Help diag a rear end noise.. :(

[wolf_walker]

Well, on the 74, after rebuilt wheel bearings, all new bushings and U-joints, brakes, shocks, lines, and adjustable strut rods, now I have a noise.

It comes on about 45mph, mid-pitched hum that gets higher as road speed increases. It's only there under load, foot off the gas and it's gone, back on it even slightly and it's there again.

The one thing I really cut corners on this thing for cost reasons was the rear differential. The car was lady driven and baby'd for 120K and had no leaks, so I figured it would last awhile longer. The fluid is fresh, with the posi lube, posi still works alright, no odd noises other than possibly this vibration.

It was sugested that the new poly front dif mount bushing may have been wrong and the pinion angle was off but that's evidently not it, I swaped in a stock one for testing and had the same noise.

Whatcha think guys? I'm pretty P.O.'d to be honest, all this work and the one thing that should have lasted seems to have not. Oh well..

How hard is it to rebuild one of these units? Or is it a better deal to just get a rebuilt one on exchange?

 

[Stingray6974]

Well I hate to be the one to tell you but..... you've got a bad pinion bearing.
Mike

 

[wolf_walker]

Well that figures, hmm..

So how long will that hold together before it goes south big time?

 

[Stingray6974]

Right now it's not very bad. As you drive it though, it's constantly breaking off small pieces of the bearing race causing wear on everything else. The sooner you fix it the better.
I wouldn't recommend buying a rebuilt unit (too expensive) unless you want to change gear ratios. I would find a shop that rebuilds rear ends and carry it in to them. The most expensive part of a rear end overhaul is the labor in removing and installing it. Buy the bearings and seals yourself. Either Timken or ACDelco. Stay away from Bower/BCA. Or you could ship it to me and I'll rebuild/restore it for you.
Mike

 

[wolf_walker]

Any idea of cost on parts/labor? I figured about the metal bits, they were aparent in the fluid when I changed it last week. Is it worth it to have the posi unit rebuilt while it's out?

 

[inferno-vette]

It could also be the wheel bearings
Paul

 

[wolf_walker]

It could also be the wheel bearings
Paul

Well I wondered about that. There new from Van Steel, and I spoke to a fellow there who was pretty sure it was in the rear end. I know it's his product and all, but they have a pretty good reputation, so I'll assume it's the rear end for now.

One thing I noticed that does kinda bother me about the bearings. The passenger side has almost no play when rocking the tire while grasping the top and bottem, while the drivers side has a noticable ammount. I know that isnt the correct way to check them on a vette, but I thought it was odd... ?

 

[bioandy]

It's curious that the "hum" started after all that work. It could very well be in your differential, but I would resolve that spindle bearing possibility. The tolerences for setting up the bearings properly, result in a seemingly tight fit. I don't believe you should be able to feel any end play by hand. The specs call for .001" to .008" as an acceptable end pay range, usually measured with a dial indicator guage. Are you sure the play you noticed was at the spindle and not any other part of your rear suspension?

Local Corvette shop recently quoted $500 to rebuild a carry-in differential unit.

Good luck. Curious to lean how you make out.

Andy

 

[wolf_walker]

Well, it may well have made noise before hand, when I started the car had sat in a barn for a decade and had no brakes at all, so it wasent driven much to start with. Factor in my usual luck and, well..

The play in that bearing, I looked at it and you could see the inner flange rock a little compared to the actual t-arm tha was stationary. It bothers me but damn, that's a lot of work to pull it and send it back, and I dont have a dial indicator handy, supose I should procure one(again)...

 

[400hp_76]

SUGGESTION

If enough clearance was not given when you installed the wheel bearings on the spindle, then the wheel bearing could have possible already worn out. If they are not installed with proper tolerances you can ruin a spindle. Again, although the wheel bearings are new that doesnt mean that they might not be damaged now if they improperly installed.

 

[wolf_walker]

Re: SUGGESTION

If enough clearance was not given when you installed the wheel bearings on the spindle, then the wheel bearing could have possible already worn out. If they are not installed with proper tolerances you can ruin a spindle. Again, although the wheel bearings are new that doesnt mean that they might not be damaged now if they improperly installed.

I know it's possible, but the bearing and rotor came as a matched assembly from Van Steel, so I'm kinda giveing them the benefit of the doubt for right now. But it's definantly possible.


OK, someone jack the back of their vette up and see how much wiggle is in that bearing using the old grab the top and bottem and shake test...

 

[MNHoosier]

May I toss something into the mix?

More of a question than an answer.

I recently purchased my Vette and one of the first things done on it was replace/repair the rear pinion seal and bushing.

I too have noticed, starting just the other day, a similar situation with mine. A higher pitched sound when accelerating. Wouldn't a worn bearing been noticed when the seal was replaced? This is not an easy DIY fix unless you really know what you are doing and have the proper equipment.

Maybe I'm noticing something else or just imagining it.

