Another good clear video and audio. Thanks for posting. I used Lucas 85W-140 gear oil and 2 bottles of GM posi additive when I refreshed mine. These differentials needed posi additive to ensure the posi discs are working properly and quietly. I had the differential out of my car while doing a rebuild of all the rear suspension. I took the rear cover off and flushed the differential with diesel fuel to clean it up. Diesel cleans well and has a lubricant in it. I was then able to check the wear pattern of the crown and pinion. Before closing it back up, I drilled and tapped a hole for a 1/4 inch pipe plug at the lowest point of the differential. It is in front of the spring leaving lots of access and not interfering with anything. Care must be taken not to run the tap all the way in or the pipe plug will not tighten and seal. I wrapped teflon tape around the plug before inserting it for added insurance. It has worked great staying tight with no leakage and making the next change very easy. I would only recommend doing this will the rear cover off your differential.
Thanks for the vid! With your help, I just changed the fluids in my 74s diff, mine hadn’t been changed in probably over 20 years as well (I haven’t driven the car yet and bought it in 2019 as a project, just putting the finishing touches on it to get it on the road at the end of September).
Nice job on the differential fluid change! I changed the fluid in my '69 Vette about a month before you did. I did it exactly the same way. After asking around for some advice, I went with a brand called Royal Purple, with the additive already in it. I didn't even notice that it was synthetic until just now. I had it changed in 2009 at a local shop. They split the differential to do it. The labor was 6 hours. However, I let it sit for a few years in my garage after that and the additive broke down. I know this because when I would drive around turns the diff would go BANG BANG BANG something fierce. At first I thought it was the U-Joints in the half shafts, so I changed them (again). Once I changed the fluid, the rear end quieted right down. So I guess @SQR is right. It does need to be changed regularly. I've already changed the fuel tank this summer, so now all I have to do is replace the spare tire carrier. Also a great video, BTW!
I’m going through the same right now. A jerky bang and pop noise when turning at low speeds. I’ve changed the half shaft U joints and it still pops. So I’m doing my differential right now. I’ve got the diff oil with additive and I also got one tube of extra additive to supplement. Fingers crossed, wish me luck. Thanks for the info.
I use the proper Gm oil and Gm additive. I remove right rear tire and go in from there... use a long extension and 12 point socket..easy. i just did it less than an hour.
Howdy Problem Solver Garage. The CRC additive packaging and labelling has changed. It is now called CRC Trans X. The size is now 206ml vs. 207. Moreover there is a big discrepency in the directions for use on the back! It now says to use 1 tube for 1-4 qts.! Your package says 1 qt. additive to 4 qts. oil. You mixed according to the labelling in your video. WTH? Which set of directions do you think is correct?
Thanks for this. Synthetic didnt exist back then but the gear oil used things like whale oil too back then so modern conventional oil is not the same as what they used in 69 either. same goes for the motor oil which should have a zddp additive added for the flat tappet cam to avoid wiping lobes/lifters. Ive also been told to add the 2 bottles of posi additive and then add enough oil till it starts to come out the fill hole and then its full. whether the diff has posi or not is one thing that has an effect on how much it takes.
Thanks for making these videos. Inherited a c3 from my Uncle and noticed that the diff is leaking. I think the fluid is slowly going onto the exhaust pipes. Noticed that there's more smoke from it burning off the pipes. Is this a bad thing? Like can it catch on fire or something?
Holy cow! I didn't even notice that. I had to go back and watch the video again, plus go out and double check mine. No wonder he found the spare tire carrier installed incorrectly. Someone was beating on this car. Must have been quite a sight to see it pulling a trailer back in the day. 😂
@@vtradio towing a trailer with a Corvette? Makes you wonder. Along those lines, the reverse lock out in a C3. Why? I don't want the steering to lock, why? To tow my Corvette? I can't figure this one out. Picture towing a 69 vette that's towing a trailer behind a motor home heading down 101 with Good Sam stickers on the back.
Synthetic diff oil makes my 72 leak even more than regular! especially when the weather is extremely hot and lubricant breaks down even thinner and leaks like a bitch!!!
