Robert Zappaterrini Posted March 15 Share Posted March 15 I am the owner of a 1966 Cadillac Deville Convertible with a controlled differential. I would like to change the differential oil, but it calls for an additive along with the differential oil. The service manual says not to use posi rear additive as it may cause chattering. It has been suggested that changing the oil with a synthetic should be ok without an additive as the synthetics contain additives that were not available back then. I do not want to create a problem. Anyone else run into this issue? Link to comment Share on other sites More sharing options...
EmTee Posted March 18 Share Posted March 18 This is the currently available GM additive: https://www.amazon.com/ACDelco-10-4003-Limited-Lubricant-Additive/dp/B000QGMXSU/ref=asc_df_B000QGMXSU?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80127027724173&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583726553782536&psc=1 On 3/15/2024 at 10:28 AM, Robert Zappaterrini said: The service manual says not to use posi rear additive as it may cause chattering. I would ask that you read the book again, as what you said above is exactly the opposite of my experience. I had chattering on a 1977 Buick until I changed the differential oil and included the GM limited-slip additive. It usually takes some amount of driving (e.g., 20 ~ 50 miles) for the additive to fully treat the clutches. Link to comment Share on other sites More sharing options...
Robert Zappaterrini Posted March 18 Author Share Posted March 18 EmTee, Thanks for the reply. The differential in a 66 Deville is a standard or what is called a controlled differential. It is not a posi and the Cadillac shop manual specifically states that adding posi traction additive will cause issues. It appears also that the additive was in the fluid back then. The parts manual for that era, which i have, does not list an additive but the differential fluid part number says for use with standard or controlled differential. i can send copies of service manual and parts manual notes if you would like to see them. Link to comment Share on other sites More sharing options...
joe_padavano Posted March 18 Share Posted March 18 Found this info from a Google search. Note that the Controlled Differential is NOT a traditional friction-type posi unit. From what I have gathered in classic Cadillac forums this is the original control diff fluid part number. Part Number 1050189 Then Part Number was superseded by part number 1050081. http://www.gmpartswiki.com/getpage?pageid=128705 Then part number 1050081 was superseded by part number 1052271. http://www.gmpartswiki.com/getpage?pageid=93213 Then the trail leads to 89021671 - 80/90W Rear Axle Lubricant Supersedes: GM# 1052271 http://www.amazon.com/Genuine-Fluid-89021671-80W-90-Lubricant/dp/B00BK7LUTM 1 Link to comment Share on other sites More sharing options...
EmTee Posted March 19 Share Posted March 19 (edited) I learned something today - never seen (or knew about) such a thing. There's probably a reason for that. I wonder what about the design would cause chatter with addition of the friction modifier? Some of the new GL-5 diff oils claim to have the positraction additive 'built-in'. I don't know whether one of those would be compatible or not. You're probably better off going with the GM oil Joe identified above. Interesting that it is rated GL-4, not -5. Edited March 19 by EmTee (see edit history) Link to comment Share on other sites More sharing options...
Lee H Posted March 19 Share Posted March 19 2 hours ago, EmTee said: I learned something today - never seen (or knew about) such a thing. Me too. Turns out it is a cone type limited slip differential (I think made by Dana). I guess the slip additives are designed for typical flat clutch pack styles. 1 1 Link to comment Share on other sites More sharing options...
rocketraider Posted March 19 Share Posted March 19 Do other vehicles use this cone clutch differential? Maybe see what their fluid recommendations are. Link to comment Share on other sites More sharing options...
joe_padavano Posted March 19 Share Posted March 19 3 hours ago, rocketraider said: Do other vehicles use this cone clutch differential? Maybe see what their fluid recommendations are. The cone clutch anti-spin differential was used in the 8.2 BOP axles in the A-body cars. Here's what Olds said under Periodic Maintenance - the same 1050081 fluid: 2 Link to comment Share on other sites More sharing options...
Lee H Posted March 19 Share Posted March 19 6 hours ago, EmTee said: Interesting that it is rated GL-4, not -5. I don’t think that’s an accident. I believe those cone clutches are a bronze, or some yellow metal alloy. The GL-5 EP grades are said have a higher sulfur content, and don’t play well with copper bases. Link to comment Share on other sites More sharing options...
TTR Posted March 19 Share Posted March 19 (edited) While I'm not familiar with cone type "controlled" differentials, it appears they probably work similarly to conventional friction disc type "limited slip" units, which usually (in vintage cars) become less or non-effective when these readily available (modern) "additives" are introduced to them, basically allowing them to slip too much. As far as I have experienced, properly set/working conventional "limited slip" differentials should be expected to exhibit certain amount tire chirping/churning/grabbing sounds when making turns while driving. Easy way to check/test if the controlled/limited traction unit is working properly is to find a large, empty paved parking lot, drive the car around in tight circle or (preferably) "8"-configuration and listen to the tires consistently chirp/grab. If none of this occur and only differential friction chatter is heard, it's likely an indication the controlled/limited traction unit may not be properly set, not working as it should or at all (i.e. possibly worn-out). Edited March 20 by TTR (see edit history) Link to comment Share on other sites More sharing options...
Bloo Posted March 20 Share Posted March 20 11 hours ago, EmTee said: Interesting that it is rated GL-4, not -5. It's probably both. I am extremely skeptical that GM even knows whether it is right for this application or not after being superseded so many times. Maybe they do, but I've seen Chrysler supersede a heat riser stop to a beige armrest in less steps than that. One possible road would be to use a Redline "NS" oil of appropriate viscosity, and then add their limited slip additive in small quantities until it stops chattering. 3 Link to comment Share on other sites More sharing options...
Robert Zappaterrini Posted March 20 Author Share Posted March 20 Thanks for all the information. I think i will go with the GM fluid and see what happens. I will save the old fluid, just in case. 1 Link to comment Share on other sites More sharing options...
Lee H Posted March 21 Share Posted March 21 If things don’t work out, there is this Lube-Gard additive that specifically calls out suitability with cone-type clutches. Could just be marketing hype, of course… Link to comment Share on other sites More sharing options...
Robert Zappaterrini Posted March 22 Author Share Posted March 22 Lee, Thank you....I did locate GM part number 89021671 at several dealers down south. I am going to get the differential fluid from them and go with that first. If anyone would like the dealers info, I would be happy to share it with everyone. Link to comment Share on other sites More sharing options...
Larry Schramm Posted March 22 Share Posted March 22 Might also look here for the limited slip differential lube. https://www.google.com/shopping/product/1?client=opera&q=89021671&prds=epd:3389448553610737954,eto:3389448553610737954_0,pid:3389448553610737954&sa=X&ved=0ahUKEwjC2_in94eFAxX7jYkEHQhXDrIQ9pwGCAU Link to comment Share on other sites More sharing options...
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