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Old 07-29-2015, 02:44 PM   #1
centuryhouse
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Why did my drive shaft just fall out of the transmission?

I was driving my new 72 GMC (350, automatic, c15) at lunch and as I started off from a signal there was a loud clang and clattering and sudden loss of drive ability.

The drive shaft yoke (?) came out of the transmission and dropped on the ground. I had to get towed home.

On my initial post on this forum 2 weeks ago, I had noted that I could see splines showing on the driveshaft and asked if this was normal. No one answered so I assumed it wasn't a big deal.

Assuming the first pic is not normal, I was thinking the previous owner may have swapped out the transmission for a different type and then not put the correct length DS in place, or else replaced the DS with one that was the wrong length.

Thoughts? I don't even know what transmission I have or how to tell. Can someone get me going in the right direction on this? My GF just wrecked her car and is borrowing my Jeep, and now my backup transportation is down.

What I posted the other week:




Today:

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Old 07-29-2015, 02:51 PM   #2
Bigdav160
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Re: Why did my drive shaft just fall out of the transmission?

I think the rear shaft is too short for your truck. Either that or your centering pins are broken on your leaf springs and the rear end is moving.
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Old 07-29-2015, 03:10 PM   #3
Keith Seymore
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Re: Why did my drive shaft just fall out of the transmission?

I'm sorry I didn't see this earlier, but the level of spline engagement in the first pic is definitely not right.

Judging by the dings in the muffler this may not be the first time that shaft has come out and banged around.

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Old 07-29-2015, 03:29 PM   #4
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Re: Why did my drive shaft just fall out of the transmission?

I remember replying to the other post that it looked like it wasn't engaged far enough, but I can't find that post anymore. Weird.

It does appear that the rear shaft is not long enough.
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Old 07-29-2015, 03:53 PM   #5
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Re: Why did my drive shaft just fall out of the transmission?

Where are these centering pins?
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Old 07-29-2015, 04:45 PM   #6
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Re: Why did my drive shaft just fall out of the transmission?

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Where are these centering pins?
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They're on the rear springs. It's the bolts that hold the spring togethior. They fit in holes in the spring perches (or saddles) that are welded to your rear end.
Looks to me that you have the wrong yoke and it hasn't been bolted back on.
There should be a centre bolt holding the yoke to the splined shaft.
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Old 07-29-2015, 04:46 PM   #7
michael bustamante
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Re: Why did my drive shaft just fall out of the transmission?

most likely too short. take a pic of the trans pan and we can tell you what kind of tranny. is it just me or is the spline shaft sticking out of the trans too far?
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Old 07-29-2015, 05:05 PM   #8
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Re: Why did my drive shaft just fall out of the transmission?

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most likely too short. take a pic of the trans pan and we can tell you what kind of tranny. is it just me or is the spline shaft sticking out of the trans too far?
It's you!!
That's not the tranny output shaft.
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Old 07-29-2015, 05:06 PM   #9
michael bustamante
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Re: Why did my drive shaft just fall out of the transmission?

i didnt think so but it looked odd to me. der.....
i just say it... its a longbed. yup that driveshaft is too short
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Old 07-29-2015, 07:23 PM   #10
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Re: Why did my drive shaft just fall out of the transmission?

I posted some wrong info. I'm still new to these trucks, only 2 weeks into it.

I've never had a rwd car that had TWO drive shafts before. So when I posted that the shaft fell out of my transmission it was inaccurate.

There apparently is a front drive shaft that comes rearward to rest in some sort of cross member piece. What is that middle piece called?

And from there a rear drive shaft meets it, and runs rearward to the differential. This is the drive shaft that fell.

To me, it looks like the front drive shaft is right - it comes to that cross member piece and seems to sit where it should.

The rear drive shaft appears to be newer - and the u-joints on it are new. This must have just been done recently, before I bought it.

The observation above that the old muffler was dented and this may have happened before seems like it might be true. I never even thought of that. Something had ripped that old muffler from its bracket and from the tailpipe - and it very well may have been this.

Anyway, the rear shaft is just a hair over 24.5" (just the shaft) or around 29" if you count the 'ears' that hold the u-joints. More pics:

Front 'spline' section near whatever that cross member is called:






Rear drive shaft, which fell down in the front:





The front yoke (?) of the rear drive shaft, which slips over the splined part:

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Old 07-29-2015, 07:37 PM   #11
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Re: Why did my drive shaft just fall out of the transmission?

The "middle part" is called a carrier bearing. Obviously it supports the 2 piece drive shaft where they meet. The rear shaft looks way too short to me.
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Old 07-29-2015, 07:47 PM   #12
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Re: Why did my drive shaft just fall out of the transmission?

I'll look at mine when I get home. Is your truck a longhorn or standard 8' bed. I think the standard 8' bed rear drive shaft is shorter than the longhorn. Like maybe replaced a bad rear shaft with the wrong one. The splined section should be engaged at least half way with no load on the rear.
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Old 07-29-2015, 08:14 PM   #13
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Re: Why did my drive shaft just fall out of the transmission?

