G-80 rear questions

Y

youngstr

Member
Joined
Jan 27, 2008
On my option list is G-80 , I'm pretty sure thats the posi rear and was standard on the grand nat models and gnx, anyway, can anyone tell me more about this rearend, is it 28 spine?
Also can anyone suggest a suitable diff upgrade re-using the stock axles as long as the splines aren't booger'd up.
Reason I ask is I just blew out the rear, pulled the cover and it looked like a claymore went off in there.... metal chunks shards, and glitter everything in there looked toasted. So please anyone that knows a good "better/stronger than stock" upgrade for that unit throw me ur suggestion. Thanx ahead of time. (good thing my income tax check gets here wed.)
 
That hurts just hearing about it. You can get a new carrier and gears which sounds like what you need. Go ahead and upgrade to a 30 spline and change the axles while you're at it to keep you out of trouble.
 
charlief1 said:
That hurts just hearing about it. You can get a new carrier and gears which sounds like what you need. Go ahead and upgrade to a 30 spline and change the axles while you're at it to keep you out of trouble.
Click to expand...

The ring and pinion were both missing chunks teeth, I guess when the bearings in there imploded it put enough play in the axle to allow the pinion to separate from the ring gear and then collide ...over and over till I got stopped. From what I saw I'm gonna need a new posi unit and with bearings and a ring and pinion set, and axles too if I go 30 spline like u suggested. Whats the advantage of 3o spines over 28?
 
Make sure it's an eaton unit. It's the stock design and it works well, not to mention that it's rebuildable where most of the others can't be rebuilt.
 
the only G body that had the G80 standard was the GNX.. it was optional on everything else..

get a 28 spine Eaton and GM gears.. it's what the GM powertrain engineers spec'ed out for it in the 80's and still works the best today.
 
Ok, hope you guys are ok helpin me build a parts list for this, I don't have pics of the destruction, but I can tell you, the posi unit is done, the axle bearings on the drivers side where in the bottom of the diff pieces of bearing and raceway, the pinion and ring are done for teeth missing and such, I'm pullin the axles tomorrow to see if the spines are messed up and that will also tell me if the shrapnel shot out the axle tube and is into the backs of the wheel bearings or not... thats where I am now. so far I,m thinking these parts are a good start:

Eaton #19557-010

1971-89 GM Car/Truck Posi Unit
  • 28-Spline Axles
  • 8.5'' Diameter Ring Gear
  • Fits 2.73 & Up Gear Ratios
  • Richmond Gear #49-0041-1K
    GM Ring & Pinion Package
  • Ratio: 3.73
  • Ring Gear: 8.5" diameter
  • Kit includes bearings and seals
    If anyone has different part suggestions please chime in, looks like I might be replacing everything inside axles maybe axles too.
 
One of the reasons I suggested the 30 spline is because you can't get the clutches to rebuild the 28 spline as easily as the 30 spline. They're a little hard to find it seems and the 30 spline you can get at the dealers or summit, ect. If there's trash in the housing you can put a towel on a broom stick and use it like a rifle cleaning rod. Just make sure to go all the way through it and putt the rag out in the same direction you started with.
 
ok, so the main benefit is the ease of getting rebuild parts for the 30 spline cause its more standard today? Thanks for the towel on the broomstick, I'm sure thats gonna come in handy.
 
youngstr said:
ok, so the main benefit is the ease of getting rebuild parts for the 30 spline cause its more standard today? Thanks for the towel on the broomstick, I'm sure thats gonna come in handy.
Click to expand...
Exactly! GM did some design changes and when they do that the guys that make the parts let them run out and usually don't make any more. The old GM 8.2" rear is almost impossible to find parts other than bearings for these days so if someone offers some up for sale they go for big money. The other advantage to going with a 30 spline is so you don't break an axle if you play hard with it.:) Even the 7.5" rear is now a 28 spline instead of the original 26 spline, and that's in the 4th gen F bodys and S-10 line. Since you're having to replace everything you might as well upgrade it now rather than break an axle and then re-do everything all over again.:)
 
Changed parts list going 30 spine:


Eaton #19559-0101988 - up GM Car/Truck Posi Unit
  • 30-Spline Axles
  • 8.5'' Diameter Ring Gear
  • Fits 2.73 & Up Gear Ratios
Only one thing concerns me about this posi unit, its the note on summits site about bearing sizes....

