B7100 lost drive in the front in 4WD

[Puriri Farm]

I recently had the front axle apart on my B7100 chasing an oil leak, and a grumbly noise. The oil leak was a damaged gasket, and the grumbly noise turned out to be flogged wheel studs. Everything else in there looked almost new despite being made in 1976. All seemed to be running just fine again after I put it back together.

But, I now have no drive to the front wheels. I did have drive there, but not any more. I can see the prop shaft turning near the hydraulic filter in 4wd, and not turning in 2wd, so I'm confident that the problem lies further forward than that.

I think I heard what sounded like a spline not quite engaged in a socket and skipping across the face when I had it loaded up to see if it was actually working. I can't see how that could happen in the pieces i had apart.

So I'm wondering if there's a shearpin in that system somewhere i could have broken, or what the most likely scenario might be?

 

[kubotasam]

I recently had the front axle apart on my B7100 chasing an oil leak, and a grumbly noise. The oil leak was a damaged gasket, and the grumbly noise turned out to be flogged wheel studs. Everything else in there looked almost new despite being made in 1976. All seemed to be running just fine again after I put it back together.
How long of a time between the repair and when you noticed no front drive?

But, I now have no drive to the front wheels. I did have drive there, but not any more. I can see the prop shaft turning near the hydraulic filter in 4wd, and not turning in 2wd, so I'm confident that the problem lies further forward than that.

I think I heard what sounded like a spline not quite engaged in a socket and skipping across the face when I had it loaded up to see if it was actually working. Could be the splined connection between the front drive shaft and the pinion shaft.
I can't see how that could happen in the pieces i had apart.
What exactly did you have apart?
So I'm wondering if there's a shearpin in that system somewhere i could have broken, or what the most likely scenario might be?
No shear pin in the front drive system.

 

[Lil Foot]

There are no shear pins in the front driveline, but there are three roll pins, two at the transmission end, and one at the differential end. Even if those pins are broken or missing, the pinion shaft is splined, and so is the u-joint that fits on it.
So, if the roll pin is missing or broken AND the splines are stripped, it could exhibit the symptoms you describe. If not, the problem must be deeper in the diff or axles.
Keep in mind if one axle is disengaged, stripped, or broken, you will have no front wheel drive. (open diff)

 

[Lil Foot]

 

[Puriri Farm]

Thanks for the guidance team, I found the trouble. A broken roll-pin at each end spline connection had allowed the prop shaft to move back enough to fettle the spline on the front diff connection.

Eventually, and purely coincidentally, it broke loose not long after I poked around in the front axle.

Of course, the long spline on the front end of the shaft that allows for length adjustment is seized, which means I can't take the shaft off as it was intended.

So, to fix it properly, I'd need to drop the front axle. But.. in a past life, the crown nut evidently kept coming off the front of that axle swing bolt. In lieu of a split pin, someone has welded it on. There goes that idea!

I'll get a replacement roll pin next time I go to town, in the meantime, I've managed to secure the joint with a section of 4" nail. Rough as, but at least it's up and working again..

Until the next weak link, or makeshift repair shows up..

 

[kubotasam]

If the splines are worn to the point of slipping I don't think that a nail or even the correct roll pin is going to hold. Sometimes they make the female spline in the yoke softer than the male spline. Perhaps you can get away with replacing just the yoke on the driveshaft.

 

[Puriri Farm]

It seemed to me like it was the outer end of the spline/cup that was worn, and that it was holding fine when properly inserted.

BUT, I was shoving some firewood around today, and lost the front drive again. I haven't had a look to see what failed this time. Will keep you posted!

 

[Puriri Farm]

Well, I found the problem, and the cause.

The shaft had been assembled incorrectly. The two ends should be 90 degrees out of phase to account for the rotation of the universals. They weren't. The slip joint between [17] and the spline was seized solid (12 tonne press moved it, but with some interesting noises!). All of which adds up to the yoke [18] pushing in and out twice per revolution, breaking its roll pin, and wearing itself out on the front drive spline.

So now I need to find a new yoke, and replace the universal core (also wrecked through taking a hiding, and never being maintained)

On the upside, when I took the cover off this time, the shaft all but fell out in my hand.

 

[kubotasam]

The shaft had been assembled incorrectly. The two ends should be 90 degrees out of phase to account for the rotation of the universals. They weren't. The slip joint between [17] and the spline was seized solid (12 tonne press moved it, but with some interesting noises!). All of which adds up to the yoke [18] pushing in and out twice per revolution, breaking its roll pin, and wearing itself out on the front drive spline.
View attachment 56054

The universal joints at the ends of the drive shaft are supposed to be in phase.
They are not supposed to be 90 degrees out. They should be exactly in line with each other.

 

[ruger1980]

The universal joints at the ends of the drive shaft are supposed to be in phase.
They are not supposed to be 90 degrees out. They should be exactly in line with each other. View attachment 56065

This is not always the case. There are applications where phasing is not conventional. You should always refer to oem documentation to determine correct phasing.

 

[whitetiger]

Well, I found the problem, and the cause.

The shaft had been assembled incorrectly. The two ends should be 90 degrees out of phase to account for the rotation of the universals. They weren't. The slip joint between [17] and the spline was seized solid (12 tonne press moved it, but with some interesting noises!). All of which adds up to the yoke [18] pushing in and out twice per revolution, breaking its roll pin, and wearing itself out on the front drive spline.

So now I need to find a new yoke, and replace the universal core (also wrecked through taking a hiding, and never being maintained)

On the upside, when I took the cover off this time, the shaft all but fell out in my hand.
View attachment 56054

The slip joint spline should have a master spline so it will only go together one way.

The yokes on the two shafts may very well be 90 degrees from each other. They have to either be inline or 90 degrees, which makes no difference in the operation as there are 4 bearing cups so there would be a pivot every 90 degrees.

 

[Puriri Farm]

There's no master spline - that slip joint yoke can go on whatever way you feel inclined.

The slip yoke was offset 45 degrees from the fixed/pinned yoke, so unless they were trying to split the difference between inline and 90 degrees, it's out of phase in any case.

I had misremembered the impact of this, and thought that the result was a slight lengthening and shortening of the effective length of the shaft rather than an eliptical speed impact on the driven member.

That pulsing torque won't have caused the failure, but I'm guessing that it wasn't doing anything good to the drive train or tire wear.

Wish me luck on finding a replacement yoke!

 

[D2Cat]

If you're using a roll pin to hold the yoke to the shaft, you might put a tie wire through the roll pin to keep it there!

 

[Puriri Farm]

put a tie wire through the roll pin to keep it there!

Great idea, I'll do that!

The roll pins on either end of this shaft were both still present, just in three pieces each, and no longer doing the job they were meant to be doing.