Unless you own the tools to make a driveshaft, you are going to have to take it to a driveline shop and have them take care of it. I'd suggest towing it and having it all done there, since you don't have much experience with 2 piece shafts. Measuring and taking them just the shaft could be more costly if it's done wrong.
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Old 07-29-2015, 08:22 PM   #14
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Re: Why did my drive shaft just fall out of the transmission?

Just checked my GMC tailshaft and the measurement of the rear shaft at the differential from center of u-joint to u-joint going forward is 28".

Name:  driveshaft - 1.jpg
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The next section going forward into the front drive shaft is around 6" from center of u-joint to end of cap.

Name:  driveshaft1 - 1.jpg
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Size:  50.6 KB

BTW, it looks like your are missing your grease dust seal cap.

HTH.
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Old 07-29-2015, 08:33 PM   #15
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Re: Why did my drive shaft just fall out of the transmission?

My trk is a 70 longbed bigblk th400. so it's not the same up front. the rear shaft measures 29 in. just like yours. so I think it's the correct rear shaft. only thing that I can think of is the rear end moved back. I never seen it happen but that shock in the picture looks like its bent around the axle housing. if it is . something ain't right. the spring pad does look a bit suspect also ?
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Old 07-29-2015, 08:38 PM   #16
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Re: Why did my drive shaft just fall out of the transmission?

are any leafs broken. I see a weird piece stickin up in the upper right hand corner of the pic and the rear end just looks kinda tipped forward
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Old 07-29-2015, 08:45 PM   #17
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Re: Why did my drive shaft just fall out of the transmission?

I don't think the rear end has rotated. The springs and shocks look fine to me. I think it is an optical dillusion. Here is what mine looked like prior to dis-assembly.

Name:  driveshaft - 1 (2).jpg
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The bottom leaf always sticks down since it is not contained with the other leafs.

Let's see what his rear shaft measures too.
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Old 07-29-2015, 10:06 PM   #18
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Re: Why did my drive shaft just fall out of the transmission?

Quote:
Originally Posted by Chucks72Longbed View Post
I'll look at mine when I get home. Is your truck a longhorn or standard 8' bed. I think the standard 8' bed rear drive shaft is shorter than the longhorn. Like maybe replaced a bad rear shaft with the wrong one. The splined section should be engaged at least half way with no load on the rear.
Mine is a long bed. The SPID indicates it was long bed originally, but when I got it they had replaced the bed with another (obvious from the different paint types).
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Old 07-29-2015, 10:10 PM   #19
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Re: Why did my drive shaft just fall out of the transmission?

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My trk is a 70 longbed bigblk th400. so it's not the same up front. the rear shaft measures 29 in. just like yours. so I think it's the correct rear shaft. only thing that I can think of is the rear end moved back. I never seen it happen but that shock in the picture looks like its bent around the axle housing. if it is . something ain't right. the spring pad does look a bit suspect also ?
The wheels / tires look fine in the wheel wells. If it had all moved, wouldn't the wheels/tires no longer be centered properly?

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Old 07-29-2015, 10:13 PM   #20
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Re: Why did my drive shaft just fall out of the transmission?

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are any leafs broken. I see a weird piece stickin up in the upper right hand corner of the pic and the rear end just looks kinda tipped forward
The weird piece you see is a hose from the differential - can't remember what they call it, but like a 'breathing tube'.
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Old 07-29-2015, 10:15 PM   #21
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Re: Why did my drive shaft just fall out of the transmission?

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Let's see what his rear shaft measures to.
The rear shaft is 29" tip to tip (meaning from the tip of the 'ear' the u-joints go into, to the other 'ear' tip.
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Old 07-29-2015, 10:32 PM   #22
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Re: Why did my drive shaft just fall out of the transmission?

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The weird piece you see is a hose from the differential - can't remember what they call it, but like a 'breathing tube'.
I see that's what it is now. that's the same length as my shaft. 29 inch tip to tip. anyone got anything longer ?
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Old 07-29-2015, 11:28 PM   #23
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Re: Why did my drive shaft just fall out of the transmission?

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I see that's what it is now. that's the same length as my shaft. 29 inch tip to tip. anyone got anything longer ?
Hmm. If the rear shaft is indeed the correct length, and the rear axle hasn't moved, then that would mean the front shaft was the wrong length.

If that were the case, it wouldn't line up right at the carrier bearing, correct?

I'm really at a loss as to what to do to get this going again.
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Old 07-30-2015, 01:52 AM   #24
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Re: Why did my drive shaft just fall out of the transmission?

that's correct. So lets start at the beginning. put your wheels straight and measure center to center on each side. get someone to help so ya get pretty close.
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Old 07-30-2015, 02:21 AM   #25
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Re: Why did my drive shaft just fall out of the transmission?

the long wheel base trucks came in 2 lengths 127 inch and 133 inch that 6 inchs looks about the distant your short?
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