Ok... I have a 72 Cutlass S with a factory 4 speed and close to 500 hp and 540 torque. Will the stock rear end handle this power level? Am I on borrowed time. I understand the variables of slapping some slicks but no, I'm running 275/45/17 BFG radials. and I have no plans of putting slicks on. How much power can these take without going away?

 

A properly maintained and or rebuilt 10 bolt 8.5 will take GOBS of torque and power.

Just remember the rear under your car is probably 3040 years old and will have slop from mileage and standard driving and sitting for years.

The maintenance to most OLD CAR rears was NIL and we always forget about them until the say hello with a whine clunk or bang and by then it is too late....


Jim

 

A rebuilt/maintained 8.5" 10-bolt,with stock shafts,can go 11:70's pretty comfortably.It's not the HP that breaks a rear,it's the torque,or blunt force thrown at it initially,whether at a stop light,or the tree.Yes,a stick-shift or trans-brake will throw more blunt force to it,compared to a regular automatic,behind the same engine. I would get a good aftermarket 30-spline carrier,and a set of aftermarket 30-sline axles for better insurance.
I did a 72 442 4-spd convertible for a customer last year,with an Olds 496 stroker,making those same power figures on the dyno,and I did a 3:08 10-bolt,in stock form.The car has stock 14" rallys & regular radial tires.It's a stock,sleeper car,with no desire to take it to the track.Just a cruiser with some extra power.

 

Well I know the origional rear end has been well maintained as far as regular lube changes and stuff but it has about 120k mikes on it and I am currently debating on stepping up to maybe a roller cam or at least 1.7 rocker arms. I just don't want a grenade back there. I will price out a better carrier and axles. At least I won't have to go with a 9 inch or something. Thanks gentlemen.

 

No,you don't need a 9" or DANA 60.You already own the 8.5,so it is also your cheapest alternative.
BTW,I like the plug for Primus.

 

So what would a decent 30 spline carrier and a pair of decent axles run these days? Does the type "O" take the same carrier?

 

The 12-bolt O-axle does not take the same carrier.They are unique to themselves.
A pair of 30-spline Moser axles,with bearings,seals,retainers,and studs,will be in the $450.00-$480.00 range,depending on shipping.As far as carriers go,I would suggest a Detroit Locker.Do not confuse this with a Tru-Trac.The detroit Locker is the most expensive,about $600.00,but you won't hurt it.If not that,then a tuned Eaton posi unit.All of the new units come with carbon clutches,which I do not like.I get the original style knurled steel clutches,and shim them as tight as possible.However,after doing this,you are about $75.00-$100.00 away from a Detroit Locker.
This is a once & done approach.
If you want to add other things like a girdle cover & a steel 1350 yoke,those are great insurance too,but I ran my 8.5" with a W27 cover,and stock yoke for more than 7 years,and has gone 10:90's@122 in my 72.That rear now has a girdle cover & steel yoke,is in a stick-shift 65,and still going.

 

I thought the 8.5 10 bolt in my car was the Type O without the joyous C clip retention.So, I'm looking at about a grand? I don't want a locker though. I had one in a Torino and that thing was kinda unsettling. Guess I'll let the wife know what Santa needs to bring me next winter ha ha...

 

The 71-72 8.5" 10-bolts have bolt-in axles,no c-clips.

 

So if I read correctly, i should be ok with my 455 rebuild along with 3.08 gears, upgrade my axles to 30 spline? I finally broke down my rear end and it does have posi along with 3.08 gears. I have no intentions on taking this car to the track. If I'm wrong please let me know if I need to upgrade my ring and pinion to 3.73.

 

I bent an axle and the housing on my original 8.5 on a mild high 13 sec car now low 13 sec car. I blame the edelbrock anti hop bars putting too much down force on the housing . I got another axle and housing and tossed the no hop bars and it has held up. The only issue i have ever had and i cant seem to ever stop the slight leak on driver side axle . It did it with the old housing and the new one with the new axle . It does not leak enough for me to say ok this has to stop but if fluid resides in that area it will drip out not alot though. Not trying to steal the thread but it's an intresting issue i have had with my 8.5

 

Dre,
Changing your gears from a 3:08 to a 3:73 does not make the rear any stronger or weaker.Put the gear in it that is best suited for the car,and what you plan on doing with it.You can keep your factory 28-spline axles & the matching posi unit.

CopperCutlass,
When those rears were assembled,the tubes were pressed into the housing,then locked into place with a plug,which can be seen from the rear,in those circle holes.Depending on how much material they filled the holes with,they could wick some oil through there,and they can also wick between the tube & pumpkin,where they are pressed together.If the rear has ever had some shock go through it,like wheel-hop,or some other violent force,it could start to work the tube loose from the pumpkin,which would also cause fluid to leak out,or increase the amount of fluid leaking out.This is about the only reason that I would weld the tubes to the pumpkin.It can help stop any oil from leaking,unless it is leaking around the plugs.It is throught that welding the tubes to the pumpkin will increase the strength of the housing,but I say no.It will just bend or break somewhere else,something is constantly putting force to it.This is no different for the 12-bolt Chevy or 8.8" Ford.The 8.5" from my 72 was is not welded,and I ran a W27 cover on it.I never had an issue with it.Now it's behind a stick-shift car,with a healthy BBO.When I ran that rear,I had SSM lift bars for the lower control arms,and I had the brackets welded in-place,to make sure they didn't move.The lift bars went with the rear,since the brackets were welded-on.