Vibration issues

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Byron Gray

Byron Gray

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Belfair Washington
I am having a vibration while driving. The vibration happens around 45-50 mph kinda smooths out around 60 mph when I'm just cruising and is most noticeable when I let off the throttle.
I have a 1973 Duster 360, 727 transmission I have a new drive shaft that was built by a shop they matched the drive shaft I had in the car before and I have the 8.75 with 3.23 gears the 741 case. 7260 small U-Joints.
I'm suspecting it's my slip yoke not engaging the output shaft properly the picture is of how the car sits now. The splines in the yoke do not start until about 1.50-2 inches in the yoke ( I haven't measured yet). I have not checked driveshaft angle yet. Would a yoke with splines that go the full length of the yoke help or re-measure for a drive shaft length?

20191027_161051.jpg
 
Hold it !! DO NOT go off into la la land. Do not make a problem where there is not one. You say you have a new drive shaft built buy "a shop". Lets start at the beginning and NOT make a new problem. The vibration is from your new drive shaft. That's it. Is that your original yoke? The 360 motor, the 727 trans,the 741 case, and the 7260 u joints are all what was there BEFORE YOU GOT THE VIBRATION.
None of that stuff matters. Is this shop a drive shaft specialty shop?
NOW HERE GOES>>>>>THEY DID NOT BALANCE THE NEW DRIVE SHAFT!!!!!!!!
 
I am back,
Oh well, here is another add on question.
What would of changed the drive shaft angle????
Why do you fell the need to check it????
 
How this all started was I changed rear gears to 3.73s 489 case that's when the vibration started I was using a combination u joint i probably wasnt using the right one I measured and may have been off my fault on that and on a test drive a u joint failed and the drive shaft came out at about 60 mph. I took it to a driveline shop and they put a new tube on it and used the same yokes at both ends. Yes they balanced it they welded a washer on the slip yoke side and put new u joints in
I then changed the pinion yoke on the differential to match the drive shaft.
It still vibrated. So I went back to the gears I had before the swap.

This vibration with the 489 case was worse and different. When you reached 40ish mph the vibration would shake the seats in the car it was that bad. It got worse when you hit the gas, less so when you let off. With the 3.73s in the 741 case, the vibration is almost the opposite: noticeable vibration at 50-60mph, getting worse with higher speed. The vibration gets worse when you let off. It also gets worse when going up a noticeable hill.


This picture is when I had the 3.73s in

20191027_133157.jpg
 
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So if I understand correctly..

  1. You had a vibration
  2. You replaced the center section
  3. You had a vibratation.
  4. You lost a driveshaft
  5. You rebuilt the driveshaft
  6. You replaced the center section with the previous center section
  7. You had a vibration.

Have you.

  1. Put the rear end of car up on jacks, with engine running and in gear and brought it up to vibration speed
  2. Had the tires balanced
  3. Checked that the vibration is not present when not in gear but at the same rpm
  4. Checked your axles for streightness
  5. Any chips on the brake drums
  6. Proven it is not the transmission
  7. Trans and engine mounts intact and bolted down propperly
  8. Previous poster pointed to pinion angle, did you change that
  9. Shock absorbers good
 
I did not have a vibration before I changed gears. I also had put new rear shocks and leaf springs. Brand new axles and it has a new rear disc conversion i drove it around like that for a few months couple 100 miles no vibration. I wanted a different gear ratio i bought a ring and pinion and built the 3.73s then the vibration started.
No I have not ran the car on Jack's
Wheels and tires are new and balanced nothing said by the shop about hard to balance.
Have not ran the car at rpm when not in gear.
I looked at the axles after I lost the drive shaft didnt see and signs of damage. I will take another closer look at them.
I have not proven it's not the transmission ( would that involve run it in gear without the driveshaft in it?)
I have not changed pinion angle (why I said I was going to check my angles because I have not done that on the car yet since I've owned it)
I just looked at the engine and transmission mounts and made sure they were good and tight engine is a solid mount and trans mount is brand new.
So I'm thinking when I lost the drive shaft I could have damaged the output shaft. Why it still vibrates when I went back to the gears I did not have a problem with.
And a slip yoke that engages the splines more. I have seen it recommends 1-1.50 inches of slip yoke exposed. I have about 2 inches now. (I understand with the output shaft damaged it would still vibrate with that change. Hence why check the trans first)
The only thing different from before I had a vibration and now aside from the new driveshaft is I went from 14 inch wheels to 15inch wheels on the front of the car. I have not changed anything else and change was the differential then the vibration started.
 
