WhiteVette09

Hey guys,

i just got got my new top end in. 350 miles into the 500 break in period and this happens... I was going 70ish on the highway with the wife in the car and I heard something snap. It didn't lock up, but when I pulled over and lifted the back end I couldn't spin either rear tire. If I was alone I probably would have tried driving it home because it seems "okay" when I'm accelerating but I can really feel it when decellerating...

so I guess my 2 questions are (1) does this sounds like differential needs to be replaced?
And 2) what should I upgrade while I have to get this fixed?

thanks in advance guys!

71VetteLover

It would really help us to know which year and whether it has a 4-speed manual or a 3-speed automatic.

ddawson

Sounds like rebuild time. After you pull the cover you will know more.

WhiteVette09

It's a 74 L82. 4 speed

71VetteLover

Okay, it is likely a differential cross shaft that has come undone and is hitting the inside of the case. Suck the oil out and if you see a lot of metallic sheen in the oil (some is normal) something inside has come apart.

BlackC3vette

Whether is is an automatic or 4 speed, its really not relevant. What noise do you hear when you backed off the throttle?

HeadsU.P.

Could be one of six U Joints. Put the rear up on jackstands, pop the tranny in neutral, grab the driveshaft, start turning.

GTR1999

Before jumping to conclusions, do as mentioned and get it in the air. It is possible a RG bolt backed out and was sheared off. It would possibly have locked up but it would be noisy. If you broke the posi it wouldn't go anywhere. There should be no play in the pinion yoke, axles will have some play - how much depends on several factors, a stock posi spring setup typically has enough load by the springs the wheels will rotate but not against each other unless you break about 40ft/lb of load. If you narrow it down to the diff, pull it and mount it on an engine stand if you have one. Pull the cover and see what it looks like. 74 diff's weren't bad, the clutches were not too good and the axle faces soft but the posi case was the better one.

Check the trailing arms for parking shoes binding, I have had some that came in were the springs broke and the shoes wore into drum hats.

Just take your time and isolate each area: arms, shafts, diff, you will find it. It was a nice day here in the NE today, I was out in my 72 all day.

bazza77

If I jack one rear wheel up I cant turn it at all in neutral as well.

Interesting to see where the actual damage is . I have driven my 77 vette home with the diff sounding like its full of loose bolts and cogs ,grinding and thumping its way around every corner like its definitely not going to make it. got home changed the oil and put new additive in and quiet and smooth as silk now . That came on suddenly on the freeway but no bang though.