Rearend Vibration

[chaztruett]

Gentlemen, ladies; First post / question after trolling the site for over a year now while looking for a truck. Wonderful site, thank you!

Brought a 68 home from NC and noticed I have a vibration from rear. I get the "roar" in the cab. (I have read ever vibration thread I could find) The vibration comes in about 30 mph + and is speed related as the frequency increases with speed. I put the truck on my lift and ran it at 40 mph and you can actually see the vibration come and go at the left tire. I swapped tires to make sure and it is not a wheel or tire. I do hear some metal noise probably from left bearing. I am not seeing / nor hearing anything strange at drive shaft or rear chunk.

Could a bad bearing cause a rhythmic vibration like this? U joint?

There seems to be a lot of lash in the rearend, not sure though? You can turn the tire about 15 degrees without engaging the rearend gears. Is that normal?

Previous owner had swapped axles sometime in past so not sure of condition nor correctness there.

Thoughts and suggestions appreciated.

Thanks in advance!

tt

[MikeB]

15 degrees rotation is probably not excessive. Since the left side is noisy and you can actually see movement at the wheel, I'd suspect the wheel bearing.

Of course you'll have to pull the rear cover, drain the gear lube, and pull the spider gear shaft so you can then push the axle inwards and remove the c-clip, which retains the axle. And since you've gone to all that trouble, you might as well replace both axle bearings and seals. Many auto parts store will loan you a bearing puller set, and a bearing/seal installation tool.

Also, now is the time to check condition of ring, pinion, and spider gears, as well as ring/pinion backlash. I can explain that here, but you can easily find "how-to" info with pictures on the Internet.

In my experience, pickup truck 12-bolts with real GM gears will last nearly forever, so hopefully you won't have any problems beyond the wheel bearings.

One more thing: If either wheel bearing is way too easy to pull, look for signs of it spinning in the axle. If that's the case, you will have to buy an "axle saver" bearing, which is an integral bearing and seal. Or potentially you can use Loctite bearing mount adhesive to install a stock bearing, assuming the fit is snug.

If you have any questions, post them with pictures.

[chaztruett]

Thanks MikeB.

Went out this morning took another ride and have new notes to add:

Vibration is not speed related but RPM related.
Comes in worse at 1900-2000 rpms
You can definitely feel a wobble in your seat and the left window moves side to side. Very Interesting...........
Driving in third gear and down shifting to 2nd gear vibration goes away as rpm's jump to 2600.
Engine seems to have more vibration than I would expect just idling. But not excessive at 2000 rpms.
Wondering if this could be torque converter and/or tranny related???

Arrgh!

thanks
tt

[MikeB]

I'd take a look at the engine and trans mounts. Also, drop the inspection cover to make sure the T/C to flex plate bolts are tight.

Take a look at the vibration damper and make sure the elastomer (which separates outer ring from inner hub) looks OK. What size engine is it supposed to be? It could be a previous owner put an externally balanced damper from a 400 on an internally balanced engine (350/327,307,305) or vice versa. If it's a small block V8, try to read the block casting numbers on the ledge behind the drivers side cylinder head.

[chaztruett]

Good stuff, have not thought about checking the TC for tightness, with so many other possibilities running through me head! I did replace one motor mount as it was broke. Tranny did appear tight at supports. Tried to jack up/move it and it was snug.

Engine is a rebuilt 350, have not pulled everything apart yet. But will.

Truck was refurbished in the late 80's early 90's i think and then owner passed away at some point. Looks like truck has sit in a basement for at least 15 years. Purchased through an estate sale.


thanks!

[geezer#99]

Check your pinion angle.
Check this link for driveline set ups and finding vibrations.
http://www2.dana.com/pdf/J3311-1-DSSP.pdf

[crazy longhorn]

Originally Posted by chaztruett

Gentlemen, ladies; First post / question after trolling the site for over a year now while looking for a truck. Wonderful site, thank you!

Brought a 68 home from NC and noticed I have a vibration from rear. I get the "roar" in the cab. (I have read ever vibration thread I could find) The vibration comes in about 30 mph + and is speed related as the frequency increases with speed. I put the truck on my lift and ran it at 40 mph and you can actually see the vibration come and go at the left tire. I swapped tires to make sure and it is not a wheel or tire. I do hear some metal noise probably from left bearing. I am not seeing / nor hearing anything strange at drive shaft or rear chunk.

