833 OD vibration

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dusterMike

dusterMike

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I have a vibration from 2500 to 3000 rpm (engine speed) in 4th gear. I cant figure it out. I have tried everything. I replaced the u-joints, slip yoke, and rebuilt the trans with new bearings and output bushing. swapped in a different rear end. tried changing the u-joint angles. had the drive shaft balanced. put the car on stands. removed the wheels, drums and axles. I know its not the engine because the vibration is dependent on output shaft speed. in 3rd gear the vibration moves to a higher rpm (approx. 3500). I even removed the slip yoke from the drive shaft, then installed it in the back of the trans and ran the engine to 3000rpm. the vibration was still there, only much less noticeable. has anyone ever seen a trans issue that could cause this?
 
Double check your driveshaft to make sure it's true. I scattered an A833 with a driveshaft that was slightly bent. Completely broke the tailshaft in to multiple pieces at about 60 mph.
 
When the drive shaft was balanced, did you include the information that it was going behind an over drive?
 
I would suspect the clutch disc, or the engine; the giveaway for me is that the vibration changes with engine rpm. I have had the discs spit springs out on me and or crack the hub retainer plates, or both, or just cast off friction material, all of which caused vibration.

You can sorta prove this by:
A) putting the trans in gear, depressing the pedal, then reving up the engine, with the car not moving, into the usual vibration zone; and then not having any vibration. This proves it's not in the engine or clutch. The disc however was stationary, being anchored by the in-gear trans and driveshaft.
B) Next, you put the trans into neutral, do not declutch, and again rev it up. Now the disc is rotating with the engine, and spinning everything inside the trans that is not integral with the mainshaft.Namely the input, the cluster and the 3 gears on the mainshaft; But not the synchronizers. Vibration now would most likely be the disc.
C) but if no vibration thus discovered, it would have to be after the trans; or remotely, something in the synchronizers or Mainshaft, which is not likely; possible yes, but not likely. You can prove this too. Drive the car up to the vibration zone in direct gear. Leave it in gear, declutch, and shut the engine off. Then a second or two later kick it into neutral, and let the pedal up. Note any vibration difference;Any vibration remaining would almost have to be after the trans.

Alternatively my CFII, has vibrated occasionally, since new. The flyweights seem to have something to do with it. Sometimes, once at cruising speed, I have to declutch and blip the throttle several times, before the vibration is minimized.
 
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I checked drive line runout in 3 places to verify it was not bent. All of my measurements were less then .020. I also checked it at the tail shaft right at the seal. I figured that was good way to verify the main shaft wasn't bent. I tried adding a clamp to the drive shaft to check the balance, but that just gave me a vibration at 1500 rpm in addition to the 2500 rpm vibration.
 
A wheel can be 100% balanced Ok in all axis yet if it has run-out in the treads, it will hop on the balancer, not vibrate........ But on the car it will shake the body up and down. You can often feel this at slow speeds.And the frequency and intensity is directly tied to speed. This I don't think has anything to do with your issue; I just thought it was worth mentioning.
 
I was reading through AJ's suggestions. particularly (C). those are some things I haven't really tried. the vibration happens from 75 to 90 mph (2500 to 3000 rpm in OD). so I was thinking I would take it up to 90, then put in neutral. I figure if the vibration is still there it has to be after the trans, but if it goes away then it must in the trans.
 
dusterMike said:
I was reading through AJ's suggestions. particularly (C). those are some things I haven't really tried. the vibration happens from 75 to 90 mph (2500 to 3000 rpm in OD). so I was thinking I would take it up to 90, then put in neutral. I figure if the vibration is still there it has to be after the trans, but if it goes away then it must in the trans.
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I really doubt that it inside the box, that OD gear is really really small. Using direct gear will bypass all the internal parts and any vibration remaining, will likely be after the trans...... if you have proven that it's not in the engine or the clutch, per the offered tests. So then in direct, you don't need to drive that fast.

Here's another tip; 30 mph is 44 feet per second. If you have a 26.7inch tire at 7 ft circumference, the tire would be rotating at ~6.3 revolutions per second. To get an idea of how fast this is, it is about as fast as you can count numbers from one to 12,repeating.
 
If it is the drive shaft it shouldn't matter what gear you are in, the vibration would be more related to the speed. Now granted you probably will still get more vibration under load.
 
I didn't think about 3rd being direct, that's a good point. I have ran the car on stands in 3rd and the vibration moves to approx. 3500rpm. which still comes out to be about 75mph. If it is the driveshaft, I'm not sure what it could be. I've tried balance and angle changes. Ive checked the run out. when i changed the balance or angles, it gave me a different vibration at a lower rpm in addition to the 75mph vibration. i do have an engine vibration in neutral, but it goes away around 1500rpm. I cant see the engine vibration being directly related to wheel and driveshaft speed.
 
Have you checked the index on the drive shaft? Mine was off after I had it shortened. I had a speed related vibration too.
 
Drive shafts have a working RPM range. They are balanced with that RPM range considered. Every drive shaft will produce a harmonic vibration or drone if it is spun out of its balance range. This is why I asked about the overdrive situation. You must multiply the RPM of "high gear" third, times .73 I think it is for the over drive. This may well give you an RPM that is out of the range of balance for a normal non OD drive shaft.
 
Plus I am not sure what speed they spin driveshafts to balance them, but I would hope it is higher than the actual speed they will be used at. and they should be quiet and balanced up to that point.
 
I called the shop that balanced the shaft for me and they said they only spun the shaft to 2500rpm. I took the shaft back and had them balance it again, but this time I specified that they spin the shaft over 3000 rpm. the guy tried to balanced it again, then called me when he was done. he said the shaft was balanced until it hit 2900 rpm, then it started going crazy and he couldn't balance it. now I am having a new shaft made.
 
Well I'm still trying to figure this out if anyone has anymore ideas. I had a new driveshaft made with 1330 ujoints, new slip yoke and new rear input yoke. I tried shimming the pinion down and up 2 degrees. I even tried shimming the trans up to change the ujoint angle. I replaced the engine vibration damper. I even tried removing the speedometer gear. The only part of the drive shaft that has any play in it is the slip yoke. the bushing and yoke are new. does anyone know the spec for trans end play? im wondering if the trans main shaft splines are worn out.
 
I finally made some progress with this issue. Even though the drive shaft was balanced twice, I decided to try and balance it myself. I installed a hose clamp in 12 different positions on the shaft and ran it up to speed. I found one spot where the added weight reduced my vibration. Im not sure if its because the shaft is still out of balance or if im compensating for a balance issue elsewhere in the drivetrain. either way the added weight is helping.
 
dusterMike said:
I finally made some progress with this issue. Even though the drive shaft was balanced twice, I decided to try and balance it myself. I installed a hose clamp in 12 different positions on the shaft and ran it up to speed. I found one spot where the added weight reduced my vibration. Im not sure if its because the shaft is still out of balance or if im compensating for a balance issue elsewhere in the drivetrain. either way the added weight is helping.
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Have you tried the doing all of tests that AJ recommended in post 4?
 
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