Bad Drive Line Vibration

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blewbyoutobad

blewbyoutobad

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Does anyone have ideas on pinion angles. I have a severe vibration that starts at 5000 and stays until redline. I have had the driveshaft balanced and u-Joints checked. The car is a 372 stroker, 904 reverse manual valve body and a 742 diff with 4:30 gears. I found a really weird thing when I pulled the driveshaft and it has a spicer 1350 on the diff and a smaller u-joint on the 904. It was like that when I bought it. Here's the pinion angles.
904 down 1/2 to 1 degree, 742 diff up 2-3 degrees and 4 degrees on the drive shaft angle. The slip joint is tight in the tranny so I don't think I have a bushing issue. To me I think I need to shim the rear. Sound right?
Thanks all
 
You definetly need to get the rearend pointed down because right now the working angle is nearly zero sitting still and the differential twists up on acceleration. The type of suspension your running determines how much down it needs to go. i.e. leaf springs need more angle than a 4 link or Cal-tracs.

The different size U-joints are somewhat common. Probably has a std. 7260 U-joint trans. yoke but the rear end has a 1350 yoke so they installed a 1350 yoke on that end of the driveshaft.
 
I would get rid of that front slip yoke and get a yoke that holds a 1350 joint. We ran the same ujoint you are running and broke 2 of them in a 1 year period ,it took the drive shaft with it along with the sprag in the trans. I called Inland Empire Driveline service and they made me up a nice aluminum shaft with 1350's on both ends and a billet slip yoke with bolt on straps .

[ame="http://youtu.be/v2lldMmyg5I"]302 Found[/ame]
 
Here's what I did the other day. I shimmed the nose down 4 Degrees on the pinion, for a total down of 1.5 degrees (with no shims it's at 2.5 degrees up). Test drove it and the vibration moved from 5000 to 5500. I think I'm going in the right direction. Tonight I will adjust the pinion snubber up until it just clears the floor. I know that's not what I need for the street but I want to stop the pinion from moving up and see if that helps. If it does then I'm thinking its a matter of shimming the pinion down a little more (maybe 6) and backing off the snubber enough that it works on the street. Total down if I shim at 6 is 3.5 degrees down. Tranny is down .5 to 1 degree. I know I need them to cancel under full power and this motor pulls through the traps at 6500. Vibration starts at 5000 with no shims.

Am I going in the right direction?
 
I may be reading something wrong here, but i have a thought/question and hope some of you will comment if you think i'm off base.

While i can see the need for tweaking the pinion down, i'm curious to why the vibration issue is at high rpm's. My opinion is that the maximum upward force on the pinion occurs under maximum load...launching, peak torque and shift points and it actually relaxes at the top end. My question is, doesn't it seem like in this situation, the vibe would show up earlier and get better down track when the pinion load/angle relaxes downward. I guess i'm just wondering if there could be two issues, like a vibe in the carrier also. I welcome comments to this post. I'd like to know if i'm missing something.
 
The pin angle won't really relax as you get upstairs.

He may have a bad angle, as rpm at the shaft increases you need to REMOVE angle, joints can only operate or oscillate at low rpms, when they are being used in performance applications then they need 0.0 angle when underload, the pin is set so that when under load it is in alignment with the shaft, in performance cars and boats there should be no angle from the motor back.
After 5000 rpm all angles should be below 3 degrees, beyond 6k and you should be at 0.0, and as you increase u joint size that limit is lower earlier.
His car seems to be acting like a bad angle.

wheelsup73 said:
It will be when he breaks it and kills his drive shaft.
Click to expand...

The front joint isn't going to break just because it is a 7260 series
 
Once you get angles figured out and corrected if necessary, check for worn tail shaft bushing that front yoke runs on.
 
If problems persist after numerous shims,you may have to cut perches off and weld new ones on.Make you angle right and be done with it.
 
Ok friends, new data. Set the vehicle at ride height. Pulled the driveshaft and made the following measurements. Pulled the tailshaft housing seal so I could get a good measurement on the end of the output and it read 3 degrees down on the end. The 8 3/4 rear pinion yoke is at 4.5 degrees down. I had added a 4 degree shim from a previous effort when I thought I had a zero tailshaft angle. I also found play in the 904 output shaft. I measured it with a dial indicator at .026". Sounds like the bushing is gone. So for now I have two questions.
1) With SS springs where should I shim the perch
2) Anyone with experience replacing the tailshaft housing bushing

Thanks for all the suggestions. I think I am finally on the right track.
 
I just read up on this subject in one of my mags. Of course I can't find the dang thing.
I remember they mentioned that you may possibly need to shim the rear u-joint up,instead of down. May be worth a shot.
 
