Is this posi, or maybe a worn out posi????

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Is this posi, or maybe a worn out posi????

Post by sportster_restorer on Sat Feb 18, 2017 11:50 am

After a cold winter (at least for Texas), not a whole lot of free time from my job, and a whole lot of problems finding replacement seats that aren't rusted away, I finally got my 74 Laguna inspected.

I went to get it inspected at this small garage near my neighborhood. The guy was busy and said I could wait or come back in about 15 mins. I had some errands I could do, so I left. Well near his garage is some pretty nice asphalt, and the Laguna was running pretty well so I came to a stop, and floored it. What to my wondering eyes should appear but two nearly equal black stripes on the pavement! I tried this again over in the adjacent industrial park, and two nearly equal stripes again. I found some safe and clean pavement again, only this time I held the brake down, floored it, and let go of the brake. This time there was one large stripe and one very small stripe. When I just floored it and got the two nearly equal stripes, it almost acted like it was limited slip.

My car is an original California-built Laguna that came with a 400 sbc with a turbo 350. I've actually tracked down previous owners to the second one and confirmed it, along with seeing a U on the VIN. This should mean the 74 was an original 400 car. The second owner supposedly blew up the 400 and replaced it with a mid 80s 350 and apparently kept the 400's 4 bbl q-jet. But single exhaust.

So my question to the forum, did the 400s come with a posi? Or did most 400s have posi's? I haven't pulled the back seat yet to look for a build sheet, but I may get to it this weekend. There is no limited slip tag on the diff like I've seen on Camaros.

I was in college back in 74 and remember everything performance got a bad name back then. Like a posi rear even though it didn't cost you gas mileage and was better in rain and snow.

I know the easy solution is to just pull the diff cover and see what's in there. But I thought I'd post and see what the forum may say.

I did raise the rear end and spun the drivers wheel and the passenger wheel went the other direction with the trans in park or neutral. That should pretty much condemn it to being an open rear, but I've heard worn out posis will do the same thing.

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Re: Is this posi, or maybe a worn out posi????

Post by Joe73 on Sat Feb 18, 2017 12:11 pm

I just checked the GM heritage paperwork for 74 and it does not list a posi as being standard on the laguna. It does mention it to be an option.

You need to pull the cover to confirm. I've been in cars with open rears that left black marks with both wheels. And I've seen posi axles spin both wheels in the same direction and in opposite directions. So the best way is to pull the cover.
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Re: Is this posi, or maybe a worn out posi????

Post by Mcarlo77 on Sat Feb 18, 2017 2:33 pm

Yeah...I'm pretty sure Posi's were optional.  And, engine size had nothing to do with it.  My '77 350-4bbl Monte has optional posi with 2.56 gears...oh, be still my heart!
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Re: Is this posi, or maybe a worn out posi????

Post by sportster_restorer on Sat Feb 18, 2017 2:40 pm

I agree that posi's weren't standard Laguna equipment. I've owned two 75 Lagunas with 350 - 2 bbls and neither had posi.

I was wondering if selecting the 400 sbc engine included posi, or if the engine option caused posi to be added as an option? If the weather continues to be nice, I may have to pull the diff cover and check it out to be sure. Heaven knows the diff fluid may have never been changed!

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2 black strips

Post by S3SS on Sat Feb 18, 2017 3:33 pm

305, 350 or 400 was an option as was the posi-trac in 76-77. I added it to all my G3's....
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Re: Is this posi, or maybe a worn out posi????

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