Hello all,

Well I drove my 73 to work Friday morning and got ¾ there and was stopping at a red light, down shifted the th400 from 3-2-1, but when I went to take off all I got heard was a horrible grinding/banging noise. Tried to select other gears but didn’t matter, same horrible noise. So shut her down and pushed to the side of the road and waited for a tow home.

So, got the rear up on jacks this am and pulled the rear wheels. Did a visual inspection, nothing looks broken, all u-joints look intact. LR hub turns freely with trans in park, RR locked and I could not turn the hub. So I tried to start the engine, still in park, got this horrible rat-a-tat-tat sound, so backed off, moved gear selector around and back to park and then successfully started the engine without any noise. Then I put it into reverse and LR does nothing but RR spins once I took my foot off the brake. Repeated this a couple of times, did not try any forward gears.

Also, when I shut the engine off I got a little short bit of the rat-a-tat noise and then some type of whoosh sound. What the heck is that!?
So do I have a diff issue and/or trans issue or what’s my next step in diagnostics.

BTW, the trans was rebuilt around 71k and car now has around 84k miles. I sometime would have a clank sound when putting it into gear, but not always, otherwise drives and shifts smoothly. The engine looks like it’s a warranty engine replacement at some time in its past as it has a CE at beginning of the engine stamp, but for a 350 it does not seem very powerful, but I’ve never had a Vette with an automatic trans before so…

I’m thinkin I’m in for an expensive trany/diff repair bill in the near future, lol.

Any help in diagnosis would be much appreciated.

Thanks in advance,
Marc

 

Put your transmission in gear with the wheels off the ground (engine off). You should not be able to turn either wheel. If a wheel turns then you have a broken side yoke on that side. You will see the half shaft turn with the tire. With the transmission in neutral you should be able to turn either wheel and notice the drive shaft rotate as you turn the wheels.

I had a similar noise. Look at mine
https://www.corvetteforum.com/forums...ide-yokes.html

 

Thanks for the reply cagotzmann,

Wow, that's some kind of torque you must have to twist it like the pix in your link shows!?

Yeah, I can spin RR freely with car in park, spins the half shaft as well so the yoke going into the diff is busted then. If I put the car in drive I get all kinds of banging, guessing that broke part is catching on something, so I'm hesitant to do that . However, I can do it in reverse and it spins the RR okay so drive shaft is turning obviously. Not sure why the broken part is not catching reverse, must be pushing it out of the way or ?. I'm not a diff guy so it'll be a tow to a shop somewhere.

 

You need to remove the diff to repair.

Mine broke due to cheap metal. That was a new part. Look for a yoke with a GM stamp on the yoke end. This is for a proper GM licensed part or GM re-tipped. The only one I was able to find with the proper GM licensed Stamp was from lonestar. Once you remove the half shaft your GM original yoke should also have the same stamp. There are other yokes that may be ok, but I wasn't about to do this repair again.

 

If the car is already on stands with the rear suspension hanging then grab the top of the wheel and pull out. You should be able to pull the rest of the shaft out of the diff if it's broken.

 

You might have broke the pinion gear " At least the Corvette rear end is fairly easy to remove
Wes

 

Is the drive from the trans connected to the diff?

 

Yes driveshaft is attached to diff, I can put it in reverse and the right rear wheel turns ok.

 

Well, not sure that this is the whole answer to the problem I experienced with all the banging and ratcheting sound I was hearing but it surely needs attention. Sending the diff to Bair's for rebuild once I get it out of the car.

From my research on the forum some have said that sound it the parking pawl in the trans. So please tell me if my next step in diagnosis make sense. Once I get the drive shaft off I'll start the engine and try the gears in the trans. I know I could get reverse to work ok after a fashion but haven't tried any forward gears.

BTW, just want to say thanks for all the information that this forum provides! What a great resource for help!

 

Well I think I found out why my one diff stub axle broke! Looks like I had a U-joint failure where one of the the caps retainer clip was missing and cap was sticking out about 1/4". That must have been causing some kinda out of balance on that half shaft due to the excesive end play!? Also the zirk fitting was broken and this cap was the farthest from the zirk, all dry and rusty looking, amazing it didn't seize!

 

Hmm, spoke to my diff repair guy (retired GM tech out of Portland, OR) who said this would not have caused the axle to break. He said was just faulty stub axle, bad quality.