I've finally gotten to the rear end in my '72. I've figured out that it's a LWB 8.5 10 bolt 3.42 posi. Now I'm stuck on what to do about it. The pinion nut had backed off at one point and the carrier has some gouges in it from the pinion. I planned on a gear change anyway. These are the three options that I'm considering....... 1) A. Rebuild the 8.5 with existing posi with new clutches, gears and axles. b. Rebuild the 8.5 with an Eaton unit, gears and axles. 2) Buy a 12 bolt complete. (leary of c clip eliminators) 3) Build a 9". ( I have a Lincoln Versaille 9" complete with disc brks. Just need to get brackets. I think it's a little narrower than the 8.5 though.) I'm looking at about $1200 to do the 8.5, about $1500 to do a 12 bolt and about $1800 to do a 9" roughly. My thoughts are to stick with the 8.5 but in the end will it hold up to 600+ hp? If I rebuild the existing posi unit, will it hold up to that kind of power? My carrier has 5 springs in it instead of the "S" spring and I don't see the clutches. Is this a decent unit? Can I upgrade to a later model Eaton unit with 30 spline and get axles to fit this rear end with 30 splines?
Well, I was going to recommend going with your 8.5 as its a very good well designed rear end with the bolt in axles until I read that you are going to be making in excess of 600 HP and the torque to go along with it. That much torque and a good set of slicks will quickly find the weakest link in you're drivetrain and in this case one of them might just be your 8.5 rear. If it were me I would go the 12 bolt route. I've got a 12 in one of my cars and the fact it has C-clips does not bother me. I've never had a bit of trouble out of them. If the thought of a Ford rear in Buick your does not bother you then thats another option. I wouldn't like it but thats just me. Oh, not to change the subject, but how are things in New Orleans now? Hopefully getting better!
I have a friend that has a warehouse full of Chevelle parts. He also has a rack with about 15 12 bolts on it. A couple were bought from the guy that I bought my car from. One of them has Strange axles, posi and 3.73's or 4.11's. If I can find him I may buy that, but he's in New Orleans which for the most part is a ghost town. It's bad. Still no electricity, no businesses, no nothing. Everything is dead(vegetation) and grey. It's going to be a long time before this city functions again.
Your posi is an Eaton unit. You should go with the 12 bolt since you easy access to them. C-clips are not a problem unless you do autocross racing. You can always go with the BOP ends on a Chevy 12 bolt which will eliminate the c-clips.
I believe the Eaton is rebuildable. I would also recommend the TA reinforced pumpkin cover. I think when you get into the 10 sec area you will reach the limit of an 8.5" I believe Greg Gessler and many others are in the low 11 second range with 8.5" rear axles.
Don't shortchange the 8.5 A-body rear... the housing was cast to take abuse (minimized pinion "flex") & bolt-in tapered bearing axles are tops. Limits... stock bolt-in 28spline axles in blueprinted 8.5 A-body posi rear, mid 1.50 60foots & mid 11's. Stick cars less. Same 8.5 rear upgraded with 30 spline HD Eaton carrier & Moser axles along with attention to detail in the set-up will get you an 8.5 A-body rear that is plenty stout, as tough as an aftermarket axled 30 spline axled 12 bolt. Low 10 sec 1/4 capability. Have built six such 30spline 8.5 A-body rears. You have the housing & they are worth some $ in an outright build & sale. Price of steel has gone up, so carriers & axles have gone up slightly, but $1200 sounds doable To build similiar strength 12 bolt upgraded Eaton carrier & with tapered bearing bolt-in axles & 3R u-joint yoke, one's easily looking at $1700+. At that price, an upgraded factory housing 12bolt A-body rear is getting close to that of a new Moser 12 bolt. Roger
BTW, the pic above is of a Warner Motive cone type 8.5 posi carrier not an Eaton. The Warner-Motive 8.5 posis are very common in '71 GS & 442 rears. For that matter, I have never ran across a factory Eaton posi in a '71, '72's however did have factory Eaton posi's. Have pulled several of the Warner Motives carriers out of '71 T/A & Fomulas as well. Like earlier 8.2 Pontiac 2 pinion cone posis, they're really not the hot ticket, the cones wear. Smart to do a breakaway test on the Warner-Motive posi's & see if they are close to tight, then if reasonably tight (above 70 ft-lbs) sell the carrier on e-Bay & upgrade to an Eaton. :3gears: Roger
Never heard of Warner Motive, who made them???? Maybe they are scarce for a reason? I thought the 4 coil spring was an Eaton design.
Thanks Roger. Next question..... If I do the 8.5 route with a new Eaton unit, the one's I see on eeekbay say everything but '71-'72 GS/Skylark and WITH "c" clips. Will this work on a bolt in axle?