NOTES:
All GM 8.5/8.6 in. Eaton differentials require special bearings. For axles with small bearing bores (race O.D. of 2.89”), usually found on vehicles prior to 1999, bearing LM102949 and race LM102911 are required. For axles with large bearing bores (race O.D. of 3.06”), usually found on vehicles from 1999 to present, bearing LM603049 and race LM603012 are required

Richmond Gear #49-0041-1K
  • GM Ring & Pinion Package
  • Ratio: 3.73
  • Ring Gear: 8.5" diameter
  • Kit includes bearings and seals
Part #: A103004 (1-Pair) Moser 30 spine
  • Mfg: GM Model: Buick Grand National, Olds Hurst
  • Year: 1984, 1985, 1986, 1987, 1988
  • Rear End: 10-Bolt Chevy Spline Count: 30
  • Length: 28 7/16" long Bolt Pattern(s): (2) 5 x 4 ¾” (.505” Knurl press-in & 1/2” X 20 threaded)



or what if I when with a different gear set and diff install set? Like this:

Eaton #19559-010 same posi unit 30 spline


Part # 10B85373M - 10 Bolt 8.5 3.73 P/S Gear -- Motive Gear
  • Ring Gear Diameter: 8.5" & 8.625"
  • Ratio: 3.73:1
  • Material: 8620
  • Mfg #: G885373
  • Pinion: 30 Spline
  • Pro/Street Motive Gear Line
JEGS Performance Products 61228 - JEGS Differential Installation Kits with Timken Bearings

The DELUXE KIT includes:
  • Pinion and carrier shims
  • Ring gear bolts
  • Marking compound and brush
  • Crush sleeve
  • Pinion seal and nut
  • Cover gasket or RTV
  • Timken® pinion & carrier bearings
  • Timken® axle bearings and seals
  • Thread locker
And of coarse the 30 spline moser axles and thier c-clip kit, as on the previous list.

I think I like the second list better, it seems to cover all the parts out to the axle.
 
Get the 3.42 gears, seriously. The engine doesn't need 3.73's unless you plan on running some really tall tires. Most of the Buick V6's will never see the benifits of reving higher than 6K and you'll loose on the top for what you've gained on the bottom.
 
charlief1 said:
Get the 3.42 gears, seriously. The engine doesn't need 3.73's unless you plan on running some really tall tires. Most of the Buick V6's will never see the benifits of reving higher than 6K and you'll loose on the top for what you've gained on the bottom.
Click to expand...

I would loose some top end but I have taken a liking to 1/8 mile, and a hot air doesn't exactly kick out a ton of ponys unless you throw a stoker kit in and a lot of money into the rest of the motor...my money this year is going in the rear axle. Wasn't 3.73 an optional gear ratio for GN's? I know the standard is 3.42

also I'm on a stock shift pattern so my tranny is gonna see 5250 and shift, wouldn't 3.73's make me quicker in 1/2/3rd but I'd loose top end which i'm ok with, I'd go from 2300rpm @65 to probably 2800 I don't know the math to figure that out, just kinda guessin.....do ya really think its gonna make that big of a difference?
 
