How long can a prop shaft be with out the use of a center surrport?

54" be altight with out one anyone know?

won't it depend on diameter, wall thicknes and material is is made from?

The Land Rover 110 300TDi Commercial 1997:
Front: 635mm
Rear: 1100mm = 43 in.


[Edited on 25/1/07 by 02GF74]

As already said depends on the diameter -- long shafts need to be a bigger dia to make them stiffer, to avoid unpleasant vibrations at motorway speeds.

istr the Austin Champ had a one piece shaft running from the front diff to the rear diff.

the shaft is 70mm o.d and the wall thickness is 1.5mm, cv joint at one end and a uj at the other, this help any?

Drive shafts have a 'critical speed' which is dependant on the factors mentioned above such as length and diameter, material and wall thickness.
You will have to calculate what the max speed your propshaft will turn based on your max road speed and your diff ratio. There are tables on the web I saw before which can help you find out what the critical speed is for a certain length of driveshaft
Rob

oh right so theres a whole engineering principle behind it, not as hit and miss as i first though. does anyone know were i could source this information?

The phenomenon is commonly known as " Whirling ".

Try do a google search for - whirling of shafts

But this may give you a taster of some of the calculations behind it.

Whirling

If it looks complicated at first sight don't let that put you off, I am sur that there are much better web sites out there that will explain it step by step - that was just the fist one I came across with an example.

Make sure you get it right...54inches is bloody long.

Seen the aftermath of a prop "go" in a BEC. ZX9 Fury with prop straight to back axle. The guy got onto the first stretch of road and the prop shattered into 3 the first time he went past 60mph....dents throughout the trans tunnel and holes in the sheets of ali. He was lucky it went through in the empty passenger side not the driver's....

Totally agree with Steve, make sure you get it right!!

54" is bloody long and 70mm isn't huge diameter, so Im fairly certain the answer will be no, if I recall correctly after Pete's BEC prop failed (the one Steve mentioned), someone on the Yahoo list caclulated that you'd need a prop of around 5.5" diameter to survive over that distance at the prop RPM attained by a BEC, which wouldnt even fit down the transmission tunnel!

so id be safe to go down the road of split prop for my own safely

does anyone know the price of prop bearings?

Your profile says a locost with Audi 5 cylinder engine. If the propshaft is for a car engine and box it will probably be more like 14" long.

You;ll need the prop made up especially I suspect. A prop for a BEC with centre bearing (usually from a Transit) is ~£200+ from the likes of Dunning and Fairbank. If you can take your existing parts along for modification it might be a bit less, but probably not a huge amount.

yea its an audi engine but its a eastwest transaxle im going to modify to achieve awd so my prop will be a good bit longer, i did a mock up sketch today to work out he lenght and it was about 50" to 51" so i factored in a few more inches just incase my drawing was wrong

can you not manufacture your own split prop?

You can, but you need to be very accurate with your machining and welding!

If the prop is going to be anywhere near you or a passenger, the potential consequences of it failing are just not worth the money saved IMHO

[Edited on 25/1/07 by ChrisGamlin]

but people make the normal prop all the time do they not, maybe i shouldent take the risk, as i guess if it breaks free from the center bearing it could become lethal and would still be being powered by the engine since it would be connected for a while and dont think i could live with killing someone because of my cheapness

guess it could be a one seater, and maybe i should sit over the prop just to test my faith in it, then after a year fit passenger seat because i trusted the prop with my life and more importantly my furture

[Edited on 25/1/07 by goodall]

Youve got it in one, unless you're a truly skilled engineer with proper equipment to do it (lathe, milling machine, TIG welding gear then something to accurately balance it) then its really not worth the risk or the eternal nagging in the back of your head every time you drive it.

I know the "book" shows the making of a prop but I think most people nowadays get them made up professionally.

FWIW it would actually be worse if it breaks away on the UJ nearest the engine because then the prop is being forcefully driven by the road wheels, so won't stop flailing until the whole car comes to a stop, taking far longer than you just killing the engine. Its also evidently been known where props break, drop from the underside of the car and dig into the tarmac, flipping the car although Ive personally not heard of any doing this.

[Edited on 25/1/07 by ChrisGamlin]

I have some pics somewhere of what a failed prop can do too the transmission tunnel, scary..........

a failed prop turned a volvo 240 over once .....