put in 8 3/4, now have vibration

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Badsport said:
Wow, that slip yoke should be in the trans more for sure. How did you measure the length for the shop? I would not drive it until the problem is corrected, you could damage the tailshaft.
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Damn. I wish it wasnt you sayin this Badsport... because I have too much respect for your mopar knowledge... which means I will likely have to concede the problem is the short shaft and spend more money getting a new (used) one and pay to balance again...

But thanks for your input BadSport. The truth hurts sometimes, but I need it.
 
Powerflite said:
Also, I am not certain, but it looks like your yoke is made for the big joint. Take the joint out from the driveshaft and try fitting the larger end into the yoke. If it fits well, you should use a standard 7290 (big) joint. I think that is all it could be as the 1350 stuff uses U-bolts instead of straps.
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u bolts instead of straps? I thnk I'm gonna have to check online for pics so I can understand.

The one I put in does not have a larger or smaller end. It was square (same dimensions every way).

But I'm hoping you may be onto something. I have a "big to small" u-joint that I used on a different a-body 15 years ago. Maybe I will try and fit the big end of that one into the yoke. I notice the yoke, where it receives the cups, is kinda cupped out itsself... like the edges are higher (maybe I should file?) and middle worn down. Maybe I'm using the wrong straps...
 
screeminDemon said:
Horror Freight, LOL I like that place! But anyways I didnt know anything about the pinion angle, do you know what the angle should be?

Here is a couple pics of front and rear ujoints: PS - who thnks the problem might be caused from my driveshaft a little too short?
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Rear u joint doesn't really look assembled right, shouldn't that cap towards the bottom of the pic. be in more with a clip ?
 
screeminDemon said:
Damn. I wish it wasnt you sayin this Badsport... because I have too much respect for your mopar knowledge... which means I will likely have to concede the problem is the short shaft and spend more money getting a new (used) one and pay to balance again...

But thanks for your input BadSport. The truth hurts sometimes, but I need it.
Click to expand...

FYI It cost me $260.00 to have a brand new shaft built at my local shop.
This included new spicer ends and u-joints.
I just took them the slip yoke and gave them the measurements.
 
screeminDemon said:
I took the shaft out last night, then re-installed it. I measured/estimated that the tongue/slip engages about 2.5" of tranny spline (tailshaft?).

I know it should be more like 4.5" however I'm still not conviced this is whats causing my vibration. Maybe... but maybe not, I dont know.

The ENTIRE drivetrain was not replaced, just the driveshaft and rear end. I was already running my new 360 and a-833 without vibration for about a year... on the original 7 1/4 rear end... probly 2.94 gear.

Thanks for you help! PS - I already had the shaft balanced (and they replaced parts of it which cost me close to $200). The shop claims they shortened it according to my request (2") and tells me I'm to blame for giving wrong instructions. I wish I had given written instructions and dimensions instead of just verbal... cuz I'm convinced they screwed up and shortened it too much. Is it possible to get more length out of it? Change the slip or something?
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Why would shorten the shaft 2" without first measuring it to even know what you need 1st...

Who gave you what instructions on this measurement ?

.

How long is that slip ? end to center of joint ?

Does the shaft you have taper at the weld yokes or is it the same diameter all the way thru ?

What diameter is the tube ?

depending what diameter it is it may be able to be retubed.... MAYbe

,
 
Supershafts said:
Why would shorten the shaft 2" without first measuring it to even know what you need 1st...

I did measure first.

Who gave you what instructions on this measurement ?

self instructed...just eyeballed it and used a measuring tape

How long is that slip ? end to center of joint ?

I don't know exactly, will have to measure and post tomorow

Does the shaft you have taper at the weld yokes or is it the same diameter all the way thru ?

same diameter all the way

What diameter is the tube ?

Will have to measure and get back to you

depending what diameter it is it may be able to be retubed.... MAYbe

I think

,
Click to expand...

PS - you sound like an expert in this area Supershafts, hence your name. Do you think this short shaft is causing my vibration, as Badsport seems to think? or do you think its a u-joint issue? Thanks for your advice!
 
