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My " beater" 66 Riv GS  3.42  Positraction is making some very scary noise  recently particularly when I am making  acuteness turns at a slow rate of speed - almost a ratcheting type of noise , happens in either direction . Sounds like  a popping and makes the car lurch a little  if that makes sense . Also the rear  end whines when it is accelerating but quiets down when speed is reached but when you accelerate it whines again until  I reach a steady speed . Don't know much about posi's other than what I read on the Internet . First thing I will do is change the fluid and I have read something about a special additive for the Posi's ?... If that doesn't quiet it down, what would I look for next ? Clutches , shims , damage to gear ?...  Know there are some Posi experts out there and would appreciate their help . Thanks 

KReed

ROA 14549

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   More than likely the whining is because tolerances have become "Sloppy" because of worn bearings. Normally replacing them will solve that problem. Continue driving & wearing a "pattern" in the old gears & you may have the problem forever until you purchase another set of hopefully good used gears.

   There was NEVER a recommended change of fluid in the diff. from the factory.  If it still has the original fluid which contains whale oil & stinks add a bottle or two of the GM ONLY posi additive. You don't have to worry about overfilling as they are ONLY 4ozs. each. Go to a big parking lot & do some figure 8's to get the additive between the clutches & it should clam down after awhile.

 

 

Tom T.

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Also, forgot to add JZRIV posted about the noises his posi was making & his solution to the problem. Do a search or maybe Jason will respond & add to this post.

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46 minutes ago, kreed said:

My " beater" 66 Riv GS  

KReed

ROA 14549

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Looks pretty nice to be a "beater."

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Had the same problem on my 65gs after taking to a shop that i will never go to again. The ratcheting noise was because they put the wrong lube oil in YOU MUST use POSI OIL. You cannnot use  standard rear end oil. After pitting the posi oil in mine the ratcheting noise was gone. It is a scary noise for sure!

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1 hour ago, RivNut said:

Looks pretty nice to be a "beater."

It's a twenty footer on paint - think somebody painted it in a Kansas sand storm ! Thanks everyone for the suggestions . It's definitely a scary sound - sounds like the rear end is falling out !  Hopefully Jason also has some pointers - will see if I can his post.

KReed

ROA 14549

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Pretty common problem on these Ken especially when they get hot. First step is the additive. As Tom said you can just add it to what's there or pull the rear cover, drain and add fresh limited slip gear lube plus the additive.  If the level is too full to add additive, just suck some oil out with a gun.

https://www.ebay.com/itm/Genuine-GM-Fluid-88900330-Limited-Slip-Axle-Lubricant-Additive-4-oz/263528044399?epid=657525475&hash=item3d5b7ed76f%3Ag%3AgDsAAOSwZDdamaTm%3Asc%3AUSPSFirstClass!15681!US!-1&_sacat=0&_nkw=gm+limited+slip+additive&_from=R40&rt=nc&_trksid=p2380057.m570.l1313.TR1.TRC0.A0.H0.Xgm+limited+slip+additive.TRS0

 

I disassembled the differential on my 66 GS to inspect and clean during the resto. Clutches and everything looked in excellent condition so figured no problems. Once driving the car it was chattering like crazy. Added more additive, no good. 50 figure 8s, no good. Pulled differential and dismantled, nothing visibly wrong. Changed lube again and tried full synthetic limited slip lube, no good. Finally a guy on V8Buick.com who is very experienced with these said just pull the preload spring pack out so I did. He promised it would still work as a posi. I had never heard of doing this. The springs are there to help create posi action under more severe variation in traction between the rear tires such as in snow/ice. Under heavy torque the beveled side gears are pushed against the clutch packs and provide posi action without the springs. The car still leaves 2 black marks w/o springs so he was right. No springs allow the clutch packs to relax and more oil to get between them and eliminate or reduce chatter.

It still bothers me I did not get to the root cause of my chatter but this was a solution that worked for me. The spring pack can be removed without pulling the differential.

 

Adding a couple more thoughts: Over the years usually the additive will take care of the problem. Years ago I had a 67 that was totally uncooperative so I disassembled the diff and noticed the clutch discs were worn almost smooth which does not allow oil to get between them. At that time I was still able to buy new clutch packs from GM. No more chatter. I also learned these clutch discs are stamped and one side has a rolled edge from the stamping process. When reinstalling the rolled edge side should all go the same direction. 2 edges facing each other will not let oil in.

Edited by JZRIV (see edit history)
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I conducted a lot of research before installing the posi on my ‘67.

