Screecher

I have a '70 cutlass convertible with the original "O" rear axle. I have the original 673 casting carrier with a crappy 2.56 gear. I want to completely rebuilt the rear axle and go to a 3.42 anti-spin. I need to know my options. I've checked Supercars Unlimited, I believe they mod a Ford Posi unit. I've poked around Randy's Ring and Pinion and haven't been 100% sure any of those units are going to fit right. I know there are some very sharp guys when it comes to this rear end and I was hoping to find the best solution. I expect to replace the carrier, ring and pinion, bearings, basically everything but the axles and tube. Any help would be appreciated.

BackInTheGame

Hey Screecher, you've come to the right place. There are at least two drive train specialists right here on C.O. I have had help and information from both of them. One is Jim of JD Race, who goes by monzaz here online. The other is Brian Trick. I don't recall Brian's CO handle at the moment.

Both guys are Tops! and great to work with.

Somebody else here on CO just offered a 3.42 R&P set for sale. I don't recall whether they were OEM or aftermarket. You may want to search the Parts for Sale forum.

I am in process of doing pretty much the same thing you are. I found online a NIB 588 carrier, and a couple years later found a NIB set of Richmond 3.42 gears. This is one of the simpler alterations possible. In my case, I need to machine about .100" off the back of the Richmond ring gear, and I've been assured everything will line right up.

Good Luck with your project!

mfpm7232

I would second the recommendation of Monzaz and Brian (507Olds?) as well as I was also facing the same decision point a couple years ago. I upgraded my '69 type O rear end (2.56 open) to 3.42 anti-spin. I purchase everything from Jim and he was great to deal with. Brian Trick also provided some great information while I was doing my homework before the purchase. Both are very helpful a wealth of info.

Best of luck with the upgrade - you'll love the end result.

oldstata

Type o rear

Yes, they modified a ford 8.8 unit to fit the housing. unfortunately as far as I know gears are still not available? Unless used or nos
I know there was talk about some gears being produced about a year ago,but have not been active to know the details. Jim is who has helped me In the past great guy very fair on helping the olds community

76olds

I don't have the Type o rear in my 76 Olds, but I purchased a posi carrier, 3:42 gears and install kit from Jim. (Monzaz) He shipped them up to Canada for me . Fantastic guy to deal with as others mentioned.

Eric

orange442

588 carriers are hard to find. A 671 carrier may be a little easier to find and it is the carrier that works with the new Richmond gears.

https://m.summitracing.com/parts/rmg-4900491

olds 307 and 403

New 3.42 and 3.90 gears are available again. Brian mentioned the new carrier bolts on and works with the new gear sets, is a clutch type rebuild able posi and will work with stock AND 71-72 corporate 8.5" factory and aftermarket axles. It will be a $1000 upgrade for the 3.90, posi and bearings but everything other than the 2004R trans which Olds and Buick embraced before chebby will be Oldsmobile.

Fun71

I was in the same position back in the 1980s with my '70 Supreme. I found a 71-72 8.5" 10 bolt rear and swapped the entire rearend, which was the simplest and least expensive option.

As has already been stated, new 3.42 gears (if you can find them) will fit the Olds 671 carrier or the "new" machined Ford 8.8 carriers. GM 3.42 gears will need a 588 carrier.

Screecher

With my existing 28 spline axles I would need a 588 carrier. I would hate to have to get axles too but that's an option to use the 672. But I don't have either lined up yet. It seems the only aftermarket new "drop in" type replacement is the Supercars Ford modified. Supercars also show they have the ring and pinion. Does anyone know what bolt pattern they use for the ring? Anybody install one of these? Problems? I kills me to use a Ford part in a GM but I'm trying to keep an open mind. Everything on my car is period correct, maybe slightly modified here and there, but still true to the year. I would like to keep it that way.😀

orange442

A 671 posi is 28 spline and the aftermarket Richmond gears are made for this carrier or the aftermarket carrier. Monzaz here on this site has had. He had the Eatons available that are direct fit for the Richmond gears.

Magna86

No one will know what posi you installed in the rear. The modified Ford units work fine and were developed so that we had other options instead of old gm units. They stopped making the clutch packs for the old GM posi's so they were no longer rebuildable but now they are being made again. But by the time you buy a core gm posi and rebuild it you are at the price of the eaton style one maybe more. Richmond sell the 3.42 and 3.90 ring gear sets and they are in stock at most places.(summit/jegs etc) so you dont have to pay Olds parts house marked up prices. Email Monzaz(Jim) or 507olds(Brain) for everything you need. They can send you all the parts and there will be no guesswork. Just take the car or rearend to your local drivetrain shop and have them do the work.(or if you feel froggy you can tackle the job yourself and they'll guide you.) Finding a 588 or the more rare 672 carrier isnt easy or cheap.

Screecher

I keep seeing Eaton popping up in the thread. Does Eaton have a carrier that fits in an "O" that you don't have to modify the housing? Is that an option with Richmond gears?

orange442

The modified 8 8 units are Eatons I believe.

Screecher

Thanks for clearing that up. I missed that somewhere along the line...

mfpm7232

Yes, I should have noted that detail in my earlier post. I purchased the Richmond gears and an Eaton posi from Jim (Monzaz).

Fun71

Sorry about saying 672 carrier when I meant 671. I corrected my post above.

The bolt pattern for the aftermarket ring gears are the same as the GM gears, and the modified Ford 8.8 carriers are drilled to fit this bolt pattern. It is a direct drop-in.

JohnnyBs68S

About 10 yrs ago (man time flies!) I did exactly that w/ my "O"; I used the Supercar's modified Ford posi, Richmond gears were still available from Jegs at that time (I used the 3.90s), Timken bearings / seals / brake parts from Rock Auto, new brake lines, etc. Had to purchase a 20-ton shop press and BFIW (big friggin' impact wrench: the 1/2" "Earthquake" from Harbor Freight did the trick), dial gauge (already had calipers and mics), and an in-lb dial-type torque wrench (for setting pinion preload / crush), and did all the work myself in my garage (get a spare crush sleeve!). Used some alum L-bracket to jig up for pinion depth measurements, but hit the right pinion shim stack on the money first try. Re-installed the axle w/ SSM lift bars for LCA, Edlebrock adjustable UCAs, a 442 rear sway and topped it off w/ a W27 cover. I've got 6-7,000 miles on it so far, no problems w/ it whatsoever.

distributorguy

Spare crush sleeve? I use a piece of black iron pipe trimmed to length. Start with .050" or so longer than the old one and trim to suit. Now you can take it apart and put it back together without worrying about losing your setting.

Stevec

Wouldn't it be easier to buy a cheby 12 bolt and build it how you want? Just saying...

monzaz

Everyone first started using FACTORY 8.8 Ford units... with the s spring like Olds original units.... They were cheap and available from Ford. NOW Ford does not even produce the 28 spline trac lock posi. They are all 31 spline units.

I used the Eaton Units right away befiore the factory units were all used up and advertised heavy that the EATON units were way better ...Now everyone else is following suite.

ANOTHER thing I do not like that Supercars and other companies do is weld the centering ring all the way around which weakens the carrier case which is cast. YOU only need to be sure it does not move from its press on spot - this does nothing more than center the ring gear...THAT IS IT. The ring gear bolt prevent the ring gear from spinning on the carrier. the 2 work together to make the integrity.

Conversion Bearings are needed to install the larger hub being unit (AGAIN which make it stronger than the stock unit) LM102949 and LM102911 x2 each.

JIm
J D