vibration & no solution...2

[De-noz]

Notice a high speed vibration if i get into the +80mph (4000 rpm)range with my 65/455- conv. / TH400
I notice it came from behind, and i´m not sure if i hear a "DDDDRRRR" that stops if i slow down, or if its only the pulsate of vibration that cross the car?? .....soooo i checked the drivline angle first, notice the Trans was 3,5 down,as long as the Pinion was 0,5 up ( digital Tool) -*

so i corrected Pinion to 3,5 up to be equal !!

NOTHING!! Vibration start at the same speed.
Change the Tires ( I talk to myself, maybe the big 295/50 are shake )

NOTHING!! Same speed same Vibration!!

The parts below are changed and now installed:*
-again new Motor mounts
-againTrans mount
-weld brackets to the boxed frame to minimize swinging from the Trans- crossmember
-new balanced driveshaft (5500 rpm)
-new U-Joints
-Transm.angle 3,5 deg.down / Pinion angle 3,5 up as i say
-Rear end overhauled /Posi-Gears-Timken bearings-old shafts!
-UMI´s rear Uppers with spherical rod ends
-Stock reinforced lowers with poly

NOTHING...NOTHING..NOTHING....still the Tiger in the Trunk

I was thinking to check
- if maybe a axle bent
- if Converter not installed correct*
- U-Joints or maybe on more time the rear end
(backlash-play-POSI Clutch-bearing???)

any input...any idea..let me know

sorry for my English

[jlcustomz]

Very aggravating problem I know.I recently found a new u-joint to be bad, causing a similar vibration. In recent research, others have had continuing problems that still tracked down to driveshaft related issues, even with new expensive parts. One person,I think on this site, did the old style driveshaft balance method of a washer on a hose clamp in different positions till vibrations improved, then welded the washer on. His was a new driveshaft. Also read an old time method of putting a quart of motor oil in the shaft & welding back up. The oil works as a dampener & coats uneven internal surfaces.
Just a few thoughts.May want to do google search on balancing you own driveshaft. I ran mine up on jackstands trying to identify the rumbling noise.

[SSLance]

What diameter is your driveshaft? I chased very similar problems and eventually upgraded from a 2.5" diameter driveshaft to a HD 3.5" diameter driveshaft and it fixed the problem immediately. The smaller driveshaft just couldn't keep from noodling at high speeds causing the vibration even though it was perfectly balanced.

[andrewb70]

Good suggestions here. I would get a dial indicator and start checking the run-out on the various driveline components. The easiest place to start is measuring the driveshaft run-out at the front and back. Other components to check are the transmission tail shaft bushing and the pinion yoke itself.

What kind of car is it? Is it lowered?

Andrew

[De-noz]

Very interesting Information.....
about the JACKSTANDS, i´m really afraid put the car on jackstand and bring to more than 4000RPM.

Maybe i check the new U-joints

[De-noz]

jlcustomz: Very interesting Information.....
about the JACKSTANDS, i´m really afraid put the car on jackstand and bring to more than 4000RPM.

Maybe i check the new U-joints

[SSLance]

Check to make sure the tailshaft bushing in the trans case is tight against the slip yoke too. Grab the front u-joint and push it up or down seeing if the shaft moves inside the trans.

A driveline vibration can cause premature wear on that bushing which can create yet another driveline vibration.

[De-noz]

What diameter is your driveshaft? I chased very similar problems and eventually upgraded from a 2.5" diameter driveshaft to a HD 3.5" diameter driveshaft and it fixed the problem immediately. The smaller driveshaft just couldn't keep from noodling at high speeds causing the vibration even though it was perfectly balanced.

It´s a 3.5" diameter driveshaft

[De-noz]

Good suggestions here. I would get a dial indicator and start checking the run-out on the various driveline components. The easiest place to start is measuring the driveshaft run-out at the front and back. Other components to check are the transmission tail shaft bushing and the pinion yoke itself.

What kind of car is it? Is it lowered?

Andrew

Car is 65 Olds conv. 455/TH400
Yes a good suggestion
Correct me if i´m wrong, but the only way to check transmission tail shaft bushing is to open the trans and look?
But how to check the pinion choke?

[jlcustomz]

As long as you're good & solid on jackstands, you're ok. I put stands under each side of rear axle; & stacked wood blocks under frame in front of rear wheels. Couldn't shake it by hand at all. Just past 3500 rpm in 6th gear I hit 160 mph, pic is about 180 mph.Crazy, but not totally stupid. 80 would be sufficient though. Keep in mind a run on jackstands is not under load.


Check the front bushing by pushing up & down on shaft & looking for any visable slack at all. With car running at idle speed on stands I carefully barely touched a magic marker to front & rear of shaft to see if I could spot any bad runout. Mine showed near perfect.
My case of a new name brand u-joint binding up on the ends is likely an unusual case, but it induced the same type of vibration as a joint too loose side to side once did. Made a constant rumbling sound like a bass note test signal at a stereo competition Also in my particular case, the extra high speed run on stands made the bad joint show itself more afterwards.

[andrewb70]

Car is 65 Olds conv. 455/TH400
Yes a good suggestion
Correct me if i´m wrong, but the only way to check transmission tail shaft bushing is to open the trans and look?
But how to check the pinion choke?

You can check the tails haft bushing by seeing how much lateral play there is in the slip yoke. When you move it, it should give some, but not a lot. If it is moving more than .020" I would be worried.

To check the pinion yoke is more tricky. NASCAR teams use a specially machined tool that installs in place of the u-joint. The dial indicator rides on this tool and thus allows to measure run out. This tool is about $300, which is nothing for a NASCAR team, but not really practical for the home mechanic. To make it worse, they only make it for the 1350 size u-joint, which is the only size used in NASCAR.

When I checked mine, I use the caps of the u-joint as my reference point. I rocked the driveshaft to find the low point on the cap, then I repeated the process on the other cap and compared the numbers. The difference in the two measurements is the runout in the pinion shaft, yoke, and u-joints. This method is not ideal, but there isn't much else to do.

Andrew