Vibration at 3200 rpm and above need help

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chasonmarose

chasonmarose

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i recently swapped out a 8 1/4 rear end for a 9 1/4 with posi and 4.11s. I have a 727 transmission and when I bring the vehicle up to 3200 and above it vibrates like crazy, feel it in the steering wheel and when the wheels are turning every 1.5 seconds seems like a vroom vroom that's when the vehicle is at 65 mph and above. Even when I'm driving in town it seems to be vibrating a little as well. Just don't know what the problem is could it be front tires out of balance? They are fairly warn off, and I noticed a small gouge on my driveshaft. Any help would be appreciated
 
Sounds like you need new tires for starters,also a new driveshaft.You can have one made by DriveLine.I,d get new U-joints also.
 
If your only change was the rear end and you didn't have the vibration problem before then it's probably the pinion angle:

http://www.moparts.org/Tech/Archive/axle/8.html

ALSO:

If there is vibration under acceleration, you need to add more downward pinion angle preload. If the opposite occurs, the vibrations tends to decrease or disappear under acceleration, you need to reduce the downward angle preload.

If the vibration steadily increases with driveshaft speed (either accelerating or decelerating) the symptom is primarily the result of a driveshaft imbalance or yoke runout. Sometimes this yoke runout problem can be improved by rotating the U-joint 180-degrees in the rear end differential yoke.

Driveshaft-related vibrations usually occur at roughly engine speed in high gear. Wheel/axle vibrations usually occur at 1/3 rd engine speed or driveshaft speed because of the differential gearing. To determining whether it is the output of the transmission or the pinion in the differential, change gears when the noise occurs and maintain speed. If the vibration/noise changes in frequency, the source is in the transmission or engine. If the frequency remains the same it is a driveline problem.


Good luck,
Treblig
 
chasonmarose said:
i recently swapped out a 8 1/4 rear end for a 9 1/4 with posi and 4.11s. I have a 727 transmission and when I bring the vehicle up to 3200 and above it vibrates like crazy, feel it in the steering wheel and when the wheels are turning every 1.5 seconds seems like a vroom vroom that's when the vehicle is at 65 mph and above. Even when I'm driving in town it seems to be vibrating a little as well. Just don't know what the problem is could it be front tires out of balance? They are fairly warn off, and I noticed a small gouge on my driveshaft. Any help would be appreciated
Click to expand...

Can I see that gouge?
Because your description sounds pretty much exactly like a bent or out of balance driveline.
(ESPECIALLY if it has no vibration when stopped and revved up)
 
Ok so I narrowed the problem down to the driveshaft causing all the grief, I set it up on jack stands in the garage and watched it spin under various rpm ranges, driveshaft is a little out of balance now how Can I fix the pinion angle? How do u adjust that?
 
chasonmarose said:
Ok so I narrowed the problem down to the driveshaft causing all the grief, I set it up on jack stands in the garage and watched it spin under various rpm ranges, driveshaft is a little out of balance now how Can I fix the pinion angle? How do u adjust that?
Click to expand...

You will need to pull that driveline and get it straightened/balanced first, as you may not have a problem with angle.
Trying to do two things like that at the same time may not work out very well in the end financially.

Pinion angle is usually adjusted with angled shims between the springs and spring perches.
 
Check and make sure the joint is the same series for the end yoke of the new diff...

pin angles cause issues at LOAD, not cruising...or far more likely to be a problem at load
 
When it was tested on the jackstands, did you perchance remove the wheels and drums, to rule them out?

In my 68 S-clone,I've run 4.10s and 4.30s, both of which excited the natural body vibration. They both made that characteristic quiet "whoop-whoop-whoop"sound throughout the car and both at 55 to 60 mph.This was not a vibration. No other gear ratio that I have run ever did this(2.76 to 3.55,3.91,4.89 and 5.13s) These were all just chunk swaps.The 4.3s were bearable but the 4.10s I sold to a guy with an E-body and problem solved. I had a 70 Swinger340 that did it too.
I think As might be allergic to 4.10s! LOL
 
The issue with going from old original 2.7 and 2.8 and 3.2 series gears and then jump to 4.1 and other series are your driveshafts were never balanced for those rpms.

That is your sounds you heard, wasn't the gears just your shaft is now operating where it never did before.

.
 
supershafts
If that was addressed to me; I had one shaft balanced for the 4.3s, and told the shop I wanted it as smooth as possible at 60mph and hopefully up to100mph.They didnt get it right the first time, so I had them do it again.The second time was better, but not by much.It was quite smooth on the jackstands.
I used a different driveshaft for the lessor chunks as the yokes were different.
I tried several different pinion angles.
It only did this at 55 to 60, and only with the 4.xx gears, and only really noticeable when cruising. I therefore attributed it to the natural body rhythm, somehow being excited by the D/S speed with the 4.xxs.

I soon pulled the 4.3s, cuz around town 1st gear was useless most of the time. I swapped in 3.55s and a 3.09 low gearset. problem solved.

I recently sold the 4.30s to a fellow with a Coronet. He hasn't called with a complaint yet.
 
Universal joints sound like they are cactus. Cactus being an Aussie saying for stuffed, rooted, buggered, knackered, broken, shagged, screwed or generally not functioning.
 
Ripper said:
Universal joints sound like they are cactus. Cactus being an Aussie saying for stuffed, rooted, buggered, knackered, broken, shagged, screwed or generally not functioning.
Click to expand...

You saw the part where he said he had a gouge in the driveline right?
That immediately points to driveline straightness or balance issue's.
 
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