Rear end ratio

[joeuser742]

Well, my ring and pinion gears are shot, a few missing teeth and have not many ideas how it could have happened. The only thing that I could think of is from towing a 16ft boat, but can't see how that would do it. I'm going to the u-pick junkyard tomorrow and look for a ring and pinion to save much $$$ and possibly learn something new. Any suggestions how the ring and pinion gears could have broken off? Where on the truck can I find the ratio of the rear end (for when I goto the junkyard)(I know how to calculate it, but can't find any markings on the truck or rear end)? And does anyone know what other cars/trucks I should be looking for at the junkyard? I have a 98 blazer.

[OverBoardProject]

There's only 1 thing that I can see.

Sheer Abuse! I'm not saying that it was you, but I've seen people running 400+ hp through these rear ends at the race track, then hit the NOS button for an additional 100+hp. They're stronger than we give then credit for. Although I will admit that they had aftermarket axles, however the gears were still stock.

I believe that there's a code in the glove box.
However I understand that GM can also punch your vin in for the code as well.

I sugest that you should talk to them about taking a complete rear end, and just leaving a HUGE core charge. It's easier to re-build a motor than a rear end if you don't know what you'r doing.
Also look for a posi unit while your at it

[blazee]

It's a common problem with GM rearends. They used crush sleeves instead of solid spacers. The crush sleeve will give and allow the pinion to run up on the ring gear causing a misalignment, which destroys the teeth.

The ratio code is in the glovebox. You'll see "GU" followed by a number, the most common is GU6 which is 3.42.

I would recommend buying the whole assembly. I paid $550 for mine.

If you don't have rear disc brakes, now is a good time to upgrade.

[MT-2500]

Count the number of teeth on ring gear and pinion.
Divide the ring gear teeth by pinion gear to get the gear ratio.
Also a lot of times the gear ratio is stamped on the ring gear.
And there is usually a tag on rear end inspection plate.
One a used one as Blazee said get the hole thing.
MT

[dmbrisket 51]

if its a 2 by any rear end will work, go with a 3.42 if you can if you want mileage, go with the 3.72 if you want low end git up n' go.... if its a 4by it needs to be a match to the truck/transfer case, and as mentioned the code is in the glove box, its a gu number, if gu isn;t there i beleve g80 is a posi rear, not sure on those ratios

[joeuser742]

Ok. There was no abuse other than towing a boat, probably no more than 2000lbs. I knew the previous owner. Never aligned a ring and pinion before, but there's always a first time, I realize what is involved. And no $$$ for a posi unit.

I like that answer that GM used the crushed sleeve and there is flex in it. Can I use solid spacers in place of the crush ring if I rebuild myself? I got a quote for $600 to have it done, but was thinking of selling the truck soon after I get this fixed. Already have the disc brakes.

There was no tag on my rear axel. Hopefully there are some tags on the ones in the junkyard.

Thanks for all the replies. I really didn't want to spend the $600, but may have no choice.

[pimprolla112]

You can get the gears from a company called day auto in texas, or day motor i cant remember off the top o my head it was 142 shipped. Then i got a rebuild kit for 89 on ebay. 175 for new axles. Paid 265 for a auburn posi and about 175 to have the whole rear rebuilt. Used gears in a junk yard arent the greatest idea, rust and mileage are a big problem, and the 7.5" isnt the greatest rear made. Look for a rear with the same bolt pattern 10 bolt if you get the cover off spin the gears till some numbers come up on the ring gear 7.5 and 7 5/8 is the same rear pretty much i put the 7 5/8 gears in my truck with no problem. Look in the glove box for the code theres a code sticker look for a GU code.

I have a set of gears i bought from a 94 v6 with 20k miles on the rear (they bought it from an older man who used it to go to the store, they turned it into a track car). Gears are pretty clean 65 shipped if you want them there 7 5/8 3.42.

[joeuser742]

pimprolla112, I sent you pm.

[joeuser742]

I'm finally back on the road. Went to the junkyard and pulled the ring, pinion, carrier, races, shims. Ring, pinion, and bearings were in great shape, looked to be recently replaced.

$600 quote to have the rear end rebuilt;
$20 for the parts from the junkyard, putting it together myself, and learning something new......priceless.