I was hoping with some miles my limited slip would quite down on turns but it isn't. I had the unit completely dissembled when I restored the car and the friction plates did not look worn at all. I did not anticipate having a problem with chatter. I've had these apart before in other cars. Had some that additive helped and one that had to have new friction plates but it was noticeably worn. I used standard 80/90wt limited slip lube with the GM additive. Anyone got any suggestions on a more slippery lubricant that might stop chatter?
I should have mentioned I am on bottle #2. I used GM additive but not GM lube. Not sure if that would make a difference. I am thinking of trying a full synthetic. Seems like I recall someone like Denny Manner saying to use synthetic for persistent chatter issues. Actually I'll be surprised if I don't have to take it back apart.
Jason, When the plates are in good condition the plates have a VERY hard time getting lube between them because they are so TIGHT after they have been taken apart & cleaned. The original "Whale" oil that was used in Posi rears has not been available for MANY years now. In a case like this what I have done in the past is after driving the car for awhile & the fluid is now HOT. Drain & re-fill (don't use any cleaners) with the proper fluid & two bottles of additive from GM. Now take it for another drive to get the oil HOT again & go to a good size parking lot & keep doing figure 8's. The fluid will work it's way between the plates & the chattering will more than likely stop. This chattering is MOST prevalent when the steering wheel is slightly turned at a stop light/sign & the car is hardly moving. It can chatter so bad you think there is something about to break/broken, but it's just the "Plates" slipping usually. I don't like using Synthetic oil in Posi rears as it usually turns out to be TOO slippery. Posi works via friction. The spider gears are WAY to small for the size of the gears & our cars & if the Posi slips from doing a burn-out (which you will probably never do) or if for some reason the Posi unit starts to slip from sand with little or no traction to one side then the spider gears will break causing further damage. Spider gears are IMPOSSIBLE to find new & used is mostly the only way. Tom T.
Thanks Tom. I'll flush and refill again. We ran about 150 mi yesterday. I kept telling wife not to worry . She was sure something was broken in the rear axle.
Jason, worry not... that posi You sold me took almost 800 km to stop chatting and i didn't make it's life easy. But like Tom said doing ''8'' figures in parking lot is the best way to lube plates. I have used Valvoline oil with one bottle of GM additive. Btw i have bought all parts to rebuild whole posi unit i only miss new shaft for spider gears. Good luck with Your car.:TU: Peace,
Thanks Kacper! I'll resist the urge to try synthetic for now. As Tom said I don't think I'll be doing burnouts:3gears:.....but I do have a gravel driveway with an uphill climb so the posi comes in real handy to prevent spin
just wondering if these clutch disc's would benefit from soaking in a friction modifier before reassembly
All I have ever used in a posi rear is this- http://www.ebay.com/itm/like/151467101797?lpid=82&chn=ps&ul_noapp=true I turn several circles in one direction, and then several circles in the other, rather than doing figure eights, but that could just be personal preference. I only ever used one tube in a diff. You will need to repeat that turning exercise every once in awhile, as well, especially if your car sits a lot.
Update: Changed oil, more GM additive, many circles and 8s. no good. Sucked that out and put synthetic in. More circles and figure 8s for 15 minutes. No change. diff has to come out and apart to see whats going on. Car is going into storage so that will have to wait until next spring.
Sometimes the clutches are just plain finicky... We have had rears that will just not shut up. You can also go composite clutches or carbon fiber if it is a EATON type unit. Shuffle the clutches, pre-lube them with the additive in between each plate...soak them. You spider gears can also be the cause of the chatter as they can be a bit worn and shiny they will climb each other a bit before pining and twisting the side gear to release the clutch pack. THIS WILL also have the same affect as clutches being warn.... AS stated you may be in for a long test out on this to find your answer. Take care, Jim Mitschke J D
Take the preload springs out and leave them out. I had posted a video awhile back,showing how to properly tuine a clutch unit,and you dop not put the spring packs back in. By not having them in,the clutches can relax from each other,while turning. Since there are springs in there,you have constant pressure on the clutches,no matter if you are turning or going straight ahead. When you turn,that can't disengage because the springs are pushing them against each other. With a properly tuned unit,the clutches will still be able to function properly as a posi. The side gears & spider gears push against each other,which will push against the clutches. This is nothing new. I have an article from 1981 that explains the same thing. The springs are basicly a crutch. The units were assembled rather vaguely,and loose,so the springs were in there to create pressure on the clutches. When reassembling the clutch packs,there is also a fromt & back to the clutches,and you need to stack them all inm the same direction for the best result.If you look at the clutches carefully,you will notice one side has sharper edges than the other.This is typical from something that is punched out. You also want to put some oil on each clutch,as you are assembling the stack.
I couldn't stand to worry about this all winter so I took today off to pull the diff. Decided to check this thread when I got up and what great timing for the last two responses. Unit is disassembled on bench. Interesting is the comment about the plates having a sharp edge on one side from the stamping process. I had never noticed that but clearly that is the case. I put two plates together with the sharp edge against each other its easy to see how that would create a sealing effect not allowing oil in. First pic is sharp edges facing/against each other and second pic is sharp edge and rounded edge facing. You can see the difference and they aren't even being squeezed by springs. I did read in the manual where it stated the clutches also get loaded by the force from the pinion gears. I had never heard of leaving the springs out though. I may try that because once it goes back together I don't want to take it back apart.
Gone through two cycles with my posi, once just doing fluid changes and once as a rebuild because I was rebuilding the whole car - posi didn't need it according to the shop, clutches measure great so that was good to hear. I never heard of the spring removal trick. That is cool. But with the springs in place here is my advice, drive it. Ensure plenty of fuel is in the tank and drive it again, you need good long duration heat cycles in the oil with long gradual turns to allow the additive to soak in as the clutches move. Worked for me twice. :beer
After much soul searching I reassembled without the preload springs. I like to keep things stock and functioning as original but made a concession here. Based on BrianTricks note and my own study, I felt the springs were mainly there for when there is a significant difference in traction between the wheels and still have posi action. Not likely this will be an issue considering how the car will be used. I wanted to see if deburring and shuffling the plates around and leaving springs in would have solved the problem but decided to go for the sure thing and leave them out. Drove car yesterday enough to get the differential heated up. No chatter and it leaves 2 black marks on the pavement as well as 2 spin marks in grass so its still working as a posi as BrianTrick stated it would. I did put in standard 90wt gear oil without additive figuring the additive was only needed due to the clutch preload. Figured without preload I didn't want/need additional friction reduction.
