Drive Shaft Stupidity.

[McRat]

Our truck is a front engine 4x4.  Up to this point, we have run all power through the transfer case with the front axles removed.

So to reduce nose weight on the truck, I found a 2WD transmission for my truck, and went to install it.  Uh, both trans and axle yokes are fixed yokes, and we run suspension in the rear.  So I need a "slip" driveshaft.  The transfer case had the slip yoke.

First shop I talked to is saying that a custom driveshaft is good to 3600rpm.  3500 rpm is factory driveshaft on bone stock pickup at the 96mph speed limiter.  Not getting a "warm fuzzy" on that shop, which is nothing new.

If I have 3.42 gears, and 32" tires, that's ~5200 driveshaft RPM at 175, which showed no problems or wear with the OEM driveshaft.  It's a very sturdy unit as are most HD truck pieces, and do not have a significant history of failure.

Is my math wrong?  Or can someone recommend a driveshaft shop that can build a 6000rpm driveshaft?

[RichFox]

I have a Ford pickup top loader three speed in my Vega. It has the fixed flange output. I like that because I can pull the trans without draining gearlube all over the floor. The driveshaft is a FWD pickup part that was bent and I got it at the local junkyard when we still had junkyards. Took it to Argo machine and had it shortened to fit the Vega and have been running it for 20 years off and on. been over 200 a few times and around 200 a few more. never had any reason to pay any attention to the driveshaft. Everything has worked fine. See how good it is to be to dumb to know it wont work.

[McRat]

I have a Ford pickup top loader three speed in my Vega. It has the fixed flange output. I like that because I can pull the trans without draining gearlube all over the floor. The driveshaft is a FWD pickup part that was bent and I got it at the local junkyard when we still had junkyards. Took it to Argo machine and had it shortened to fit the Vega and have been running it for 20 years off and on. been over 200 a few times and around 200 a few more. never had any reason to pay any attention to the driveshaft. Everything has worked fine. See how good it is to be to dumb to know it wont work.

Thanks for the reply!

Is it a slip-style?  Two piece?

[Glen]

Talk to Gale Banks on the drive line

[McRat]

Thanks! 

[RichFox]

I have a Ford pickup top loader three speed in my Vega. It has the fixed flange output. I like that because I can pull the trans without draining gearlube all over the floor. The driveshaft is a FWD pickup part that was bent and I got it at the local junkyard when we still had junkyards. Took it to Argo machine and had it shortened to fit the Vega and have been running it for 20 years off and on. been over 200 a few times and around 200 a few more. never had any reason to pay any attention to the driveshaft. Everything has worked fine. See how good it is to be to dumb to know it wont work.

Thanks for the reply!

Is it a slip-style?  Two piece?

Yes

[panic]

Mark Williams's site has some data for driveshaft speed vs. length vs. diameter:

http://www.markwilliams.com/driveshafttech.aspx

Looks like the speed varies inverse to the length squared.

[McRat]

Mark Williams's site has some data for driveshaft speed vs. length vs. diameter:

http://www.markwilliams.com/driveshafttech.aspx

Thanks!

That put my mind to rest.  Even the longest custom driveshafts are over 4000rpm.

[Jonny Hotnuts]

what is your reasoning for wanting to reduce frontal weight?

~JH

[McRat]

what is your reasoning for wanting to reduce frontal weight?

~JH

Safety.  Front end originally weighed over 4000lb which puts added stress on tires that was not necessary.  I've dropped it down to ~3500lb.  Trying to keep the entire weight to under 7000lb for Bonneville.

And my trailer is only supposed to hold 6,000lb.

[Jonny Hotnuts]

good answer.

~JH

[Dean Los Angeles]

I looked at the Mark Williams page on critical driveshaft speed and my first thought was WHOOO!

13,000 rpm is fast for anything. Just try to imagine a heavy driveshaft coming apart at that rpm.

We machine at work at 12,000 rpm and when the spindle is running you can put your hand on the spindle housing and cannot tell it is running.

It's all about balance. For the driveshaft to live at that speed the balance is critical. Don't think for a minute that it is any less critical at 6,000 rpm.

[panic]

Yup - and if you ever see any scars, shiny spots, dings etc. it's got to be checked for balance again. Just kicking up a rock into the tube may cause a failure, and it won't feel bad until it's spinning really fast.

I'm compulsive because I was a passenger in a car that ran over the shaft at only about 100, did several 360s before stopping (one of Ehrenberg's "true tales of street racing" from the 1960s...).

[jacksoni]

My first year at Bonneville, on about the second run I made (having blown up a motor first run and changed it) had the drive shaft break in the middle at about 125-130. Broke the front of the differential, back of the trans, bent the block plate, broke several bellhousing "ears" off the block ( aluminum) , made the shaft tunnel in floor abut twice as big as used to be and took out the seat belt mounts as well as nearly my A**. Qualified too.  Fixed it all and were in line next morning ( engine wouldn't start as the timing got moved around but we re qualified and eventually set record.) Biggest problem was the grief we got from the staff cause we left some parts on the track 

Get some one make you a good shaft and take good care of it.

[RichFox]

Did I mention that my driveshaft is very short? That may make a difference.