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marjoa · 09-18-2016, 09:14 PM

Looked at a 38', DP, 300 ISC, little over 110K on a spartan chassis MH today and one of the things I checked for was whether the "U" joints had been greased or not. They had not. Dry as a bone. Upon further inspection, I grabbed the drive shaft and was able to rotate it back and forth about a 1/2" or so. Not back & forth—long ways—from the transmission to the differential but "rotating it around" it had this 1/2" play. I don't ever remember a drive shaft having this play. My instincts tell me there should be NO play here at all. The MH was parked, transmission in PARK, still in it's raised height position with bags still full and jacks just kissing the ground. Is this Drive shaft play normal?

thx

FIRE UP · 09-18-2016, 09:31 PM

Quote:

Originally Posted by marjoa

Looked at a 38', DP, 300 ISC, little over 110K on a spartan chassis MH today and one of the things I checked for was whether the "U" joints had been greased or not. They had not. Dry as a bone. Upon further inspection, I grabbed the drive shaft and was able to rotate it back and forth about a 1/2" or so. Not back & forth—long ways—from the transmission to the differential but "rotating it around" it had this 1/2" play. I don't ever remember a drive shaft having this play. My instincts tell me there should be NO play here at all. The MH was parked, transmission in PARK, still in it's raised height position with bags still full and jacks just kissing the ground. Is this Drive shaft play normal?

thx

Well,
A 1/2" of rotational play is not good, AT ALL! Now, if it's play in the splines where the two sections slide back and forth, it's not quite as bad but, STILL BAD. But, if it's play in the actual u-joints, I wouldn't drive that thing ONE INCH! IN all reality, there should be no play at all, in any section of that drive shaft or, input into either end, the trans or the diff. If you've got play that you can see at the diff yoke, that coach is in some serious trouble.

But, if it's just worn u-joints, no biggie. They just need to be replaced. Now, if there's that kind of play in the u-joints, I'd take a serious look at where the cups reside. It's possible that they've been hammered into and oval shape. Now, your in for some expense instead of just replacing U-joints. Good luck.

Scott

marjoa · 09-19-2016, 02:48 AM

Quote:

Originally Posted by FIRE UP

Well,
A 1/2" of rotational play is not good, AT ALL! Now, if it's play in the splines where the two sections slide back and forth, it's not quite as bad but, STILL BAD. But, if it's play in the actual u-joints, I wouldn't drive that thing ONE INCH! IN all reality, there should be no play at all, in any section of that drive shaft or, input into either end, the trans or the diff. If you've got play that you can see at the diff yoke, that coach is in some serious trouble.

But, if it's just worn u-joints, no biggie. They just need to be replaced. Now, if there's that kind of play in the u-joints, I'd take a serious look at where the cups reside. It's possible that they've been hammered into and oval shape. Now, your in for some expense instead of just replacing U-joints. Good luck.

Scott

Yeah, I didn't think there was supposed to be any play "AT ALL". Now whether it's play in the splines or not I have no idea. You obviously can't see in there to tell. But there was definitely 1/2" or maybe a tad more rotational "slop" or "play" in the drive shaft as you turned it with your hand. I have replaced several "U" joints in my life so I totally agree you about that if there was 1/2" play there I'd be afraid to turn it around in a parking lot let alone drive it.

thx

marjoa · 09-19-2016, 03:52 AM

Now whether it's play in the splines or not I have no idea. You obviously can't see in there to tell.

I miss read this and answered incorrectly. I should have said, I did move it back & forth and I did not feel any play in the splines.

twinboat · 09-19-2016, 04:54 AM

To start, there is no PARK in that transmission, so that end can simply turn free.

If the whole shaft is turning, end for end, you may be feeling the play in the rear differential gears.

With the combination of the pinion spline, gear set backlash, spider gears, and axle spline play, what you feel may be normal.

Hire a mechanic to check it out.

jacwjames · 09-19-2016, 06:05 AM

X2 on what Twinboat posted.

I can grab my drive shaft and rock it back and forth with some play rotationally but everything is tight.