Depends on the bearing surface of the slip, if that slip is 9" long than there should be plenty in the bushing.
detroit made slips for mopar ranging from 5" to 9.8" long, some were counter bored 1" some were countered 3", there are so many different factory slips for the only 2 transmissions mopar used that it is amazing

It's not the spline engagement, what people don't understand is the spline engagement only needs to be the same as the diameter of the spline...

If the spline is for example that of the 727 1.3, then the spline engagement only needs to be 1.3".... It's what is in the bushing, the trans tail bushings are anywhere from 1.37 to 2.8 in trans tailhousings and it's how much of the ground hub is in that, if you have 2.5 or so in then the slip should be supported.

You need to give more detail on the vibe, does it come in at ___ speed and it gets better or worse as speed increases, does it ever get better after a certain speed....

You changed several things at once, i had thought you only dropped one center for another and went from most normal fact ratios of 2.9 or 3.2 to 3.9 and that alone can make a vibe as now the shaft is at a rpm it never was before..

Now why the shaft was shortened is beyond me, if you couldn't get the shaft in then you had a reason to shorten it, otherwise the instruction you were given to measure from where to where when you have the shaft is also beyond me why that was done.

I do driveline work, and yes many people get online and ask others what to do and get a measurment form others and then they got a problem, and then they gotta pay twice. It's why i always say, measure your own car and ask what your local driveline shop wants you to do.

I can't tell you how many people shortened a shaft and then had to spend more for a longer slip or retube, or in many cases make a new one..

I can also tell you it can also be in the shops balancing, but i need more detail of whats going on.
.
 
Supershafts said:
You need to give more detail on the vibe, does it come in at ___ speed and it gets better or worse as speed increases, does it ever get better after a certain speed....

Now why the shaft was shortened is beyond me, if you couldn't get the shaft in then you had a reason to shorten it, otherwise the instruction you were given to measure from where to where when you have the shaft is also beyond me why that was done.


I can't tell you how many people shortened a shaft and then had to spend more for a longer slip or retube, or in many cases make a new one..

i need more detail of whats going on.
.
Click to expand...

Thanks for your reply Supershafts. The shaft had to be shortened because It was the original shaft, designed for the original 7 1/4 rear end. After installing 8 3/4 rear end the shaft was too long and would not fit.

And I also put in new axles and new brakes.

After all that the vibration started: it begins as a fine vibe around 40-45 mph then gets more coarse and stronger as I get faster. By the time I hit 70 its pretty bad, enough to disourage me from going any faster. If I'm going down a big hill and coast in neutral the vibration is really bad.

I pulled the axles back out, they looked great, then re-installed. Since then I've been messing with the rear u-joint. I just don't know if I should focus on the joints or if the short shaft is the problem. Thanks for all your help!
 
If the vibe is getting worse with speed, then you have a issue with the shaft itself or you may not have 2.5 or more in the bushing.

coasting in nuetral rules out the front half of the trans and everything in front of it, which leaves the shaft and rear, and for the rear to make a vibration it'll usually not going to be able to get to speed again.
A bent wheel or even loose wheel can too, but i'd look at the shaft and see exactly what is what, is it a long slip or short slip, is there 2.5 or better in the bushing or is it just short of that.


.
 
When you measured did you have the suspension loaded? (jack stands under the diff itself)

Form where to where did you measure and what was that number?

What is the length center to center on the caps in the shaft?

What trans do you have?
 
Thanks for the additional input fellas. Unfortunately I've been really sick the past few days and unable to get back under and measure or take more pics.

From everything I've read, I think its time to bite the bullet and take my driveshaft into the shop again... see what they can do with it. My best estimate is the slip is about 6 to 6.5" long, so maybe they can put a longer one on it. If not, I guess I'll have to pay for a new driveshaft and eat some crow. Won't be the first time, and probly not the last either...
:eek:ops:

PS - Badsport: my tranny is a833 with OD
 
If it were me I would call around to some other shops in the area, the 200 they charged you is out of line IMO. Like I said I got mine done for 90 bucks.

