'65 Corvette - limited slip differential question

[Oliver S.]

The limited slip differential in my '65 Corvette is filled with the appropriate diff. oil and 2 bottles the GM LSD additive.
Today we drove 120 miles with the top down. 70 miles on curvy country roads up some hills and down some valleys to enjoy the landscape. Speed varied between 40mph to 60mph. Maybe once I felt a slight tension in the diff when turning left.
In order to get home faster we decided to take the Autobahn (I live in Germany) for the last 50 miles - speed constantly between 60 - 70 mph. After we left the Autobahn there was a loud noise from the diff. as well as some slight mechanical tension/release could be felt ... but no staggering of the wheels - this was all at low speeds in curves or when slowly accelerating around the corner after a full stop. So 70 miles at lower speed with no noise and then after additional 50 miles with higher speed the diff makes noise and tension/release could be felt. Is this normal or at least tolerable?


Oliver

[Bill W.]

Re: '65 Corvette - limited slip differential question

Oliver,
Find a nice vacant parking lot and with the steering wheel locked in a left turn slowly do 5 or 6 circles while gently getting on and off gas, now repeat the process going right. What this will do is separate the posi plates allowing lube between them. If this procedure does not fix your problem you will probably need repair work. Let us know what happens. Good luck! Bill

[Oliver S.]

Re: '65 Corvette - limited slip differential question

Bill, I think I'll replace the diff. oil. Ever since the diff. oil was replaced in 2011 because the diff. was resealed I have been experiencing noise issues every now and then. It wasn't done by me but a shop.
I heard GM#1052358 diff. oil is discontinued. What is a good replacement or alternative brand?
Oliver

[Stephen L.]

Re: '65 Corvette - limited slip differential question

I would replace the gear oil with the appropriate weight. Most have a "positraction additive. Additionally I'd install an additional bottle of positraction additive. The do the circles and figure eights.
I don't know if this is available in Germany, but the Automotive stores in the US sell these products

[Gary R.]

Re: '65 Corvette - limited slip differential question

Oliver,
Could simply be the oil in the diff now, as the others mentioned. I would give the car a good looking over with it in the air. If there is nothing obvious then suck out the old oil and get 2 bottles of the GM additive and with either 90wt or 85-140 gear oil. You don't need fancy snake oils or synthetic oil. When I build diff's for non NCRS cars I always put in a drain plug to make a diff oil change a simple deal, you'll have to use a vacuum pump to get it out. Hopefully you can get the correct oils in Germany, I ship diffs all over the world and only have the GM additive in them, the customers always had a source for oils such as I use, Lucas or GM.

Do the figure 8's in a parking lot afterwards. If that doesn't solve the problem or you hear more loud noises you better drop the diff and pull the cover. The 65-68 Eaton posi cases were better then the 63-64's but not by a lot. They are very prone to crack over time and lock up the diff. I'm not saying this is your problem, lets stick with the oil change and GM additive install. Use 2 bottles of it too, it is not as good as it once was.

[Duke W.]

Re: '65 Corvette - limited slip differential question

Bill, I think I'll replace the diff. oil. Ever since the diff. oil was replaced in 2011 because the diff. was resealed I have been experiencing noise issues every now and then. It wasn't done by me but a shop. I heard GM#1052358 diff. oil is discontinued. What is a good replacement or alternative brand? Oliver

All OEMs the offer clutch type LSDs use the same additive. It's available in the US at NAPA. As far as the Eurozone is concerned, it's the same as required by the LDS of a late eighties Merc 190E 16V. I'm sure you can get it at a Merc dealer, and likely it's available in the European aftermarket, too.

[Joe L.]

Re: '65 Corvette - limited slip differential question

Bill, I think I'll replace the diff. oil. Ever since the diff. oil was replaced in 2011 because the diff. was resealed I have been experiencing noise issues every now and then. It wasn't done by me but a shop.
I heard GM#1052358 diff. oil is discontinued. What is a good replacement or alternative brand?
Oliver

Oliver------


The GM posi additive, GM #1052358, is replaced by GM #88900330.

[Dan H.]

Re: '65 Corvette - limited slip differential question

Hi Oliver, have the same problem with my 64 with an Eaton posi unit. Added another bottle of additive, did figure 8s etc, no help. It's back in the shop where the clutch disc were installed about 2000 miles ago, acts like it's locking up. Will let you know what the cure is if they find it.
Dan

[Timothy B.]

Re: '65 Corvette - limited slip differential question

Dan,

The problem could be the backlash is to tight on the differential gears.

[Dan H.]

Re: '65 Corvette - limited slip differential question

Totally agree, they're revisiting the rear end this week to fix it.

[Oliver S.]

Re: '65 Corvette - limited slip differential question

I've ordered 2 GM LSD bottles and 2l 80w90 GL5 oil (3.7 pints ~ 1.75l). Furthermore my 3/4 8-point socket for the differential plug is already here. So all is prepared but there is one remaining question: Do I have to use a gasket for the plug? The red LSD tag was removed (and stored) last time because oil leaked when it was installed. So I think I won't the tag, too.

Oliver

[Dan H.]

Re: '65 Corvette - limited slip differential question

Oliver, you'll need to put thread sealant on the plug threads or it will leak. I use loctight 545 red sealant. Any good one should work.
Dan

[Oliver S.]

Re: '65 Corvette - limited slip differential question

Short update: I changed the diff. oil and discovered that 250ml were missing although the diff didn't leak. The garage used a copper ring for sealing the diff plug omitting the red tag for the LSD.
I found an old posting by Gary Ramadey who recommended Permatex High Temp sealant for the diff plug. I tried it and put the red tag on the plug. Then I did the recommended '8' and drove 15 miles (more not possible) to see afterwards if the diff oil leaks at the plug (I assumed the diff oil is sufficiently warmed up) - fortunately it didn't. Furthermore, my initial feeling when driving is that the rear runs 'smoother' now.

Oliver

[Gary R.]

Re: '65 Corvette - limited slip differential question

Oliver
One note on using the Permatex High Temp thread sealant. I found it works great to seal threads BUT it also will act like a thread locker too. I used to use it for magnetic drain plugs I tapped into differentials but sometimes the plug was locked and customers had a hard time removing it. A touch of heat will loosen them up. I call Permatex about this and was told it was not a thread locker and I was wrong. None the less it does lock threads. I only use it on steering box bearing preload adjusting nuts now. You can use #2 Permatex on the plug and it will seal it as well.

[Oliver S.]

Re: '65 Corvette - limited slip differential question

Gary,

after finding an older posting by you regarding Permatex High Temp sealant I checked their product description in which it is stated that it locks and seals BUT it is also mentioned that it lubricates threads for easy assembly and disassembly and suggested application is rear axle fill plug.
After receiving it I tried Permatex on a test thread following the instructions. After two days I removed the nut and off it went without problems. This convinced me to employ it for the diff plug. But I applied it sparingly with a toothpick in order to minimize locking, which remains to be seen (hopefully in many many years).

https://www.permatex.com/products/thread-compounds/thread-sealants/permatex-high-temperature-thread-sealant/

Oliver