ga

If you have an occasional growl in the rear end, as I did, here is what I have discovered: I have a Limited Slip Diff (which I didn't know) & had Swepco put in the tranny about 6 months ago. Ever since then, only once in a while, usually after the tranny was warmed up a bit, there was a growl in the rear end, like you had studded snow tires on the back. Turns out that the LSD doesn't like Swepco (too light) & needs a thicker, more viscous fluid. Also added in the GM reccomended fluid for their posi-trac cars, and bingo, growl is toast. I posted a question regarding this a while ago and a number of people responded with this exact fix, so my hat is off to all of the very knowledgable Rennlisters out there. There is a massive amount of brain power and experience within this group. Today was just the first opportunity that I have had to do something about the "growl in the rear".
Thank you, ga

JES1680

How timely. I put Swepco in about 2 weeks ago and have noticed exactly what you are describing, but couldn't figure out what it was.
What is the GM fluid that you mentioned? Do you add it to the Swepco or do I need to drain and re-fill?

Thanks

ga

So you must have a Limited Slip Diff..........drained it, put in the recommended tranny oil, and added the GM fluid as well. The place that I go to knew about the posi-trac GM stuff, so they just ordered it from their parts supplier and put it in. Someone in Rennlist will know it's actual name, though, or try google-ing it.
ga

JES1680

Yes I have factory LSD.
Did a search and couldn't find much info on this.
Wondering if I just add the GM additive to the Swepco(the tranny shifts so nice with it), if that will be ok.
Anyone know?

theiceman

I have an LSD also and would be interested to hear more .

GA I guess your mech did it so you don't know the ratios of how much "recomended tranny oil" and how much GM adative. Would be good to know ..

ga

Sorry for the delay, Ice. The invoice says," 3 x GL 50, 1 x Differential Additive. The GL50 was a yellow bottled Pennzoil product with the tapered "squirt" top, specifically for LSD's, and the GM LSD additive was a squirt tube, like a 2 or 3 x bigger giant toothpaste tube that the mechanic just sqeezed into the fill hole. I called the shop, and they said that the GM LSD works best, but every manufacturer has one, and to give a call to GM re: their LSD Diff. Additive. I think that the Pennzoil product is pretty standard, and you just put in as much as is required in the manual re: fluid changes (like 3 litres or so) & then squeeze in the GM additive after that. Hope that helps.
ga

ga

By the way.....have been driving around alot since the fluid change, and the "growl" is gone completely !!! Amazing how a different type of oil could make that much difference!
ga

WolfeMacleod

I have a question about this "Growling"

I notice that when I let off the gas, I do get a very slight "growl" that transfers itself through the gas pedal and the shifter...you can feel it as a vibration in your hand and foot. As long as you are on he gas even a little bit, no growl.
Audibly, it's sort of a "whirrrrrrrrrrr" that sounds maybe like a Tie-fighter in Star Wars, only not so loud.

So, is this the sort of thing you' referring to, or are you talking about a constant growl?

I have LSD, too.

theiceman

Great info guys , think I will do some research . I do not think I have a growl but I am always game to try something new .. I did have a sort of growl but that is when i am in too high a gear , ( like going 60km/hr in 5th ) but I think that is normal and is my car telling me " don't be an idiot " ...

JES1680

I've only heard the growl a couple times, but not for a while now and only during, Low speed turns. I got the 4 oz bottle of GM additive. I'm going to add it to my Swepco filled tranny this weekend and see what happens. Should I start getting the growl on a regular bassis I'll move to the LSD reccomended stuff.

ga

The mechanic said that there are 2 "clutch-like" set-ups inside the diff on the LSD, one on either side, that transfers the power from one side to the other, thus giving us that limited slip action when one rear wheel is slipping in gravel, on a wet surface, snow, etc. The Swepco that I had put in about a year ago is too viscous (slippery) for these "clutches", so when you go around a corner, as one wheel has to spin quicker than the other to make the corner, as the LSD is transferring power, the "clutches" slip because the Swepco isn't thick & heavy enough. As soon as I changed back to regular tranny oil/fluid, with the GM LSD additive, after about 1 mile that slipping was gone. Completly gone. So that was the explanation I got, and it made sense to me.
ga

Dave Thomas

This is GM part # 1052358, available at http://www.gmpartsdirect.com for less than $5.00/bottle.

theiceman

Great info .. not sure if I can add the adative no though .. please update us JES ( as long as you don't mind being the guinee pig ) I think I will go your route for now if it works.