 

[wolf_walker]

It's hard to say, especially when one is relativly new to vette's in general. I need to go listen to a few more of them. Any non-serious resto vette seems to have some noise from the rear, it's too complicated to not make noise it seems.

I'm sure I could rebuild the thing, trouble is I dont have the proper measuring tools and such. I left all my better mechenicing toys in Oklahoma for my old man to use a few years ago.

 

[400hp_76]

I am in the same boat

My vette has been in the shop for almost 5 months. It caught on fire in late December and hasnt seen the road since. I should get it back from the body shop in the next two weeks, but that is not what i wanted to say. Before my vette caught on fire, i noticed a slight rumble, that gradually got worse as i increased speed. i have replace the spindle and bearings(the whole works) on one side but the other side seems fine. My problem may be the driveshaft u joints. It could also be the same problem you are experiencing. so please keep me up to date on your findings.

 

[400hp_76]

one other thing

YOU SHOULD HEAR THE NOISE GOING 155MPH. That will get the adrenaline flowing. the thought in the back of your mind,wondering if something is gonna break. ha

 

[wolf_walker]

Re: one other thing

YOU SHOULD HEAR THE NOISE GOING 155MPH. That will get the adrenaline flowing. the thought in the back of your mind,wondering if something is gonna break. ha

Been there, sorta, I had a friend's 72 Challenger @ about 145 a few years ago and the front sway bar came loose on one side, end link AND frame bushing, should have seen the sparks. Man...


The u-joints were another thing I wondered about. The center drive shaft went together more or less OK, but the half shaft's, jeez. Problem with them was when pressing the joint in, the U shaped ends would flex and the joint wouldnt actually move, I eventually had to rig up a spacer to hold it apart to let me get the joint centered enough to put the clips in, and some of them the clips are still really tight. I've done my share of joints and have a hydralic press for it, and I've never had something do that. Does not inspire confidence.

So now what? Rebuild the rear end, see if that fixes it, check the suposidly new and very expensive bearings, then do I dont know what to the darn U-joints if the noise is still there. May as well tear it all apart and rebuild it AGAIN.

I'd give a lot for there to be a plain old 12 bolt under there...


un

happy

one each

 

[bioandy]

Pinion seal replacement is also a critical procedure - affecting preload on the pinion. Shop manual has lots to say on this subject

Going through similar situation as you guys. That being a rear suspension rebuild, on a recently aquired 70 Roadster. Among other things, I had to change the differential cover because of a broken spring mounting tab. While I had the unit out of the car, I carried it to the local Corvette specialist to check out. Seems like I have a very sound differential except for worn posi clutches. I'm a daily driver, not a racer. Think I'll put my torque wrench on it to confirm his findings before deciding to how to proceed.

Anybody ever replace a cluch pack?

 

[wolf_walker]

Pinion seal replacement is also a critical procedure - affecting preload on the pinion. Shop manual has lots to say on this subject

Going through similar situation as you guys. That being a rear suspension rebuild, on a recently aquired 70 Roadster. Among other things, I had to change the differential cover because of a broken spring mounting tab. While I had the unit out of the car, I carried it to the local Corvette specialist to check out. Seems like I have a very sound differential except for worn posi clutches. I'm a daily driver, not a racer. Think I'll put my torque wrench on it to confirm his findings before deciding to how to proceed.

Anybody ever replace a cluch pack?

As I recall the clutch pack is less technical than setting the gear mesch and all that with the differential, but you'd want to check a service manual. Moroso used to sell a complete unit under the name Brute Strength that everyone liked a while back..

The posi is probibly shot to **** in mine too, this car is going to have a $4K rear suspension before it's done with...

 

[FrankM]

I am placing my money on ring/pinion gear noise. It usually won't get worse and will be an annoyance more than anything else.
The alignment of the gears is very important and often times a slight bit of wear in an unusual pattern will get you to this point.

A bearing will usually be noisy no matter what speed (will usually vary in intensity) and the noise will be a growl type at that. Side gear and pinion bearings will react differently when on a test drive.

I have also seen differential mounts amplify the (gear whine) noise due to a slight collapsing and deteriation of the rubber.

the only solution is new ring/pinion gears. Need to be set up properly too or else you will be back to square one very quickly.

 

[wolf_walker]

I am placing my money on ring/pinion gear noise. It usually won't get worse and will be an annoyance more than anything else.
The alignment of the gears is very important and often times a slight bit of wear in an unusual pattern will get you to this point.

A bearing will usually be noisy no matter what speed (will usually vary in intensity) and the noise will be a growl type at that. Side gear and pinion bearings will react differently when on a test drive.

I have also seen differential mounts amplify the (gear whine) noise due to a slight collapsing and deteriation of the rubber.

the only solution is new ring/pinion gears. Need to be set up properly too or else you will be back to square one very quickly.

Yeah, I'll likely yank the rear end and either buy the tools or have it farmed out and redone. I still wonder about that bearing's looseness though. I HATE doing things over again..