If it has not been greased in 110K miles I would just go ahead and buy new U-joints and install. While doing this take the drive shaft apart and check for slop in the splines.

I bought a set to keep as spares on my rig when i got ~100K miles on it. A set cost ~$100.

After having a radiator failure and being towed I had to remove and fix the time or phase of the driveshaft after the repair shop put it in wrong. While removing I could not get one of the end caps off, ended up breaking. I installed 1 of my new U-joints.

mackwrench · 09-19-2016, 10:10 AM

OP, 1/2" is nothing. That's called backlash. The rear end gear set ring and pinion has clearance that will allow about that much. Your Allison does not a a "park" feature. The trans is shifted into neutral, and parking brake applied. There will be no load on the driveline and it will move

If the rear end does not whine, roar or "clunk" when decelerating, all's good.

The lack of driveline maintenance is not unheard of on motor coach. However, without disassembling the u-joints, you may not can tell if they have been greased.

My $.02 is if there is not any up/down/movement at the u-joint, I would grease them and rock on. The joints are sealed and unless someone pushed a lot of grease though them you may not see it.

skypilot_1 · 09-19-2016, 10:19 AM

Edit

**JohnRR** · 09-19-2016, 10:28 AM

I think there is some misunderstanding of terminology here there will be a certain amount of backlash as Mack stated in any driveline when tension is taken off it.

I wipe all excess grease off so as not to have spray in the surrounding areas, after going down the road a bit it looks like mine have not been greased/flushed recently.

skypilot_1 · 09-19-2016, 10:30 AM

"there should be no play at all, in any section of that drive shaft or, input into either end, the trans or the diff. If you've got play that you can see at the diff yoke, that coach is in some serious trouble."

Id get a second and professional opinion on that. jus sayn

mackwrench · 09-19-2016, 10:33 AM

Quote:

Originally Posted by skypilot_1

Id get a second and professional opinion on that. jus sayn

Ain't that what the internet is for? ha-ha

But truly the best advice on this thread.

jelag · 09-19-2016, 11:32 AM

its easy to see play in ujoints that are cars and light trucks... but often a bad joint on a class 5 to 8 truck is harder to see because of the size and weight of the shaft.. its easier to see worn out joints with a pry bar in the yoke placing pressure against the joint and seeing how much play is between the cross itself and the cup on the end of the cross... this is the play you need to look for and correct when you find it...

If the shaft is long enough you should also look for broken rubber in the mounting of the carrier bearing in the center of the shaft.. moving the shaft from side to side and look for damaged rubber will identify a bad carrier bearing...

But I agree with the above. a 1/2" of rotational play is most often in the ring & pinion gear in the rear end... and based on the diameter of the ring gear and the way the pinion is set in the ring gear... a 1/2" of rotational play can easily be normal...

FIRE UP · 09-19-2016, 11:54 AM

OK Gang,
I have to apologize. Insert foot....
In my semi-technical experience with messing with cars/trucks/motorcycles and more over the years, I've really not experienced any play in any drive shaft that did NOT HAVE A PROBLEM. As in a bad set of u-joints, damaged spline etc. But, I just went out and slid under our coach, and that approximately 24" long drive shaft DOES have about, 1/2" rotational play in it. And, it's in the diff gears, not anywhere else. Or should I say, it's inside the differential which, could mean it also involves any potential play in axle splines too.

But, in any case, I usually try to be as close to accurate in my answers as possible. But, in this case, not so good. Sorry.
Scott

marjoa · 09-19-2016, 07:38 PM

Thanks for the posts.

Yeah my mistake about saying it was in park. Your right, it was in "N" with the EB on. Sorry about that.

We decided not to pursue this MH because it simply wasn't big enough overall, and I'm 6'3" and the head room was just not enough for me. I felt like a giant in this thing. I also felt it was under powered with the 300 cummins. It just didn't have any "Umff". Maybe I was expecting to much I don't know.

But back to the topic. I asked this question just to further my knowledge of what to look for in the future and whats normal & what isn't. So from what I'm reading here, rotational play of a 1/2" is normal. Back & forth or end to end is not. I already know how to spot bad U joints and what to look for there.

Thanks guys.