wildcatmom

Hello everyone. We recently purchased a 1969 cutlass supreme. It has a 12 bolt open rear end, and my son wants to change the gears to 373. Of course it needs bearings as well. The question I need help with... Should he change to a limited slip? The shop wants an extra $900 in parts and another $450 in labor to do the job. I think that's really expensive and this is his first car. Any advice? And they quoted me $750 to change existing gear, bearings, etc.

Tony72Cutlass'S'

welcome to classic olds.

From a different perspective, even if you spend 1500 dollars on your rear end, you'll spend a fortune in gas if you're cruising on the highway alot.

I've got 2.73 gears in my cutlass. I can still roast tires all day long if i want to. On the highway it's fantastic.

joe_padavano

Welcome.

First question is, are you sure this is a "12-bolt"? Except for cars built in Canada, all 1969 Cutlii received a Type O axle. The Type O has 12 bolts on the cover, but only ten bolts holding the 8.5" ring gear. This is completely different from the Chevy 12 bolt, which does have 12 bolts holding an 8.875" ring gear. Parts for the Type O are VERY difficult (though not impossible) to find, and most shops are not aware that they are not Chevy axles.

wildcatmom

Joe, I questioned the 12 bolt thing just from research. He said they opened it up and it is 12 bolt inside??? And he referred to it as a Chevy rear end. Now the car is from New York, so maybe it was made in Canada. I think I'll pay a visit and have them show me. However, I still need to know if we should go with the posi or what they're calling "no slip". Isn't there a less expensive way to get both wheels turning?

joe_padavano

The VIN will tell you if it's a Canadian built car or not (the seventh character will be the number "1" instead of a letter for the assembly plant). If the rear cover has an inverted "V" stamped in it, it's a Chevy axle. If the cover is smooth, it's a Type O.

Posi/limited slip/anti-spin (Oldsmobile's term) is all the same thing. These use a clutch-based system that locks the two pinion gears together if one wheel starts spinning. There are other non-clutch methods such as the Torsen and Detroit Locker systems, but those are more expensive. The inexpensive options involve welding the spider gears, installing a spool, or othewise rigidly locking the two axles together. None of these are recommended for street use. The two rear tires need to travel along different arcs when you go around a corner, so there needs to be a differential action - othewise one tire is forced to skid and this can lead to loss of control under low traction conditions.

DENT

Welcome to the forum. I would go with the positrack if it was my car. Post some pics when you can.

wildcatmom

It's definitely a 12 bolt olds (10 bolt inside). He was referring to the outer bolts. I do trust this shop. They work on the classics and have an outstanding reputation, but I'm still hesitant to sink $2100 on the conversion to get it to 373 posi with new bearings. They use high end parts, so he said I could bring in my own parts and they'd do the labor. Opinions on cost? Too much?
Thanks!

oldstata

Look up brain ( 507olds ) or Jim ( monzaz)
I know Brain has rebuilt units for around 1400 pulse shipping

I have pretty much the same rear end and I know they will sell you the parts for alot less if you can set it up yourself if memory serves me corrects it was around 600 for everything except gears

don71

I think that's too much money but how much is customer service worth to you? Most of us would try to get that number down.

oldstata

Here is a thread to look at
https://classicoldsmobile.com/forums...141#post583141

jag1886

You need to buy the parts yourself and then have them installed, I converted my rear end to a 3:90 posi and parts and labor where only $800, I have a 10 bolt but there isn't that much difference in price. I did a new ring and pinion posi unit and all new bearings.
Just because a shop has a good rep for good work doesn't mean they aren't ripping you off on the parts.
For $2100 I'd buy a Currie rear end and bolt it in myself.