Hello George. Warner-Motive was large automotive concern. Easy way to spot this style carrier, as it is the clamshell carrier design... similiar to an 8.2 "Pontiac" 4 pinion carrier, but with stamped steel preload plates & springs. Just the presence of springs & plates does not make a posi carrier an Eaton. Most posi carriers have some form of preload spring, whether cone or clutch. Not sure about Buick factory service manuals, but '71-73 Pontiac service manuals refer to the Warner-Motive carrier & have pictures of them disassembled. One of my 1st experiences with the Warner-Motive 8.5 posi carriers was about 12 years ago when a friend/customer brought his original '71 Formula rear in for me to rebuild substituting an "S" spring 8.5 carrier. The cone type W-M carrier was toast & the spider gear pin was heavily galled... never fun removal. Ended up taking big vicegrips & a similiar diameter spider pin & began to beat on the pin with a sledge to move the stuck pin toward the pinion. The process is to carefully beat the pin forward enough that I can rotate the carrier, & take the torch to the pin, then repeat. Without carefully doing this, the c-clips will not drop & carrier will not come out. Long story short, it was busy day, & I went inside to answer the phone & while inside my customer proceeded to 'help" by beating on the pin. I went back outside & asked him to lay off, as one can only move the pin so far, or one will not be able to rotate the carrier & cut the nub off. Needless to say, got off the phone, & he had knocked the pin up against the inside of the rearend housing, & the carrier would not rotate... This really p!ssed me off...j ust another reason why I seldom need "help". I'm sure you've seen the shop sign regarding how much it will cost ya if, that is why I run a "closed" shop. Anyway, I had a really BIG problem, only way to get the carrier out & save the housing, was to degrease the r/e as well as possible with the carrier in it, & take a bigger cutting torch head than I owned to the carrier case... Tons of fun, & tons more work than friendly deal I had previously offered :af: To solve the problem, I ended up building this customer another r/e off another housing, & as a result his rear was no longer original housing. Original r/e went into my "to do" rack. Several years later, I ended up paying a local heavy duty truck repair guy to cut up the carrier with his monster torch. Cost $85 just to get the carrier out Only good thing about the deal, is another contact had a '71 automatic T/A that was missing it's original coded rear, so I built this rear up for him & it now dates & codes his restored car. Nightmare jobs seem to always be memorable, so in detailing above mess, hopefully others will read, & in same situation not repeat the same error p Roger
Reynold, The new Eaton 30 spline posi will work fine, you will have to use different carrier bearing & races than oem. Roger
Is this the one I need.... 89-Up Car/Truck, 30-Spline Axle, 8.50'' Ring Gear, 2.76-Up Gear Ratio 362-19559-010 Requires bearing kit P/N 873-D1585.
Nope, wasn't short changeing the 71-72 Buick/Olds A-bodys 8.5 rearends at all. I actually prefer those rear-ends over the others due to the fact they were well made and have a large amount of parts readily available for them and they had the bolt in axles. 600+HP 455 Buick motors will probaly make 600+ of torque, mix that with a good set of slicks and thats where I start to get a little nervous with the 8.5. I have no doubt its been done before so who can really say for sure. As for cost, well I rebuilt my 12 bolt last year and it cost me about $900 for everything. Heres how it broke down-1.12 bolt from junkyard=$150 2.Eaton posi unit=$320 3.US Gear 3.42 ring and pinion=$170 4.Complete bearing kit(including the outer wheel bearings)=$145 5.Moroso rear chrome cover=$40 6.3 bottles of Mobil 1 gear lube=$25. I reused the axles as they were in fine shape. The rear was out of a Canadian built 69 Skylark, so the the axles are stronger than the standard Chevelle 12 bolt axles to begin with.
I'm still on the fence about what axle to use. I measured the rear end in the car and it's like 61" and the 9" that I have is 58 1/2" from flange to flange. I can get a bracket kit from Currie for $150, but I'm not totally certain on how to make absolute sure that the brackets are in the right position. The easiest thing would be to grab the 12 bolt but I can't find my buddy. I haven't heard from him since before the storm. I'm leaning away from the 8.5, but the only thing that would make me reuse it if I can use the 30 spline Eaton posi and have Strange or Moser make custom axles for that rear end with 30 splines instead of 28.
