Rear end question

[Nachos82]

I pulled the cover off the rear to change the oil for a trip I am going on soon. I was wondering since it is off, if someone that knows rears can help make a positive ID on this rear. It is in my '67 1/2 ton, the code list in the glove box said it should have the G80 rear in it. From what I have found, this is supposed to be a "locking-differential" rear end. I was just wondering if someone could tell me 100% what I got. I want to try and find the codes on the ring gear while I am in there to see what ratio it is also. Here is a picture for your viewing pleasure, thanks.

Edit: Almost forgot the main reason I posted. Should I be running any type of additive from GM? I know, or have been told you should run some friction modifier with the limited slips. Does this one need it, or is straight gear oil fine for this? Thanks again.

[70rs/ss]

Yep, posi (12 bolt), clean that thing up!!! Use a couple of cans of brake cleaner in there to clean it up, once it is clean (and dry, that's why you use brake cleaner, as it evaporates with no residue). Buy Royal Purple or the like (Synthetic) in gear lube and add the GM posi addative (local GM dealer will have it). As for the ratio, there are two numbers stamped into the ring gear (big gear) it'll look like this: 56:98 (example only) divide the big number by the little and you'll get 4.11 or 3.73, etc etc as in 4.11 posi 3.73 posi. BTW was it a L6 motor? I have had several inline six trucks and they all had 4:11 posi in them.

[Nachos82]

70rs/ss, thanks for the fast verification of the rear. I was looking on the left side when facing the ring gear and the only numbers I could find are 30060, and 55 11. Is there a different place to look then where I am looking? I will let this thing apart since it needs the GM additive and I dont have any with me. I still need to work on getting the fill plug out. The guy before me has it all rounded off and it may be a challenge to get out. The truck is a factory 327 with 4-speed transmission. I know that number 55 11 does not sound very right for a ratio. I need to look around more and hopefully find it somewhere. Maybe after a good cleaning with break cleaner I can see it easy. Thanks again.

[Nachos82]

Well, I never did find any numbers that amounted to anything. I did find that the 11 55, was really 11 99. I am sure that is not anything like a ratio, but who knows. It is buttoned back up and ready to go. I should change out the tranny oil while I am in the changing mood. I may look on the axle tubes for the code there that tells what ratio is should be. I really don't care, was just wondering while I was in there.

[mnunn454]

Nacho, Thanks for the pictures.

It's definitely a Posi (springs like that aren't used in an open rear end).

As for the gearing ratio, simply count the number of teeth on the ring gear, and divide that by the number of teeth on the pinion gear (using chalk or soapstone may help). In the example above (55:11) you'd get 5:1. If teh ring gear has 41 teeth and teh pinion 10, you'd get 4.10:1 etc.

Either way, nice rear end. It's probably worth $1,500 or more.

As for spraying it down with brake cleaner, I'd go easy on that. It doesn't take much to ruin those bearings. Personally, I'd just replace the old natural fluid with new natural gear lube plus some posi additive and let it go at that. JMO.

[Nachos82]

I should have taken an after picture when I got done using 2, 16oz cans of Brake cleaner like 70rs/ss suggested above. This thing looks way better now then that nasty black picture up there. It even seems to shift into gear smoother (I am sure it is just me thinking this, but it seems to go right in now) . I think she is a happy girl now with fresh oil out back.

[corn]

Originally Posted by mnunn454

Either way, nice rear end. It's probably worth $1,500 or more.

.

For real?

[Longhorn Man]

maybe if it was a camaro 12 bolt.

[72armyswbtruck]

$1500 wow then I just lost my shorts on a 67 with factory posi that I sold for $900 and that was the whole truck

[krue]

1500 is a little optimistic.

[mnunn454]

Okay, so I am being a little generous, but to purchase a 12-bolt posi via aftermarket will run 1800 and up. I still think to someone whose application requires that rear end, it's worth well over a grand. Looked at another way, if you took a run-of-the-mill "open" 12 bolt for about $100 and had someone convert it to a new posi with new gears, you'd spend over a grand by the time you're done.

[mark's68]

to id the gear raito look along the edge of the ring gear, there should be numbers stamped into it do the math big/little and that is it.

[Longhorn Man]

ahhh, you're comparing the cost of new stuff and labor verses 40 year old parts.

[Nachos82]

Well, just a little update on this. I think it may have been low on oil before the change. Now with the new oil and the GM additive, this thing will chirp the tires on a hard turn (as in you can tell it is a posi now). I guess it is finally doing things like it was built to. I am as happy as can be with the outcome. Maybe when I rebuild it, I will bother to find out what ratio it really is. Till then I am just driving it like it was made for.

[DieselEater]

I know you don't want to open it up again........but there is a formula you could use with RPM at 4th gear 1:1, and some other measurements to get an idea. I'll look for the formula and post if I find it. Or you could use the jack it up and mark the driveline method......

A......