myolds

I just purchased a 1970 442 W30 that has been stored away in a garage since 1976. I'm trying to ID, and believe the differential is not original. I'm having a difficult time locating the date stamp. It appears to be a 10 bolt, type O, 8.5". Carrier has the part # of 725. Did these come in any 1970 442s?

joe_padavano

The inverted "V" notch in the cover screams "Chevy" axle. A ten bolt cover of any type would not be original in your car - it should have come with a Type O that had a 12 bolt cover and a 10 bolt, 8.5" diameter ring gear. I can't tell in the picture - are the axle shafts retained with C-clips or not? If so, it's definitely a Chevy 10-bolt with 8.5" ring gear. While not correct, it's frankly just as strong as the Type O, with the exception of the C-clip axle retention. On the other hand, parts are MUCH easier to find.

monzaz

Yes you are totally correct. 8.5 10 bolt corperate olds rear. 725 726 carriers.

I think the 725 was the 2.73 -4.56 and up 3 series
the 726 was the 2.41-2.56 carrier.

It could be vise versa on the 725 726 thing but those are the correct numbers for the carriers

IT is not original to a 1970 UNLESS they started to put these into 442 late in the 1970 year run? The drive shaft would have to of been shorten by about an 1" making this a NOT so easy swap. SO either someone went through some trouble or it did come factory.

I have listed that 1971 1972 was the years the corp 8.5 was used. BUT you know how that always goes... If you run out of diffs you use what yah got deal.

The yoke will have 4 bolts holding 2 flat arced straps over the u-joint cup for an 8.5. all other BOP rears were u-bolt.
A chevy cover has the eyebow cover (axle bearing oiler cover) that has a crease across the whole cover from left to right.
the olds cover had only 1/2 the eyebrow. Until the 1973 era then everything withthe covers got messy...lol. Now they just use one cover and it is smooth with ring gear buldge.

Just some extra info... Chevy a-body cars 1965-1972 with c-clip retention were never 8.5 they are all 8.2 1973 was the first years for chevy using the 8.5 in a A-body car. Camaros started in the 1970 2nd gen cars. Even Pontiac ran the 10 bolt 8.2 to the end of the 1972 muscle car era...NO 8.5 in thier cars either. BUICK and OLDS were the ones with the 8.5 bolt in axle rears 1971 1972 The buick 8.5 has a couple other tell tail signs of 8.5 and the cover for the buicks LOOKS almost like the 10 bolt 8.2 BOP covers. But that is another forum...lol.

Hope this helps.

You can buy any gear ratio from any 8.5 axle 1970 -2008 and it will fit. The posis can be used from 1970 -1987 cars and even trucks from 1974 -1989 28 spline in this rear.

We use 30 spline moser custom axles and 30 spline aftermarket posi units to make these rears as good as chevy 12 bolt rears.

I like them alot I would keep it if your not looking for an all out original car.

myolds

Thanks...that really helps a lot. It has a 42/13 or 3.23, nice gear for the car. I received 4 drive shafts with the car (I'll need to check). The engine and trans are out of the car and not original. So, I need to decide to replace with the stock type O, 12 bolt or stay with this one. I appreciate the quick response.

myolds

I found a code on the axle tube. Would this be the ratio and date?

monzaz

Well unfortunely it is not readable...At least for me. Can you type in the letters and numbers for me on the thread. Jim

monzaz

Well the driveshafts will differ with the trans you go with too. 400TH will have a larger yoke the 350th will have a small yoke 27 spline which is very commn on most vehicles.

400 tranny will be longer making the drive shaft even shorter. the 350th will increase the length needed. Jim

myolds

The stamped number is SS 0018. Its on the axle tube, passenger side, engine side of tube.

monzaz

this is the 10 bolt rear or the 'O' type rear again were trying to Id ratio code? Jim

I have SS as a 2.41 gear ratio in the olds rears.

Maybe someone swapped the ratio. Does not seem to be a posi option code either??? Jim

myolds

Thanks again..I think we've determined this is not the stock rear and someone has changed the ratio to a 3.23 and upgraded to a posi carrier.

Mike