Well I pulled the 1970 out of hibernation for the first drive of the season last night, and here it is all dusty etc.:



But the car is grumpy. The day I put it away in the fall I was stepping into the throttle a little and when I let off I heard a very loud bang from under the car and slightly to the rear...thought I had run over a big rock and it hit the undercarriage or something. Pulled over and couldn't find anything wrong, car was running fine. Noticed when I got back to my place that the normally very mild oil leak I had in the area of the rear main was now quite severe...say a puddle three inches in diameter sitting in one spot at idle for five minutes or so. Still trying to fix this problem.

Car drove fine last night...until I gave it a shot and the bang was back when I let off the throttle, happened twice. I inspected my u-joints in the fall and all were tight, almost new, and I put new motor mounts in at that time. Replaced the rear differential fluid with GM gear oil and a tube of GM posi additive. Differential seems to be sweating a bit, and I know the rear seal on my transmission needs to be replaced, but the fluid level is ok. Will be putting it on the hoist tonight...any thoughts?

 

Only thought I had was - Wow.....beautiful car!


Sorry if that's is no help at all !

 

I would check the pinion bushing and maybe even the bushing holding the rear axle assembly. Something is shifting, so grab a pry bar and see what wiggles...

 

Once you can look underneath, you will probably find the problem quickly. I'd drive slowly until you determine what's going on. Anything at this point would be pure speculation. Good luck.

 

Can't get it on the lift until tomorrow night now. I'm really hoping for slop in the drivetrain somewhere that is the root cause...there's no whining or other noises from the rear diff, etc., and the transmission shifts fine with no noises, etc.

 

you may not be burning all of the fuel and it is getting in the exhaust and igniting when you let off the gas. Just a thought

 

Hi Phil, the car definitely runs rich, but this isn't that kind of sound. Very much a metallic sound, like a missed shift without the grind. Appreciate the reply.

 

As hugie suggested, sounds like the nut fell off your pinion (Snubber) mount. A good test is to give it a little gas in reverse. You should hear your bang again.

 

Will try tonight. What's the fix like for this if I find it to be correct?

 

My money is on the pinion bushing as well. If things aren't rusted up too bad, you just need a new bushing. Should probably replace the bolt as well if you're ordering parts. I think you'll have to drop the driveshaft to get at it, if I remember correctly. Of course this means you are going to check your U-joints while you are in there. And of course, have a look at the seal at the rear of the transmission. You may wish to replace that while you're in there. You know what? Just rebuild the whole care while you're at it.

 

Thanks guys...what is the name for this part that I should search for? Tried "pinion bushing" at Corvette Central and came up empty. I actually do need to replace the rear seal on the trans, so that will be a good oppotunity.

 

Pinion Sunbber Cushion. You can replace it without dropping the drive shaft you may have to rotate the shaft but you can get to it.

Tip: buy the whole kit new bolts and washer as well.

 

Thanks Roco!

I'll try to get some pics while I'm under there.

 

Is this the guy?

http://www.parts123.com/parts123/yb....Z5Z5Z50000050G

 

I did mine last summer and ended up cutting the bolt off that's the reason I recommended getting new hardware.
Nice car by the way.

 

Yes,

 

Thanks again.

 

No, this is the guy

http://willcoxcorvette.com/product_i...ducts_id=24293

Obviously the same part but a little cheaper, especially when you add the forum discount.

You should be able to do the job without removing the drive shaft but it is a little fiddly. I'd also suggest adding a drop of Loctite on the nut when you assemble it. Not sure why these like to come loose, but they do.

 

Sweet looking car.

Welcome to C3 Maintenance 101. "Today's chapter begins with replacing the pinion snubber cushion. If you all will turn to page 193 of your AIM guides, you will find ..."

Good luck. The snubber cushion was going to be my guess, too.

 

You guys get gold stars. Got the car on the lift tonight and here's what I found: