brainsoft

I have had a mild clicking noise from the rear end since I got the car (1.5yrs). Just recently a new more more concerning noise popped up.

When highway driving, 100-120km/h, if I take my foot right off the gas there is a whopping noise from the back end. If simply ease of the pedal it does not happen, only when I drop out the throttle completely in the 100-120km/h range, like coasting down to traffic on the highway.

Any thoughts?

1980 L-48 stock drivetrain

sstopczy

It could be a bad U-joint that you only hear when you let off the gas due to flexing of the trailing arm bushings. If that is the case, you will want to replace the bushing and U-joints. Replacing the bushings requires a lot of work and at that point to might as well rebuild the arms. Get under it and move things around. Is there any play in the side yokes coming off your differential? They tend to were down over time and you can get some play in those that might manifest itself only when you let off the gas.

Rayvan

What the guy up there said X 2.

Get ahead of the issue before it gets worse. I let it get worse and ended up on the side of a street with a bent wheel...luckily the place I broke down in didn't put me in immediate danger.

Ivan

brainsoft

I had a lie down out there last night and I see one of the half shaft ujoints is a bit rusty, the others looked better. I know that all the bushings back there are deteriorated pretty badly too. I need to get the thing up in the air so I can get under there a bit better and try to see if anything stands out.

This all sounds like a large expensive job

"Trailing arms" is the rear leaf spring suspension? I have read a lot of member posts mentioning getting them done, but I'm positive nothing has been done back there for quite some time.

Anyone know how many shop labour hours are listed for 6 ujoint replacement and trailing arm rebuilding?

MelWff

no grease fitting on the half shaft u-joints?

brainsoft

Well just read 10 pages about trailing arms... definitely not something I want to get involved with, but at least I know what everyone is talking about.

I'm not sure, I can't get my head under there far enough without getting the *** up in the air a bit, which is always problematic without putting it in the driveway. Working in a 1 car garage is crap. I don't even have a work bench.... I don't even have a vice! So far if I cannot do it on the car or in my lap I have to think twice or get someone else to do it

I think that if I have to replace u-joints, it won't be in my garage

brainsoft

Did the stock half shafts have grease fittings?

brainsoft

Still haven't been able to get the car up yet, hopefully tomorrow. Reading a bit in the shop manual about the rear end and the troubleshooting guide is leaning heavily to it being gear noise, very specific to abnormal wear patterns in the ring and pinion gears.

Noise is only in the 100-120km/h range and only in a coast condition, not in drive or float. I can float down through the range with no problems, but coasting produces the sound.

Now, I know nothing about rear differentials. To me they are filled with mystery like automagic transmissions. Fixing this is just not an option this year, but am I in danger if I stay out of that coast range? Am I going to strip the teeth off and destroy everything? Keeping in mind that it is not a race car, just a Sunday driver. I'm taking it out to show my 82yo Grandfather who is very excited by the prospect and I just need to be reassured that I will be fine as long as I take it easy.

dochorsepower

You will probably hear more funny sounds before it gets worse. Do yourself a favor and start researching good, knowledgeable Corvette shops to have a complete rear rebuild. You can't trust a rear end rebuild to just any mechanic and especially Bubba.

brainsoft

Well I guess the first step is change the diff oil with the proper additive and see how she likes it. The car has seen more miles in the last year than the last 10 probably, couldn't say when the last time it was changed was

brainsoft

Yea, I need to start preparing the wife for the price to rebuild the back end, I have no idea what it would cost for a high-quality job, I now there are some very tricky bits back there.

Any ballpark idea if my parts or decent for reuse?

Ontario73

My car makes a similar clicking noise when coasting; although at lower speeds. In may case its a rear brake rotor that is slightly warped (PO drilled the rivets for some reason). I would certainly check out all of the less costly areas before diving into a full rear end rebuild.

Even if it is in the differential or rear axles/bearings it will get much worse before it becomes a cause for concern. The best analogy I have heard regarding rear gears and bearings: They are like a nagging wife; they are going to make a lot of noise for a long time before they even get close to leaving you!

Brcmpbl

I can't tell from your post if the "whopping" noise happens once when you let off the throttle, or if the noise is continuous after letting off the throttle.

If it is continuous, the posts above might be on point.

If it is a one time noise right when you let off the throttle, I would have a hard look at the rear differential front mount (some call it a snubber). That is an easy fix, and a common problem area.

I would certainly change the fluid in the differential as well - start small, that's the cheapest rule.

kjbuster1

Original U joints did not have grease fittings. One of our experts just recommended not to use them for replacements either.

waljr

my clicking was broken return springs on the top of the park brake tagging the back of the wheel studs -clearly not the cause of your "whooping",but might be the click.

brainsoft

Thanks for the feedback guys! Got the car up on a lift on Friday had a look at some things. The trailing arms are good, having already been rebuilt by the looks of it. Bushings are good, suspension looks okay too. Confident one of the noises is from the rear parking brakes, which I have a rebuild kit for in the garage. There is some bearing noise in the differential as well, and the other noise is probably coming from there as well. We've decided to wait until we pull it off the road and pull the diff for rebuild over the winter.

I had a bunch of noises come out on our trip this weekend actually. A v-belt started to fray and a metal wire was making a slight tinking noise. We got off the highway and the blower fan decided to give out in the loudest way possible (startling to say the least), and now there's some other noise I haven't located yet, but it sounds like it's coming from the dash area as well (even though the fan is now off). Lots of little projects to tackle this month and next spring... never a dull moment eh?

brainsoft

Oh and I think the half-shafts have grease nipples to boot!