youngstr said:
I would loose some top end but I have taken a liking to 1/8 mile, and a hot air doesn't exactly kick out a ton of ponys unless you throw a stoker kit in and a lot of money into the rest of the motor...my money this year is going in the rear axle. Wasn't 3.73 an optional gear ratio for GN's? I know the standard is 3.42

also I'm on a stock shift pattern so my tranny is gonna see 5250 and shift, wouldn't 3.73's make me quicker in 1/2/3rd but I'd loose top end which i'm ok with, I'd go from 2300rpm @65 to probably 2800 I don't know the math to figure that out, just kinda guessin.....do ya really think its gonna make that big of a difference?
Click to expand...
You need to get the right converter for the car. You might pick up a slight increase on the times but the biggest thing with any car is getting traction. If you go with the 3.73's then other issues will pop up since the RPM's will be higher on a more consistant level. What size tires do you have on it now? If you go with a 28-29 inch tall tire you'll be about the same as the stock gears and tires so it won't make any difference. If you got the stock height tire then you can go up in size, get more meat under the rear, and not change anything else.
 
youngstr said:
. . . . also I'm on a stock shift pattern so my tranny is gonna see 5250 and shift, wouldn't 3.73's make me quicker in 1/2/3rd but I'd loose top end which i'm ok with, I'd go from 2300rpm @65 to probably 2800 I don't know the math to figure that out, just kinda guessin.....do ya really think its gonna make that big of a difference?
Click to expand...
Here are some good calculators for you to play around with.
http://www.tciauto.com/tc/racing-calculators/

BTW, the "ratio" discussion is very interesting.
Even a HA can leave the line with with +200 hp/torque.
Some have even gone to the 3.23 ratio to load the turbo, and to stay in first and second longer, but you need the HP to pull the gear on the big end.

Having said all that, you can't go wrong with the proven 3.42 ratio.
If you can hook, the 3.73 would be better, for short distances.
How "short" really depends on the converter slip and rpm.
I like the 1/8 mile as well, and prefer it over the 1/4.
Anyway . . . . Just thinking out loud.

Let us know what you decide and how it works.
 
I got 245 55's on the back on 17's they don't rub even on bumps, got stock springs in the back, front is lowered. I'm thinking of going 245 60 next tire change out, the 55's are about a half inch over the stock height. And yeah, I was gonna get the trans done this spring until the above happened, I was thinking of minor upgrades to the trans and a slightly higher stall maybe 2800 finally got my ta33c done but its sitting on the shelf till the motor gets done. long todo list, and it only gets done as the cash comes in....such is life.
 
Jerryl said:
Here are some good calculators for you to play around with.
http://www.tciauto.com/tc/racing-calculators/

BTW, the "ratio" discussion is very interesting.
Even a HA can leave the line with with +200 hp/torque.
Some have even gone to the 3.23 ratio to load the turbo, and to stay in first and second longer.

Having said all that, you can't go wrong with the proven 3.42 ratio.
If you can hook, the 3.73 would be better, for short distances.
How short dpends on the converter slip and rpm.
I like the 1/8 mile as well, and prefer it over the 1/4.
Anyway . . . . Just thinking out loud.
Click to expand...

I didn't think of it from that angle, I think I need to flip on the xbox and play with gear ratios in forza to get the feel of that idea.

Whats our transmission ratio? anyone ?
 
stay with the 3.42 and you can easily go 255/60 with no issues. i run 275/60/16 on a gta rim with alum drum with NO MODS and it don't rub
 
Jerryl said:
2.74 first, 1.57 second, 1.00 third, .67 fourth.
Credit: D. Wang. http://www.drwtransmission.com/thm_200-4r.htm

What is the 1/8 mile mph goal?
Click to expand...


Had to dig out some time slips, current is 69.90 69.98 and 70.38 mph on 3 dif runs, I'd like to change that to between 80 and 90 mph, but the motor and trans just can't put enough power down to do that in thier current state. Thats why I was kickin the ratio change idea around.
 
Worst came to worst if I don't like it I could just buy 3.42 and swap, and if ya think about it I would have a lot of before and after data cause those time slips are from when it had 3.42's in it. I plan on running this spring down in nc, I would gladly share that data on this board. That way the other hot airs would have that info available to them to help them decide what they want to do with thiers.
 
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