Question: howling rear end noise

[Lil_Star's 79 Vette]

When I let off the gas, going faster than 50mph I am getting a loud howling noise coming from the rear end. I know possi's are generally a little louder but this seems quite loud. I have been told it is most likely the pinion bearing and not the gears. Is this true? and how easy would this be to replace. I know the rear end will probly have to be dropped out, to get to it. Will it be easy to get the bearing out without having to spend a lot of money?

 

[Mac]

Rear diffs have so many rotating parts which can howl that it's almost impossible to guess...

-Mac

 

[TimAT]

I hate to be the bearer of bad news, but a howl on the coast side is just about always the ring and pinion. The only way to know for sure is to pull it out, and check the gear wear pattern.

When you're coasting, the ring gear is trying to drive the pinion forward and down. Opposite when you accelerate. It's also loading the rear pinion bearing against the race. Problem is, to replace the rear bearing, you have to pull the rear axle completely apart.

 

[Lil_Star's 79 Vette]

So if I drop the half shafts on both sides, I can replace the bearings without dropping the rear end out? Ive had the shafts out last year when I did ujoints. So I know they will come out easy. And arent the rear ends in the 79 vette a 308 gear? O ya and the rear end in the car had 75,000 miles on it. I didnt think that was a lot of miles for it to be that worn.

 

[GTR1999]

It's not the posi, but the gears. 78-79 stock diffs are not the best of the run although the gears were pretty good. If there is only 75k miles on it that is a surprise but if someone was in there then setup would be my concern. I just did a diff for a 69 that was rebuilt prior and had the same issue. I had the same with my 72 with new gears, everything was correct but the gears were bad. Once I replaced them again it was fine.

308 gears were used with automatics most of the time with 355's as an option.
If you have a stock 79 then I would look at the side yokes as well probably worn out. The posi clutches are also weaker.

I have a lot of info on diff's posted that will help you.

 

[Hib Halverson]

If you have howl on coast, there are no easy fixes. As others have suggested, it is probable the ring-and-pinion have worn.

Unfortunately, the axle needs to be overhauled.

How is it that a rear axle assy could wear out in 75,000 miles? It's either "GTR99's" suggestion--a previous faulty overhaul--or incorrect lubricant or failure to periodically change the lubricant.

 

[Lil_Star's 79 Vette]

Ok, I checked the half shafts today and they seem not to have any play in them from side to side movement. So im hoping its mainly the bearings making the noise. What is all involved in removing the center section? Drop exhaust, Rear tire cover, Leaf spring,? Anything else that I should be awear of. I dont want any surprises or dont want to break anything. Will I need any special tools? Where on the vehicle can I find out what type of rear end it is? Its a 1979 with the 350 in it. and any suggestions on what type of fluid to use? thanks....

 

[GTR1999]

I pm'd you my number in CT. It would be easier to answer then type it all out.

 

[Lil_Star's 79 Vette]

What is all involved in removing the center section? Drop exhaust, Rear tire cover, Leaf spring,? Anything else that I should be awear of. I dont want any surprises or dont want to break anything. Will I need any special tools? Where on the vehicle can I find out what type of rear end it is? Its a 1979 with the 350 in it.

 

[JohnZ]

What is all involved in removing the center section? Drop exhaust, Rear tire cover, Leaf spring,? Anything else that I should be awear of. I dont want any surprises or dont want to break anything. Will I need any special tools? Where on the vehicle can I find out what type of rear end it is? Its a 1979 with the 350 in it.

Do you have the Shop Manual? Everything except the trailing arms has to come out, and you'll need a BIG prybar to pop the differential crossmember off the frame on both sides. Then you can remove the diff from the crossmember.

The diff ratio code and assembly date are stamped on the bottom of the housing, between the spring retaining plate and the camber strut bracket. The first two digits are the ratio code; OM = 3.36, OH = 3.55, OJ = 3.70 (unless someone has been inside it already and swapped the ring and pinion).

 

[Lil_Star's 79 Vette]

You said there are only those three codes on the rear end. I thought most of the rear ends stock are 3.08? What is the code for that?

 

[JohnZ]

You said there are only those three codes on the rear end. I thought most of the rear ends stock are 3.08? What is the code for that?

The 3.08:1 ratio wasn't available in 1979; 3.36 was the standard ratio with a base engine 4-speed, 3.55 was standard with the base engine or L-82 and TH350, and 3.70 was the standard ratio with an L-82 4-speed, with 3.36 optional. 1978 was the last year for the 3.08, and all 1980's had a 3.07.

 

[Lil_Star's 79 Vette]

Ok, I looked at the rear end today. On the driver side of the car stamped on the housing was the number OH48I. So this means I have 3.55 gears? That explains why I only get 13 miles per gallon...

 

[TimAT]

Ol' Red (my 69) may be something of an oddball. The 4:11 will roll out by removing the driveshaft, front support, half shafts and the bolts that hold it to the rear cover. I've heard that it won't come out that way, but mine will, has, and does.

 

[Lil_Star's 79 Vette]

ya actually thats how my manual for vettes says that is how you remove it. You also need to remove the camber shafts from the rear end too. but I think I am going to replace the leaf spring too, so ill drop the rear cover too.

 

[JohnZ]

Ok, I looked at the rear end today. On the driver side of the car stamped on the housing was the number OH48I. So this means I have 3.55 gears? That explains why I only get 13 miles per gallon...

The ratio and assembly date are stamped on the BOTTOM flange of the diff housing, not on the side; usually takes a good cleaning to see them, as it's not a machined surface.

 

[Lil_Star's 79 Vette]

its not under the leaf spring. correct? other wise I would have to remove the spring to see the number because it attaches to the bottom of the rear diff. The number that I found is towards the bottom of the diff on the driver side right next to the camber adjustment .but is on the side but right near the bottom....as far as it looks it says OH48l

 

[Lil_Star's 79 Vette]

Rebuilding Rearend

this is the pattern we have so far..and that its not under a heavy load... Does this look right?

 

[GTR1999]

Pattern is too deep, reshim it and check it.

 

[Chas]

My 2 cents.....

this is the pattern we have so far..and that its not under a heavy load... Does this look right?

I have been around enuf to know that the best man to get that rear end fixed properly lives in your state.

GTR1999 knows more about them than anyone I have heard of or know. He has probably forgotten more than most "rear end specialist" will ever know.

Pay close attention to what he offers you dude......