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76 Pacer - Rear End Vibration

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mantonas View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote mantonas Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2017 at 8:38pm
I had a chance to work on the car after work today, so I put the rear axle on jackstands. Before I unbolted the driveshaft, I grabbed the yoke and tried to move it by hand and it definitely rattled around a bit. I made sure that the rattle was not happening at the rear axle or at the u-joints (makes sense, they're new): it was definitely rattling around in the transmission. I inspected the outside of the yoke: it looked pretty good. Shiny, no scoring, a few discolored patches from minor corrosion, but no ridge at the point where it transitions to the part that is outside the transmission output seal. I looked into the end of the yoke at the splines, and i couldn't see anything bad, but it could be very worn out and I wouldn't be able to tell from looking at it. I'm thinking it's the extension housing bushing that the slip yoke fits into.

I'm taking it to the driveshaft shop tomorrow, I'll see what they say. I am also going to start calling around to find a transmission shop that can replace the extension housing bushing. 

I also want to get ready in case I need a new slip yoke. I have not had any luck finding one that is identified as a direct replacement for a 76 Pacer with an automatic transmission, but I'm sure they're out there. Does anybody know where I can get one? I'm thinking that I might be able to use one from a Chrysler product with a 904 transmission. I might have to use a different kind of u-joint, but that's okay.
1976 AMC Pacer X
1978 AMC Pacer V8
1987 Jeep Grand Wagoneer
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Post Options Post Options   Thanks (1) Thanks(1)   Quote mantonas Quote  Post ReplyReply Direct Link To This Post Posted: Aug/05/2017 at 3:02pm
I took the driveshaft to the shop on Thursday and I heard back from them yesterday. Turns out the driveshaft has problems. It's apparently pretty significantly out of straight and out of balance; they said at about 2100 rpm it starts to vibrate. That's pretty low, and it may line up with the fact that I start feeling the vibration starting at around 45 mph. They gave me a few options and I picked having them fabricate a whole new driveshaft for me with new yokes and tubing, balanced, with new Spicer u-joints (lifetime warranty on the u-joints). They also said my slip yoke looked good and they will polish it for me.

They did not do any work with transmissions but gave me the name of a shop who might be able to replace my tailshaft housing bushing. Who knows, maybe a new driveshaft will solve the vibration problem and I won't need to replace it.
1976 AMC Pacer X
1978 AMC Pacer V8
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Aug/08/2017 at 8:00am
The bushing isn't too hard to replace. Hardest to get the old one out! Stick the new one in the freezer for a few hours with the housing in the sun getting warm (or in a 150-200 degree oven - just warm though!). Then drive it in with a wood block on the end of the bushing.

If you don't want to do it yourself take the housing off (easy since driveshaft is off) and just take it to the trans shop. Will be a lot cheaper that way, and quicker to get it back.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mantonas Quote  Post ReplyReply Direct Link To This Post Posted: Sep/01/2017 at 9:30am
I was hoping that the driveshaft would solve the problems, but it didn't. I now have a driveshaft that's worth at least 10 percent of the total value of the car. Talk about spending your children's inheritance. Anyway, the vibration is still there but now it's different. It starts at about 45 mph and sort of ends around 55 mph. Previously it would just continue to get worse the faster I went. I have now had it up to around 80 mph and while it is loud and feels like the world is coming to an end at that speed it's not because of the vibration. So I'm back to the bushing.

I called a transmission shop and they told me it would cost between $250 and $300 for them to replace it. If you want to do it with the transmission still in the car, then you need the mother of all special tools. Knowing that this car essentially has a Chrysler 904 Torqueflite in it I looked for the tool and this appears to be it:

https://www.atsg.us/atsg/extension-housing-bushing-remover-installer-and-output-shaft-support-fixture-party-t-0160-a.html

Still expensive ($179, presumably plus shipping and maybe tax) and I don't know if I would trust myself to use it properly.

Then yesterday I had a bit of good luck. A friend of mine from work gave me the name of a transmission repair guy that he has used who he says is good. This friend of mine has 5 kids and is the sole earner for his family, so when he says somebody is good, there's an unspoken "and cheap" that follows. And he was right: this transmission repair guy said he would remove the extension housing, knock out the bushing and replace it, and, while he was there, replace the tailshaft bearing, for a grand total of $100! 