Sp the plan is to remove the 4 degree shim and replace the tailshaft bushing then give it a try. If SS springs can move up 5 degrees on acceleration I may need to use my 2 degree shim in the down position on the third member. It will take a week to get the bushing and get it installed.
 
Supershafts said:
The pin angle won't really relax as you get
The front joint isn't going to break just because it is a 7260 series
Click to expand...
It is a weak link and we broke 2 of them with my 360 motor running 10.90s. My stroker would kill that joint in no time and anybody racing should run 1350 joints period. You should run a video camera under the car and watch whats going on under there.

73wheelstander.jpg
 
Thats a great idea wheelsup about the video camera. I am trying to locate parts locally. Im in the Houston area.
Thanks
 
Blewbyyou I'm not saying the tailshaft bushing isn't bad since I'm not there to see it but just so you know the yoke has to be in place to get a proper reading as it's what contacts the bushing. The output shaft is held in place by the output shaft bearing and due to it being nearly a foot forward of where your measuring the least bit of slop in the bearing will be magnified several times over. Put the yoke back in and re-measure the play and see what you have.
 
Thanks for the info fishy68. This measurent was taken with the driveshaft in place. I wish I could see a cut away of how all this fits together. I'll search for a repair manual.
 
You probably had other issues, or junk joints, i have many customers cars in the 1.2 60's on 1310 and lots of mopar SS cars on lightened 7260 stuff. I even have 2 customers using 10/30 joints going better than 10.0 on a 3" AL shaft that even my calculations say it's questionable....
Your car for whatever reasons may have had something else going on, compound angles, being as dodge offsets everything to the side and then some diff companies set the end yoke in center, or you had another angle.

When was the joint breaking ?

I had a video cam under cars back in the 80's, i also understand that a spring is really 2 sections and each section needs to be modified for what it is being asked to do power and ride control.



wheelsup73 said:
It is a weak link and we broke 2 of them with my 360 motor running 10.90s. My stroker would kill that joint in no time and anybody racing should run 1350 joints period. You should run a video camera under the car and watch whats going on under there.

73wheelstander.jpg
Click to expand...
 
Hey Supershafts
I have not broken any u-joints yet. Just the bad vibes coming in at 5000 to redline. I have tried different leaf spring shims and calculated a cancel angle using 5 degrees for upward pinion movement with the SS springs. Funny thing today, I pulled the 4 degree shims and installed 2 degree. This was all done at ride height with 4.5 degrees down on the pinion with the 4 degree shims. The tranny is at 3 down. After installing the 2 degree shims I measured at the same exact place on the pinion yoke and had 4 degrees down. The car was not moved between measurements with the 4 degree and 2 degree shims. I feel like I'm chasing my tail. Even after a rebalance on the drive shaft I still have this doubt in the back of my mind. I probably need to find another shop and see what they find. I spoke with Rick Allison at AandA Transmission and have a tailhousing bushing coming. It is suspect at this point. This vibe is speed related.
Thanks for your comments.
 
5000 rpm and better shaft speed you should be below 4 degrees and approaching no angle, however have you had any change at all with all the changes you have made in this thread or nothing at all.

I deal with vibrations all the time only thing is i can't ride with you, I would set the pin so it is at 0.0 with the shaft under load.

Is this car all factory or has things been changed, is the rear factory or aftermarket.

Try the bushing at the tailhousing if it's bad it will show something, then what is this shaft that's in the car ? factory or aftermarket or something found in a JY that just works for the length you needed, this is what happens when you have the wrong shaft for the speed it is being asked to do and they vibrate like that just before they break.

As for the balancing at the shop, does the vibe get worse or start to get better after 5500 or by 5500 it feels the same and at 6200 it feels better.

If its doing anything different you need to see another shop for balancing, many driveline shops use a machine that spins shafts at 500 rpm and makes calculations that doesn't work for what the shaft will need at 3000, none of that type machine make calculations for beyond that.
.
 
Supershafts
Nothing I have tried works. Last night I took off the drag radials and installed radials from my Dart. A much smaller tire in width and diameter but they are new and just balanced. It did clear up the low speed vibrations, 30mph but nothing changed at the top end. I have adjusted pinion angles and rebalanced the driveshaft. The shaft was made for the car 8 years ago. It has the correct yoke engagement at the tranny. I can pull the new axles and third member from my Dart and try them, but first I will set the pinion to 0 and install the drag radials after I get them balanced and let you know.
Thanks for the help.
 
What is the length and diameter of the shaft ? with no change at all with any of the angle adjustments you made its making me think its something else.
When you make a angle adjustment something should change, even if by 500 rpm, but something should change.
What is happening if you try and exceed the speed at 5k? what does it feel like at 55 and 6k
 
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