Could a bad bearing cause a rhythmic vibration like this? U joint?

There seems to be a lot of lash in the rearend, not sure though? You can turn the tire about 15 degrees without engaging the rearend gears. Is that normal?

Previous owner had swapped axles sometime in past so not sure of condition nor correctness there.

Thoughts and suggestions appreciated.

Thanks in advance!

tt

If you think noise/vibe in LH side, you might pop the wheel & drum...put a dial indicator on the axle face, & see if you have any run out? Longhorn

[Keith Seymore]

Here is a link to flow chart on fixing vibration problems.

If you can follow the thought process shown in the flow charts then you can fix anything.

It's all about separating the things you don't need to care about from the things you do. It sounds like you are already heading down that path if you have determined it is engine rpm related, rather than vehicle speed related. That will let you disregard anything that is not moving when the vehicle is stationary.

K

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

[chaztruett]

Best article I have seen on this subject. Thanks tt

Originally Posted by geezer#99

Check your pinion angle.
Check this link for driveline set ups and finding vibrations.
http://www2.dana.com/pdf/J3311-1-DSSP.pdf

[geezer#99]

There will be a test!! LOL!!
Here's another.
http://www.drivetrain.com/parts_cata..._problems.html

[chaztruett]

Another good article! Thanks for input!

thanks!
tt

Originally Posted by Keith Seymore

Here is a link to flow chart on fixing vibration problems.





If you can follow the thought process shown in the flow charts then you can fix anything.

It's all about separating the things you don't need to care about from the things you do. It sounds like you are already heading down that path if you have determined it is engine rpm related, rather than vehicle speed related. That will let you disregard anything that is not moving when the vehicle is stationary.

K

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

[MikeB]

Guys, the vibration is RPM-related, not road speed. That would tend to eliminate anything behind the trans output shaft, wouldn't it?

And it may not be as bad with no load on the engine, like when it's revved in Park.

[MikeB]

What I should have said is: The reason it's not as bad when revved in Park is probably because there is no load on the engine.

BTW, how the heck do you edit your own posts here? Seems like I used to be able to do it.

[chaztruett]

OK, notes for today. And thanks for all the input, this is a new adventure for me working on an old truck. My life thus far has been under C3 Corvettes for last 25 years! LOL

Went though as many checks as I could. Running truck on lift etc. I rotated the drive shaft at the rear end (Rotated u joint 180 degrees) and the vibration dang near shook the truck apart. Possible drive shaft slung some weights?
Pulled fan and installed electrics to make sure not the clutch on fan.
Checked angles on drive shaft and to my surprise they were pretty much correct. Difference of 3 degrees. Not perfect but ok, i guess.
Pulleys and Harmonic balance appear to all be good.
Taking shaft to balancer shop on way to work today.
Pulled rear cover and this is what I found. Kinda interesting. Anything in here I should check for while it is apart? Reckon I should pull the pinion and back out to correct clearance?

Again, thanks to all for the help! I'll keep you posted.

[chaztruett]

Thanks!

Originally Posted by geezer#99

There will be a test!! LOL!!
Here's another.
http://www.drivetrain.com/parts_cata..._problems.html

[geezer#99]

Interesting chew marks on the carrier from the pinion gear. Hope that was from a previous failure. You might need to change it out.
Checking pinion angles should be done with the suspension loaded.

[Captainfab]

If the differential is not making noise and if the pinion feels tight, I would leave it alone. The wear pattern looks a little close to the toe of the tooth, but it should be fine. My guess is that the tooth marks on the carrier are from a previous gear set.

[chaztruett]

Thanks! No noise, appears to be good. Really hate to dig into this with no knowledge of how to put it back together. No known gear guys near me, which means I would have to learn by trial and error!

Originally Posted by Captainfab

If the differential is not making noise and if the pinion feels tight, I would leave it alone. The wear pattern looks a little close to the toe of the tooth, but it should be fine. My guess is that the tooth marks on the carrier are from a previous gear set.

