88" Propshaft Length's Front & Rear

[tuko]

Flipping through the Haynes manual today the figures for the front and rear propshafts length's caught my attention. On the 88", the front Prop length is 23.812in and the rear prop length is 21.812in. What intrigued me was that there was exactly 2" difference between them, the front being the longest.

So I began thinking, if you lifted an 88" say 2" then the front prop should fit perfectly into the rear giving the same placement on the slip joint. In theory this sounds as if it would work but has anybody ever done this before or know if it is plausible?

Comments?

Todd.

[secondjeremy]

The shafts are the same length on an 86in S1 - with the front shaft being lengthened when the front axle was moved forward 2 in to allow for the longer OHV 2 litre diesel engine (which was the origins of the 2.25 engine we all know and love.) and the wheelbase became 88in.

[ian_s]

i think you'd have to lift it a lot more than 2 inches to need a 2 inch longer propshaft

[zim]

the length doesn't increase by 2" though

[tuko]

If you move or lower the axle 2" farther away from the frame, wouldn't the "distance" from the transfer case and the diff increase equally?

If not is there a formula to figure out the correct propshaft length required?

Todd.

[Daan]

Wellits an angle, which changes when you lift it, so with your sin, cos and tan knowledge gained at school, I am sure you can work it out!

There are more options: I run a standard rear prop on the back of my hybrid, and a defender 90 rear at the front. Not sure how would work out on your setup, I have used a lt230 box and the wheelbase of 89". Hardly any lift at all.

You obviously can gain a bit of length with your extended joke idea (never realised it would fit), although that doesnt work on a defender prop.

daan

[ian_s]

it's all to do with Pythagoras:

"In any right triangle, the area of the square whose side is the hypotenuse (the side opposite the right angle) is equal to the sum of the areas of the squares whose sides are the two legs (the two sides that meet at a right angle)."

consider this: the propshaft is the hypotenuse, the horizontal distance between the output/input flanges is one of the legs, and the vertical distance is the second leg.

by lifting the vehicle by 2 inches, only the vertical leg will be increased, the horizontal leg will stay the same.

from memory, i *THINK* the input flange is about 7 inches lower than the output flange (this may be way out)

we know from the haynes book you quoted above that the propshaft is 21.812 inches

working with these figures we get a horizontal distance of 20.658 inches - only 1.15 inches shorter than the prop.

(in theory) the horizontal distance wont change when we apply the lift.

so working backwards, now with a vertical distance of 9 inches we get a propshaft distance of 22.533 inches - only 0.8 inches longer than the original.

to get a propshaft length of 23.812 inches you'd need to lift it by about 4.8 inches.

HTH

Ian

[ian_s]

just to add: this is a landrover - the rules of physics may not actually apply here

[tuko]

Ian,

Your posts are educational and has sheds light on question that I had. Math was never a strong subject for me way back when....

Many thanks,

Todd.