rear end noise

[klb76]

While driving my vette back to school yesterday I found a new noise... It seems that when I am in 4th gear between 2800 and 3000 RPMs there is a "grinding sound". It sounds like it is coming from the rear end. However it doesn't make the sound in any other gear. I have noticed I clunk sometimes when starting out in first gear. Because of this I checked the U-joints and they seem fine? Do I need to get my rear end re-built? and if so how much is that going to set me back? P.S. I think my transmission is an M-21 or a M-22... thats what the last mechanic told me when we fixed my linkage.

[Bob Chadwick]

When was the last time posi additive was added. While this is not the typical description associated with the need, it is cheap and can't hurt.

[78SilvAnniv]

How about checking the side yokes?
Silver

[Eric]

Is the sound more evident when you are accelerating(not necessarily getting into it)? And is it more of a humming noise than a grind? Does the noise seem to be coming from the right of the driver's seat? If you answered yes to any of these questions then chances are pretty good that you have a bad pinion bearing - not pretty at all.

Mike (Stingray6974) is the resident expert on the subject and will probably be able to give a more accurate description of the noise. Bad news is that the rear end will have to come out and most likely get rebuilt.

For your sake, I hope it isn't that but if you answered yes above it doesn't look good.

Best of luck!

[klb76]

oh boy... when i first got the car it had no fluid, which was this summer... I checked it before driving so i didn't put any miles on it like that but who knows about before... but now it is properly filled will fluid... now about this noise thing... when I "get into" it the noise isn't really apperant at all... however when I either go above 3000 RPM and coast down, or when I just slightly give it gas through that range it always happens... and it doesn't really sound as if it is the middle of the car but more in the rear... but on that same note the exhaust is sooo loud that the sound may be right beside me... and as far as humming... if it is a hum it is a very cynical grinding type hum... as I mentioned before this is only in fourth gear... and finally, no i haven't checked the side yokes as of yet... will tonight tho... Thanks for the help everyone

[Stingray6974]

From what you've said I think Eric hit it on the head. You have all the symptons of bad pinion bearings. Normally side yokes don't make noise. However in the case of 77 4-spd, his yokes were so bad they were grinding on the diff housing. Check the movement in the yokes, look for clean metal shavings, and look for any grease leaking around the pinion seal.

Mike

[klb76]

alright i checked out the side yokes and they appear alright... there isn't any metal shavings there... I don't think there is any grease leaking from the seal either... although it could use cleaned up around there. If it was the pinion bearing wouldn't i hear the noise in all gears? I had already planned on taking the rear end apart anyway so this isn't that big of a concern, about what kind of price tag am I looking at to get a rebuild by someone who knows what they are doing?

[Stingray6974]

As the bearings get worse you will eventually hear it at slower speeds. I rebuild them for $150 plus parts. Bearings, seals, gasket, etc. normally runs around $110. This does not include ring and pinion gears or the clutchpack. I am currently working a deal with a supplier to get side yokes at a good price.

Mike

[klb76]

haha... pushing that new paint job further back every day... what is the easiest way to tell for sure if needs rebuilt? If i wanted to change the gearing now would be the time to do it right? Hopefully I can turn this problem into a Mod... I just went out and cleaned everything up on the rear end there, gonna take it out for a little drive around campus and see what happens... I don't know if this is related but I think I heard a knocking sound when going around a corner earlier today... It may just be me listening for something that isn't there but I wondered if that signals something?

[Stingray6974]

Well the easiest way to tell is when parts start hitting the ground. Going by age and milage and the noises you hear is the other way. The rear end is the only thing that will make a whine or howl under light accel or decell when in high gear. If it did it in 1, 2 or 3 but not 4 you would have bad bearings in the trans. This would be the best time to change gear ratio's. Jack up one side of the car, L or R, until that rear tire is off the ground. Push the top of the tire in hard. See how much play it has.

Mike

[klb76]

Alright that sounds like a plan for tommorow... Thanks for the refresher on the "Rear End Update" topic. By the way the pics show some quality work! Your help has been awesome today! Any suggestions on good gear ratio's? A 75 owner in my town has 389 and I liked that alot better then my 308....

[klb76]

When parts start hitting the ground!!!! haha I just caught that... now I am going to have nightmares for weeks about my ride falling apart!!

[Stingray6974]

Depends on how much driving you do. Mostly in town 3.70 is real good. If you do a lot of hiway 3.55 or 3.36.

Mike

[klb76]

alright... I got out and jacked up the car... When I pushed in on the wheels there was virtually no play at all... both sides seem to be the same... I did notice for sure there is a noise going around hard corners at decent speed, 20 mph, coming from the rear end... and last night while drifting backwards on a hill I hit the break and there were some "creaking sounds" from the rear end... and also, no grease around the pinion bearing...

[vigman]

Did you check the rear bearings for PLAY?

Do you have the KUNK sound going from rev to fwd & back again....that would indicate bad U joints... and or worn flanges.


Are they the Original U joints? How do they look..old funky.. brown stains @ the seals?

Hows the tranny fluid?


More Data please....

Vig!