John Hughes

Hi,

Im a first time vette owner as of last week. I found a nice car for a reasonable price that drove well, sounded great and just scratched the itch Ive had for years.

Ive owned many cars, and done plenty of work myself, but the rear of these cars as you guys know is something totally different than all of my old solid rear axle Fbody cars.

Anyway, to cut to the chase. I bought the car and drove it for a few days. Then, a few days ago, After driving it up the road for a small cruise, I get it home and decide to let me son drive it. He puts it in the reverse and well, my problems commence.

It started popping, like something is binding up and unbinding and binding and such. A grinding type sound, but again, its mostly a popping and unpopping type of sound. Once the car is up to speed it goes away. It does it whether you are going forward or in reverse.

So after asking some local guys I know for some general recommendations. They suggested that it could be the ujoints in the half shafts. Well, that was something I could handle myself so I tackled that today. Unfortunately for me, my problem remains. The owner suggested that it might be the drivers side strut rod as they had replaced the one on the passenger side last year. There does seem to be some play there...but not knowing these cars, I wasnt sure if thats the case. Regardless, It doesnt seem like play is something they should have so I guess Im going to tackle that next.

Anyway, the strut rods along with a gear oil change are things Im probably going to try and handle this week...but Im all ears and more than willing to ask and take any help/good advice that I can.

Thanks in advance.

John

Kirk H

Sounds exactly like happens when you need to do a gear oil change. You need to make sure you use the additive for the posi clutches so they don't grab or chatter or groan. Mine were not making noise but the clutches were grabbing and letting go, making it feel as though the car wanted to pull to one side. After the change, no problems at all. They also recommend a number of hard figure eights in a parking lot somewhere to get the fluid fully coating the clutches. How many figure eights? Doesn't really matter cause it's fun and you won't want to stop!
Let us know what happens.

John Hughes

Thanks so much for the encouragement. I hope youre right. At least its something I know I can accomplish. Fingers crosse.

Stephen Irons

I'd go along with that. New oil and definitely the additive. The figure of eights should be tight, but slowly driven, allowing the oil to get into the clutches.

And yes, change the strut rod, or the bushes at least. I put poly bushes in our about 20 years ago - wonderful!

Wee

If it's worse when turning it is most likely the the clutches sticking. Mine did much the same even after changing the gear oil.....I had to change it again with the proper oil and (2) bottles of ACDelco additive. I have a 72, I'm not sure what kind and weight oil a 79 needs....Maybe some else can chime in on that question.

Brian

John Hughes

Thanks guys.

It doesnt make more noise in turns or anything, its just doing it going slowly. Once the car is up to speed it all goes away.

Its loud when its slow...and making me nervous...but totally gone at speed.

Anyway, thanks again. I purchased my oil and additives this afternoon and hope to tackle it Tues. if I get a chance. Fingers crossed.

croaker

[QUOTEMine was doing that mostly when crawling along and turns. Changed oil with two bottles GM additive all good now.[/QUOTE]

cobrachuck

Agree with above.
This is what I do with these old cars,
I have had several over the years 2 @ present.
This car is new to you so bring as much up to date as possible.
Replace the drive shaft u joints they are a ware item. When changing the rear fluid,
With the rear wheels off the ground on jack stands, check the rear wheel bearings for wear, move the tire 12:00 to 6:00 there will some movement normal play is 1/8 to 3/8".

John Hughes

I have to admit, you guys are making me feel really good that my problem could be this simple. Whew...would be a load off of my mind.

I did go ahead and replace all of the ujoints on the half shafts. I didnt look at the ones on the driveshaft though, and I guess I should have. Although I must say, the half shafts werent that bad...just some minor scarring on some of the shafts.

As far as checking the wheel bearings, Im not sure what youre saying. Rotate them 12 to 6...but where should I see or feel the play? Im all for bringing everything I can up to date. My son didnt realize how I wasnt upset about the time we spent changing the ujoints...but I tried to explain that while it might not have been a problem...now, it shouldnt be for quite some time. One less thing to worry about.

Anyway, I will be sure to check that all over once I get back under there. Thanks so much for the tips. Ive got a few more issues I want to take care of at some point, (such as the gauges not working, and so forth) but none that stop me from driving it other than this at the moment. Looking forward to hopefully years of enjoyment.

LongRoadHome

"checking the wheel bearings, Im not sure what youre saying. Rotate them 12 to 6...but where should I see or feel the play?"
cobrachuck meant grabbing top and bottom of tire/wheel, push and pull in and out (tilt).

Your popping noises are what I had, too, and now completely silent after 2 consecutive oil changes; exception being that I didn't remove all the old oil first time.

You'll want to try and suck the old stuff out as much as possible. I used a handheld oil pump from Harbor Freight Tools. Didn't even attempt to flush the stuff out with kerosene or anything, just some fresh oil and a couple bottles of AC Delco additive the first go around.

I also put in 1 quart of 85W-140 along with Valvoline 80W-90 "limited slip" gear oil since it's the hot summer time anyway. And so I could remove a quart and add the normal 80W-90 oil later on to be sure the "clutch packs" in the differential will be okay.

Curious about bearings and half-shafts myself because ever since new brake calipers and rotors I've had a squeak-squeak-squeak at drivers rear wheel. Found a message thread just now describing same, mentions 12 and 6 o'clock positions being for checking "u-joints and side yoke play".


https://www.corvetteforum.com/forums/c3-tech-performance/1685435-test-for-bad-u-joint-vs-wheel-bearings.html

3 and 9 o'clock for bearings.

I'm fairly sure you'll eliminate that popping crunch of the differential just like I did.

John Hughes

Thanks man,

I now understand the 12-6 thing. (Sometimes my brain doesnt work)

I also picked up a hand pump today from harbor freight just for that reason. Im going to try and get as much out as I possibly can.

I checked all of that when I had it up, and all of that felt solid. Whew. I have a feeling replacing the bearings isnt something I want to tackle any time soon. (if the videos Ive seen are any indication)

Thanks again everyone. Im really excited to do this now...Youve almost convinced me that Im going to be lucky...for once.

Stephen Irons

I think a little clarification is needed here? If you want to check the bearings then grasp the wheel at 9 and 3 O'clock and rock it on the 12 and 6 axis. If you rock it on the 9 and 3 axis you feel the driveshaft yoke end-play. That's also worth checking - there should be some, but not a lot! On that subject, some of the drive shaft yokes will wear on the inside, allowing them to move inwards, in the worst cases to the pint of the yokes hitting the diff case! So, always worth a "glance" at that!

For the diff, I use the GM oil and two bottles of additive. The oil rating is 80/90 I believe. Ensure the car is level when you refill and fill to the drain plug. I think you'll find that the '79 the plug is a taper fit like my '78. I put a turn or two of PTFE tape on it, as I don't want to overtighten, but I do want it to seal.

John Hughes

I just wanted to update everyone. This evening I was able to change out the gear oil (man, using that cheap harbor freight pump ruled) Anyway, It seems to have fixed my problem. I will have to drive it more to be 100%, but Im 99% now. Thanks so much for the direction and help.

Im looking forward to getting her to where I want her...but enjoying her all the way.

I might as well include a pic. Its not the color I want...but thats something Im willing to work on. The car is really clean of rust, very tight, and runs great. Interior could use some cleaning, but its all there and not tore up. Console gauges arent working, and a few other things...but for a 5k car Im feeling pretty good about it now. Anyway, thanks again.