Did you replace the bushing in the transmission tailshaft? That bushing is what keeps the driveshaft from flopping around.

An old rule of thumb is one inch of yoke showing with the weight of the car on the rear axle or tires. And check for the yoke bottoming out on the trans output shaft, too.
 
Byron,Thank you for your post #7. Helps a bunch. REREAD your last 8 words...You have been doing a lot of u joint and yoke switching around. In the 3rd line you state "I bought a ring and pinion and built the 3.73s THEN THE VIBRATION STARTED"
I might look real close at the u joint straps. There are a lot of them of different styles and sizes. That could of gave you the first time vibration, sent the drive shaft flying, and still giving you the vibration.
Did you say you have solid motor mounts? Just curious. But my real question here is what transmission mount did you put on and when did you put it on?
After breaking two tail shafts (on the track, with a big mess) we found out it was the new polyurethane transmission mount and went back to the original.
 
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pt70 said:
Did you replace the bushing in the transmission tailshaft? That bushing is what keeps the driveshaft from flopping around.

An old rule of thumb is one inch of yoke showing with the weight of the car on the rear axle or tires. And check for the yoke bottoming out on the trans output shaft, too.
Click to expand...
I do have a new tail shaft bushing I can put in.
 
Donnie514 said:
Byron,Thank you for your post #7. Helps a bunch. REREAD your last 8 words...You have been doing a lot of u joint and yoke switching around. In the 3rd line you state "I bought a ring and pinion and built the 3.73s THEN THE VIBRATION STARTED"
I might look real close at the u joint straps. There are a lot of them of different styles and sizes. That could of gave you the first time vibration, sent the drive shaft flying, and still giving you the vibration.
Did you say you have solid motor mounts? Just curious. But my real question here is what transmission mount did you put on and when did you put it on?
After breaking two tail shafts (on the track, with a big mess) we found out it was the new polyurethane transmission mount and went back to the original.
Click to expand...

Yes after I got a new drive shaft I got a pinion yoke for the 3.73s to match the drive shaft u joints the 7260 ones. And a new set of straps as well still vibrated. The 3.23s already have the small u joint pinion yoke.
Yes my motor mounts are I call solid no rubber.
And I got my trans mount from auto zone I'd say it's a stock replacement mount
 
Can you move the slip yoke around in the trans?

More than original slip yoke?
 
When you lost the driveshaft was it the rear that failed or the front.

My thinking is if the output shaft has a lot of play it might be flopping around at speed. And would change depending on accel or decel.
 
Dana67Dart said:
When you lost the driveshaft was it the rear that failed or the front.

My thinking is if the output shaft has a lot of play it might be flopping around at speed. And would change depending on accel or decel.
Click to expand...
I want to say it failed at the rear but I'm not 100 percent sure on it. I have a new bushing for the tail shaft and I was looking into a slip yoke that has the spline threw the whole yoke. Mine the splines start like 1.50 inches if not more in the slip yoke.
 
Could be a bent tail shaft. U said u changed the leafs and raised the front end. Both of those things will change the pinion angle. Check that also. Kim
 
The better driveshaft shops wil want the front and rear yokes your are planning to use during the balancing.
Have you experience at changing ring and pinion gears,
Have you thoroughly checked that your trans was not damaged from the driveshaft failure, did you check your trans overrunning clutch for damage after the driveshaft failure. You could be flirting a trans explosion if the roller clutch was damaged from the driveshaft failure.
 
