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Discussion Starter · #1 ·
I have a 3:55 posi in my Nomad. When I turn from stop I can feel some binding. What I used to think was my brake pads clunking, I now think is my posi binding. It's been doing it for some time. It happens on both right and left turns. Its more noticeable with the windows down and reflecting off of highway block-partitions. Does anybody know whats going on or have had this happen to them????
 

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John may be right, a buddy of mine has the same problem only on a left turn, he thinks that it could be coming from the axle but his not quite sure, he still drives the car but not regularly, his take is when it breaks its easier to fix :)
 

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Discussion Starter · #5 ·
John and Angs, I went on line and looked up other peoples situations. Some said you have to put an additive for the posi clutches, which I have not. So, tomorrow I'm going to the store and pick up some G.M. posi additive. It sure is worth a try. One guy said he put it in and in 35 miles the noise went away. At this time I'm thinking A C Delco additive. If someone thinks of a better brand please chime in. P.S. I read Delco makes it for G.M.
 

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I hope you get off that easy Arnie. I screwed mine up by running two slightly different diameter tires in the back and fried the clutches in under 50 miles. I learned a long time ago that posi rear ends require Posi lube ALWAYS. Keep us posted.
 

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I had this exact problem with the posi in my wife's 68 Corvette. I thought I needed a new rear so I went to a local Corvette shop here in NY and told him what was happening. He sold me two bottles of posi lube and one bottle of posi additive. I went home and change out the fluid and it has not made any noise since. That was about 15 years ago.....Your posi clutch pack is sticking......Change the fluid and use the additive.

Don
 

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John and Angs, I went on line and looked up other peoples situations. Some said you have to put an additive for the posi clutches, which I have not. So, tomorrow I'm going to the store and pick up some G.M. posi additive. It sure is worth a try. One guy said he put it in and in 35 miles the noise went away. At this time I'm thinking A C Delco additive. If someone thinks of a better brand please chime in. P.S. I read Delco makes it for G.M.
Drain and refill the rear. Use the GM additive (2) and non synthetic gear oil, These old units don't usually react very well to the synthetic stuff. After putting it in take the car to a parking lot and do a few slow circles in both directions and you should be good to go. :tu
 

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When I put a posi in my 72 Cheyanne I used Penzoil 90w and additive, it soiunded like a spoon in the garbage disposal on corners. Drained that crap out and installed GM lube and additive no more noise, I have rebuilt many Posi rears without replacing clutches, but I always use GM lube or recently I have used Chevron Delo 90W. I own 14 cars and trucks equiped with posi and only my Z28s and Corvette came factory equiped, the rest I installed.
 

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Discussion Starter · #10 ·
Thanks guys, I think I will change the the diff. oil. I had refilled with Valvoline 80/90 gear lube late last year. Since I don't drive it in the winter,I thought. I heard a lot of Royal Purple so, I'm going to go that route. The rear end is out of a '79 Trans Am. Guess I should have mention that before but forgot. The dealership said that they only put in the synthetic type. I guess he does a lot of newer stuff so they pretty much do all synthetic.
 

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Thanks guys, I think I will change the the diff. oil. I had refilled with Valvoline 80/90 gear lube late last year. Since I don't drive it in the winter,I thought. I heard a lot of Royal Purple so, I'm going to go that route. The rear end is out of a '79 Trans Am. Guess I should have mention that before but forgot. The dealership said that they only put in the synthetic type. I guess he does a lot of newer stuff so they pretty much do all synthetic.
Just an FYI on Royal Purple, I had a customer come to me with a rear end noise complaint when turning in 70's GM. I took it for a ride and the clutches were chattering on corners. I noticed the rear cover looked like it was just off and resealed. I asked him what was done and he replied he went to have the oil changed at a quick lube place and they recommended he change the rear gear oil and of course upsold him to Royal Purple. I asked if there were any issues before the gear lube change and he said "none". I drained it and put non synthetic gear oil back in along with some posi additive and the noises were gone. You can decide from there what the problem was. Also the shop that does all my rear axle rebuilds says NEVER use synthetic oil in a GM posi rear. :anim_25:
 

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My recollection was that the GM posi additive smelled to high heaven and a parts guy years age told me it had whale oil or some such natural component which is why it smelled so bad but worked so well.
 

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I had a carrier bearing go out of our GMC Yukon rear end at 90K miles. I figured the grindings had ruined all the other bearings so I called a junk yard to see if they had a complete 3.42 ratio rear end. The first thing they said was "no, but we can put on the waiting list, it's 5 people deep". Then he asked if it had factory synthetic lube in it. He said there is lots of people with bad bearings because of the light weight synthetic gear oil. I replaced all the bearings and filled it up with 80w90. My 89 GMC has the same rear end and 250K miles with 90 wt lube so I figured it can't hurt anything.
 

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Just a tip.
Put your additive in first.
Gear oil in second.
 

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I am in the middle of swapping out the 4.88 posi in my '56 & putting a completely different 4.11 posi carrier in it. The guy that I bought it from was bragging up the noise it made when cornering as proof that it was recently rebuilt. Nice & tight he said. :tu And it looks to be rebuilt to me. But.........when I drained the fluid, it looked like automatic transmission fluid to me. Red & certainly not thick enough to be 80 or 90 wt. So I will be taking a trip to the Chebby dealer in the morning to get the correct lube. Having not had a posi that I had to put together in 40 years or so, I really appreciate the info.
 

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The rear end is out of a '79 Trans Am. Guess I should have mention that before but forgot.
Wanted to ask if the Trans Am rear end was factory disc brake?
 
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