A Slip Yoke With A Two Piece?

[Nitekruizer]

I'm wondering if a transmission with a slip yoke can be used with a two-piece driveshaft? Should I do this or will it cause something nasty to happen?

[PhantomoftheBumpside]

It depends on the angles and lengths.

[Whateverman]

the front half will most likely need to be shortened but as long as the steady bearing is good you won't have any problems

[PhantomoftheBumpside]

Hang on... most likely... you will need to have a drive line shop custom make your two piece once you have your critical measurements. Your output angle is probably between 5-6º and you are going to want to cancel that out through the entire setup. If you just shorten the first shaft, you can be causing an extreme angle at the carrier bearing.

Customary driveline design will tell you the split should be 40 front, 60 rear and this would be a good point to aim for which probably means shortening the rear shaft more than the front shaft and relocating the carrier from the 'normal' position it would have been if it were there.

The main reason for two piece design is to ensure your drive line stays away from it's critical speed, because this design improves this factor, you can also look at smaller diameter shafts in addition to perfecting the placement of your carrier to give added clearance to other objects underneath if needed or convenient.

You will want the unit to be perfectly balanced, any imperfections will cancel out any advantages to a two piece shaft. You also don't want to shift things too much and create extreme angles (which is one reason why you don't want to just shorten the front shaft). You could also consider modifying the engine and/or transmission mounts to a lesser angle to ensure no binding. If you reduce the output angle to zero, you can use the carrier without a wedge shim and you can also set the rear pinion angle to zero. This will make the only drive line angles equal in the rear shaft when the vehicle is level.

[Whateverman]

Needing to get a shortened stock type 2pc driveshaft built by a shop because of pinion and driveline angles ?
The front half of the shaft is pretty much inline with the trans and stays that way because the steady bearing is bolted in the same location as stock- the rear shaft is the same length ...... the angle of the dangle is the same as it always was

Just bring your old one into a machine shop and get em to shorten the front half to suit your application ,they'll balance the thing and put a fresh steady bearing on it ---from my repeated personal experience they will also give you a sales pitch saying you really should get them to build you a new shaft,but will happily take your money nonetheless
I've done this at least 5 times,and never had any problems with any of the shafts i had shortened

[PhantomoftheBumpside]

Nope, just like a triangle, if you shorten the side, you change the angle. The engine and trans point down in Ford trucks about 5-6º, the carrier bearing has an angled mount it bolts to in order to take out part of the angle on the way to the rear (keeping the resultant angles to the recommended max of about 3º). If you put in a longer trans or trans & transfer, then it will be hanging even closer to the ground at the output, unless you've modified the mounts. This means your shorter shaft is going to start lower and at a greater angle than stock. Depending on how much, this can be a very drastic compound angle (because the drive line path is not straight), and not changing the mount angle of the carrier will focus most of the vibration there.

If you don't believe me read a geometry book and the Dana Driveshaft Installation Manual...

If you did this 5 times with two-piece drive lines, you probably weren't feeling the surge because you were close enough keep the vibration low (within a couple of º) and the additional vibration was absorbed by the carrier bearing rubber. The carrier bearings on those projects will fail long before they should, and if the shortened shafts weren't balanced properly or phased correctly, they are going to have a diminished critical speed and their failure, already hastened, will approach at light speed once the carrier gets loose and they start really surging unevenly from ever changing angles under load at highway speed. Especially if you shortened any of the shafts was because you stuffed in an overdrive...

[Nitekruizer]

Thanks for the replies guys. By "something nasty to happen" my concern was that the slip yoke might let the small shaft move back and forth causing the steady bearing to come apart or that it would destroy the transmission's rear seal and maybe even eventually allow the yoke to rub against the tail housing of the tranny. I was going to shorten the front shaft by 3.625" but I could push the yoke further in to the tranny which would effectively allow the shaft to be 1/2" to 3/4" longer. I had measured for the yoke to be out of the transmission by aproxiamately 1". I'm not really sure if I should leave any slack there or if the yoke should be almost all the way in ,say 1/8" or so for example ?

[PhantomoftheBumpside]

Not really a good idea. Remember, as solid as your truck looks, it is not rigid. You need the room in the slip to allow for things like twisting and flexing of the frame. Even a tiny amount of the up and down of the rear is going to be translated into lateral movement in the carrier and front shaft as well.

[Whateverman]

I'm not an engineer ---always wanted to drive a train, never have....but i do know this:

the driveshaft in my truck has over 200 000 mi on it since being shortened ,its made to go behind a c4 w/ slip yoke tailshaft

its outlasted 3 j-yard C4's autos in 2 different trucks and has been subjected to (except in the last 3yrs when my truck was retired from daily driver duty) a fair amount of abuse on a very very regular basis -street racing,trailer towing and hauling construction materials....,never had a lick of trouble with it


i will eventually get a new one made because the center slip yoke (behind the steady bearing ) splines are getting a little worn out which causes a little "clunk" when the truck gets put into gear

[PhantomoftheBumpside]

So this was the same two piece drive line 5 times?

Did you cut and weld it? Or was it a shop?

Did you change the joints each time?

What did your junk yard C4's die from?

[Whateverman]

-i've had 5 different shafts made (shortened) for different trucks (and a van) because i've swapped trannys from whatever to whichever either just because i could or i needed to for some reason or other and so on and so forth
- i had an automotive machine shop do them for me - i wanted them to be balanced,have new steady bearings & etc. ..... and have someone else to blame if anything was wrong
- the machine shop i use puts new u-joints in as part of the deal
my c4's died from :
(1) - being a type F loving,but exceptionally leaky enviro-disaster that ended up having all the clutch material washed off by having a load of dexron II put into it (that was the last time i ever loaned my truck out) ....that was really sad cuz that one had a shift kit in it
(2) missing 3rd gear when manually shifting a cheap-@$$ floorshifter and getting crammed first into reverse and then back into 2nd
gear at full throttle - while street racing - it didn't blow apart but it was unable to shift itself automatically without jamming on the 1st -2nd shift and locking up.......couldn't afford to fix it so limped the truck around for a couple of years like that....gently and manually shifted.

(3) hit a large rock - not quite rate-able as a boulder,but pretty impressive nonetheless, during a rockslide and had the trans pan mashed into the valvebody. ...was lucky i didn't fly over the guard rail and into the canyon because we were airborne ......the trans still made it the rest of the 300 mi trip home ,but it had to be retired due to the cracks in the case around the pan