Duane said:
The better driveshaft shops wil want the front and rear yokes your are planning to use during the balancing.
Have you experience at changing ring and pinion gears,
Have you thoroughly checked that your trans was not damaged from the driveshaft failure, did you check your trans overrunning clutch for damage after the driveshaft failure. You could be flirting a trans explosion if the roller clutch was damaged from the driveshaft failure.
Click to expand...
Agreed. Kim
 
I didnt rise the front I only went from 14inch to 15inch wheels. I didnt adjust suspension. I kept the same tire size. I changed leaf's because the old ones were old and sagged. I didn't have the issue when I changed the leaf's. This issue began when I I swapped in the different gear set.
The shop had the old shaft and used the old front and rear yoke on the new shaft when they made it.
I was at my school when I put the gears together I had help from my instructor still not saying I didn't do something wrong. That's why I went back to the gears I had in before I had the issue.
I still had the 14s on the front when the vibration began
I ran the car with out the drive shaft to see if I could feel I vibration in the transmission I did not feel any weird vibrations. I am planning on removing the rear tail housing and checking the shaft and replacing the rear bushing to. so no I have not looked through the transmission yet. Have not had time to do so. Still have not ran the car on stands to find any other causes yet.
 
Byron Gray said:
I didnt rise the front I only went from 14inch to 15inch wheels. I didnt adjust suspension. I kept the same tire size. I changed leaf's because the old ones were old and sagged. I didn't have the issue when I changed the leaf's. This issue began when I I swapped in the different gear set.
The shop had the old shaft and used the old front and rear yoke on the new shaft when they made it.
I was at my school when I put the gears together I had help from my instructor still not saying I didn't do something wrong. That's why I went back to the gears I had in before I had the issue.
I still had the 14s on the front when the vibration began
I ran the car with out the drive shaft to see if I could feel I vibration in the transmission I did not feel any weird vibrations. I am planning on removing the rear tail housing and checking the shaft and replacing the rear bushing to. so no I have not looked through the transmission yet. Have not had time to do so. Still have not ran the car on stands to find any other causes yet.
Click to expand...
I will say it again. A drive line failure always calls for an inspection of the roller clutch in the trans. If it is failed the trans could explode if it's a 727. This could also be your vibration. You need to totally disassemble the trans, not just the tail shaft.
 
Duane said:
I will say it again. A drive line failure always calls for an inspection of the roller clutch in the trans. If it is failed the trans could explode if it's a 727. This could also be your vibration. You need to totally disassemble the trans, not just the tail shaft.
Click to expand...
I totally agree with this. Kim
 
Not an automatic guy but it sound's like Duane has some good advice.

In the OP picture it appears the housing is drilled for a balancer weight. Since the vibration was an after effect to the gear change, I'm sure this would not be his issue. I'll just post net found pictures for reference what it looks like……...
upload_2019-11-4_13-59-39.png


upload_2019-11-4_14-3-21.png
 
Well, that short driveshaft is asking for problems. But did you check the movement of the u-joints for binding? The binding makes them vibrate, but the binding also indicates a probable off center condition that will REALLY make it vibrate. You could put stands under the axle and run it with the wheels and tires and brake drums off..just don't hit the brake.
 
Daves69 said:
Not an automatic guy but it sound's like Duane has some good advice.

In the OP picture it appears the housing is drilled for a balancer weight. Since the vibration was an after effect to the gear change, I'm sure this would not be his issue. I'll just post net found pictures for reference what it looks like……...
View attachment 1715418509

View attachment 1715418510
Click to expand...
I am not saying his vibration problem is the trans. I am saying that when his driveshaft fell out of the car at 60 mph that could have created a separate problem. I've seen plenty of torqueflites blow up at the track because a previous driveline failure damaged the roller clutch and it was not checked. Later the trans is run again and kaboom.
 
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