So that's going to be my next step. I need to get into his shop sometime after Labor Day and I will see what it's like after that. If it still vibrates, I will probably start thinking about replacing rear wheel bearings. I've done a somewhat half-assed search for parts in preparation for that and I haven't found any, so that could be a problem.

Another data point: I read on some forum that maybe a vibration like this could be from the engine. It could be as simple as an engine cooling fan that's out of balance. The post said to throw it in neutral while the vibration is happening and see if it stops. So I did that, and it did stop, for a few seconds, then it started to come back. I interpret that to mean that when the transmission stops applying torque to the slip yoke, it disrupts the vibration, sort of like stomping on the brakes in a solid front axle Jeep to stop death wobble (some of you know what I mean!). You stop the vibrations temporarily by disturbing the system, but it eventually comes back. So I don't think it's coming from the engine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Sep/01/2017 at 10:32am
Did you ever install that new transmission mount you bought? I just spent two months chasing a similar problem. Turned out to be the tranny mount. $8.99 at O'Reilly's and took all of 15 minutes to install.

The clue was the pinion angle. Transmission angle measured at the yoke and rear diff angle measured at flat spot on bottom of case should be within a couple degrees of each other. Mine differed by about 6 degrees because missing rubber of the mount was causing the rear of tranny to droop by about two inches. Tranny mount can appear good until you look closely and realize that the metal "blade" part of the mount is no longer bonded to the rubber.

Edited by CamJam - Sep/01/2017 at 10:43am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mantonas Quote  Post ReplyReply Direct Link To This Post Posted: Sep/01/2017 at 10:56am
No! I never did that! Thanks for reminding me. I think I have one, I just need to put it in. It's heck getting old and forgetting things all the time.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Sep/01/2017 at 11:38am
Originally posted by mantonas mantonas wrote:

No! I never did that! Thanks for reminding me. I think I have one, I just need to put it in. It's heck getting old and forgetting things all the time.

Well if not, they're only $8.99 at O'Reillys (assuming you have the 232 motor) same as what I paid for the Javelin with a 998 transmission. Different part number, but the design of yours is the same as mine-- just probably a different height.  You can see how the right angle metal "blade" is (barely) attached to the rubber.  In my case, half the rubber was gone entirely. 
 

Just FYI, the mount as pictured in the O'Reilly's photo is upside down.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73Gremlin401 Quote  Post ReplyReply Direct Link To This Post Posted: Sep/01/2017 at 5:22pm
Originally posted by CamJam CamJam wrote:

Originally posted by mantonas mantonas wrote:

No! I never did that! Thanks for reminding me. I think I have one, I just need to put it in. It's heck getting old and forgetting things all the time.

Well if not, they're only $8.99 at O'Reillys (assuming you have the 232 motor) same as what I paid for the Javelin with a 998 transmission. Different part number, but the design of yours is the same as mine-- just probably a different height.  You can see how the right angle metal "blade" is (barely) attached to the rubber.  In my case, half the rubber was gone entirely. 
 

Just FYI, the mount as pictured in the O'Reilly's photo is upside down.


What he said.  X2.  If that mount is toast, and from what you've written earlier it is, you can do all the balancing and parts changing you want...and you'll still have vibration.  Thing to remember is that an AMC 6 cylinder engine with an automatic transmission is roughly 1/2 the length of the entire car - which also means that the torque of the engine has a very long 'beam' to exert it's force on - and the only thing that is keeping it in check is the rear mount.  Can't tell you how many of those I've broken over the years, and many times not from abuse - a big ol block of rubber that has oil spraying on it all the time is only gonna last but just so long.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Sep/01/2017 at 6:33pm
Yep, and those Torqueflites do like to leak!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Sep/02/2017 at 8:38am
I had some driveline vibrations and couldn't figure them out. Took the driveshaft to a shop for balancing and making an inch longer, and they found the splines were damaged in the yoke and binding a bit. Said that was more likely my problem than length (had 2.50" inside trans, 2.25" out -- Jag IRS so not much in/out movement). Lengthened it anyway, but got a new yoke also. Problem solved! So check and see if the yoke slides in/out easily while you have the trans out. I was going to change the housing bushing again as I thought that was the source of a bit of bind. I'd changed it myself years ago, thought maybe I'd deformed it a bit when driving in. The new one slid in/out perfectly though. This was an AW4 trans, but that shouldn't matter.
Frank Swygert
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