More on 12 bolt upgrade pricing... Starting with a rel affordable, lets say under $200 clean & bare '68+ 12 bolt Chevelle housing. To add jigwelded aftermarket ends, tapered bearing Moser axles, upgrade with an Eaton 3 series carrier to the equivalent of a Brute Strength carrier, then add reasonable priced assembly with quality new gears & quality bearings, one is easily looking at $1700 US, if not more. Still need to factor in cost of a 3R u-joint yoke unless one is lucky enough to stumble across a "Canadian" 12 bolt or one out of a factory 455 equipped Pontiac A-body. Iceman, while the stock c-clip axles in the BOP equipped 12bolts & LS6-L78 Chevelle 12 bolts are stronger than the normal 12bolt axle, they have been known to break in even high 11 sec A-bodys. The lh HD 12 bolt axle in my 455 HO GT-37 broke in the late '70's. Resulting damage tore up lh 1/4 panel:rant: Installation of a pair of HD aftermarket axles, at the time, would have run 20 times less what it has cost to replace the lh 1/4 with an nos panel. For same car, having the choice to build any rear to go back in this car, the selection was easy... an upgraded 8.5 A-body rear (an A10 bearing hsg) with a HD Eaton posi. Just to keep "the look", before the build, the 8.5 hsg was drilled, plugged in a few holes, & tapped to accept a stock 12 bolt cover... rearend now looks very stock from rear bumper view. The 30 spline tapered bearing axles will never break, not for how quick the GT-37 is, or for my plans with it. In similiar weight A-bodys the 8.5 has proven itself more than capable. Ck out www.Pontiacstreetperformance.com & the Torquepower (street/strip car) build section, many many of the mid to low 11 sec street/strip A-bodys in DFW & TX area are running the 8.5 A-Body. Many have for over a decade. Having built numerous 12 bolt & 8.5 posi'd rears that live in the low tens in 3600-3850lb A-bodys, there is little reason to bypass their use. Where both the 12 bolt & 8.5 hit the wall is when one is applying waaaay too much torque for a posi rear... where one truly needs a spool. 9" A-body rears... last month I shipped out a factory nodular 9" case, daytona pinion support, & matching yoke. Customer has what will prob be no more than mid- low 11 sec auto trans A-body. He "had" to have a 9" p He will also need to buy adjust upper control arms (more $$$) to get his newly fabricated 9" to correct fit. In my experience, geometry is always off with the fabricated 9" A-body rears, & one will need the adj uppers. Without saving by shopping used on the case & pinion support, & finding a few other deals, this customer would easily be in a $2200 9" rearend. $2000+ spent to go with a 9", where a lightly upgraded 8.5 10 bolt or 12 bolt would more than suffice for years & years. Doesn't really make sense. :3gears: Roger
Roger My goal is 10.80's w/an 11.0:1 462 w/Stg 2's,TH400 and 3.73's or 4.10's. My car is non a/c and no power anything so I'm guessing the weight at 3800#. Do you think this is 'do' able with an 8.5, strange/moser axles and an Eaton posi? The strength is the only issue I have with an 8.5. I really like the bolt in axles over "c" clip eliminators. How do I know if I have an A-10 bearing housing?
12 bolt rear I just had a 12 bolt - narrowed with new style big ford bearings & moser axles for about $700.00. This price included additional welding of brackets & shock mounts. I need to decide on brakes..with this set-up I can go with drum or disc brakes - $300.00 - $500.00. Picked up a series 3 Auburn carrier for about $320.00. Plus gears & install kit - $340.00 It starts to get expensive. Tom :TU:
I called Strange who I liked dealing with in the past. Explained what axle I have. "We don't make axles with that small diameter shaft that your rear end has." Next, called Moser, "Sure, we can make your axles based on your measurements for $415 for axles, brgs, studs."(I explained that I wanted stock dimension axles for A body 10 bolt, BUT with 30 splines instead of 28). Next I called Randy's Ring and Pinion for info about Eaton posi's. I've seen HD Eaton's w/800# of preload vs. standard 400#, but for 28 spline. I talked to a salesman who seemed to know a great deal about 10 bolts. I gave the application and said that I wanted to use standard length custom cut axles in a 30 spline but couldn't find a 30 spline Eaton HD posi (800#). Then the usual confusion that I had to go thru with EVERYBODY else. "No, it's not an 8.2, Buick went to 8.5 in '71". "Yes, it HAS a 10 bolt cover, but it's an 8.5 not 8.2". I actually had to disassemble the rear end to prove what it was. FINALLY, he understood that it was a TRUE 8.5 10 bolt. He recommended staying with the 10 bolt over the 12 bolt based on parts availability and the fact that he said he'd sold more parts to guys with broken 12 bolts while running slicks than any other. He gave me prices on a custom built Eaton HD 30 spline at $479. (a regular Eaton rear, disassembled and reassembled with HD parts), Yukon 3.73's, bearing kit for the carrier and T/A cover for $886. W/O the cover was $739. So I'll be into the 10 bolt w/Moser axles,bearings, studs, gears, Eaton HD posi for about $1400. Did I miss anything?
