Read several threads about new gears etc. I have a 1972 Buick Skylark Custom that could do with some rear end improvement (like the rest of us!). Don't know a lot about this but I've decided, unless someone with some expertise on this subject advices otherwise, to go for an Eaton Posi unit with 3.42 gears. I have original 10 bolt differential and gears (not sure of ratio) and had transmission rebuilt 2 years ago with a shift kit (NO overdrive). Could this posi unit be put into existing differential housing? AND supplier wants some info. to order correct unit. Here's what he wants to know and how/where do I get this info? -ring gear diameter -axle shaft diameter and spline -gear ratio -small bearing bores (race OD 2.89") Thanks for any help!! Craig
Craig, not sure why you posted in the "Help From Above" Forum.:laugh: I think we can help you without the need for divine intervention.:TU: Your 72 came with the 8.5 10 bolt rear, and that is a good strong rear with great parts availability. However, we are talking about a car that is now 43 years old, and unless you have owned it from new, there is always the possibility that parts get changed out. You need to verify that it is indeed an 8.5. Look at the rear cover. There are 2 right angle lugs circled in this photo. http://jdrace.com/diff_id/10b85/10b85_1.jpg http://jdrace.com/diff_id/10b85.htm# Then look at where the rear u joint is attached to the yoke. The 8.5 will have brackets with 2 cap screws that hold the u joint to the yoke. If you see U bolts with nuts, it isn't an 8.5. Odds are you still have the original 8.5 rear. It has 28 spline bolt in axles. You can get the Eaton Posi everywhere. http://www.jegs.com/i/Eaton/362/19557-010/10002/-1?parentProductId=750876#moreDetails I would contact Jim Mitchke (Monzaz on V8). He may offer better prices. As far as ratio goes, there should be a 2 or 3 letter code stamped into the left axle tube. That will identify what was in there originally. You can also pull the cover and there will be 2 numbers stamped into the ring gear. Divide the smaller into the bigger and you will have your ratio. http://www.crankshaftcoalition.com/wiki/Gear_ratio_check Odds are a 1972 Buick Skylark Custom with a 350-2 bbl came with peg leg 2.56 gears. Doesn't really matter as you will be buying a new posi carrier.
thanks Larry! you're a true "angel". don't know why I posted it there either. musta been a slip of the keys or brain. great info!! THANKS!
Hello. I found this information online when I was trying to figure out what ratio/ carrier was in my 72 custom convertible. Unfortunately, I cannot remember which website I found this info on. I did write down the specific codes for the 72 axle. So, provided that your axle has not been changed in the past at some point, you should be able to match these codes to the stamped letters on the passenger side axle. I found the letters on the passenger side axle tube stamped slightly below the centerline of the axle housing 4-5" from the diff( wish I had taken some pics ) I did have to scrape some crud off before I could make out the letters. Here are the codes for 72 axles/diffs . 1971-1972 Buick 10 bolt id codes : Ratio----Open----Posi 2.56---- LKB---- LTB 2.73---- LLB---- LOB 3.08---- LAB---- LSB 3.42---- LHB---- LWB B is missing on 72 models Hope this helps. It was very enlightening to me, was able to find out I had a 2.56 ratio open diff. with the LK code I found stamped ( explains the sluggishness) So, I have made plans to swap the gears, replace bearings, and install an auburn pro series diff. I will most likely have an old school muscle car do the gear swap install after I bring him the axle housing. I find the website again, I will try and post a link..
You're welcome Craig. From what I understand our 10 bolts are an 8.2 , not an 8.5. Let me know how it turns out. I would prefer to do it myself, but there are some specialty tools i don't own, and I have never done one. So , I'll strip mine down, and take the parts to this mechanic. I ma certainly not going to pay a speed shop in Colorado springs $1200 to do the job !
I would find a shop who will do the rear end rebuild with the vehicle on a lift, then you do not have to remove the rear end.
Like Bruno said, in 1972, the stock 10 bolt is an 8.5, not an 8.2. It is very easy to tell the difference. The 8.5 will have metal brackets and cap screws securing the rear u joint to the yoke, the 8.2 uses u bolts and nuts.
