Long road trip with the 66 Riviera GS - lots of fun! I noticed that the locking rear differential would knock very loudly when cornering at the gas station, etc. after long periods on the road. This does not happen at all when the differential is cool. I've heard that Equa-Torque lube additive can help reduce this problem. Any other solutions out there? This is a full locker differential - not a posi/limited slip rearend. thx!
I had the same problem. I opened it up and found a broken spider gear washer:eek2: I decided it was time for a new posi unit and replaced it with a new Eaton unit. No more binding on the corners. You may want to try fresh gear lube with new additive first and inspect for broken parts.
I do not believe rears back in the day had full lock up with out clutches or cones etc. So that being said you most likely have a limited slip unit (these units have clutches and or cones and some form of preload spring or beveled clutch to keep the unit locked until the force of the torsion in the axle makes the unit disengage (SLIP) in a turn. That is where we get the name limited slip differential. If you ever open take a few shots of unit in different locations of the revolution. Then we can determine what you have. Power lock type or Eaton or Auburn etc. OR maybe there is some kind of locker I have never seen before??? Never know. I would say change the fluid and make sure you have at least 8oz. of limited slip additive and try again. If that does not do it I would say it will need to come apart and gone through. We recondition units if the parts are available in the market and even can if they are not all depends on the trouble with the unit. Jim
Jim - do you have particular fluids and limited slip additives you prefer and suggest for these units? i'm going to open it up this weekend to change the fluid and take a look. thx.
I've used a GM posi lube additive before, think it's still available. I had a Chevelle with a 12 bolt posi that absolutely made the car lurch in turns when the posi was hot. Used a bottle of the additive, it cured the problem right away.
Finally got it open to change the fluid and took the pictures below. i was told that the carrier is full locker style, but it looks like limited slip/posi to me. other opinions? going to put in sta-lube 80/90W limited slip gear oil and a tube of equa-torque that will hopefully smooth out the cornering knocks.
It's the original posi, limited slip w/clutch packs. I've never needed anything more than a bottle of the limited slip additive from GM Parts to keep them quiet. Devon
Is the GM limited slip additive superior to Sta-lube additive for this application? The 1966 manual says you should flush the posi-differential with 30W oil if the wrong gear oil was suspected. The flush procedure: fill with 30W, lift rear wheels of car, drive car no faster than 30 mph 3-4 minutes, drain 30W, repeat one more time with 30W. Is this still recommended practice?
Sure, the flush procedure can only help if something was in there that shouldn't have been. Regarding one additive brand vs another, I have no experience with other brands, as I've never had any reason to switch brands in the last 25 years or so. Devon
FYI. Don't use a synthetic, too slippery. The posi will now have little or no resistence. In this case the ole dino oil is the better choice with the additive.
my 70 chevelle posi also had a noise from day one. returned the car to the dealer. they flushed/changed the lubricant. the wrong oil had been in the rear end. back then, they used whale oil for the posi.
Gee and you wonder why the species was almost extinct...lol. They used and still do use it for a ton of stuff. Jim
Interesting, I had a similar noise/catching problem with my Estate Wagon with the limited slip. I changed the lube, put in Mobil 1 synthetic gear lube and the GM additive and it has run great ever since. I must have missed the information about synthetic vs. dino oil. Of course I am not out trying to light 'm up with this car - just pulling the camper (and I haven't been stuck yet to test it all out)!
My Eaton Posi came with a warning not to use synthetic gear oil. It would void the warranty. I use Valvoline 80W/90 with a bottle of GM additive.
2 Qts of Sta-lube 80/90W hypoid limited-slip gear oil, plus 2 oz. of Equa-Torque additive mellowed out all of the knocks. Thanks to all for the helpful advice. Followed the flush procedure in the shop manual just in case - 2x with 30W oil running elevated car 3min @ less than 30mph. It seemed like overkill, but the lack of replacement parts is a little scary.