When you find said shop ask them specifically how they want you to measure it. The shop I use wants a measurement from the end of the tailshaft, not the output shaft, to the flat spot on the rear yoke where the strap bolts on and they figure from there.

If that yoke is indeed 6.5 inches it looks like you have about 5 of it exposed, too much IMO, especially if the first little bit of the splines inside have been machined down.

When measuring make sure you have the rear suspension loaded with full weight of the car on it, not hanging.

When it's all assembled and full weight on the suspension about 1 inch maybe just a smidge more OK, should be showing on that slip.

That may or may not be your problem, but the way it looks now if it's the short slip yoke would make me uncomfortable driving it. IF that thing blows apart and the shaft drops and hits the road , hang on. I had one let go on me about 35 years ago and it dug into the pavement and lifted the a$$ end of my car about three feet off the ground and set me sideways in the road, I was lucky it didn't roll.
 
My best estimate is the slip is about 6 to 6.5" long, so maybe they can put a longer one on it.
Click to expand...

If they have some factory versions then you could do that, if not and you gotta get a new shaft might as well upgrade then




The shop I use wants a measurement from the end of the tailshaft, not the output shaft
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The output shaft is the tailshaft, that is the correct term to describe it output, it surely isn't the input shaft.

The right way to measure it is if the slip yoke is there that is going to be used, always use that bottomed out then there can be no mistakes with trans that have other issues of internal designs on the output shafts, if no slip yoke is present then the output shaft and the seal location to center or face.
Many shops don't do this and this is why mistakes happen with output shafts that have o-ring issues.
 
Update: I got a new driveshaft the correct length installed a while back (I haven't been on this site for a while) and it turned out that it did not change anything.
Still a bad vibration over 60mph and downright scary beyond 70mph. So I've been driving around the past few years mostly staying off the freeway.

Now: Recently did some suspension work including new manual steering box (old one had excessive play), new torsion bars 1.03, added front sway bar and rear sway bar, rebuilt front lower control arms, 4 new Bilstien shocks, rebuilt rear leafs. Also note that I removed the rear long shackles that I was using as a cheap lift kit and the vehicle pretty much sits level now.

Vibration problem is now fixed!!! I've been up over 80mph without a problem.
Question: What do you think fixed it?
 
screeminDemon said:
Update: I got a new driveshaft the correct length installed a while back (I haven't been on this site for a while) and it turned out that it did not change anything.
Still a bad vibration over 60mph and downright scary beyond 70mph. So I've been driving around the past few years mostly staying off the freeway.

Now: Recently did some suspension work including new manual steering box (old one had excessive play), new torsion bars 1.03, added front sway bar and rear sway bar, rebuilt front lower control arms, 4 new Bilstien shocks, rebuilt rear leafs. Also note that I removed the rear long shackles that I was using as a cheap lift kit and the vehicle pretty much sits level now.

Vibration problem is now fixed!!! I've been up over 80mph without a problem.
Question: What do you think fixed it?
Click to expand...
You corrected the pinion angle in the rear when you made those mods. Way to go!
 
screeminDemon said:
Update: I got a new driveshaft the correct length installed a while back (I haven't been on this site for a while) and it turned out that it did not change anything.
Still a bad vibration over 60mph and downright scary beyond 70mph. So I've been driving around the past few years mostly staying off the freeway.

Now: Recently did some suspension work including new manual steering box (old one had excessive play), new torsion bars 1.03, added front sway bar and rear sway bar, rebuilt front lower control arms, 4 new Bilstien shocks, rebuilt rear leafs. Also note that I removed the rear long shackles that I was using as a cheap lift kit and the vehicle pretty much sits level now.

Vibration problem is now fixed!!! I've been up over 80mph without a problem.
Question: What do you think fixed it?
Click to expand...

Or, the front yoke stopped flopping around because it was deeper into the trans.
 
I think it was the corrected pinion angle. That was part of the most recent upgrades. I fixed the yoke problem with a new driveshaft long ago and the horrible high speed problem persisted after that
 
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