Turns out all new rear axle fluid for our cars already have the “posi” additive incorporated in the mixture. There should be no need to add the additive as once was true in the past. (Even though the additive is still sold) 

What the hay - it won’t hurt if you do. I would change all the seals while at it too. Don’t forget Rivieras axle/ shafts have their unique angle.

Best of luck.

Edited by PWB (see edit history)

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When the posi in my '77 Century started chattering I drained it and replaced it with oil & additive from the GM dealer.  Expensive, as oil goes, but it did the trick and was cheaper than pulling it apart!  ;)

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Thanks very much to all . Tried the additive tonight - took a little fluid out - could only get a bout 4 oz in before it began running out. Drove it about 20 miles  but no figure  8's . Couldn't tell much difference when I parked it but hopefully it will improve . I am going to try the preload spring idea Jason - just got hit the books and figure out how to do it . Does any one know if the clutches are still available ? Appreciate all the  great advice . 

KReed

ROA 14549

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Figure 8s create maximum slippage of the clutches which promotes faster oil impregnation. I would not expect to see difference with a 20 mile normal drive.

 

Pretty sure clutches are available. Just not sure of a source off the top of my head. I recall Monzaz over at V8Buick saying they were available in the aftermarket. He may even supply them. I remember the clutch pack I got from GM in the late 80s had a different design that let more oil in. Obviously they knew those units were problematic.

 

Warning this is from memory:

To remove the spring pack. (Check shop manual - there is a nice exploded visual illustration of the differential)

Raise and support axle

Disconnect lower shock mounts,

Remove panhard rod that crosses in front of diff cover,

Raise and support frame to get gas tank up for more working clearance. Or you can remove wheels and lower the rear axle down.

Remove diff cover,  (I don't recall having to pull axles but if you see they protrude into the hole in spring back plates, they will need pulled)

Rotate diff to a location where the diff pinion shaft retaining bolt can be removed and the opening is accessible to slide out the spring pack, be sure there is clearance so the pin can slide out without hitting the housing.

Remove diff pinion shaft, (DO NOT ROTATE DIFF ONCE PINION SHAFT IS OUT),

Slide/pry out the 2 springs and plates together, reinstall pinion shaft and retaining bolt, 

Pull the remaining oil out that will be laying in front and wipe sediment clean,

Clean gasket surfaces, use very thin coat of RTV on both sides of gasket spread with finger, install cover and fill.

 

(FYI NOTE the only place I can find the correct cover gasket is from CARS (other suppliers listings say they have but its the wrong gasket)

 

 

 

 

Edited by JZRIV (see edit history)

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I have experienced clutch chattering in my `60`s Buicks after operating for an extended period of time without turns, ie, for an extended interstate trip. The first turn after exiting the off ramp can be a wake up call! This has always been cured by operating the diff thru a few turns to get the oil back between the clutch plates. My point is that it is absolutely necessary to operate the diff thru some figure 8`s after adding the additive to get same between the clutch plates in order to evaluate the effect of the additive

Tom Mooney

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Thanks again Jason and Tom. - figures of 8's coming up his PM ! If no luck, will try the preload spring . Great description of "how to " - thanks Jason 

KReed

ROA 14549

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Good Info for many of us that own other GM vehicles. 

 

I have a 72 Grand Prix that is experiencing the chatter while turning but only after driving a while. I installed the Castrol Limited Slip Diff oil after a recent service but was suspect it wasn't enough. The car is a "Barn Find" with only 35k miles so I had no point of reference as what it drove like prior to the fluid change. 

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50 or so figures of 8's later, the popping /ratcheting sound is much improved. Think it will have to do for now . Running a straight line is no problem at all - rubber even when it shifts !  Next up is a paint job on this twenty footer. Thanks for all the help everyone .

KReed

ROA 14549 

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Update:  I installed  2 - 4 oz bottles of AC Delco Limited slip axle lubricant and all works fine. One post on a Chevy forum from a guy said he tried a brand other than GM and the chatter was still there. After installing the GM stuff, all was good. Enough for me to not cheap out and buy another brand. Other posts from people stated 1 bottle was not enough, hence me using 2. 

https://www.amazon.com/ACDelco-10-4003-Limited-Lubricant-Additive/dp/B000QGMXSU/ref=sr_1_1?s=automotive&ie=UTF8&qid=1539917182&sr=1-1&keywords=ac+delco+limited+slip+additive

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Agree Paul - that is the best additive . 

KReed

ROA 14549

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