will NEVER increase your FE, unless your original equipment was so far out of whack you shouldn't have been driving it.

After working for a company in Binghamton, NY, I designed a 1 piece CV shaft for FWD cars that had no bearings and would still flex under suspension loads, worked out the design w/ the engineers, and had it blueprinted. Don't care enough to apply for a patent, honestly, since I can prove intellectual property.

Maybe, some day, I'll get around and work on it. Probably not, though. It would be alot of work for minimal gain. You simply don't lose that much energy through the CV shafts or driveshaft.

For your friend, I'm sure he found something, but I don't know if I believe 15HP from harmonic vibration. Why haven't I heard about this on every other (professional) BSF racer?
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Old 10-30-2009, 05:02 AM   #5 (permalink)
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Same here, always replaced 2 piece drive shafts with single unit, more durable.
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Old 10-30-2009, 10:07 AM   #6 (permalink)
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My Effer has a 2pc shaft for now, after the 4wd conversion It will be getting a 1 pc Aluminum shaft.
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Old 10-30-2009, 01:12 PM   #7 (permalink)
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I agree with Frank too.

But how about keep a 1 piece driveline and use something like this, rather than a standard u-joint which actually binds a bit when turning?

Thompson Couplings Ltd
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Old 10-30-2009, 01:15 PM   #8 (permalink)
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wagonman76 -

I've seen (somewhere) where people have modded their drive shafts to use standard CV joints instead of universal "cross" joints.

I have no data or anything to go by other than intuition, but I do know that CV's don't bind like cross-u's do.
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Old 10-30-2009, 06:30 PM   #9 (permalink)
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The binding of a universal joint occurs at extreme angles ( like in an off-raod vehicle's driveshaft or front wheel drive axles) which is why CV joints are used in such applications. A CV joint has more bearing surfaces than a simple u-joint which usually means more friction. Does anyone have any data to support/refute this?
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Old 10-30-2009, 09:09 PM   #10 (permalink)
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Quote:
Originally Posted by micondie View Post
The binding of a universal joint occurs at extreme angles ( like in an off-raod vehicle's driveshaft or front wheel drive axles) which is why CV joints are used in such applications. A CV joint has more bearing surfaces than a simple u-joint which usually means more friction. Does anyone have any data to support/refute this?
It depends on the type of CV joint. There are triangulated CV joints, then there are the types that you normally find in sets of impact tools as well, and a few other types beyond those that I've only seen on paper.

The CV type that you normally find on cars is the triangulated one. It has three bearings that have X surface area, which actually appears to be similar, if not slightly less, contacted surface area than the needle bearings in U-joints of comparable sizes.

The CV type that is commonly used in impact tool sets (wobble adapter) is just a ball in socket design with an arm or 3 that extends from the socket into the ball. The ball is slotted to allow it to move freely over those arms, while still being able to make every movement that a ball should be able to make without binding. Those setups are seldom good for more than about 45* of usable angle, though, where U-joints can function at a higher angle, but seldom last very long when made to.

The bearing contacted surface for the ball in socket design is less than that of the U-joint or the triangulated CV joint for a similar sized piece.

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