[chaztruett]

Update for the weekend.

Had drive shaft balanced and he put alot of weight on both ends. Thinking this could be good.
New bearings rear, good.
Installed shaft, put rear cover on, good.
Shined her up, told the wife lets go for a ride.
Headed out, all appeared good, NO noise nor vibration at 2000 rpms, wahoo. Parked to eat, came out, drove off. Vibration is back at 2000 rpm's! Arrgh! Dang it!

The only thing I can attribute this to is the transmission/torq converter. When fluid gets hot it starts being goofy on me. BTW, best I can tell this truck was restored in the late 80's early 90's. Owner passed away and then it sit in garage for maybe 15 years, probably never moved nor cranked. Fluid appears just changed.

Plans are to change to 700r4 over winter so guess Ill go ahead and do it now. (hate to think about how many 700r4 tranny's I have given away, pulled from corvettes, wish I had one of those back!)

Any ideas welcomed! Thanks to all on this new adventure!
tt

[68gmsee]

Before replacing the transmission.

Another test that you can do (if you haven't already) is to unbolt the torque converter from flywheel and pry it back away from the engine. It should move slightly so it does not make contact (I've heard of some tying it back to insure it stays away from flexplate). Rev the engine to the rpm where it starts to act up. If it doesn't vibrate, more than likely it's the t.c.

[chaztruett]

You da man! I think someone earlier had mentioned this, but had somewhat forgot about it.
The vibration comes in about 1900-2000 and grows while under load.
I tied the TC back, run the engine slowly up to 2000 and viola! The vibration is there! Not as significant without load nor amplified through out drive train.
Now on to looking at Harmonic Balancer closer and then I looked, again at the passenger side motor mount. I had to replace the driver side mount as soon as I got it home.
I slowly jacked the engine and eventhough the mount appears in tack, the rubber was compressed and it does move up and down about 1/4- 3/8 inch. The center bolt is tight but again the mount rubber is shot. 2 weeks ago I checked it quickly and did not see an issue.
Today I will replace this mount and we will see if this is the whole problem. Betting it is.

Thank you!

tt

Originally Posted by 68gmsee

Before replacing the transmission.

Another test that you can do (if you haven't already) is to unbolt the torque converter from flywheel and pry it back away from the engine. It should move slightly so it does not make contact (I've heard of some tying it back to insure it stays away from flexplate). Rev the engine to the rpm where it starts to act up. If it doesn't vibrate, more than likely it's the t.c.

[MikeB]

I know you were told the engine is a 350, but have you confirmed that with the block casting # on the block ledge behind the drivers side cylinder head? If it is a 350, neither the damper nor the flexplate should have a counterbalance weight.

400 flexplate with welded-on counterweight:



400 damper with eccentric weighting cast-in:



An exception is an 1986-up 350 with one piece rear main seal. These engines used a neutral balance damper with a counter-weighted flexplate. But the bolt pattern on the rear of the crankshaft is tighter, so there's no chance of a neutral balance flexplate being installed.

[chaztruett]

Good call! I attempted to retrieve #'s before, but headed to my shop right now and will get them. May have to use a mirror?

And yes, with this truck it is like a Christmas gift every time I get into something. It has been modified in past and with no notes, it is a challenge to figure out what the previous owner has done.

Thanks
tt

Originally Posted by MikeB

I know you were told the engine is a 350, but have you confirmed that with the block casting # on the block ledge behind the drivers side cylinder head? If it is a 350, neither the damper nor the flexplate should have a counterbalance weight.

400 flexplate with welded-on counterweight:



400 damper with eccentric weighting cast-in:



An exception is an 1986-up 350 with one piece rear main seal. These engines used a neutral balance damper with a counter-weighted flexplate. But the bolt pattern on the rear of the crankshaft is tighter, so there's no chance of a neutral balance flexplate being installed.

[chaztruett]

This is the only #'s I could find. This is just behind head on Driver Side.



I am seeing 897001 Maybe???

[chaztruett]

I found this casting # ID. Maybe this is a 302?

3970010 Small Block V8 1969 302, 4 bolt, Camaro Z28