Rear axle replacement

[Ricko1966]

Does anyone know what an RPO code is for?

You do realize if someone has changed gears the rpo code is irrelevant? 90% of anything I ever owned was regeared.

 

[Ricko1966]

P.O. any updates,progress

 

[59840Surfer]

You do realize if someone has changed gears the rpo code is irrelevant? 90% of anything I ever owned was regeared.

"IF" being the operative here --- it doesn't always work out that they've been changed - especially when it means two gear sets.

The RPO is still a good starting place.

100% of everything I've ever owned (7 K5s, 3 K1500 Sierras, 1 K40 box van, not counting a couple of Trail Blazers) have had the OE gears and NOT been changed.

100% trumps 90%.

 

[bucket]

"IF" being the operative here --- it doesn't always work out that they've been changed - especially when it means two gear sets.

The RPO is still a good starting place.

100% of everything I've ever owned (7 K5s, 3 K1500 Sierras, 1 K40 box van, not counting a couple of Trail Blazers) have had the OE gears and NOT been changed.

100% trumps 90%.

That's very true, it's still a good starting point. I've had somewhere around 60 cars and trucks, I can only recall 2.5 of them that had be re-geared. Only one of them was a surprise.

 

[Frankenchevy]

That's very true, it's still a good starting point. I've had somewhere around 60 cars and trucks, I can only recall 2.5 of them that had be re-geared. Only one of them was a surprise.

The one that was 0.5 regeared would be interesting when shifted into 4wd…unless it was set up for mud racing.

 

[bucket]

The one that was 0.5 regeared would be interesting when shifted into 4wd…unless it was set up for mud racing.

It was a '77 K5 that the rear 3.73 axle had been swapped out for a 3.08 axle. The PO found out about it the hard way, lol. He wasn't the best at diagnostics and replaced the trans and t-case before he figured out what was wrong.

 

[Ricko1966]

"IF" being the operative here --- it doesn't always work out that they've been changed - especially when it means two gear sets.

The RPO is still a good starting place.

100% of everything I've ever owned (7 K5s, 3 K1500 Sierras, 1 K40 box van, not counting a couple of Trail Blazers) have had the OE gears and NOT been changed.

100% trumps 90%.

Now go back to post 17 which is what I was talking about and quoting. At this point when you have the ring and pinion this close,to take pics that I can see the teeth. Why wouldn't you just count teeth?Why would I tell him to look up the RPO? No guess work there at all. Count the teeth it's 100 percent.

 

[AuroraGirl]

It was a '77 K5 that the rear 3.73 axle had been swapped out for a 3.08 axle. The PO found out about it the hard way, lol. He wasn't the best at diagnostics and replaced the trans and t-case before he figured out what was wrong.

im sure theres a way to change your tire size to accomodate that... LOL.. imagine. the opposite of squatting before it was cool. Or would it be squatting?

 

[59840Surfer]

Now go back to post 17 which is what I was talking about and quoting. At this point when you have the ring and pinion this close,to take pics that I can see the teeth. Why wouldn't you just count teeth?Why would I tell him to look up the RPO? No guess work there at all. Count the teeth it's 100 percent.

If you have the cover off - the gear count is OEM-stamped into the outer periphery of the ring and on the inside stub of the pinion.

Most times, the number will appear like this ---> 33:6 or something like that.

These gears are machined together and have match-marks to keep someone from putting the wrong gears together and shipping them out as a pair.

I had the gear count on my old OE (3.08:1) gears and the same metric was stamped on the ring gear I got to replace them.

Funny enough --- GU4 is the same RPO code posted in my glovebox for 3.08:1 too!

Whatdoyouknowabouthtat?

 

[AuroraGirl]

I was going to say, both axles coming out is likely from a broken carrier. Axle C-clips can't just fall out unless something else goes wrong. I'll bet the truck is equipped with a G80 Gov-Loc as well, which is why it all went kaboom. People like to talk about how the 10bolt version of the Gov-Loc isn't as bad as folks make it out to be, but it didn't get the nickname of "Gov-Bomb" for no reason.

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Saw this and thought of you, something to show that g80 substantially decreased in nuking rear ends lol

 

[Turbo4whl]

Saw this and thought of you, something to show that g80 substantially decreased in nuking rear ends lol

Okay Taylor, since you brought this old thread back up with some info I didn't know, it also explains why the G80's still failed. Think of the operator that was accustomed to driving with the G80, then it didn't work. Now trying to move the vehicle on ice or whatever and the speedo says 30MPH but the vehicle is not moving. The spinning wheel is going 60MPH. What if they even revved it to 50 or 60MPH on the speedo??

The learning moment, like and oil pump that runs out of oil, the side gears and spider gears also run out of oil. What happens, cavitation occurs in the oil pump. Cavitation also happens to the side and spider gears of the drive axle. With enough cavitation the teeth of the gears break apart. A large enough piece will break off, boom goes the diff!

In the picture on post 17 of this thread you can see the cavitation on the side gear. It looks like maybe rust, but it is not, that is cavitation. Also keep in mind the the spider gears are spinning twice as fast as the side gears. One more thing, in the G80 the side and spider gears are smaller to fit all the other parts of the govern lock.

Okay remember, if you start to hear or feel grinding making a tight turn, time to check your axle. Save money buying a few parts instead of the whole shebang.

 

[AuroraGirl]

Okay Taylor, since you brought this old thread back up with some info I didn't know, it also explains why the G80's still failed. Think of the operator that was accustomed to driving with the G80, then it didn't work. Now trying to move the vehicle on ice or whatever and the speedo says 30MPH but the vehicle is not moving. The spinning wheel is going 60MPH. What if they even revved it to 50 or 60MPH on the speedo??

The learning moment, like and oil pump that runs out of oil, the side gears and spider gears also run out of oil. What happens, cavitation occurs in the oil pump. Cavitation also happens to the side and spider gears of the drive axle. With enough cavitation the teeth of the gears break apart. A large enough piece will break off, boom goes the diff!

In the picture on post 17 of this thread you can see the cavitation on the side gear. It looks like maybe rust, but it is not, that is cavitation. Also keep in mind the the spider gears are spinning twice as fast as the side gears. One more thing, in the G80 the side and spider gears are smaller to fit all the other parts of the govern lock.

Okay remember, if you start to hear or feel grinding making a tight turn, time to check your axle. Save money buying a few parts instead of the whole shebang.

thank you i appreciate that explanation

The OPs failure mode of his axle shaft exploding outward, and the level of the on the side gear..could the fluid have been low? i ask because if it was filled to the normal level, wouldnt the cavitation be higher up or less there? would also have meant more heat + friction + wear on already weak parts

 

[Turbo4whl]

i ask because if it was filled to the normal level, wouldnt the cavitation be higher up or less there?

The side and spider gears cavitation is because the gears move in and out of the oil as the diff spins. They push and pull off creating the vacuum that causes the cavitation. The ring and pinion gears are hypoid cut and they slide against each other.