I have a 3-series GM posi carrier and I was curious which differential is the strongest available for the 8.5" 10 bolt rear? I was looking at Detroit locker and the new Eaton differential. How much stronger is the Eaton over the factory 3-series carrier? Also, where would the detroit locker fit in strength wise? I've been looking at a 12 bolt rear, but alot of people told me my 10 bolt will hold up fine with the power my engine is putting out. Thanks.
I think you are right about what you have being fine at your power level, assuming everything is in good shape. I don't know where the Eaton fits into the mix, but the Detroit Locker is generally considered the next strongest thing to a spool. I caution you to take all of the negative comments on the DL with a grain of salt. Every person I have known that has actually owned one liked it (including me). There are alot of people out there that have not had a DL that talk about excessive noise, banging, etc. I have what is known as a "soft locker" and I have only heard one noise from it since I've had it. If you make a very sharp turn while significantly on the throttle occasionally it won't unlock immediately. What then happens is there is a bang noise when it finally releases. This isn't all the time, but just in the off circumstance that you are turning sharp and using a bit of a heavy throttle at the same time. Lastly, I think that the NASCAR take-outs you find on ebay are a little different in that they don't use what is known as "unlocking rings." These may make more noise than the soft locker. They are for a 9" ford, so in your case don't apply. If you couldn't tell, I am enthusiastic about the DL and would use one in an HP application if I were in the market for a new posi unit. In your case, I would install the HD heat treated spider/side gears and put your factory carrier back in. Assuming that the s/s gears are available for the 8.5; I'm a bit more familliar with the 12-bolts. Gosh, I re-read your post and see you are considering your present 8.2, an 8.5, and a 12-bolt. I would run the 8.2 until it breaks (if ever), then replace it with an 8.5 (cheaper and as good as a 12-bolt). Besides, the 12-bolt has C-clips and you don't want to deal with that unless you have to. Unless you are going to do some serious gear banging or holeshots with slicks, I think the 8.2 will last a long time.
Thanks Adam. Currently I have a 8.5" as the 8.2 blew out a long time ago. I figure I would replace the axles with strange units and install c-clip eliminators while I'm at it. My biggest concern is the 28 splines and which carrier could handle the power I'm putting out the best.
Have never installed an 8.5 Detroit locker in a car rear, only experience is in 4WD truck rear axle. The 30 spline 8.5 Eatons can be upgraded to thicker plates & 800# springs. With 30 spline Moser axles, lh billet cap, upgraded Eaton carrier, an 8.5 should be more than strong enough for low 10 sec 3500-3700 footbraked A-body. Want to go a lot quicker & worried about posi capability, go with 33 spline Strange spool & Strange axles as either a Detroit locker or home brewed "Brute strength" 30 spline Eaton are going to limit streetability some, so why not go with a 33 spline spool? One of the attributes of 71-72 8.5 a-body rear, no c-clips required. Shame 12 bolts didn't come from the factory with tapered bearing bolt in axles. BTW, mid 11's seem to be the limit on blueprinted stock posi 8.5 A-body rears in footbraked 3700 A-bodys. Been my experience, that the open style #8 carriers will usually go before an axle. :3gears: Roger
I appreciate the advice Roger :TU: One more thing, is there isn't that much of a drivability difference between a 30 spline Eaton posi setup and a 33 spline spool? My main concern is reliability and performance even though most of the miles will be more street than strip. Being the car isn't a daily driver I'm looking more on the performance factor.
Rob, A normal new Eaton posi unit is going to have thinner plates & somewhere around 300# preload springs. The Brute Strength 12 bolt carriers & the (now extinct) 28 spline Brute Strength 8.5 posi carriers both have thicker plates, stiffer springs. To recreate in a new 30 spline Eaton 8.5 carrier, Randys has the thicker plates & stiffer springs. The Brute Strength type carriers are not known for their "smooooth stock type" operation, one will usually know one is back there, not as bad as a spool, but the carrier will try & stay locked, & one will feel some of this when turning corners. With your signature combo, a manual transmission, & slicks, I'd recommend an upgrade to 33 spline spool & custom axles & lh billet cap. On the street, without the traction afforded with slicks @ the strip, you should be more than fine with upgraded 30 spline carrier, billet lh cap, & 30 spline axles. Am currently building a very similiar 30 spline 8.5 A-body rear, it's going behind a TKO600 & an E-headed 400 Pontiac (dyno'ed at 482 hp) & is going in a '69 GTO. Have built several similiar 30 spline 8.5 A-body rears that have held up well in low 10 sec footbraked A-bodys. :3gears: Roger
Stock 2 & 3 series & many 4 series 12 bolt posi carriers are not that strong. The 12 bolt posi actually has much smaller spider gears than a stock 8.5 posi, thus it is not that hard to find the limit of a stock 3 series carrier. Looking for a strong 3 series 12 bolt carrier, ck out a new Strange R5087 with 10-17 spider gear to side gear count. :3gears: Roger
By carrier, if you need a singletrack 12 bolt car carrier, I should have several. Might shoot me an PM this weekend & I will double ck what I have while out organizing & getting ready for ship outs. Roger
Roger, How much help is it to add the heat treated HD spiders and sides to a stock 3-series 12-bolt carrier? Thanks for the great knowledge you offer us on the BB!
Hi, The stock 18/10 spiders in my 12 bolt worked till I got my 60fts in the mid 1.5s, it held 5 passes and then blew them into pieces right on the line.They held for years at 1.65 60 fts. The spiders broke before the stock axles. I had a guy get me some eaton 17/10 spiders and have gone 1.48-1.52 60fts and so far its holding together. I also went to yukon axles and mark williams C clip eliminators at the same time. I did take a tooth off the stock GM ring gear at the end of last year though. Also what is the number of teeth on the 8.5 posi spiders? I have a 4 series 12 bolt posi with 16/10 spiders in it. Every one tells me that they never had a 16/10 spider set for a 12 bolt so I am wondering if someone stuck in some 8.5 spiders. The 10 tooth gears are so big that a stock 12 bolt plate won't fit between them, the 16/10 pressure plates are about a 1/4" narrower to fit. I wish I had a good camera to take a picture of these gears to show people what I mean and that I can count gear teeth. Tom
